Detection of Nocturnal Desaturation and Hypercapnia Using Accelerometer- Integrated Pulse Oximetry: A Prospective Observational Study

Detection of Nocturnal Desaturation and Hypercapnia Using Accelerometer- Integrated Pulse Oximetry: A Prospective Observational Study | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Detection of Nocturnal Desaturation and Hypercapnia Using Accelerometer- Integrated Pulse Oximetry: A Prospective Observational Study Takamasa Kitajima, Hideki Tajima, Eri Nohara, Shiori Jinno, Chie Morimoto, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7506324/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 06 Jan, 2026 Read the published version in Respiratory Research → Version 1 posted 11 You are reading this latest preprint version Abstract Background Sleep-related hypoventilation, particularly during rapid eye movement (REM) sleep, has been linked to pulmonary hypertension and recurrent exacerbations in individuals with advanced chronic respiratory or neuromuscular diseases. Overnight pulse oximetry (OPO) serves as a valuable screening tool to depict episodic oxygen desaturation resulting from sleep-related hypoventilation. However, differentiating nocturnal desaturation caused by physical activity from that attributable to sleep-related hypoventilation remains clinically challenging. This study aimed to determine whether the integration of accelerometer data with OPO readings can assist in distinguishing exertional nocturnal desaturation from desaturation due to sleep-related hypoventilation. Methods Between July 2021 and December 2022, a prospective enrollment was conducted among consecutive individuals with stable chronic respiratory disorders who reported worsening exertional dyspnea. Participants underwent overnight monitoring involving transcutaneous carbon dioxide pressure (PtcCO₂) and pulse oximetry integrated with accelerometer sensors. The frequency of exertion-associated desaturation events was compared between participant self-reports and acceleration-derived data. Additionally, the diagnostic accuracy of accelerometer-integrated pulse oximetry for detecting episodic nocturnal hypercapnia was assessed using PtcCO₂ monitoring as the reference standard. Results Thirty-six individuals were enrolled, with a median age of 78.0 (IQR: 72.0–82.0) years and a mean daytime arterial carbon dioxide pressure (PaCO₂) of 42.4 ± 6.9 mmHg. Of the 89 desaturation events observed, 56 (62.9%) were identified as exertion-related using accelerometer data, including 19 events (21.3%) that were not self-reported. The device demonstrated a sensitivity of 100% (95%CI: 79.6–100%) and a specificity of 75.7% (95%CI: 64.8–84.0%) in identifying episodic nocturnal hypoxia associated with hypercapnia. Conclusion Among individuals with suspected sleep-related breathing disorders, accelerometer-integrated pulse oximetry may serve as a valuable tool to distinguish nocturnal desaturation episodes caused by exertion from those due to sleep-related hypoventilation. These findings suggest that accelerometer-integrated pulse oximetry could offer a feasible screening method for detecting sleep-related hypoventilation in outpatient settings lacking access to PtcCO 2 monitoring. Nocturnal exertional desaturation episodic nocturnal hypercapnia pulse oximetry sleep-related hypoventilation COPD transcutaneous carbon dioxide monitoring diagnostic accuracy Figures Figure 1 Figure 2 Figure 3 Figure 4 Background Sleep-related hypoventilation frequently occurs in individuals with chronic obstructive pulmonary disease (COPD), neuromuscular disease (NMD), and chest wall disorders, with a reported prevalence ranging from 9–43% 1–3 . This condition is attributed to reduced physiological ventilation during sleep and progressive deterioration of respiratory function due to the underlying disease 4 . Sleep-related hypoventilation initially manifests during rapid eye movement (REM) sleep and subsequently progresses into non-REM sleep 5 . During REM sleep, activity of the intercostal and accessory respiratory muscles decreases, while hypoxic and hypercapnic ventilatory responses are blunted 6 , resulting in episodic reductions in minute ventilation, oxygen desaturation, and transient elevations in arterial partial pressure of carbon dioxide (PaCO₂) 3 . Recurrent nocturnal and early morning elevations in PaCO₂ due to sleep-related hypoventilation may lead to sustained daytime hypercapnia 3 , a condition associated with increased risk of exacerbations and mortality 7 , 8 . Although evaluation of sleep-related hypoventilation is crucial, its clinical daytime presentation is often nonspecific, and standard respiratory function tests inadequately predict nocturnal hypoventilation 5 . Therefore, overnight monitoring of respiratory parameters and carbon dioxide levels is recommended for assessing high-risk populations 5 . Recently, transcutaneous carbon dioxide pressure (PtcCO₂) monitoring has emerged as a noninvasive modality for evaluating hypoventilation during sleep 9 . Episodic nocturnal hypercapnia (eNH), primarily corresponding to REM sleep-related hypoventilation, has previously been defined based on PtcCO₂ monitoring 10 , 11 .In individuals with COPD, eNH has been associated with pulmonary hypertension and a history of frequent exacerbations 10 , 11 . Naito et al. also reported that eNH has also been linked to future use of home noninvasive ventilation (NIV) and mortality among individuals with NMD 12 . Furthermore, the use of NIV specifically targeting eNH has demonstrated a reduction in exacerbation frequency in patients with COPD 10 . Consequently, PtcCO₂ monitoring serves as a valuable tool for the assessment of sleep-related hypoventilation and the initiation of NIV. However, overnight PtcCO₂ monitoring remains technically complex, cost-prohibitive, and is not widely accessible in North America 13 , 14 , and Japan. In Japan, overnight PtcCO₂ monitoring is typically performed during hospitalization, rather than in the home setting. Therefore, the use of PtcCO₂ monitoring as a screening modality for large populations suspected of sleep-related hypoventilation remains limited. Overnight pulse oximetry (OPO) represents a cost-effective, safe, and reliable modality for assessing the cardiorespiratory function in outpatient settings 15 – 17 . It is particularly known for its simplicity and accuracy in detecting sleep-related breathing disorders 18 – 20 . OPO may also facilitate the detection of sleep-related hypoventilation, manifested as episodic nocturnal desaturation, without requiring overnight PtcCO₂ monitoring. Nocturnal oxygen desaturation has been previously documented in individuals with COPD, interstitial lung disease (ILD), restrictive thoracic disease, and NMD 21 – 25 . In REM sleep-related hypoventilation, prolonged episodes of oxygen desaturation lasting 5–30 min and recurring every 90–120 min throughout the night are commonly observed 13 , 26 . This episodic nocturnal desaturation has been associated with adverse clinical outcomes 21 . However, distinguishing whether episodic nocturnal desaturations arise from exertional activity (e.g., nocturnal ambulation) or from sleep-related hypoventilation remains challenging based solely on OPO data. This diagnostic challenge stems from the similarity in desaturation waveforms observed in REM sleep-related hypoventilation and exertional hypoxia. Recent evidence suggests that wrist-worn accelerometers may serve as physiological markers of nocturnal exertional events 27 . It was hypothesized that accelerometer-integrated pulse oximetry could distinguish between exertion-induced nocturnal desaturation and that resulting from hypoventilation during sleep. Accordingly, this study aimed to evaluate whether overnight accelerometer-integrated pulse oximetry could effectively distinguish between hypoxia secondary to exertion and that due to sleep-related hypoventilation. The diagnostic accuracy of accelerometer-integrated pulse oximetry for detecting eNH was prospectively validated against PtcCO₂ monitoring. This approach may facilitate broader implementation of outpatient screening for sleep-related hypoventilation, especially in resource-constrained settings. Methods Patients A prospective observational study was conducted to evaluate the diagnostic accuracy of accelerometer-integrated pulse oximetry in detecting episodic nocturnal hypercapnia among individuals with suspected sleep-related breathing disorders. Consecutive, clinically stable patients admitted to the Medical Research Institute, KITANO HOSPITAL, for evaluation of suspected exertional dyspnea worsening were enrolled between July 2021 and December 2022. The inclusion criteria for this study were as follows: (1) age ≥ 20 years, (2) medical history of chronic pulmonary disease, and (3) absence of long-term oxygen therapy use. Exclusion criteria were: (1) a pre-existing diagnosis of obstructive sleep apnea, (2) monitoring duration for pulse oximetry and PtcCO₂ of less than four hours, and (3) sustained nocturna SpO₂ levels below 85%. Sample size determination was guided by feasibility considerations and the availability of eligible participants during the study period. Measurements and data collection Sociodemographic, clinical, and laboratory data were extracted from electronic medical records. Body mass index (BMI) was calculated as weight in kilograms divided by height in meters squared (kg/m². Pulmonary function tests were performed by trained personnel in accordance with the American Thoracic Society and European Respiratory Society guidelines 28 . Arterial blood gas analysis was performed during the day in the supine position using the RAPIDLAB 1200 System (Siemens Healthcare Diagnostics Incorporated, USA). All arterial blood gas samples were obtained while patients were breathing ambient air. Overnight evaluations without supplemental oxygen administration were performed using PtcCO 2 monitoring with the SenTec Digital Monitor (SenTec, Therwil, Switzerland) and accelerometer-integrated pulse oximetry with the PULSOX-500i (KONICAMINOLTA, INC, Tokyo, Japan). During sleep, each patient wore the accelerometer-integrated pulse oximetry device on one wrist and a finger-mounted probe measuring SpO₂. Patients were instructed to press the event marker or manually record their behaviors during the night. Pulse oximetry data were analyzed using the DS-500 (KONICAMINOLTA, INC, Tokyo, Japan) (Fig. 1 ). Two board-certified respiratory specialists, each with over ten years of clinical experience, independently evaluated the PtcCO₂ and pulse oximetry data. Definition of oxygen desaturation event, possible eNH, and eNH The most widely accepted definition of exercise-induced desaturation is a reduction in oxygen saturation greater than 4% from baseline and/or a SpO₂ below 90% during the 6-min walk test 29 – 31 . In accordance with prior research, oxygen desaturation events in the this study were defined as a decrease in SpO₂ of ≥ 4% from baseline and a sustained SpO₂ <90% for at least 5 minutes, measured using accelerometer-integrated pulse oximetry. Possible eNH was defined as a ≥ 4% desaturation from baseline and SpO₂ <90% for ≥ 5 min continuously, without exertional acceleration data on accelerometer-integrated pulse oximetry. Exertion was identified using acceleration data, as described in the supplementary materials. eNH was defined as a ≥ 5 mmHg increase from baseline PtcCO₂ from baseline, accompanied by SpO₂ <90% for ≥ 5 min continuously, occurring at least once during the night, according to previously established criteria (Fig. 1 ) 10 , 11 . Subclinical eNH was defined as a sustained increase in PtcCO₂ of ≥ 3 mmHg but < 5 mmHg from baseline for at least 5 min, accompanied by oxygen desaturation to below 90% (Additional Fig. 1 ). Event-specific and patient-level analyses of oxygen desaturation were conducted in this study. In the event-specific analysis, each oxygen desaturation event was assessed to determine whether it was due to sleep-related hypoventilation. Conversely, patient-specific analysis involved identifying the presence of sleep-related hypoventilation-induced desaturation on an individual basis. Patients were classified as having eNH if at least one eNH event was identified during overnight monitoring. Overnight accelerometer-integrated pulse oximetry data were used to extract mean SpO₂, time spent with SpO₂ <90% (T90), 3% oxygen desaturation index (ODI), and mean pulse rate. Nocturnal mean and maximal PtcCO₂ values were also obtained from overnight PtcCO₂ monitoring. To facilitate analysis using modified SpO₂ waveforms, desaturation dip intervals were identified and the waveform was reconstructed accordingly. Detailed methodologies for processing the modified SpO₂ waveforms is provided in the additional materials. Analysis using the modified SpO₂ waveforms demonstrated a flattened sawtooth pattern, typically observed in cases of sleep apnea or signal artifact. Ethics and statistics The study was conducted in compliance with the ethical guidelines of the Japanese Ministry of Health, Labor, and Welfare and received approval the Institutional Review Board of the Medical Research Institute, KITANO HOSPITAL Ethics Committee (Ethics Board approval number: P2102009). All participants provided written informed consent prior to study enrollment. In addition, the confidentiality of personal information was maintained in accordance with established ethical guidelines. The Shapiro–Wilk test was used to assess the normality of data distribution. Parametric variables are presented as mean ± standard deviation, whereas nonparametric variables are reported as median (interquartile range [IQR]). Group comparisons were performed using Student's t-test for normally distributed data with equal variances, Welch's t-test for data with unequal variances, and the Mann–Whitney U test for non-normally distributed data. Diagnostic performance is expressed in terms of sensitivity and specificity with corresponding 95% confidence intervals (CIs). A p-value of less than 0.05 was considered statistically significant for all analyses. All statistical analyses were performed using IBM SPSS Statistics for Windows version 25 (IBM Corp., Armonk, N.Y., USA). Results This section summarizes the clinical characteristics of the study cohort and evaluates the diagnostic efficacy of accelerometer-integrated pulse oximetry for identifying episodic nocturnal hypercapnia. Figure 2 illustrates the patient selection flowchart used in this study. In total of 36 patients (30 men and 6 women) met the inclusion criteria. Table 1 presents patient characteristics, including a median age of 78.0 (72.0–82.0) years and a low BMI of 21.5 (16.5–24.2) kg/m². COPD was diagnosed in 66.7% of the patients. The mean forced expiratory volume in 1 second (FEV₁, % of predicted value) and FEV₁/ forced vital capacity (FVC) ratio were 44.2 ± 17.8% and 58.6 (27.3–78.6), respectively, in the overall patient group. Daytime PaO₂, PaCO₂, and bicarbonate (HCO₃⁻) levels were 75.9 (60.3–85.5) mmHg, 42.4 ± 6.9 mmHg, and 26.5 ± 3.6 mmol/L, respectively. Table 1 Patient characteristics Variable All (n = 36) Age (y) [IQR] 78.0 (72.0–82.0) male sex (%) 79.1 Body mass index (kg/m 2 ) [IQR] 21.5 (16.5–24.2) Underlying disease COPD (%) 66.7 Interstitial lung disease (%) 19.4 Restrictive lung disease (%) 5.6 Others (%) 8.3 FEV 1 (% of predicted value) 44.2 ± 17.8 FVC (% of predicted value) 70.5 ± 22.9 FEV 1 / FVC ratio [IQR] 58.6 (27.3–78.6) pH 7.41 ± 0.03 PaCO 2 (mmHg) 42.4 ± 6.9 PaO 2 (mmHg) [IQR] 75.9 (60.3–85.5) Bicarbonate (mmol/L) 26.5 ± 3.6 Overnight pulse oximetry and PtcCO 2 monitoring analysis Overnight accelerometer-integrated pulse oximetry and PtcCO₂ monitoring results are summarized in Table 2 . The mean values of SpO₂, 3% ODI, and T90 were 92.4% (90.8–93.9%), 8.8/h (4.2–18.6/ h), and 11.1% (1.4–31.1%), respectively. The mean and maximum values of PtcCO₂ were 41.2 mmHg (39.7–45.8 mmHg) and 45.9 mmHg (43.5–55.9 mmHg), respectively. Table 2 Data of accelerometer-integrated pulse oximetry and transcutaneous carbon dioxide pressure monitoring Variable All (n = 36) Accelerometer-integrated pulse oximetry Recording time (minutes) [IQR] 469 (432–494) Mean SpO 2 (%) [IQR] 92.4 (90.8–93.9) Lowest SpO 2 (%) [IQR] 81.3 (75.3–85.7) 3% ODI (/ hour) [IQR] 8.8 (4.2–18.6) T88 (%) [IQR] 3.5 (0.5–14.8) T90 (%) [IQR] 11.1 (1.4–31.1) T90 > 30% (persons) 9 Mean pulse rate (times / mins) 71.9 ± 8.8 PtcCO 2 monitoring Recording time (minutes) [IQR] 7:43 (7:12–8:14) Mean PtcCO 2 (mmHg) [IQR] 41.2 (39.7–45.8) Maximum PtcCO 2 (mmHg) [IQR] 45.9 (43.5–55.9) PtcCO 2 > 50 mmHg (%) [IQR] 0.0 (0.0–7.5) Differentiation between episodic nocturnal desaturation events with and without exertion in event-specific analysis In the event-specific analysis, the accelerometer-integrated pulse oximeter revealed a total of 89 episodic desaturation events (2.4 ± 1.7 events per patient). When pulse oximeter data were analyzed in conjunction with accelerometer readings, 56 of the 89 events (62.9%) were classified as exertion-related. Among the 56 exertional events, 37 (66.1%) were attributed to patient-reported exertion. However, 19 events (32.9%) showed exertional patterns based on accelerometer data, although patient-reported exertion was not confirmed (Additional Fig. 3 A). Diagnostic accuracy of possible eNH on an accelerometer-integrated pulse oximetry in event-specific analysis In the event-specific analysis, 33 of the 89 events (37.1%) were identified as positive for suspected eNH. Among these 33 events, 15 were confirmed as true positive cases of eNH, whereas 18 did not meet the established diagnostic criteria (Additional Fig. 3 A). The accelerometer-integrated pulse oximetry demonstrated a sensitivity of 100% (95%CI: 79.6–100%) and a specificity of 75.7% (95%CI: 64.8–84.2%) in detecting suspected eNH. The device yielded a positive predictive value of 45.5% (95%CI: 29.8–62.0%) and a negative predictive value of 100% (95%CI: 93.6–100%) in identifying suspected eNH. Diagnostic accuracy of possible eNH using modified SpO 2 waveform on an accelerometer-integrated pulse oximetry in event-specific analysis Upon analysis with modified SpO₂ waveforms, the number of episodic desaturation events decreased from 89 to 74, attributable to the flattening of the sawtooth pattern typically observed in transient sleep apnea or motion artifacts (Additional Fig. 4 ). When pulse oximetry data incorporating modified SpO₂ waveforms were analyzed, the number of exertion-related episodic desaturation events decreased from 56 to 48 events. In contrast, possible eNH increased from 26 events, as determined by the original SpO₂ waveform, to 33 events. Among the 26 events, 15 were diagnosed as true positive cases of eNH, whereas the remaining 11 did not meet the diagnostic criteria for eNH. The sensitivity and specificity of accelerometer-integrated pulse oximetry for detecting eNH were 100% (95%CI: 72.2–100%) and 81.4% (95%CI: 69.9–89.3%), respectively. Differentiation between episodic nocturnal desaturation events with and without exertion in patient-specific analysis In the patient-specific analysis, 31 out of 36 patients experienced at least one episodic nocturnal desaturation event (Fig. 2 ). When pulse oximetry data were evaluated with added acceleration data, 19 of these patients were identified as having exclusively exertion-induced episodic desaturation events. However, 54.8% (17 out of 31) were classified as positive for possible eNH (Fig. 2 ). Of these 17 patients, 10 were confirmed as true positives of eNH, while the remaining 7 did not meet the diagnostic criteria (Fig. 2 , Additional Fig. 3 B). Diagnostic accuracy of possible eNH on an accelerometer-integrated pulse oximetry in patient-specific analysis Accelerometer-integrated pulse oximetry demonstrated a sensitivity of 100% (95%CI: 100–100%) and a specificity of 73.1% (95%CI: 53.9–86.3%) for detecting eNH. It also yielded a positive predictive value of 58.8% (95%CI: 36.0–78.4%) and a negative predictive value of 100% (95%CI: 83.2–100%) for detecting eNH. Among the seven patients who fulfilled the criteria for possible eNH but did not meet the definitive diagnostic threshold, five were identified as having subclinical eNH. Upon inclusion of subclinical eNH in the diagnostic criteria, the sensitivity and specificity of accelerometer-integrated pulse oximetry increased to 100% (95%CI: 79.6–100%) and 90.5% (95%CI: 71.1–97.3%), respectively. Comparison based on episodic nocturnal hypercapnia Table 3 presents patient characteristics and data obtained from overnight monitoring using accelerometer-integrated pulse oximetry and PtcCO₂, comparing results between patients with and without eNH. Figures 3 and 4 presents comparative analyses of the key parameters associated with eNH and possible eNH, as identified through varying assessment methods. No statistically significant differences were observed in PaO₂, BMI, and mean SpO₂. However, patients diagnosed with eNH group exhibited significantly elevated levels of PaCO₂ (Fig. 3 A), HCO₃⁻, and mean PtcCO₂ (Fig. 4 A). Table 3 Characteristics of patients with and without episodic nocturnal hypercapnia Variable Patients with eNH (n = 10) Patients without eNH (n = 26) P PaO 2 (mmHg) [IQR] 74.9 (66.7–90.7) 77.4 (60.3–85.5) 0.804 PaCO 2 (mmHg) 48.6 ± 5.6 38.5 ± 4.5 < 0.001* Bicarbonate (mmol/L) 29.4 ± 3.1 24.8 ± 2.8 < 0.001* Body mass index (kg/m 2 ) [IQR] 16.6 (14.1–23.7) 21.5 (18.0–24.1) 0.198 Mean SpO 2 (%) [IQR] 90.6 ± 3.0 92.6 ± 2.8 0.113 3% ODI (/ hour) [IQR] 14.8 (5.7–26.2) 7.5 (3.1–14.7) 0.155 T88 (%) [IQR] 9.8 (1.4–32.7.0) 3.9 (0.2–7.5) 0.053 Mean PtcCO 2 (mmHg) [IQR] 49.8 (41.6–56.0) 40.3 (36.4–45.1) 0.001* Maximum PtcCO 2 (mmHg) [IQR] 56.4 (47.7–61.1) 44.0 (40.4–50.2) 0.001* Comparison based on possible episodic nocturnal hypercapnia Table 4 presents patient characteristics and overnight monitoring using accelerometer-integrated pulse oximetry and PtcCO₂, comparing results between patients with possible eNH and those without. No statistically significant differences were observed in PaO₂, mean SpO₂, and mean PtcCO₂. However, patients classified with possible eNH group showed significantly elevated levels of PaCO₂ (Fig. 3 B). In analyses incorporating the modified SpO₂ waveform, patients with possible eNH exhibited significantly elevated levels of daytime PaCO₂, HCO₃⁻, mean PtcCO₂, and maximum PtcCO₂ compared to those without possible eNH (Fig. 3 C, Fig. 4 C, Additional Table 1 ). Table 4 Characteristics of patients with and without possible episodic nocturnal hypercapnia Variable Patients with possible eNH (n = 17) Patients without possible eNH (n = 19) p PaO 2 (mmHg) [IQR] 77.1 (60.4–87.8) 74.7 (62.4–82.3) 0.682 PaCO 2 (mmHg) 44.3 ± 7.7 39.2 ± 4.5 0.041* Bicarbonate (mmol/L) 27.4 ± 3.9 25.1 ± 2.8 0.077 Body mass index (kg/m 2 ) [IQR] 17.3 (15.1–24.2) 21.7 (19.7–24.2) 0.184 Mean SpO 2 (%) [IQR] 92.8 (89.8–93.5) 92.3 (91.1–94.6) 0.165 3% ODI (/ hour) [IQR] 10.2 (3.3–13.9) 7.5 (3.4–13.9) 0.616 T88 (%) [IQR] 3.2 (0.9–21.8) 4.6 (0.1–7.0) 0.138 Mean PtcCO 2 (mmHg) [IQR] 43.4 (40.5–54.7) 40.3 (38.0–45.5) 0.093 Maximum PtcCO 2 (mmHg) [IQR] 49.3 (44.5–60.4) 44.4 (41.9–45.5) 0.257 Discussion This study evaluated the utility of nocturnal accelerometer-integrated pulse oximetry for identifying the presence of elevated eNH as indicated by PtcCO₂ monitoring, corresponding to sleep-related hypoventilation, particularly during REM sleep, in individuals with chronic respiratory disease. Among 89 identified episodic desaturation events, accelerometer-integrated pulse oximetry excluded 56 (62.9%), that were attributable to exertion. In event-specific analysis, the sensitivity and specificity of accelerometer-integrated pulse oximetry in detecting eNH were 100% and 75.7%, respectively. Accelerometer-integrated pulse oximetry is useful in differentiating episodic nocturnal desaturation events with hypercapnia due to hypoventilation from exertional desaturation events and in screening for sleep-related hypoventilation. In OPO, distinguishing between desaturation waveforms resulting from sleep-related hypoventilation and those due to physical exertion is challenging, as their patterns are often similar. Typically, self-reported behavior logs are employed to identify exertion-induced desaturation events. However, the findings of the present study indicated that self-reported behavior logs may lack reliability. In 19 of 56 exertional desaturation events (33.9%), patient-reported exertion was not corroborated by objective data. Previous research similarly identified discrepancies between self-reported physical activity and accelerometer data, although the assessment methods differed from those used in the current study 32 . As a result, patients may not be able to complete the self-report accurately. These inaccuracies in self-documented behavior record sheets may affect the interpretation of previous clinical trials on nocturnal oxygen therapy 33 . The clinical utility of oxygen therapy for nocturnal hypoxemia should be re-assessed following an accurate differentiation between exertion-related and hypoventilation-related desaturation. Daytime hypercapnia is associated with frequent exacerbations and poor prognosis in patients with COPD 7 , 8 . Hypercapnic respiratory failure manifests earlier during sleep than during wakefulness 5 , 34 . This is because sleep has adverse effects on breathing, including disturbances in respiratory control, respiratory muscle function, and lung mechanics 5 . Sleep-related alterations in respiratory control involve decreased chemoreceptor sensitivity, diminished ventilatory responses, and reduced function of accessory respiratory muscles, particularly during REM sleep 5 , 35 . eNH has been reported to be associated with elevated daytime PaCO₂, pulmonary hypertension, and frequent exacerbations in advanced COPD. In contrast, in neuromuscular disorders, eNH is linked to greater use of home NIV and an increased risk of mortality 12 . Thus, eNH is considered an important surrogate marker of poor outcomes that can be assessed noninvasively through PtcCO₂ monitoring. However, PtcCO₂ monitoring is more complex and costlier than OPO 13 , 14 , and requires hospitalization for nighttime monitoring in Japan. To address this, the diagnostic accuracy of accelerometer-integrated pulse oximetry was evaluated as an alternative to PtcCO₂ monitoring for identifying eNH, a surrogate indicator of REM sleep-related hypoventilation. The method demonstrated sufficient sensitivity and specificity for detecting eNH. In this present study, patients with possible eNH indicated by accelerometer-integrated pulse oximetry exhibited higher daytime PaCO₂ levels than those without possible eNH. These findings are consistent with previous studies that compared patients with and without eNH 11 . These results suggest that accelerometer-integrated pulse oximetry could serve as a practical screening tool for eNH prior to conducting PtcCO₂ monitoring. In the patient-specific analysis conducted in this study, the specificity of accelerometer-integrated pulse oximetry for detecting eNH was 73.1%, which was lower than the anticipated value. Review of the false-positive cases revealed that five out of seven patients (71.4%) exhibited a marked decrease in SpO₂ without a corresponding increase in PtcCO₂, defined as a rise of ≥ 3 mmHg but < 5 mmHg from baseline for more than 5 min. Inclusion of subclinical eNH within the diagnostic criteria increased the specificity of accelerometer-integrated pulse oximetry for detecting eNH to 90.5 It is plausible that certain instances of sleep-related hypoventilation induced a more substantial reduction in SpO₂ accompanied by only a minimal elevation in PtcCO₂ (≥ 3 mmHg to < 5 mmHg). However, notably, PtcCO₂ may also increase during REM sleep in healthy individuals. Further investigation is needed to determine the clinical relevance of subclinical eNH. A review of our false-positive cases indicated that recurrent oxygen desaturations caused by transient sleep apnea events or signal artifacts may have contributed to the overdiagnosis of possible eNH (Additional Fig. 4 ). To reduce the confounding influence of coexisting sleep apnea or signal artifacts on diagnostic accuracy, modified SpO₂ waveforms were employed, and possible eNH was re-evaluated. The accuracy of detecting eNH using accelerometer-integrated pulse oximetry improved from 75.7–81.4% in event-specific analyses. Additionally, in the analysis using the modified SpO₂ waveform, daytime PaCO₂, HCO₃⁻, mean PtcCO₂, and maximum PtcCO₂ were significantly higher in patients with possible eNH compared to others (Fig. 3 C, Fig. 4 C, Additional Table 1 ). These findings were consistent with the overall assessment outcomes for eNH. Therefore, the application of the modified SpO₂ waveform may facilitate the identification of episodic oxygen desaturation events attributable to hypoventilation; however, this approach may compromise the sensitivity of sleep apnea detection. Nonetheless, further research is warranted to validate the effectiveness of the waveform modification technique utilized in this study. Limitation The present study has some limitations. First, the study enrolled a relatively small cohort of stable, hospitalized patients with suspected sleep-related breathing disorders at a single general hospital. To the best of our knowledge, this is the first study to evaluate the effectiveness of accelerometer-integrated pulse oximetry. The findings may inform novel approaches to evaluating patients with respiratory failure and optimizing treatment strategies. Second, the association between possible eNH and adverse outcomes, such as exacerbation frequency or mortality in chronic respiratory failure, was not investigated. Nonetheless, previous studies have reported associations between eNH and increased exacerbation frequency and mortality 10 – 12 . In cases diagnosed as possible eNH, transcutaneous carbon dioxide (PtcCO₂) monitoring is recommended to confirm the diagnosis. Conclusion In conclusion, this observational study demonstrated that accelerometer-integrated pulse oximetry effectively distinguishes desaturation resulting from nocturnal physical activity from that caused by sleep-related hypoventilation. The findings also indicated that accelerometer-integrated pulse oximetry may serve as a useful tool for screening early screening eNH. Further investigations involving larger, multicenter cohorts with extended longitudinal follow-up are warranted to assess the long-term clinical utility of accelerometer-integrated pulse oximetry. Abbreviations OPO Overnight pulse oximetry SpO 2 oxygen saturation eNH episodic nocturnal hypercapnia REM rapid eye movement PtcCO 2 transcutaneous carbon dioxide pressure NIV non-invasive ventilation COPD chronic obstructive pulmonary disease ILD interstitial lung disease NMD neuromuscular disease T90 SpO 2 below 90% during sleep ODI oxygen desaturation index Cis confidence intervals PaO 2 arterial oxygen pressure FEV 1 forced expiratory volume in 1 s HCO 3 − bicarbonate BMI body max index PaCO 2 arterial partial carbon dioxide pressure FEV 1 forced expiratory volume in 1 second FVC forced vital capacity Declarations Ethics Approval and Consent to Participate: The study was conducted in accordance with the ethical guidelines of the Japanese Ministry of Health, Labor, and Welfare and was approved by the Institutional Review Board of the Medical Research Institute, KITANO HOSPITAL Ethics Committee (Ethics Board approval number: P2102009). Written informed consent was obtained from all patients. Additionally, we prioritized the protection of personal information in compliance with ethical guidelines. Consent for Publication: Written informed consent for publication of anonymized clinical details and/or accompanying data was obtained from all participants included in this study. All identifying information has been removed to protect participant privacy. Availability of Data and Materials : The datasets generated and/or analyzed during this study are available from the corresponding author upon reasonable request. Conflicts of interest: TK received honoraria for lectures from Teijin Pharma Limited. MF received a research grant from KONICA MINOLTA, INC. HT and AM are employees of KONICA MINOLTA, INC. All other authors declare no conflicts of interest. Funding: This study was financially supported by KONICA MINOLTA, INC Acknowledgments: We thank Toshiro Katayama for providing valuable advice on statistical analysis. We also acknowledge Ryo Yamanaka, Atsushi Funauchi, Shinya Tsukamoto, Yasumitsu Ueki, Hirotaka Tamesada, Takamitsu Imoto, and Yoko Hamakawa for their contributions to data collection. Author Contributions: TK is the guarantor of the manuscript and assumes full responsibility for its content. HT contributed to study design, data collection, data analysis, and manuscript editing. EN contributed to data collection and manuscript editing. SJ contributed to data collection, data analysis, and manuscript editing. CM, DI, and SM contributed to data collection and manuscript editing. AM contributed to study design, data analysis, and manuscript editing. MF, as senior author, contributed to study design, data analysis, manuscript drafting, and manuscript editing. All authors read and approved the final manuscript. References Hilbert J. Sleep-disordered breathing in neuromuscular and chest wall diseases. Clin Chest Med. 2018;39(2):309–24. Aboussouan LS, Mireles-Cabodevila E. 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PLoS ONE. 2020;15(4):e0232420. Lacasse Y, Sériès F, Corbeil F, et al. Randomized trial of nocturnal oxygen in chronic obstructive pulmonary disease. N Engl J Med. 2020;383(12):1129–38. Boing S, Randerath WJ. Chronic hypoventilation syndromes and sleep-related hypoventilation. J Thorac Dis. 2015;7(8):1273–85. Johnson MW, Remmers JE. Accessory muscle activity during sleep in chronic obstructive pulmonary disease. J Appl Physiol Respir Environ Exerc Physiol. 1984;57(4):1011–7. Additional Declarations No competing interests reported. Supplementary Files ULSOXAdditionalFigure1.tif ULSOXAdditionalFigure2A.tif ULSOXAdditionalFigure2B.tif ULSOXAdditionalFigure2C.tif ULSOXAdditionalFigure3A.tif ULSOXAdditionalFigure3B.tif ULSOXAdditionalFigure4.tif Additionalmaterial.docx Cite Share Download PDF Status: Published Journal Publication published 06 Jan, 2026 Read the published version in Respiratory Research → Version 1 posted Editorial decision: Revision requested 30 Oct, 2025 Reviews received at journal 27 Oct, 2025 Reviews received at journal 21 Oct, 2025 Reviews received at journal 14 Oct, 2025 Reviewers agreed at journal 07 Oct, 2025 Reviewers agreed at journal 29 Sep, 2025 Reviewers agreed at journal 29 Sep, 2025 Reviewers invited by journal 28 Sep, 2025 Editor assigned by journal 03 Sep, 2025 Submission checks completed at journal 02 Sep, 2025 First submitted to journal 01 Sep, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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1","display":"","copyAsset":false,"role":"figure","size":475507,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEpisodic nocturnal hypercapnia and desaturation event due to exertion.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eNotes:\u003c/strong\u003e Events were assessed using overnight accelerometer-integrated pulse oximetry and PtcCO₂ monitoring. Grey arrows indicate episodic desaturation events. Black arrowheads indicate episodic nocturnal hypercapnia, characterized by desaturation events and concurrent increases in PtcCO₂ without acceleration data. When desaturation events are accompanied by acceleration, they are attributed to exertion.\u003c/p\u003e\n\u003cp\u003eAbbreviations:\u003cstrong\u003e \u003c/strong\u003ePtcCO\u003csub\u003e2\u003c/sub\u003e: transcutaneous carbon dioxide pressure SpO\u003csub\u003e2\u003c/sub\u003e: oxygen saturation\u003c/p\u003e","description":"","filename":"ULSOXFigure1.png","url":"https://assets-eu.researchsquare.com/files/rs-7506324/v1/5abe8446db246daae87cf67a.png"},{"id":93250295,"identity":"7434ab45-d5d9-4c70-8b45-0f656b09d4f0","added_by":"auto","created_at":"2025-10-10 15:43:08","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":306527,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePatient selection flow diagram\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAbbreviations:\u003cstrong\u003e \u003c/strong\u003ePtcCO\u003csub\u003e2\u003c/sub\u003e: transcutaneous carbon dioxide pressure SpO\u003csub\u003e2\u003c/sub\u003e: oxygen saturation eNH: episodic nocturnal hypercapnia.\u003c/p\u003e","description":"","filename":"ULSOXFigure2.png","url":"https://assets-eu.researchsquare.com/files/rs-7506324/v1/4ea18ac39ed33f55e32ddc08.png"},{"id":93252632,"identity":"21d136db-b7d1-4d6d-b7ff-885ecaf8f053","added_by":"auto","created_at":"2025-10-10 15:59:08","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":222639,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eComparison of daytime arterial carbon dioxide pressure among three groups.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eNotes: \u003c/strong\u003eGroups were classified based on the presence or absence of episodic nocturnal hypercapnia and identification via modified SpO₂ waveforms.\u003cbr\u003e\nA: Daytime PaCO₂ compared between patients with and without episodic nocturnal hypercapnia.\u003cbr\u003e\nB: Comparison of PaCO₂ based on possible episodic nocturnal hypercapnia.\u003cbr\u003e\nC: Comparison of PaCO₂ among groups stratified by possible episodic nocturnal hypercapnia identified through modified SpO₂ waveforms.\u003c/p\u003e\n\u003cp\u003eAbbreviations: PaCO\u003csub\u003e2\u003c/sub\u003e: arterial carbon dioxide pressure eNH: episodic nocturnal hypercapnia\u003c/p\u003e","description":"","filename":"ULSOXFigure3.png","url":"https://assets-eu.researchsquare.com/files/rs-7506324/v1/240b468ecbe04ca035d4da70.png"},{"id":93251602,"identity":"cbad62fc-3f5a-4bcb-9342-33fc2ebfc5af","added_by":"auto","created_at":"2025-10-10 15:51:08","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":210032,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eComparison of transcutaneous carbon dioxide pressure among the three groups.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eNotes:\u003c/strong\u003e A: Comparison of PtcCO₂ in patients with and without episodic nocturnal hypercapnia.\u003cbr\u003e\nB: PtcCO₂ compared between those with and without possible episodic nocturnal hypercapnia.\u003cbr\u003e\nC: PtcCO₂ compared among groups defined by possible episodic nocturnal hypercapnia identified using modified SpO₂ waveforms.\u003c/p\u003e\n\u003cp\u003eAbbreviations: PtcCO\u003csub\u003e2\u003c/sub\u003e: transcutaneous carbon dioxide pressure eNH: episodic nocturnal hypercapnia\u003c/p\u003e","description":"","filename":"ULSOXFigure4.png","url":"https://assets-eu.researchsquare.com/files/rs-7506324/v1/587ac6ee2d031d8436965ceb.png"},{"id":100069166,"identity":"422acd1e-d7cf-46fc-ae47-4c7697aa9ca7","added_by":"auto","created_at":"2026-01-12 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15:43:08","extension":"docx","order_by":8,"title":"","display":"","copyAsset":false,"role":"supplement","size":18178,"visible":true,"origin":"","legend":"","description":"","filename":"Additionalmaterial.docx","url":"https://assets-eu.researchsquare.com/files/rs-7506324/v1/157391e6453eb4d1a00fbfcb.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Detection of Nocturnal Desaturation and Hypercapnia Using Accelerometer- Integrated Pulse Oximetry: A Prospective Observational Study","fulltext":[{"header":"Background","content":"\u003cp\u003eSleep-related hypoventilation frequently occurs in individuals with chronic obstructive pulmonary disease (COPD), neuromuscular disease (NMD), and chest wall disorders, with a reported prevalence ranging from 9\u0026ndash;43%\u003csup\u003e1\u0026ndash;3\u003c/sup\u003e. This condition is attributed to reduced physiological ventilation during sleep and progressive deterioration of respiratory function due to the underlying disease\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. Sleep-related hypoventilation initially manifests during rapid eye movement (REM) sleep and subsequently progresses into non-REM sleep\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e. During REM sleep, activity of the intercostal and accessory respiratory muscles decreases, while hypoxic and hypercapnic ventilatory responses are blunted\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e, resulting in episodic reductions in minute ventilation, oxygen desaturation, and transient elevations in arterial partial pressure of carbon dioxide (PaCO₂)\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. Recurrent nocturnal and early morning elevations in PaCO₂ due to sleep-related hypoventilation may lead to sustained daytime hypercapnia\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e, a condition associated with increased risk of exacerbations and mortality\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e,\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. Although evaluation of sleep-related hypoventilation is crucial, its clinical daytime presentation is often nonspecific, and standard respiratory function tests inadequately predict nocturnal hypoventilation\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e. Therefore, overnight monitoring of respiratory parameters and carbon dioxide levels is recommended for assessing high-risk populations\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eRecently, transcutaneous carbon dioxide pressure (PtcCO₂) monitoring has emerged as a noninvasive modality for evaluating hypoventilation during sleep\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e. Episodic nocturnal hypercapnia (eNH), primarily corresponding to REM sleep-related hypoventilation, has previously been defined based on PtcCO₂ monitoring\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e,\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e.In individuals with COPD, eNH has been associated with pulmonary hypertension and a history of frequent exacerbations\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e,\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. \u003cem\u003eNaito\u003c/em\u003e et al. also reported that eNH has also been linked to future use of home noninvasive ventilation (NIV) and mortality among individuals with NMD\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. Furthermore, the use of NIV specifically targeting eNH has demonstrated a reduction in exacerbation frequency in patients with COPD\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e. Consequently, PtcCO₂ monitoring serves as a valuable tool for the assessment of sleep-related hypoventilation and the initiation of NIV. However, overnight PtcCO₂ monitoring remains technically complex, cost-prohibitive, and is not widely accessible in North America\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e,\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e, and Japan. In Japan, overnight PtcCO₂ monitoring is typically performed during hospitalization, rather than in the home setting. Therefore, the use of PtcCO₂ monitoring as a screening modality for large populations suspected of sleep-related hypoventilation remains limited.\u003c/p\u003e\u003cp\u003eOvernight pulse oximetry (OPO) represents a cost-effective, safe, and reliable modality for assessing the cardiorespiratory function in outpatient settings\u003csup\u003e\u003cspan additionalcitationids=\"CR16\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e. It is particularly known for its simplicity and accuracy in detecting sleep-related breathing disorders\u003csup\u003e\u003cspan additionalcitationids=\"CR19\" citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e. OPO may also facilitate the detection of sleep-related hypoventilation, manifested as episodic nocturnal desaturation, without requiring overnight PtcCO₂ monitoring. Nocturnal oxygen desaturation has been previously documented in individuals with COPD, interstitial lung disease (ILD), restrictive thoracic disease, and NMD \u003csup\u003e\u003cspan additionalcitationids=\"CR22 CR23 CR24\" citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e. In REM sleep-related hypoventilation, prolonged episodes of oxygen desaturation lasting 5\u0026ndash;30 min and recurring every 90\u0026ndash;120 min throughout the night are commonly observed\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e,\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e. This episodic nocturnal desaturation has been associated with adverse clinical outcomes\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e. However, distinguishing whether episodic nocturnal desaturations arise from exertional activity (e.g., nocturnal ambulation) or from sleep-related hypoventilation remains challenging based solely on OPO data. This diagnostic challenge stems from the similarity in desaturation waveforms observed in REM sleep-related hypoventilation and exertional hypoxia.\u003c/p\u003e\u003cp\u003eRecent evidence suggests that wrist-worn accelerometers may serve as physiological markers of nocturnal exertional events\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e. It was hypothesized that accelerometer-integrated pulse oximetry could distinguish between exertion-induced nocturnal desaturation and that resulting from hypoventilation during sleep.\u003c/p\u003e\u003cp\u003eAccordingly, this study aimed to evaluate whether overnight accelerometer-integrated pulse oximetry could effectively distinguish between hypoxia secondary to exertion and that due to sleep-related hypoventilation. The diagnostic accuracy of accelerometer-integrated pulse oximetry for detecting eNH was prospectively validated against PtcCO₂ monitoring. This approach may facilitate broader implementation of outpatient screening for sleep-related hypoventilation, especially in resource-constrained settings.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003ePatients\u003c/h2\u003e\u003cp\u003eA prospective observational study was conducted to evaluate the diagnostic accuracy of accelerometer-integrated pulse oximetry in detecting episodic nocturnal hypercapnia among individuals with suspected sleep-related breathing disorders. Consecutive, clinically stable patients admitted to the Medical Research Institute, KITANO HOSPITAL, for evaluation of suspected exertional dyspnea worsening were enrolled between July 2021 and December 2022. The inclusion criteria for this study were as follows: (1) age\u0026thinsp;\u0026ge;\u0026thinsp;20 years, (2) medical history of chronic pulmonary disease, and (3) absence of long-term oxygen therapy use. Exclusion criteria were: (1) a pre-existing diagnosis of obstructive sleep apnea, (2) monitoring duration for pulse oximetry and PtcCO₂ of less than four hours, and (3) sustained nocturna SpO₂ levels below 85%. Sample size determination was guided by feasibility considerations and the availability of eligible participants during the study period.\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eMeasurements and data collection\u003c/h3\u003e\n\u003cp\u003eSociodemographic, clinical, and laboratory data were extracted from electronic medical records. Body mass index (BMI) was calculated as weight in kilograms divided by height in meters squared (kg/m\u0026sup2;. Pulmonary function tests were performed by trained personnel in accordance with the American Thoracic Society and European Respiratory Society guidelines\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. Arterial blood gas analysis was performed during the day in the supine position using the RAPIDLAB 1200 System (Siemens Healthcare Diagnostics Incorporated, USA). All arterial blood gas samples were obtained while patients were breathing ambient air. Overnight evaluations without supplemental oxygen administration were performed using PtcCO\u003csub\u003e2\u003c/sub\u003e monitoring with the SenTec Digital Monitor (SenTec, Therwil, Switzerland) and accelerometer-integrated pulse oximetry with the PULSOX-500i (KONICAMINOLTA, INC, Tokyo, Japan). During sleep, each patient wore the accelerometer-integrated pulse oximetry device on one wrist and a finger-mounted probe measuring SpO₂. Patients were instructed to press the event marker or manually record their behaviors during the night. Pulse oximetry data were analyzed using the DS-500 (KONICAMINOLTA, INC, Tokyo, Japan) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Two board-certified respiratory specialists, each with over ten years of clinical experience, independently evaluated the PtcCO₂ and pulse oximetry data.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\n\u003ch3\u003eDefinition of oxygen desaturation event, possible eNH, and eNH\u003c/h3\u003e\n\u003cp\u003eThe most widely accepted definition of exercise-induced desaturation is a reduction in oxygen saturation greater than 4% from baseline and/or a SpO₂ below 90% during the 6-min walk test \u003csup\u003e\u003cspan additionalcitationids=\"CR30\" citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e. In accordance with prior research, oxygen desaturation events in the this study were defined as a decrease in SpO₂ of \u0026ge;\u0026thinsp;4% from baseline and a sustained SpO₂ \u0026lt;90% for at least 5 minutes, measured using accelerometer-integrated pulse oximetry. Possible eNH was defined as a\u0026thinsp;\u0026ge;\u0026thinsp;4% desaturation from baseline and SpO₂ \u0026lt;90% for \u0026ge;\u0026thinsp;5 min continuously, without exertional acceleration data on accelerometer-integrated pulse oximetry. Exertion was identified using acceleration data, as described in the supplementary materials. eNH was defined as a\u0026thinsp;\u0026ge;\u0026thinsp;5 mmHg increase from baseline PtcCO₂ from baseline, accompanied by SpO₂ \u0026lt;90% for \u0026ge;\u0026thinsp;5 min continuously, occurring at least once during the night, according to previously established criteria (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e)\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e,\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. Subclinical eNH was defined as a sustained increase in PtcCO₂ of \u0026ge;\u0026thinsp;3 mmHg but \u0026lt;\u0026thinsp;5 mmHg from baseline for at least 5 min, accompanied by oxygen desaturation to below 90% (Additional Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eEvent-specific and patient-level analyses of oxygen desaturation were conducted in this study. In the event-specific analysis, each oxygen desaturation event was assessed to determine whether it was due to sleep-related hypoventilation. Conversely, patient-specific analysis involved identifying the presence of sleep-related hypoventilation-induced desaturation on an individual basis. Patients were classified as having eNH if at least one eNH event was identified during overnight monitoring.\u003c/p\u003e\u003cp\u003eOvernight accelerometer-integrated pulse oximetry data were used to extract mean SpO₂, time spent with SpO₂ \u0026lt;90% (T90), 3% oxygen desaturation index (ODI), and mean pulse rate. Nocturnal mean and maximal PtcCO₂ values were also obtained from overnight PtcCO₂ monitoring. To facilitate analysis using modified SpO₂ waveforms, desaturation dip intervals were identified and the waveform was reconstructed accordingly. Detailed methodologies for processing the modified SpO₂ waveforms is provided in the additional materials. Analysis using the modified SpO₂ waveforms demonstrated a flattened sawtooth pattern, typically observed in cases of sleep apnea or signal artifact.\u003c/p\u003e\n\u003ch3\u003eEthics and statistics\u003c/h3\u003e\n\u003cp\u003e The study was conducted in compliance with the ethical guidelines of the Japanese Ministry of Health, Labor, and Welfare and received approval the Institutional Review Board of the Medical Research Institute, KITANO HOSPITAL Ethics Committee (Ethics Board approval number: P2102009). All participants provided written informed consent prior to study enrollment. In addition, the confidentiality of personal information was maintained in accordance with established ethical guidelines.\u003c/p\u003e\u003cp\u003eThe Shapiro\u0026ndash;Wilk test was used to assess the normality of data distribution. Parametric variables are presented as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation, whereas nonparametric variables are reported as median (interquartile range [IQR]). Group comparisons were performed using Student's t-test for normally distributed data with equal variances, Welch's t-test for data with unequal variances, and the Mann\u0026ndash;Whitney U test for non-normally distributed data. Diagnostic performance is expressed in terms of sensitivity and specificity with corresponding 95% confidence intervals (CIs). A p-value of less than 0.05 was considered statistically significant for all analyses. All statistical analyses were performed using IBM SPSS Statistics for Windows version 25 (IBM Corp., Armonk, N.Y., USA).\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eThis section summarizes the clinical characteristics of the study cohort and evaluates the diagnostic efficacy of accelerometer-integrated pulse oximetry for identifying episodic nocturnal hypercapnia. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e illustrates the patient selection flowchart used in this study. In total of 36 patients (30 men and 6 women) met the inclusion criteria. Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e presents patient characteristics, including a median age of 78.0 (72.0\u0026ndash;82.0) years and a low BMI of 21.5 (16.5\u0026ndash;24.2) kg/m\u0026sup2;. COPD was diagnosed in 66.7% of the patients. The mean forced expiratory volume in 1 second (FEV₁, % of predicted value) and FEV₁/ forced vital capacity (FVC) ratio were 44.2\u0026thinsp;\u0026plusmn;\u0026thinsp;17.8% and 58.6 (27.3\u0026ndash;78.6), respectively, in the overall patient group. Daytime PaO₂, PaCO₂, and bicarbonate (HCO₃⁻) levels were 75.9 (60.3\u0026ndash;85.5) mmHg, 42.4\u0026thinsp;\u0026plusmn;\u0026thinsp;6.9 mmHg, and 26.5\u0026thinsp;\u0026plusmn;\u0026thinsp;3.6 mmol/L, respectively.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003ePatient characteristics\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"2\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eVariable\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eAll (n\u0026thinsp;=\u0026thinsp;36)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAge (y) [IQR]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e78.0 (72.0\u0026ndash;82.0)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003emale sex (%)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e79.1\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eBody mass index (kg/m\u003csup\u003e2\u003c/sup\u003e) [IQR]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e21.5 (16.5\u0026ndash;24.2)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eUnderlying disease\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCOPD (%)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e66.7\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eInterstitial lung disease (%)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e19.4\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eRestrictive lung disease (%)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e5.6\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eOthers (%)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e8.3\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFEV\u003csub\u003e1\u003c/sub\u003e (% of predicted value)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e44.2\u0026thinsp;\u0026plusmn;\u0026thinsp;17.8\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFVC (% of predicted value)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e70.5\u0026thinsp;\u0026plusmn;\u0026thinsp;22.9\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFEV\u003csub\u003e1\u003c/sub\u003e/ FVC ratio [IQR]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e58.6 (27.3\u0026ndash;78.6)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003epH\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e7.41\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePaCO\u003csub\u003e2\u003c/sub\u003e (mmHg)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e42.4\u0026thinsp;\u0026plusmn;\u0026thinsp;6.9\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePaO\u003csub\u003e2\u003c/sub\u003e (mmHg) [IQR]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e75.9 (60.3\u0026ndash;85.5)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eBicarbonate (mmol/L)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e26.5\u0026thinsp;\u0026plusmn;\u0026thinsp;3.6\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003eOvernight pulse oximetry and PtcCO\u003csub\u003e2\u003c/sub\u003e monitoring analysis\u003c/h2\u003e\u003cp\u003eOvernight accelerometer-integrated pulse oximetry and PtcCO₂ monitoring results are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The mean values of SpO₂, 3% ODI, and T90 were 92.4% (90.8\u0026ndash;93.9%), 8.8/h (4.2\u0026ndash;18.6/ h), and 11.1% (1.4\u0026ndash;31.1%), respectively. The mean and maximum values of PtcCO₂ were 41.2 mmHg (39.7\u0026ndash;45.8 mmHg) and 45.9 mmHg (43.5\u0026ndash;55.9 mmHg), respectively.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eData of accelerometer-integrated pulse oximetry and transcutaneous carbon dioxide pressure monitoring\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"2\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eVariable\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eAll (n\u0026thinsp;=\u0026thinsp;36)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eAccelerometer-integrated pulse oximetry\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eRecording time (minutes) [IQR]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e469 (432\u0026ndash;494)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMean SpO\u003csub\u003e2\u003c/sub\u003e (%) [IQR]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e92.4 (90.8\u0026ndash;93.9)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eLowest SpO\u003csub\u003e2\u003c/sub\u003e (%) [IQR]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e81.3 (75.3\u0026ndash;85.7)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e3% ODI (/ hour) [IQR]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e8.8 (4.2\u0026ndash;18.6)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eT88 (%) [IQR]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e3.5 (0.5\u0026ndash;14.8)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eT90 (%) [IQR]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e11.1 (1.4\u0026ndash;31.1)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eT90\u0026thinsp;\u0026gt;\u0026thinsp;30% (persons)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e9\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMean pulse rate (times / mins)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e71.9\u0026thinsp;\u0026plusmn;\u0026thinsp;8.8\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003ePtcCO\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e \u003cb\u003emonitoring\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eRecording time (minutes) [IQR]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e7:43 (7:12\u0026ndash;8:14)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMean PtcCO\u003csub\u003e2\u003c/sub\u003e (mmHg) [IQR]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e41.2 (39.7\u0026ndash;45.8)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMaximum PtcCO\u003csub\u003e2\u003c/sub\u003e (mmHg) [IQR]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e45.9 (43.5\u0026ndash;55.9)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePtcCO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;\u0026gt;\u0026thinsp;50 mmHg (%) [IQR]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.0 (0.0\u0026ndash;7.5)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eDifferentiation between episodic nocturnal desaturation events with and without exertion in event-specific analysis\u003c/h3\u003e\n\u003cp\u003eIn the event-specific analysis, the accelerometer-integrated pulse oximeter revealed a total of 89 episodic desaturation events (2.4\u0026thinsp;\u0026plusmn;\u0026thinsp;1.7 events per patient). When pulse oximeter data were analyzed in conjunction with accelerometer readings, 56 of the 89 events (62.9%) were classified as exertion-related. Among the 56 exertional events, 37 (66.1%) were attributed to patient-reported exertion. However, 19 events (32.9%) showed exertional patterns based on accelerometer data, although patient-reported exertion was not confirmed (Additional Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\n\u003ch3\u003eDiagnostic accuracy of possible eNH on an accelerometer-integrated pulse oximetry in event-specific analysis\u003c/h3\u003e\n\u003cp\u003eIn the event-specific analysis, 33 of the 89 events (37.1%) were identified as positive for suspected eNH. Among these 33 events, 15 were confirmed as true positive cases of eNH, whereas 18 did not meet the established diagnostic criteria (Additional Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA). The accelerometer-integrated pulse oximetry demonstrated a sensitivity of 100% (95%CI: 79.6\u0026ndash;100%) and a specificity of 75.7% (95%CI: 64.8\u0026ndash;84.2%) in detecting suspected eNH. The device yielded a positive predictive value of 45.5% (95%CI: 29.8\u0026ndash;62.0%) and a negative predictive value of 100% (95%CI: 93.6\u0026ndash;100%) in identifying suspected eNH.\u003c/p\u003e\u003cp\u003e\u003cb\u003eDiagnostic accuracy of possible eNH using modified SpO\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e \u003cb\u003ewaveform on an accelerometer-integrated pulse oximetry in event-specific analysis\u003c/b\u003e\u003c/p\u003e\u003cp\u003eUpon analysis with modified SpO₂ waveforms, the number of episodic desaturation events decreased from 89 to 74, attributable to the flattening of the sawtooth pattern typically observed in transient sleep apnea or motion artifacts (Additional Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). When pulse oximetry data incorporating modified SpO₂ waveforms were analyzed, the number of exertion-related episodic desaturation events decreased from 56 to 48 events. In contrast, possible eNH increased from 26 events, as determined by the original SpO₂ waveform, to 33 events.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eAmong the 26 events, 15 were diagnosed as true positive cases of eNH, whereas the remaining 11 did not meet the diagnostic criteria for eNH. The sensitivity and specificity of accelerometer-integrated pulse oximetry for detecting eNH were 100% (95%CI: 72.2\u0026ndash;100%) and 81.4% (95%CI: 69.9\u0026ndash;89.3%), respectively.\u003c/p\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003eDifferentiation between episodic nocturnal desaturation events with and without exertion in patient-specific analysis\u003c/h2\u003e\u003cp\u003eIn the patient-specific analysis, 31 out of 36 patients experienced at least one episodic nocturnal desaturation event (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). When pulse oximetry data were evaluated with added acceleration data, 19 of these patients were identified as having exclusively exertion-induced episodic desaturation events. However, 54.8% (17 out of 31) were classified as positive for possible eNH (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Of these 17 patients, 10 were confirmed as true positives of eNH, while the remaining 7 did not meet the diagnostic criteria (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, Additional Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003eDiagnostic accuracy of possible eNH on an accelerometer-integrated pulse oximetry in patient-specific analysis\u003c/h2\u003e\u003cp\u003eAccelerometer-integrated pulse oximetry demonstrated a sensitivity of 100% (95%CI: 100\u0026ndash;100%) and a specificity of 73.1% (95%CI: 53.9\u0026ndash;86.3%) for detecting eNH. It also yielded a positive predictive value of 58.8% (95%CI: 36.0\u0026ndash;78.4%) and a negative predictive value of 100% (95%CI: 83.2\u0026ndash;100%) for detecting eNH.\u003c/p\u003e\u003cp\u003eAmong the seven patients who fulfilled the criteria for possible eNH but did not meet the definitive diagnostic threshold, five were identified as having subclinical eNH. Upon inclusion of subclinical eNH in the diagnostic criteria, the sensitivity and specificity of accelerometer-integrated pulse oximetry increased to 100% (95%CI: 79.6\u0026ndash;100%) and 90.5% (95%CI: 71.1\u0026ndash;97.3%), respectively.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003eComparison based on episodic nocturnal hypercapnia\u003c/h2\u003e\u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e presents patient characteristics and data obtained from overnight monitoring using accelerometer-integrated pulse oximetry and PtcCO₂, comparing results between patients with and without eNH. Figures\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e presents comparative analyses of the key parameters associated with eNH and possible eNH, as identified through varying assessment methods. No statistically significant differences were observed in PaO₂, BMI, and mean SpO₂. However, patients diagnosed with eNH group exhibited significantly elevated levels of PaCO₂ (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA), HCO₃⁻, and mean PtcCO₂ (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA).\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eCharacteristics of patients with and without episodic nocturnal hypercapnia\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eVariable\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePatients with eNH\u003c/p\u003e\u003cp\u003e(n\u0026thinsp;=\u0026thinsp;10)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePatients without eNH\u003c/p\u003e\u003cp\u003e(n\u0026thinsp;=\u0026thinsp;26)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePaO\u003csub\u003e2\u003c/sub\u003e (mmHg) [IQR]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e74.9 (66.7\u0026ndash;90.7)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e77.4 (60.3\u0026ndash;85.5)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e\u003cem\u003e0.804\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePaCO\u003csub\u003e2\u003c/sub\u003e (mmHg)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e48.6\u0026thinsp;\u0026plusmn;\u0026thinsp;5.6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e38.5\u0026thinsp;\u0026plusmn;\u0026thinsp;4.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e\u003cem\u003e\u0026lt;\u0026thinsp;0.001*\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eBicarbonate (mmol/L)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e29.4\u0026thinsp;\u0026plusmn;\u0026thinsp;3.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e24.8\u0026thinsp;\u0026plusmn;\u0026thinsp;2.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e\u003cem\u003e\u0026lt;\u0026thinsp;0.001*\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eBody mass index (kg/m\u003csup\u003e2\u003c/sup\u003e) [IQR]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e16.6 (14.1\u0026ndash;23.7)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e21.5 (18.0\u0026ndash;24.1)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e\u003cem\u003e0.198\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMean SpO\u003csub\u003e2\u003c/sub\u003e (%) [IQR]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e90.6\u0026thinsp;\u0026plusmn;\u0026thinsp;3.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e92.6\u0026thinsp;\u0026plusmn;\u0026thinsp;2.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e\u003cem\u003e0.113\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e3% ODI (/ hour) [IQR]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e14.8 (5.7\u0026ndash;26.2)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e7.5 (3.1\u0026ndash;14.7)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e\u003cem\u003e0.155\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eT88 (%) [IQR]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e9.8 (1.4\u0026ndash;32.7.0)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e3.9 (0.2\u0026ndash;7.5)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e\u003cem\u003e0.053\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMean PtcCO\u003csub\u003e2\u003c/sub\u003e (mmHg) [IQR]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e49.8 (41.6\u0026ndash;56.0)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e40.3 (36.4\u0026ndash;45.1)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e\u003cem\u003e0.001*\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMaximum PtcCO\u003csub\u003e2\u003c/sub\u003e (mmHg) [IQR]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e56.4 (47.7\u0026ndash;61.1)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e44.0 (40.4\u0026ndash;50.2)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e\u003cem\u003e0.001*\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\u003ch2\u003eComparison based on possible episodic nocturnal hypercapnia\u003c/h2\u003e\u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e presents patient characteristics and overnight monitoring using accelerometer-integrated pulse oximetry and PtcCO₂, comparing results between patients with possible eNH and those without. No statistically significant differences were observed in PaO₂, mean SpO₂, and mean PtcCO₂. However, patients classified with possible eNH group showed significantly elevated levels of PaCO₂ (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB). In analyses incorporating the modified SpO₂ waveform, patients with possible eNH exhibited significantly elevated levels of daytime PaCO₂, HCO₃⁻, mean PtcCO₂, and maximum PtcCO₂ compared to those without possible eNH (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eC, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eC, Additional Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eCharacteristics of patients with and without possible episodic nocturnal hypercapnia\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eVariable\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePatients with possible eNH\u003c/p\u003e\u003cp\u003e(n\u0026thinsp;=\u0026thinsp;17)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePatients without possible eNH\u003c/p\u003e\u003cp\u003e(n\u0026thinsp;=\u0026thinsp;19)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u003cem\u003ep\u003c/em\u003e\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePaO\u003csub\u003e2\u003c/sub\u003e (mmHg) [IQR]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e77.1 (60.4\u0026ndash;87.8)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e74.7 (62.4\u0026ndash;82.3)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e\u003cem\u003e0.682\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePaCO\u003csub\u003e2\u003c/sub\u003e (mmHg)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e44.3\u0026thinsp;\u0026plusmn;\u0026thinsp;7.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e39.2\u0026thinsp;\u0026plusmn;\u0026thinsp;4.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e\u003cem\u003e0.041*\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eBicarbonate (mmol/L)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e27.4\u0026thinsp;\u0026plusmn;\u0026thinsp;3.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e25.1\u0026thinsp;\u0026plusmn;\u0026thinsp;2.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e\u003cem\u003e0.077\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eBody mass index (kg/m\u003csup\u003e2\u003c/sup\u003e) [IQR]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e17.3 (15.1\u0026ndash;24.2)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e21.7 (19.7\u0026ndash;24.2)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e\u003cem\u003e0.184\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMean SpO\u003csub\u003e2\u003c/sub\u003e (%) [IQR]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e92.8 (89.8\u0026ndash;93.5)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e92.3 (91.1\u0026ndash;94.6)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e\u003cem\u003e0.165\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e3% ODI (/ hour) [IQR]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e10.2 (3.3\u0026ndash;13.9)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e7.5 (3.4\u0026ndash;13.9)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e\u003cem\u003e0.616\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eT88 (%) [IQR]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e3.2 (0.9\u0026ndash;21.8)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e4.6 (0.1\u0026ndash;7.0)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e\u003cem\u003e0.138\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMean PtcCO\u003csub\u003e2\u003c/sub\u003e (mmHg) [IQR]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e43.4 (40.5\u0026ndash;54.7)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e40.3 (38.0\u0026ndash;45.5)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e\u003cem\u003e0.093\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMaximum PtcCO\u003csub\u003e2\u003c/sub\u003e (mmHg) [IQR]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e49.3 (44.5\u0026ndash;60.4)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e44.4 (41.9\u0026ndash;45.5)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e\u003cem\u003e0.257\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eThis study evaluated the utility of nocturnal accelerometer-integrated pulse oximetry for identifying the presence of elevated eNH as indicated by PtcCO₂ monitoring, corresponding to sleep-related hypoventilation, particularly during REM sleep, in individuals with chronic respiratory disease. Among 89 identified episodic desaturation events, accelerometer-integrated pulse oximetry excluded 56 (62.9%), that were attributable to exertion. In event-specific analysis, the sensitivity and specificity of accelerometer-integrated pulse oximetry in detecting eNH were 100% and 75.7%, respectively. Accelerometer-integrated pulse oximetry is useful in differentiating episodic nocturnal desaturation events with hypercapnia due to hypoventilation from exertional desaturation events and in screening for sleep-related hypoventilation.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eIn OPO, distinguishing between desaturation waveforms resulting from sleep-related hypoventilation and those due to physical exertion is challenging, as their patterns are often similar. Typically, self-reported behavior logs are employed to identify exertion-induced desaturation events. However, the findings of the present study indicated that self-reported behavior logs may lack reliability. In 19 of 56 exertional desaturation events (33.9%), patient-reported exertion was not corroborated by objective data. Previous research similarly identified discrepancies between self-reported physical activity and accelerometer data, although the assessment methods differed from those used in the current study\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e. As a result, patients may not be able to complete the self-report accurately. These inaccuracies in self-documented behavior record sheets may affect the interpretation of previous clinical trials on nocturnal oxygen therapy\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e. The clinical utility of oxygen therapy for nocturnal hypoxemia should be re-assessed following an accurate differentiation between exertion-related and hypoventilation-related desaturation.\u003c/p\u003e\u003cp\u003eDaytime hypercapnia is associated with frequent exacerbations and poor prognosis in patients with COPD \u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e,\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. Hypercapnic respiratory failure manifests earlier during sleep than during wakefulness\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e,\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e. This is because sleep has adverse effects on breathing, including disturbances in respiratory control, respiratory muscle function, and lung mechanics\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e. Sleep-related alterations in respiratory control involve decreased chemoreceptor sensitivity, diminished ventilatory responses, and reduced function of accessory respiratory muscles, particularly during REM sleep\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e,\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e. eNH has been reported to be associated with elevated daytime PaCO₂, pulmonary hypertension, and frequent exacerbations in advanced COPD. In contrast, in neuromuscular disorders, eNH is linked to greater use of home NIV and an increased risk of mortality\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. Thus, eNH is considered an important surrogate marker of poor outcomes that can be assessed noninvasively through PtcCO₂ monitoring. However, PtcCO₂ monitoring is more complex and costlier than OPO\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e,\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e, and requires hospitalization for nighttime monitoring in Japan. To address this, the diagnostic accuracy of accelerometer-integrated pulse oximetry was evaluated as an alternative to PtcCO₂ monitoring for identifying eNH, a surrogate indicator of REM sleep-related hypoventilation. The method demonstrated sufficient sensitivity and specificity for detecting eNH. In this present study, patients with possible eNH indicated by accelerometer-integrated pulse oximetry exhibited higher daytime PaCO₂ levels than those without possible eNH. These findings are consistent with previous studies that compared patients with and without eNH\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. These results suggest that accelerometer-integrated pulse oximetry could serve as a practical screening tool for eNH prior to conducting PtcCO₂ monitoring.\u003c/p\u003e\u003cp\u003eIn the patient-specific analysis conducted in this study, the specificity of accelerometer-integrated pulse oximetry for detecting eNH was 73.1%, which was lower than the anticipated value. Review of the false-positive cases revealed that five out of seven patients (71.4%) exhibited a marked decrease in SpO₂ without a corresponding increase in PtcCO₂, defined as a rise of \u0026ge;\u0026thinsp;3 mmHg but \u0026lt;\u0026thinsp;5 mmHg from baseline for more than 5 min. Inclusion of subclinical eNH within the diagnostic criteria increased the specificity of accelerometer-integrated pulse oximetry for detecting eNH to 90.5 It is plausible that certain instances of sleep-related hypoventilation induced a more substantial reduction in SpO₂ accompanied by only a minimal elevation in PtcCO₂ (\u0026ge;\u0026thinsp;3 mmHg to \u0026lt;\u0026thinsp;5 mmHg). However, notably, PtcCO₂ may also increase during REM sleep in healthy individuals. Further investigation is needed to determine the clinical relevance of subclinical eNH.\u003c/p\u003e\u003cp\u003eA review of our false-positive cases indicated that recurrent oxygen desaturations caused by transient sleep apnea events or signal artifacts may have contributed to the overdiagnosis of possible eNH (Additional Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). To reduce the confounding influence of coexisting sleep apnea or signal artifacts on diagnostic accuracy, modified SpO₂ waveforms were employed, and possible eNH was re-evaluated. The accuracy of detecting eNH using accelerometer-integrated pulse oximetry improved from 75.7\u0026ndash;81.4% in event-specific analyses. Additionally, in the analysis using the modified SpO₂ waveform, daytime PaCO₂, HCO₃⁻, mean PtcCO₂, and maximum PtcCO₂ were significantly higher in patients with possible eNH compared to others (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eC, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eC, Additional Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). These findings were consistent with the overall assessment outcomes for eNH. Therefore, the application of the modified SpO₂ waveform may facilitate the identification of episodic oxygen desaturation events attributable to hypoventilation; however, this approach may compromise the sensitivity of sleep apnea detection. Nonetheless, further research is warranted to validate the effectiveness of the waveform modification technique utilized in this study.\u003c/p\u003e\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\u003ch2\u003eLimitation\u003c/h2\u003e\u003cp\u003eThe present study has some limitations. First, the study enrolled a relatively small cohort of stable, hospitalized patients with suspected sleep-related breathing disorders at a single general hospital. To the best of our knowledge, this is the first study to evaluate the effectiveness of accelerometer-integrated pulse oximetry. The findings may inform novel approaches to evaluating patients with respiratory failure and optimizing treatment strategies. Second, the association between possible eNH and adverse outcomes, such as exacerbation frequency or mortality in chronic respiratory failure, was not investigated. Nonetheless, previous studies have reported associations between eNH and increased exacerbation frequency and mortality\u003csup\u003e\u003cspan additionalcitationids=\"CR11\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. In cases diagnosed as possible eNH, transcutaneous carbon dioxide (PtcCO₂) monitoring is recommended to confirm the diagnosis.\u003c/p\u003e\u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn conclusion, this observational study demonstrated that accelerometer-integrated pulse oximetry effectively distinguishes desaturation resulting from nocturnal physical activity from that caused by sleep-related hypoventilation. The findings also indicated that accelerometer-integrated pulse oximetry may serve as a useful tool for screening early screening eNH. Further investigations involving larger, multicenter cohorts with extended longitudinal follow-up are warranted to assess the long-term clinical utility of accelerometer-integrated pulse oximetry.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cdiv class=\"DefinitionList\"\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eOPO\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eOvernight pulse oximetry\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eSpO\u003csub\u003e2\u003c/sub\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eoxygen saturation\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eeNH\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eepisodic nocturnal hypercapnia\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eREM\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003erapid eye movement\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003ePtcCO\u003csub\u003e2\u003c/sub\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003etranscutaneous carbon dioxide pressure\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eNIV\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003enon-invasive ventilation\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eCOPD\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003echronic obstructive pulmonary disease\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eILD\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003einterstitial lung disease\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eNMD\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eneuromuscular disease\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eT90\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eSpO\u003csub\u003e2\u003c/sub\u003e below 90% during sleep\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eODI\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eoxygen desaturation index\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eCis\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003econfidence intervals\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003ePaO\u003csub\u003e2\u003c/sub\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003earterial oxygen pressure\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eFEV\u003csub\u003e1\u003c/sub\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eforced expiratory volume in 1 s\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eHCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003ebicarbonate\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eBMI\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003ebody max index\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003ePaCO\u003csub\u003e2\u003c/sub\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003earterial partial carbon dioxide pressure\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eFEV\u003csub\u003e1\u003c/sub\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eforced expiratory volume in 1 second\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003eFVC\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eforced vital capacity\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics Approval and Consent to Participate:\u0026nbsp;\u003c/strong\u003eThe study was conducted in accordance with the ethical guidelines of the Japanese Ministry of Health, Labor, and Welfare and was approved by the Institutional Review Board of the Medical Research Institute, KITANO HOSPITAL Ethics Committee (Ethics Board approval number: P2102009). Written informed consent was obtained from all patients. Additionally, we prioritized the protection of personal information in compliance with ethical guidelines.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for Publication:\u003c/strong\u003e Written informed consent for publication of anonymized clinical details and/or accompanying data was obtained from all participants included in this study. All identifying information has been removed to protect participant privacy.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of Data and Materials\u003c/strong\u003e: The datasets generated and/or analyzed during this study are available from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of interest:\u0026nbsp;\u003c/strong\u003eTK received honoraria for lectures from Teijin Pharma Limited. MF received a research grant from KONICA MINOLTA, INC. HT and AM are employees of KONICA MINOLTA, INC. All other authors declare no conflicts of interest.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding:\u0026nbsp;\u003c/strong\u003eThis study was financially supported by KONICA MINOLTA, INC\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments:\u003c/strong\u003e We thank Toshiro Katayama for providing valuable advice on statistical analysis. We also acknowledge Ryo Yamanaka, Atsushi Funauchi, Shinya Tsukamoto, Yasumitsu Ueki, Hirotaka Tamesada, Takamitsu Imoto, and Yoko Hamakawa for their contributions to data collection.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions:\u003c/strong\u003e TK is the guarantor of the manuscript and assumes full responsibility for its content. HT contributed to study design, data collection, data analysis, and manuscript editing. EN contributed to data collection and manuscript editing. SJ contributed to data collection, data analysis, and manuscript editing. CM, DI, and SM contributed to data collection and manuscript editing. AM contributed to study design, data analysis, and manuscript editing. MF, as senior author, contributed to study design, data analysis, manuscript drafting, and manuscript editing. All authors read and approved the final manuscript.\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eHilbert J. Sleep-disordered breathing in neuromuscular and chest wall diseases. Clin Chest Med. 2018;39(2):309\u0026ndash;24.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAboussouan LS, Mireles-Cabodevila E. Sleep-disordered breathing in neuromuscular disease: diagnostic and therapeutic challenges. Chest. 2017;152(4):880\u0026ndash;92.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eO'Donoghue FJ, Catcheside PG, Ellis EE, et al. Sleep hypoventilation in hypercapnic chronic obstructive pulmonary disease: prevalence and associated factors. 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Oxygen desaturation in 6-min walk test is a risk factor for adverse outcomes in COPD. Eur Respir J. 2016;48(1):82\u0026ndash;91.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eCrisafulli E, Iattoni A, Venturelli E, et al. Predicting walking-induced oxygen desaturations in COPD patients: a statistical model. Respir Care. 2013;58(9):1495\u0026ndash;503.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ePerez T, Desl\u0026eacute;e G, Burgel PR, et al. Predictors in routine practice of 6-min walking distance and oxygen desaturation in patients with COPD: impact of comorbidities. Int J Chron Obstruct Pulmon Dis. 2019;14:1399\u0026ndash;410.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eFerrari GLM, Kovalskys I, Fisberg M, et al. Comparison of self-report versus accelerometer-measured physical activity and sedentary behaviors and their association with body composition in Latin American countries. PLoS ONE. 2020;15(4):e0232420.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLacasse Y, S\u0026eacute;ri\u0026egrave;s F, Corbeil F, et al. Randomized trial of nocturnal oxygen in chronic obstructive pulmonary disease. N Engl J Med. 2020;383(12):1129\u0026ndash;38.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBoing S, Randerath WJ. Chronic hypoventilation syndromes and sleep-related hypoventilation. J Thorac Dis. 2015;7(8):1273\u0026ndash;85.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eJohnson MW, Remmers JE. Accessory muscle activity during sleep in chronic obstructive pulmonary disease. J Appl Physiol Respir Environ Exerc Physiol. 1984;57(4):1011\u0026ndash;7.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"respiratory-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"rere","sideBox":"Learn more about [Respiratory Research](http://respiratory-research.biomedcentral.com/)","snPcode":"12931","submissionUrl":"https://submission.nature.com/new-submission/12931/3","title":"Respiratory Research","twitterHandle":"@RespiratoryBMC","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Nocturnal exertional desaturation, episodic nocturnal hypercapnia, pulse oximetry, sleep-related hypoventilation, COPD, transcutaneous carbon dioxide monitoring, diagnostic accuracy","lastPublishedDoi":"10.21203/rs.3.rs-7506324/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7506324/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e\u003cp\u003eSleep-related hypoventilation, particularly during rapid eye movement (REM) sleep, has been linked to pulmonary hypertension and recurrent exacerbations in individuals with advanced chronic respiratory or neuromuscular diseases. Overnight pulse oximetry (OPO) serves as a valuable screening tool to depict episodic oxygen desaturation resulting from sleep-related hypoventilation. However, differentiating nocturnal desaturation caused by physical activity from that attributable to sleep-related hypoventilation remains clinically challenging. This study aimed to determine whether the integration of accelerometer data with OPO readings can assist in distinguishing exertional nocturnal desaturation from desaturation due to sleep-related hypoventilation.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e\u003cp\u003eBetween July 2021 and December 2022, a prospective enrollment was conducted among consecutive individuals with stable chronic respiratory disorders who reported worsening exertional dyspnea. Participants underwent overnight monitoring involving transcutaneous carbon dioxide pressure (PtcCO₂) and pulse oximetry integrated with accelerometer sensors. The frequency of exertion-associated desaturation events was compared between participant self-reports and acceleration-derived data. Additionally, the diagnostic accuracy of accelerometer-integrated pulse oximetry for detecting episodic nocturnal hypercapnia was assessed using PtcCO₂ monitoring as the reference standard.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e\u003cp\u003eThirty-six individuals were enrolled, with a median age of 78.0 (IQR: 72.0\u0026ndash;82.0) years and a mean daytime arterial carbon dioxide pressure (PaCO₂) of 42.4\u0026thinsp;\u0026plusmn;\u0026thinsp;6.9 mmHg. Of the 89 desaturation events observed, 56 (62.9%) were identified as exertion-related using accelerometer data, including 19 events (21.3%) that were not self-reported. The device demonstrated a sensitivity of 100% (95%CI: 79.6\u0026ndash;100%) and a specificity of 75.7% (95%CI: 64.8\u0026ndash;84.0%) in identifying episodic nocturnal hypoxia associated with hypercapnia.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e\u003cp\u003eAmong individuals with suspected sleep-related breathing disorders, accelerometer-integrated pulse oximetry may serve as a valuable tool to distinguish nocturnal desaturation episodes caused by exertion from those due to sleep-related hypoventilation. These findings suggest that accelerometer-integrated pulse oximetry could offer a feasible screening method for detecting sleep-related hypoventilation in outpatient settings lacking access to PtcCO\u003csub\u003e2\u003c/sub\u003e monitoring.\u003c/p\u003e","manuscriptTitle":"Detection of Nocturnal Desaturation and Hypercapnia Using Accelerometer- Integrated Pulse Oximetry: A Prospective Observational Study","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-10 15:43:03","doi":"10.21203/rs.3.rs-7506324/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-10-30T18:42:47+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-10-27T08:23:49+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-10-21T22:02:08+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-10-14T15:51:38+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"248340449809613393818325741428899826106","date":"2025-10-07T04:41:43+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"18428073738005308989670497348827378194","date":"2025-09-30T00:14:17+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"249965619238145022519395736708439621089","date":"2025-09-29T11:26:16+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-09-28T09:57:13+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-09-03T04:34:27+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-09-03T03:59:15+00:00","index":"","fulltext":""},{"type":"submitted","content":"Respiratory Research","date":"2025-09-01T08:50:37+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"respiratory-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"rere","sideBox":"Learn more about [Respiratory Research](http://respiratory-research.biomedcentral.com/)","snPcode":"12931","submissionUrl":"https://submission.nature.com/new-submission/12931/3","title":"Respiratory Research","twitterHandle":"@RespiratoryBMC","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"c5155339-027e-4aef-b3a4-1db258807b93","owner":[],"postedDate":"October 10th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-01-12T16:01:58+00:00","versionOfRecord":{"articleIdentity":"rs-7506324","link":"https://doi.org/10.1186/s12931-025-03477-2","journal":{"identity":"respiratory-research","isVorOnly":false,"title":"Respiratory Research"},"publishedOn":"2026-01-06 15:56:57","publishedOnDateReadable":"January 6th, 2026"},"versionCreatedAt":"2025-10-10 15:43:03","video":"","vorDoi":"10.1186/s12931-025-03477-2","vorDoiUrl":"https://doi.org/10.1186/s12931-025-03477-2","workflowStages":[]},"version":"v1","identity":"rs-7506324","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7506324","identity":"rs-7506324","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}