Diagnostic Clues for Low-Pressure Female Bladder Outlet Obstruction Overlooked by Conventional Urodynamics

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However, low-pressure, low-flow variants are frequently overlooked by conventional urodynamic studies. This study aims to identify clinical predictors of low-pressure bladder outlet obstruction in women categorized as non-obstructed by standard criteria. Methods We retrospectively reviewed women with lower urinary tract symptoms who underwent videourodynamics between 2012 and 2020. Conventional obstruction was defined as maximal flow rate of less than 12 milliliters per second combined with a detrusor pressure at maximal flow of greater than 20 centimeters of water. Patients not meeting these parameters were evaluated for low-pressure obstruction, confirmed via fluoroscopic evidence during videourodynamics. Results Among 419 women classified as non-obstructed by conventional urodynamics, 128 (30.5%) demonstrated low-pressure bladder outlet obstruction on videourodynamics. Multivariable logistic regression identified a history of anti-incontinence or pelvic organ prolapse surgery and an International Prostate Symptom Score voiding-to-storage subscore ratio greater than 1 as significant independent predictors. Conversely, age 70 years or older and a mean flow rate of 10 milliliters per second or greater served as independent negative predictors. Conclusions Approximately 30% of women deemed non-obstructed by conventional urodynamics exhibit low-pressure bladder outlet obstruction. Clinicians should prioritize further evaluation with videourodynamics in patients with prior anti-incontinence surgery, a high voiding-to-storage ratio, younger age, or low mean flow rates to prevent misdiagnosis. age bladder outlet obstruction low-pressure bladder outlet obstruction mean flow rate videourodynamics INTRODUCTION Bladder outlet obstruction (BOO) is a common cause of lower urinary tract symptoms (LUTS) in men, diagnosed through widely accepted pressure–flow nomograms[1]. In contrast, female BOO is less studied; while rarely diagnosed in general practice, incidence in specialized centers reaches 29%[2]. Standard male nomograms are inapplicable to women due to lower detrusor pressures and differing voiding mechanics. Although several urodynamic criteria and nomograms have been proposed for women, none have gained widespread acceptance due to limited diagnostic accuracy[3]. The International Continence Society defines female BOO by reduced flow rate and/or the presence of increased postvoid residual volume and elevated detrusor pressure[4]. Conceptually, women with high-pressure, low-flow urodynamic profiles are diagnosed with BOO. All proposed criteria based on pressure–flow studies are primarily intended to identify high-pressure, low-flow obstruction patterns[3]. However, recent studies have revealed that in women with BOO accompanied by detrusor underactivity, a low-pressure, low-flow pattern may also be observed[5]. Moreover, such low-pressure, low-flow BOO may be overlooked in conventional urodynamics (UDS). Videourodynamics (VUDS) provides additional diagnostic value for identifying BOO in these patients. A clear understanding of the location of BOO through VUDS is critical for achieving the desired therapeutic outcomes. Nevertheless, because of its limited availability and radiation exposure, VUDS is not routinely performed in women with voiding dysfunction, potentially resulting in misdiagnosis and undertreatment. In this study, we reviewed our VUDS database and used VUDS as the gold standard for diagnosing BOO. This study aims to identify key parameters indicative of low-pressure, low-flow BOO in women who are classified as non-BOO by conventional UDS. METHODS We retrospectively reviewed women with complex or refractory LUTS who underwent VUDS at our institution—a tertiary referral female urology and urodynamics unit in Taiwan—between July 2012 and October 2020 (supplementary Fig. S1 ). Patients with neurogenic bladder or incomplete data were excluded. The study was approved by the Institutional Review Board (TPEVGH-IRB 2021-02-007BC) LUTS were evaluated using the International Prostate Symptom Score (IPSS), which includes seven questions addressing voiding symptoms (incomplete emptying, intermittency, weak stream, and straining) and storage symptoms (frequency, urgency, and nocturia)[6]. Each question is scored from 0 to 5, with higher scores indicating greater severity of the symptom. VUDS was performed with the patient in the sitting position. Intravesical and abdominal pressures were measured using an 8-Fr transurethral catheter and a 24-Fr rectal balloon catheter, respectively. Filling cystometrography was conducted at a constant filling rate of 30 ml/min. Female BOO was defined as a free maximal flow rate (Qmax) 20 cmH 2 O (high-pressure, low-flow BOO) based on conventional UDS[7], or radiographic evidence of obstruction between the bladder neck and distal urethra during a sustained detrusor contraction on VUDS[8]. Low-pressure BOO was defined as BOO confirmed on VUDS with a PdetQmax ≤ 20 cmH 2 O[5]. Supplementary Figure S2 presents representative VUDS findings of patients with detrusor underactivity, both with and without BOO. The interpretation of VUDS findings was performed independently by two urologists specializing in functional urology who were not blinded to clinical and uroflowmetry data. In the event of a diagnostic disagreement between the two primary reviewers, a third senior urologist was consulted to provide an additional assessment, and the final diagnosis was established based on majority consensus. All statistical analyses were performed using SPSS Statistics for Mac, version 24.0 (IBM Corp., Armonk, NY, USA). Descriptive statistical analyses were conducted according to the presence or absence of low-pressure BOO among patients without high-pressure, low-flow BOO (classified as non-BOO based on conventional UDS). Descriptive data are expressed as the mean ± standard deviation or as number (percentage). Pearson’s chi-squared test and Student’s t-test were applied to compare participants with and without low-pressure BOO, depending on whether the variables were categorical or continuous. Factors associated with low-pressure BOO were evaluated using univariate and multivariate logistic regression analyses. Statistical significance was set at P < 0.05. RESULTS Patient Characteristics A total of 540 VUDS records were reviewed, including 121 cases with BOO and 419 without BOO, based on the high-pressure, low-flow criteria. Among the 419 cases classified as non-BOO by these criteria, 128 (30.5%) demonstrated fluoroscopic evidence of BOO with low detrusor pressure on VUDS. The clinical characteristics of patients without high-pressure, low-flow BOO are presented in Table 1 . Table 1 Clinical characteristics of participants without high-pressure, low-flow bladder outlet obstruction Total (N = 419) Non-BOO (N = 291) Low pressure BOO (N = 128) P - value Pdet at Qmax (cmH 2 O) 16.5 ± 12.1 19.0 ± 13.1 10.7 ± 6.5 < 0.001 Age (yrs) 60.9 ± 13.5 60.8 ± 13.5 61.1 ± 13.5 0.793 Age ≥ 70 yrs 117 (27.9%) 86 (29.6%) 31 (24.2%) 0.262 Diabetes mellitus 40 (9.5%) 27 (9.3%) 13 (10.2%) 0.778 Hx of pelvic surgery 155 (37.0%) 102 (35.1%) 53 (41.4%) 0.215 Hx of transvaginal SUI/POP surgery 53 (12.6%) 30 (10.3%) 23 (18.0%) 0.030 Uroflowmetry Qmax (mL/sec) 20.2 ± 9.2 21.8 ± 9.5 16.6 ± 7.1 < 0.001 Qmax ≥ 15 mL/sec 304 (72.6%) 228 (79.4%) 76 (59.8%) < 0.001 Qmean (mL/sec) 9.5 ± 5.1 10.6 ± 5.3 7.1 ± 3.3 < 0.001 Qmean ≥ 10 mL/sec 168 (40.1%) 147 (51.2%) 21 (16.5%) < 0.001 Post-void residual (mL) 27.3 ± 58.7 24.8 ± 52.6 33.3 ± 70.6 0.179 IPSS Total score 15.4 ± 8.4 14.0 ± 7.9 18.7 ± 8.8 1 166 (39.6%) 99 (34.0%) 67 (52.3%) < 0.001 Data are presented as mean ± SD or n (%). Bold indicates statistically significant values P < 0.05. Hx, history; Pdet, detrusor pressure; Qmax, maximal flow rate; Qmean, mean flow rate; SUI, stress urinary incontinence; POP, pelvic organ prolapse; IPSS, International Prostate Symptom Score; V/S, voiding/storage subscore ratio. No significant differences were found in mean age (61.1 ± 13.5 vs. 60.8 ± 13.5 years, P = 0.793) or diabetes prevalence between the low-pressure BOO and non-BOO groups. The proportion of patients with a history of transvaginal stress urinary incontinence or pelvic organ prolapse (SUI/POP) surgery was significantly higher in the low-pressure BOO group (18.0% vs. 10.3%, P = 0.030). Uroflowmetry Parameters and Symptoms Qmax and Qmean were significantly reduced in the low-pressure BOO group compared with the non-BOO group (P < 0.001). Only 16.5% of low-pressure BOO patients achieved Qmean ≥ 10 mL/sec, compared with 51.2% of non-BOO patients ( P < 0.001). Post-void residual (PVR) volume showed no significant difference. Additionally, low-pressure BOO patients reported higher IPSS total scores (18.7 ± 8.8 vs. 14.0 ± 7.9, P 1 (52.3% vs. 34.0%, P < 0.001). Predictive Factors for Low-Pressure BOO Univariate Analysis Univariate logistic regression analysis identified several factors associated with low-pressure BOO (Table 2 ). Prior transvaginal SUI/POP surgery (odds ratio [OR] = 1.906, 95% confidence interval [CI] : 1.058–3.433, P = 0.032), and V/S ratio > 1 (OR = 2.179, 95% CI: 1.253–3.356, P < 0.001) were significantly associated with low-pressure BOO. Qmax ≥ 15 mL/sec (OR = 0.386, 95% CI: 0.244–0.608, P < 0.001) and Qmean ≥ 10 mL/sec (OR = 0.189, 95% CI: 0.112–0.318, P < 0.001) were negatively associated with low-pressure BOO. Age ≥ 70 years and diabetes mellitus did not reach statistical significance. Table 2 Univariate and multivariate analysis of risk factors of low pressure bladder outlet obstruction Univariate analysis Multivariate analysis OR 95% CI P -value OR 95% CI P -value Age ≥ 70 yrs 0.762 0.473–1.227 0.263 0.542 0.310–0.948 0.032 Diabetes mellitus 1.105 0.551–2.219 0.778 1.340 0.619–2.900 0.457 Hx of transvaginal SUI/POP surgery 1.906 1.058–3.433 0.032 2.071 1.057–4.058 0.034 Qmax ≥ 15 mL/sec 0.386 0.244–0.608 < 0.001 0.657 0.384–1.126 0.127 Qmean ≥ 10 mL/sec 0.189 0.112–0.318 < 0.001 0.208 0.112–0.384 1 2.179 1.253–3.356 < 0.001 1.721 1.076–2.755 0.023 Bold indicates statistically significant values P < 0.05. Hx, history; SUI, stress urinary incontinence; POP, pelvic organ prolapse; Qmax, maximal flow rate; Qmean, mean flow rate; V/S, voiding/storage subscore ratio; OR, odds ratio; CI, confidence interval. Multivariate Analysis After adjusting for potential confounding factors, the following independent predictors of low-pressure BOO were identified: Prior transvaginal SUI/POP surgery remained significantly associated with an increased risk of low-pressure BOO (adjusted OR = 2.071, 95% CI: 1.057–4.058, P = 0.034). Qmean ≥ 10 mL/sec was independently associated with a reduced risk of low-pressure BOO (adjusted OR = 0.208, 95% CI: 0.112–0.384, P 1 showed a positive association with low-pressure BOO (adjusted OR = 1.721, 95% CI: 1.076–2.755, P = 0.023). Age ≥ 70 years demonstrated a protective effect (adjusted OR = 0.542, 95% CI: 0.310–0.948, P = 0.032). Qmax ≥ 15 mL/sec did not maintain statistical significance in the multivariate analysis (adjusted OR = 0.657, 95% CI: 0.384–1.126, P = 0.127). Diabetes mellitus remained non-significant (adjusted OR = 1.340, 95% CI: 0.619–2.900, P = 0.457). DISCUSSION Our study found that the prevalence of low-pressure BOO was 30.5% among women classified as non-BOO based on high-pressure, low-flow criteria. This high misdiagnosis rate is consistent with the observation by Chow et al. that approximately one-fifth of women with detrusor underactivity–like urodynamic profiles harbor occult BOO detectable only by VUDS[5]. While Chow et al. focused on identifying predictive urodynamic parameters for occult BOO, our study emphasizes noninvasive assessments—such as uroflowmetry, clinical history, and questionnaires—to provide complementary clinical insights for identifying women with potential low-pressure BOO who may benefit from further evaluation with VUDS. The overall prevalence of BOO following urethral sling surgery in previous studies is reported to be as high as 24%[9,10]. Ross et al. demonstrated that patients with chronic urinary symptoms and a history of urethral sling surgery have a 60% prevalence of BOO, which was defined as a sustained detrusor pressure > 20 cmH₂O with Qmax < 12 mL/s or the presence of fluoroscopic evidence of an obstructing sling[11], though they did not distinguish between high-pressure and low-pressure obstruction patterns. Our finding that prior SUI/POP surgery doubles the risk of low-pressure BOO is consistent with this literature, but specifically highlights the low-pressure phenotype. Several mechanisms may explain SUI/POP surgery-related low-pressure BOO. First, midurethral sling placement or anterior colporrhaphy may cause direct bladder denervation during dissection, impairing detrusor contractility while simultaneously increasing outlet resistance. This “dual insult” would produce the characteristic low-pressure, low-flow BOO observed in our cohort. Second, periurethral fibrosis and altered bladder neck anatomy following SUI /POP surgery may increase baseline outlet resistance, requiring compensatory increases in detrusor pressure that cannot be sustained long-term, leading to detrusor decompensation[12]. The finding that Qmean ≥ 10 mL/sec reduces the risk of low-pressure BOO establishes mean flow rate as a strong protective factor. This association was even stronger than that of Qmax, which lost statistical significance in the multivariate analysis. Although Qmax has traditionally served as the primary uroflowmetry parameter for BOO screening, our results suggest that Qmean may offer superior discriminatory value. This aligns with recent findings showing that Qmean provides superior diagnostic accuracy compared with Qmax (AUC 0.729 vs. 0.636) and offers markedly higher diagnostic efficiency (specificity 42.3% vs. 26.9%; Youden index 0.41 vs. 0.24). Importantly, inclusion of Qmean in full predictive models substantially enhances BOO discrimination (AUC 0.813), whereas removing Qmean leads to a dramatic loss of performance, including a 34.6% drop in specificity and a 0.31 reduction in Youden index[13]. However, this study focused exclusively on men and did not report detrusor pressure data. Qmax is highly susceptible to transient detrusor power and abdominal straining, particularly in the presence of detrusor underactivity. Because most patients with low-pressure BOO are unable to generate sustained detrusor contractions, abdominal straining is frequently employed to overcome urethral resistance, thereby disproportionately influencing Qmax. In contrast, Qmean—by averaging flow across the entire voiding phase—provides a more stable surrogate of overall voiding performance and bladder outlet resistance. One of the most intriguing findings of this study is that age ≥ 70 years is independently protective against low-pressure BOO. This finding contradicts the conventional assumption that advanced age universally increases the risk of voiding dysfunction. Consistent with our results, Wu et al. demonstrated an age-related increase in detrusor underactivity accompanied by a decrease in the prevalence of BOO[14]. Rajasekaran et al. reported a significant age-related decrease in urethral sphincter muscle thickness and closure function in a rabbit mode[15]. In a cadaveric study of women, Perucchini et al. demonstrated age-related loss of striated muscle at the bladder neck and along the dorsal wall of the urethra[16]. Similarly, Lau et al. showed that maximal urethral closure pressure was significantly reduced in older women, indicating progressive urethral intrinsic sphincter deficiency with advancing age[17]. An age-related decline in urethral closure pressure may reduce outlet resistance sufficiently to prevent the development of BOO. The association between V/S ratio > 1 and increased low-pressure BOO risk suggests that symptom pattern analysis may complement urodynamic testing. A V/S ratio > 1 indicates predominance of voiding symptoms over storage symptoms, theoretically reflecting obstructive pathology. Choi et al. found that among female patients presenting with voiding difficulty, the mean IPSS voiding and storage subscores were 12.0 ± 5.0 and 8.4 ± 3.4, respectively[18]. Most patients were diagnosed with BOO (87.2%), whereas only 12.8% had detrusor underactivity. Hsiao et al. reported that a significantly higher V/S ratio was observed in women with bladder outlet–related lower urinary tract dysfunction, and that a V/S ratio ≥ 1.33 had the best predictive value, with a high negative predictive value (97.4%)[19]. Therefore, the predominance of voiding symptoms, defined as a V/S ratio > 1 in our study, may help distinguish BOO from other lower urinary tract dysfunctions. In our study, diabetes mellitus was not associated with low-pressure BOO in either univariate or multivariate analyses. Diabetic bladder dysfunction is a well-recognized complication of diabetes mellitus, typically developing in middle-aged or elderly patients with long-standing and poorly controlled disease. It encompasses a spectrum of clinical manifestations, ranging from bladder overactivity to impaired detrusor contractility[20]. In contrast, relatively few studies have examined the effects of diabetes mellitus on urethral function. Limited evidence suggests that diabetes may impair urethral function, characterized by increased urethral pressure during micturition and disrupted coordination of voiding[21]. Therefore, although diabetes mellitus is classically associated with bladder dysfunction, it may contribute to both BOO and detrusor underactivity. Furthermore, the duration, control, and complications of diabetes mellitus were not clarified, and different risk profiles might affect diabetes mellitus–related lower urinary tract dysfunction. This study has several strengths. First, the relatively large sample size provides robust characterization of low-pressure BOO, which is often neglected in women with low-pressure urodynamic profiles. Second, multivariable analysis controlling for potential confounders enabled the identification of independent predictive factors for low-pressure BOO, including age, surgical history, symptom patterns, and Qmean. Third, our results challenge the conventional assumption that female BOO uniformly presents with elevated voiding pressures. Several limitations of this study warrant consideration. First, its retrospective, cross-sectional design precludes the establishment of definitive causal relationships. While a history of anti-incontinence surgery or pelvic organ prolapse repair was strongly associated with low-pressure BOO, we cannot ascertain whether the obstruction developed as a direct consequence of the procedure or existed preoperatively. Second, although VUDS is the current gold standard for diagnosing female BOO, the radiographic interpretation of obstruction remains somewhat subjective and may be influenced by the observer’s experience. To mitigate this, we utilized a consensus-based approach with multiple expert reviewers. Third, as a single-center study conducted at a tertiary referral unit, our population may be subject to referral bias, potentially limiting the generalizability of our findings to primary care settings. Finally, while we identified specific clinical and uroflowmetry "clues" for low-pressure BOO, these parameters require further validation in independent, prospective cohorts to confirm their diagnostic utility in broader clinical practice. CONCLUSIONS Approximately 30% of women classified as non-BOO by conventional UDS are actually identified as having low-pressure BOO when evaluated with VUDS. This high prevalence suggests that conventional pressure-flow studies alone are insufficient to exclude obstruction in women with complex lower urinary tract symptoms. For patients initially diagnosed as non-BOO by conventional UDS, we identified several significant diagnostic clues for occult low-pressure BOO: a history of anti-incontinence or pelvic organ prolapse surgery, a V/S ratio > 1, age < 70 years, or a mean flow rate < 10 mL/s. These indicators should prompt clinicians to consider further evaluation with VUDS to prevent missed diagnoses. While these findings provide a practical screening approach, the retrospective nature and subjective interpretation of imaging in this study necessitate future prospective, multi-center trials to validate these clinical clues in broader populations. Declarations Acknowledgments None Funding : This work was supported by the Yan Ching-Ling Medical Foundation (Grant No. CI-112-20). Conflict of Interest : The authors declare no conflict of interest. Ethical Approval : The protocol for this research project has been approved by the Research Ethics Committee of Taipei Veterans General Hospital (approval No. TPEVGH-IRB 2021-02-007BC) and it conforms to the provisions of the Declaration of Helsinki. Informed Consent : This retrospective study used existing medical records, and individual informed consent was waived by the Institutional Review Board. Data Availability : The datasets analyzed during this study are available from the corresponding author upon reasonable request. 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Int Neurourol J 23:91-99. https://doi.org/10.5213/inj.1938050.025 Additional Declarations No competing interests reported. Supplementary Files SupplementaryFigures.docx Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 27 Apr, 2026 Reviews received at journal 21 Apr, 2026 Reviewers agreed at journal 19 Apr, 2026 Reviews received at journal 18 Apr, 2026 Reviewers agreed at journal 14 Apr, 2026 Reviewers agreed at journal 01 Apr, 2026 Reviewers agreed at journal 03 Mar, 2026 Reviewers invited by journal 26 Feb, 2026 Editor assigned by journal 17 Feb, 2026 Submission checks completed at journal 17 Feb, 2026 First submitted to journal 16 Feb, 2026 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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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8890223","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":597339864,"identity":"863d3467-5b3c-4591-8d77-bd22911426a0","order_by":0,"name":"Yu-Hua Fan","email":"","orcid":"","institution":"Taipei Veterans General Hospital","correspondingAuthor":false,"prefix":"","firstName":"Yu-Hua","middleName":"","lastName":"Fan","suffix":""},{"id":597339867,"identity":"f9f70b83-cc1a-4606-8cf4-e9ab8648f52d","order_by":1,"name":"Lun-Hsiang Yuan","email":"","orcid":"","institution":"National Taiwan University Hospital","correspondingAuthor":false,"prefix":"","firstName":"Lun-Hsiang","middleName":"","lastName":"Yuan","suffix":""},{"id":597339868,"identity":"90705133-09cb-416b-a79b-4c6a792f22e3","order_by":2,"name":"Chih-Chieh Lin","email":"","orcid":"","institution":"Taipei Veterans General Hospital","correspondingAuthor":false,"prefix":"","firstName":"Chih-Chieh","middleName":"","lastName":"Lin","suffix":""},{"id":597339869,"identity":"25aa57c0-612f-4b5d-96ef-9b2426b6f2e2","order_by":3,"name":"Ming-Hsuan Ku","email":"","orcid":"","institution":"Taipei Veterans General Hospital","correspondingAuthor":false,"prefix":"","firstName":"Ming-Hsuan","middleName":"","lastName":"Ku","suffix":""},{"id":597339870,"identity":"d8ad7595-89f6-432a-a741-10f36ff9c5f1","order_by":4,"name":"Eric Yi-Hsiu Huang","email":"","orcid":"","institution":"Taipei Veterans General Hospital","correspondingAuthor":false,"prefix":"","firstName":"Eric","middleName":"Yi-Hsiu","lastName":"Huang","suffix":""},{"id":597339871,"identity":"e05976bd-7831-447a-b1c3-01cf2995ebf6","order_by":5,"name":"Wei-Ming Cheng","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA0klEQVRIiWNgGAWjYLACxgYgwQ4iDCxI0cJzAKRFghQtEgkgJhFa5CNyTDf83GGTJx/5/OqGHwUSDPzt3Ql4tRjeyDG72Xsmrdjwdk7ZzR6gwyTOnN2AX8uM3G23GdsOJ26cnZN2gweoxUAilygt/xM3zjyTdvMPMVrkJcBaDiTOl2A/dpsoWwx43n+72duWnLiBJ4fttoyBBA9Bv8i3p6Xd+Nlmlzi//fizm2/+2Mjxt/cSsOUAnMFjAKJ58CoH29IAZ7A/IKh6FIyCUTAKRiYAAC+zTrTX/qKYAAAAAElFTkSuQmCC","orcid":"","institution":"National Yang Ming Chiao Tung University","correspondingAuthor":true,"prefix":"","firstName":"Wei-Ming","middleName":"","lastName":"Cheng","suffix":""},{"id":597339872,"identity":"827bc9e2-692b-42a7-934d-1c8b37624544","order_by":6,"name":"Chih-Yu Yang","email":"","orcid":"","institution":"Taipei Veterans General Hospital","correspondingAuthor":false,"prefix":"","firstName":"Chih-Yu","middleName":"","lastName":"Yang","suffix":""}],"badges":[],"createdAt":"2026-02-16 06:24:35","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8890223/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8890223/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":104401312,"identity":"d1e46bd4-d58a-49f2-a945-ee18a5022d23","added_by":"auto","created_at":"2026-03-11 12:12:21","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":600193,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8890223/v1/d6261112-e78a-4418-b756-84bbb3479ae8.pdf"},{"id":103851051,"identity":"6d874bd8-48ba-43f0-b97f-05d1ccdf6874","added_by":"auto","created_at":"2026-03-03 16:42:00","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":1415571,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryFigures.docx","url":"https://assets-eu.researchsquare.com/files/rs-8890223/v1/8286c2dfaf4119238c30f20a.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Diagnostic Clues for Low-Pressure Female Bladder Outlet Obstruction Overlooked by Conventional Urodynamics","fulltext":[{"header":"INTRODUCTION","content":"\u003cp\u003eBladder outlet obstruction (BOO) is a common cause of lower urinary tract symptoms (LUTS) in men, diagnosed through widely accepted pressure\u0026ndash;flow nomograms[1]. In contrast, female BOO is less studied; while rarely diagnosed in general practice, incidence in specialized centers reaches 29%[2]. Standard male nomograms are inapplicable to women due to lower detrusor pressures and differing voiding mechanics. Although several urodynamic criteria and nomograms have been proposed for women, none have gained widespread acceptance due to limited diagnostic accuracy[3].\u003c/p\u003e \u003cp\u003eThe International Continence Society defines female BOO by reduced flow rate and/or the presence of increased postvoid residual volume and elevated detrusor pressure[4]. Conceptually, women with high-pressure, low-flow urodynamic profiles are diagnosed with BOO. All proposed criteria based on pressure\u0026ndash;flow studies are primarily intended to identify high-pressure, low-flow obstruction patterns[3]. However, recent studies have revealed that in women with BOO accompanied by detrusor underactivity, a low-pressure, low-flow pattern may also be observed[5]. Moreover, such low-pressure, low-flow BOO may be overlooked in conventional urodynamics (UDS). Videourodynamics (VUDS) provides additional diagnostic value for identifying BOO in these patients. A clear understanding of the location of BOO through VUDS is critical for achieving the desired therapeutic outcomes. Nevertheless, because of its limited availability and radiation exposure, VUDS is not routinely performed in women with voiding dysfunction, potentially resulting in misdiagnosis and undertreatment.\u003c/p\u003e \u003cp\u003eIn this study, we reviewed our VUDS database and used VUDS as the gold standard for diagnosing BOO. This study aims to identify key parameters indicative of low-pressure, low-flow BOO in women who are classified as non-BOO by conventional UDS.\u003c/p\u003e"},{"header":"METHODS","content":"\u003cp\u003e We retrospectively reviewed women with complex or refractory LUTS who underwent VUDS at our institution\u0026mdash;a tertiary referral female urology and urodynamics unit in Taiwan\u0026mdash;between July 2012 and October 2020 (supplementary Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). Patients with neurogenic bladder or incomplete data were excluded. The study was approved by the Institutional Review Board (TPEVGH-IRB 2021-02-007BC)\u003c/p\u003e \u003cp\u003eLUTS were evaluated using the International Prostate Symptom Score (IPSS), which includes seven questions addressing voiding symptoms (incomplete emptying, intermittency, weak stream, and straining) and storage symptoms (frequency, urgency, and nocturia)[6]. Each question is scored from 0 to 5, with higher scores indicating greater severity of the symptom.\u003c/p\u003e \u003cp\u003eVUDS was performed with the patient in the sitting position. Intravesical and abdominal pressures were measured using an 8-Fr transurethral catheter and a 24-Fr rectal balloon catheter, respectively. Filling cystometrography was conducted at a constant filling rate of 30 ml/min. Female BOO was defined as a free maximal flow rate (Qmax)\u0026thinsp;\u0026lt;\u0026thinsp;12 mL/s with a detrusor pressure at Qmax (PdetQmax)\u0026thinsp;\u0026gt;\u0026thinsp;20 cmH\u003csub\u003e2\u003c/sub\u003eO (high-pressure, low-flow BOO) based on conventional UDS[7], or radiographic evidence of obstruction between the bladder neck and distal urethra during a sustained detrusor contraction on VUDS[8]. Low-pressure BOO was defined as BOO confirmed on VUDS with a PdetQmax\u0026thinsp;\u0026le;\u0026thinsp;20 cmH\u003csub\u003e2\u003c/sub\u003eO[5]. Supplementary Figure S2 presents representative VUDS findings of patients with detrusor underactivity, both with and without BOO. The interpretation of VUDS findings was performed independently by two urologists specializing in functional urology who were not blinded to clinical and uroflowmetry data. In the event of a diagnostic disagreement between the two primary reviewers, a third senior urologist was consulted to provide an additional assessment, and the final diagnosis was established based on majority consensus.\u003c/p\u003e \u003cp\u003eAll statistical analyses were performed using SPSS Statistics for Mac, version 24.0 (IBM Corp., Armonk, NY, USA). Descriptive statistical analyses were conducted according to the presence or absence of low-pressure BOO among patients without high-pressure, low-flow BOO (classified as non-BOO based on conventional UDS). Descriptive data are expressed as the mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation or as number (percentage). Pearson\u0026rsquo;s chi-squared test and Student\u0026rsquo;s t-test were applied to compare participants with and without low-pressure BOO, depending on whether the variables were categorical or continuous. Factors associated with low-pressure BOO were evaluated using univariate and multivariate logistic regression analyses. Statistical significance was set at P\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e"},{"header":"RESULTS","content":"\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003ePatient Characteristics\u003c/h2\u003e \u003cp\u003eA total of 540 VUDS records were reviewed, including 121 cases with BOO and 419 without BOO, based on the high-pressure, low-flow criteria. Among the 419 cases classified as non-BOO by these criteria, 128 (30.5%) demonstrated fluoroscopic evidence of BOO with low detrusor pressure on VUDS. The clinical characteristics of patients without high-pressure, low-flow BOO are presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\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\u003eClinical characteristics of participants without high-pressure, low-flow bladder outlet obstruction\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\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 \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTotal (N\u0026thinsp;=\u0026thinsp;419)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNon-BOO (N\u0026thinsp;=\u0026thinsp;291)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLow pressure BOO (N\u0026thinsp;=\u0026thinsp;128)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e- value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePdet at Qmax (cmH\u003csub\u003e2\u003c/sub\u003eO)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e16.5\u0026thinsp;\u0026plusmn;\u0026thinsp;12.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e19.0\u0026thinsp;\u0026plusmn;\u0026thinsp;13.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10.7\u0026thinsp;\u0026plusmn;\u0026thinsp;6.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026thinsp;0.001\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge (yrs)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e60.9\u0026thinsp;\u0026plusmn;\u0026thinsp;13.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e60.8\u0026thinsp;\u0026plusmn;\u0026thinsp;13.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e61.1\u0026thinsp;\u0026plusmn;\u0026thinsp;13.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.793\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge\u0026thinsp;\u0026ge;\u0026thinsp;70 yrs\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e117 (27.9%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e86 (29.6%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e31 (24.2%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.262\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDiabetes mellitus\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e40 (9.5%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e27 (9.3%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e13 (10.2%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.778\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHx of pelvic surgery\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e155 (37.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e102 (35.1%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e53 (41.4%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.215\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHx of transvaginal SUI/POP surgery\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e53 (12.6%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e30 (10.3%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e23 (18.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e0.030\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eUroflowmetry\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQmax (mL/sec)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e20.2\u0026thinsp;\u0026plusmn;\u0026thinsp;9.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e21.8\u0026thinsp;\u0026plusmn;\u0026thinsp;9.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e16.6\u0026thinsp;\u0026plusmn;\u0026thinsp;7.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026thinsp;0.001\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQmax\u0026thinsp;\u0026ge;\u0026thinsp;15 mL/sec\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e304 (72.6%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e228 (79.4%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e76 (59.8%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026thinsp;0.001\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQmean (mL/sec)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e9.5\u0026thinsp;\u0026plusmn;\u0026thinsp;5.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e10.6\u0026thinsp;\u0026plusmn;\u0026thinsp;5.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e7.1\u0026thinsp;\u0026plusmn;\u0026thinsp;3.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026thinsp;0.001\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQmean\u0026thinsp;\u0026ge;\u0026thinsp;10 mL/sec\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e168 (40.1%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e147 (51.2%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e21 (16.5%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026thinsp;0.001\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePost-void residual (mL)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e27.3\u0026thinsp;\u0026plusmn;\u0026thinsp;58.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e24.8\u0026thinsp;\u0026plusmn;\u0026thinsp;52.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e33.3\u0026thinsp;\u0026plusmn;\u0026thinsp;70.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.179\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIPSS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal score\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e15.4\u0026thinsp;\u0026plusmn;\u0026thinsp;8.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e14.0\u0026thinsp;\u0026plusmn;\u0026thinsp;7.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e18.7\u0026thinsp;\u0026plusmn;\u0026thinsp;8.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026thinsp;0.001\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eV/S\u0026thinsp;\u0026gt;\u0026thinsp;1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e166 (39.6%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e99 (34.0%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e67 (52.3%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026thinsp;0.001\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"5\" nameend=\"c5\" namest=\"c1\"\u003e \u003cp\u003eData are presented as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD or n (%). Bold indicates statistically significant values P\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e \u003cp\u003eHx, history; Pdet, detrusor pressure; Qmax, maximal flow rate; Qmean, mean flow rate; SUI, stress urinary incontinence; POP, pelvic organ prolapse; IPSS, International Prostate Symptom Score; V/S, voiding/storage subscore ratio.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eNo significant differences were found in mean age (61.1\u0026thinsp;\u0026plusmn;\u0026thinsp;13.5 vs. 60.8\u0026thinsp;\u0026plusmn;\u0026thinsp;13.5 years, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.793) or diabetes prevalence between the low-pressure BOO and non-BOO groups. The proportion of patients with a history of transvaginal stress urinary incontinence or pelvic organ prolapse (SUI/POP) surgery was significantly higher in the low-pressure BOO group (18.0% vs. 10.3%, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.030).\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eUroflowmetry Parameters and Symptoms\u003c/h3\u003e\n\u003cp\u003eQmax and Qmean were significantly reduced in the low-pressure BOO group compared with the non-BOO group (P\u0026thinsp;\u0026lt;\u0026thinsp;0.001). Only 16.5% of low-pressure BOO patients achieved Qmean\u0026thinsp;\u0026ge;\u0026thinsp;10 mL/sec, compared with 51.2% of non-BOO patients (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001). Post-void residual (PVR) volume showed no significant difference. Additionally, low-pressure BOO patients reported higher IPSS total scores (18.7\u0026thinsp;\u0026plusmn;\u0026thinsp;8.8 vs. 14.0\u0026thinsp;\u0026plusmn;\u0026thinsp;7.9, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001) and a higher frequency of V/S ratios\u0026thinsp;\u0026gt;\u0026thinsp;1 (52.3% vs. 34.0%, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001).\u003c/p\u003e\n\u003ch3\u003ePredictive Factors for Low-Pressure BOO\u003c/h3\u003e\n\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eUnivariate Analysis\u003c/h2\u003e \u003cp\u003eUnivariate logistic regression analysis identified several factors associated with low-pressure BOO (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Prior transvaginal SUI/POP surgery (odds ratio [OR]\u0026thinsp;=\u0026thinsp;1.906, 95% confidence interval [CI] : 1.058\u0026ndash;3.433, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.032), and V/S ratio\u0026thinsp;\u0026gt;\u0026thinsp;1 (OR\u0026thinsp;=\u0026thinsp;2.179, 95% CI: 1.253\u0026ndash;3.356, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001) were significantly associated with low-pressure BOO. Qmax\u0026thinsp;\u0026ge;\u0026thinsp;15 mL/sec (OR\u0026thinsp;=\u0026thinsp;0.386, 95% CI: 0.244\u0026ndash;0.608, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001) and Qmean\u0026thinsp;\u0026ge;\u0026thinsp;10 mL/sec (OR\u0026thinsp;=\u0026thinsp;0.189, 95% CI: 0.112\u0026ndash;0.318, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001) were negatively associated with low-pressure BOO. Age\u0026thinsp;\u0026ge;\u0026thinsp;70 years and diabetes mellitus did not reach statistical significance.\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\u003eUnivariate and multivariate analysis of risk factors of low pressure bladder outlet obstruction\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\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 \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e \u003cp\u003eUnivariate analysis\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c8\" namest=\"c6\"\u003e \u003cp\u003eMultivariate analysis\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOR\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e95% CI\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e-value\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eOR\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003e95% CI\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e-value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge\u0026thinsp;\u0026ge;\u0026thinsp;70 yrs\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.762\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.473\u0026ndash;1.227\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.263\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.542\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.310\u0026ndash;0.948\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e\u003cb\u003e0.032\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDiabetes mellitus\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.105\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.551\u0026ndash;2.219\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.778\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.340\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.619\u0026ndash;2.900\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.457\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHx of transvaginal SUI/POP surgery\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.906\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.058\u0026ndash;3.433\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e0.032\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e2.071\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1.057\u0026ndash;4.058\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e\u003cb\u003e0.034\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQmax\u0026thinsp;\u0026ge;\u0026thinsp;15 mL/sec\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.386\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.244\u0026ndash;0.608\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026thinsp;0.001\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.657\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.384\u0026ndash;1.126\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.127\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eQmean\u0026thinsp;\u0026ge;\u0026thinsp;10 mL/sec\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.189\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.112\u0026ndash;0.318\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026thinsp;0.001\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.208\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.112\u0026ndash;0.384\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026thinsp;0.001\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eV/S\u0026thinsp;\u0026gt;\u0026thinsp;1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.179\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.253\u0026ndash;3.356\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026thinsp;0.001\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.721\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1.076\u0026ndash;2.755\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e\u003cb\u003e0.023\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"8\" nameend=\"c8\" namest=\"c1\"\u003e \u003cp\u003eBold indicates statistically significant values P\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e \u003cp\u003eHx, history; SUI, stress urinary incontinence; POP, pelvic organ prolapse; Qmax, maximal flow rate; Qmean, mean flow rate; V/S, voiding/storage subscore ratio; OR, odds ratio; CI, confidence interval.\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=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eMultivariate Analysis\u003c/h2\u003e \u003cp\u003eAfter adjusting for potential confounding factors, the following independent predictors of low-pressure BOO were identified:\u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003ePrior transvaginal SUI/POP surgery remained significantly associated with an increased risk of low-pressure BOO (adjusted OR\u0026thinsp;=\u0026thinsp;2.071, 95% CI: 1.057\u0026ndash;4.058, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.034).\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eQmean\u0026thinsp;\u0026ge;\u0026thinsp;10 mL/sec was independently associated with a reduced risk of low-pressure BOO (adjusted OR\u0026thinsp;=\u0026thinsp;0.208, 95% CI: 0.112\u0026ndash;0.384, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001).\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eA V/S ratio\u0026thinsp;\u0026gt;\u0026thinsp;1 showed a positive association with low-pressure BOO (adjusted OR\u0026thinsp;=\u0026thinsp;1.721, 95% CI: 1.076\u0026ndash;2.755, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.023).\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eAge\u0026thinsp;\u0026ge;\u0026thinsp;70 years demonstrated a protective effect (adjusted OR\u0026thinsp;=\u0026thinsp;0.542, 95% CI: 0.310\u0026ndash;0.948, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.032).\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003cp\u003eQmax\u0026thinsp;\u0026ge;\u0026thinsp;15 mL/sec did not maintain statistical significance in the multivariate analysis (adjusted OR\u0026thinsp;=\u0026thinsp;0.657, 95% CI: 0.384\u0026ndash;1.126, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.127). Diabetes mellitus remained non-significant (adjusted OR\u0026thinsp;=\u0026thinsp;1.340, 95% CI: 0.619\u0026ndash;2.900, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.457).\u003c/p\u003e \u003c/div\u003e"},{"header":"DISCUSSION","content":"\u003cp\u003eOur study found that the prevalence of low-pressure BOO was 30.5% among women classified as non-BOO based on high-pressure, low-flow criteria. This high misdiagnosis rate is consistent with the observation by Chow et al. that approximately one-fifth of women with detrusor underactivity\u0026ndash;like urodynamic profiles harbor occult BOO detectable only by VUDS[5]. While Chow et al. focused on identifying predictive urodynamic parameters for occult BOO, our study emphasizes noninvasive assessments\u0026mdash;such as uroflowmetry, clinical history, and questionnaires\u0026mdash;to provide complementary clinical insights for identifying women with potential low-pressure BOO who may benefit from further evaluation with VUDS.\u003c/p\u003e \u003cp\u003eThe overall prevalence of BOO following urethral sling surgery in previous studies is reported to be as high as 24%[9,10]. Ross et al. demonstrated that patients with chronic urinary symptoms and a history of urethral sling surgery have a 60% prevalence of BOO, which was defined as a sustained detrusor pressure\u0026thinsp;\u0026gt;\u0026thinsp;20 cmH₂O with Qmax\u0026thinsp;\u0026lt;\u0026thinsp;12 mL/s or the presence of fluoroscopic evidence of an obstructing sling[11], though they did not distinguish between high-pressure and low-pressure obstruction patterns. Our finding that prior SUI/POP surgery doubles the risk of low-pressure BOO is consistent with this literature, but specifically highlights the low-pressure phenotype. Several mechanisms may explain SUI/POP surgery-related low-pressure BOO. First, midurethral sling placement or anterior colporrhaphy may cause direct bladder denervation during dissection, impairing detrusor contractility while simultaneously increasing outlet resistance. This \u0026ldquo;dual insult\u0026rdquo; would produce the characteristic low-pressure, low-flow BOO observed in our cohort. Second, periurethral fibrosis and altered bladder neck anatomy following SUI /POP surgery may increase baseline outlet resistance, requiring compensatory increases in detrusor pressure that cannot be sustained long-term, leading to detrusor decompensation[12].\u003c/p\u003e \u003cp\u003eThe finding that Qmean\u0026thinsp;\u0026ge;\u0026thinsp;10 mL/sec reduces the risk of low-pressure BOO establishes mean flow rate as a strong protective factor. This association was even stronger than that of Qmax, which lost statistical significance in the multivariate analysis. Although Qmax has traditionally served as the primary uroflowmetry parameter for BOO screening, our results suggest that Qmean may offer superior discriminatory value. This aligns with recent findings showing that Qmean provides superior diagnostic accuracy compared with Qmax (AUC 0.729 vs. 0.636) and offers markedly higher diagnostic efficiency (specificity 42.3% vs. 26.9%; Youden index 0.41 vs. 0.24). Importantly, inclusion of Qmean in full predictive models substantially enhances BOO discrimination (AUC 0.813), whereas removing Qmean leads to a dramatic loss of performance, including a 34.6% drop in specificity and a 0.31 reduction in Youden index[13]. However, this study focused exclusively on men and did not report detrusor pressure data. Qmax is highly susceptible to transient detrusor power and abdominal straining, particularly in the presence of detrusor underactivity. Because most patients with low-pressure BOO are unable to generate sustained detrusor contractions, abdominal straining is frequently employed to overcome urethral resistance, thereby disproportionately influencing Qmax. In contrast, Qmean\u0026mdash;by averaging flow across the entire voiding phase\u0026mdash;provides a more stable surrogate of overall voiding performance and bladder outlet resistance.\u003c/p\u003e \u003cp\u003eOne of the most intriguing findings of this study is that age\u0026thinsp;\u0026ge;\u0026thinsp;70 years is independently protective against low-pressure BOO. This finding contradicts the conventional assumption that advanced age universally increases the risk of voiding dysfunction. Consistent with our results, Wu et al. demonstrated an age-related increase in detrusor underactivity accompanied by a decrease in the prevalence of BOO[14]. Rajasekaran et al. reported a significant age-related decrease in urethral sphincter muscle thickness and closure function in a rabbit mode[15]. In a cadaveric study of women, Perucchini et al. demonstrated age-related loss of striated muscle at the bladder neck and along the dorsal wall of the urethra[16]. Similarly, Lau et al. showed that maximal urethral closure pressure was significantly reduced in older women, indicating progressive urethral intrinsic sphincter deficiency with advancing age[17]. An age-related decline in urethral closure pressure may reduce outlet resistance sufficiently to prevent the development of BOO.\u003c/p\u003e \u003cp\u003eThe association between V/S ratio\u0026thinsp;\u0026gt;\u0026thinsp;1 and increased low-pressure BOO risk suggests that symptom pattern analysis may complement urodynamic testing. A V/S ratio\u0026thinsp;\u0026gt;\u0026thinsp;1 indicates predominance of voiding symptoms over storage symptoms, theoretically reflecting obstructive pathology. Choi et al. found that among female patients presenting with voiding difficulty, the mean IPSS voiding and storage subscores were 12.0\u0026thinsp;\u0026plusmn;\u0026thinsp;5.0 and 8.4\u0026thinsp;\u0026plusmn;\u0026thinsp;3.4, respectively[18]. Most patients were diagnosed with BOO (87.2%), whereas only 12.8% had detrusor underactivity. Hsiao et al. reported that a significantly higher V/S ratio was observed in women with bladder outlet\u0026ndash;related lower urinary tract dysfunction, and that a V/S ratio\u0026thinsp;\u0026ge;\u0026thinsp;1.33 had the best predictive value, with a high negative predictive value (97.4%)[19]. Therefore, the predominance of voiding symptoms, defined as a V/S ratio\u0026thinsp;\u0026gt;\u0026thinsp;1 in our study, may help distinguish BOO from other lower urinary tract dysfunctions.\u003c/p\u003e \u003cp\u003eIn our study, diabetes mellitus was not associated with low-pressure BOO in either univariate or multivariate analyses. Diabetic bladder dysfunction is a well-recognized complication of diabetes mellitus, typically developing in middle-aged or elderly patients with long-standing and poorly controlled disease. It encompasses a spectrum of clinical manifestations, ranging from bladder overactivity to impaired detrusor contractility[20]. In contrast, relatively few studies have examined the effects of diabetes mellitus on urethral function. Limited evidence suggests that diabetes may impair urethral function, characterized by increased urethral pressure during micturition and disrupted coordination of voiding[21]. Therefore, although diabetes mellitus is classically associated with bladder dysfunction, it may contribute to both BOO and detrusor underactivity. Furthermore, the duration, control, and complications of diabetes mellitus were not clarified, and different risk profiles might affect diabetes mellitus\u0026ndash;related lower urinary tract dysfunction.\u003c/p\u003e \u003cp\u003eThis study has several strengths. First, the relatively large sample size provides robust characterization of low-pressure BOO, which is often neglected in women with low-pressure urodynamic profiles. Second, multivariable analysis controlling for potential confounders enabled the identification of independent predictive factors for low-pressure BOO, including age, surgical history, symptom patterns, and Qmean. Third, our results challenge the conventional assumption that female BOO uniformly presents with elevated voiding pressures.\u003c/p\u003e \u003cp\u003eSeveral limitations of this study warrant consideration. First, its retrospective, cross-sectional design precludes the establishment of definitive causal relationships. While a history of anti-incontinence surgery or pelvic organ prolapse repair was strongly associated with low-pressure BOO, we cannot ascertain whether the obstruction developed as a direct consequence of the procedure or existed preoperatively. Second, although VUDS is the current gold standard for diagnosing female BOO, the radiographic interpretation of obstruction remains somewhat subjective and may be influenced by the observer\u0026rsquo;s experience. To mitigate this, we utilized a consensus-based approach with multiple expert reviewers. Third, as a single-center study conducted at a tertiary referral unit, our population may be subject to referral bias, potentially limiting the generalizability of our findings to primary care settings. Finally, while we identified specific clinical and uroflowmetry \"clues\" for low-pressure BOO, these parameters require further validation in independent, prospective cohorts to confirm their diagnostic utility in broader clinical practice.\u003c/p\u003e"},{"header":"CONCLUSIONS","content":"\u003cp\u003eApproximately 30% of women classified as non-BOO by conventional UDS are actually identified as having low-pressure BOO when evaluated with VUDS. This high prevalence suggests that conventional pressure-flow studies alone are insufficient to exclude obstruction in women with complex lower urinary tract symptoms.\u003c/p\u003e \u003cp\u003eFor patients initially diagnosed as non-BOO by conventional UDS, we identified several significant diagnostic clues for occult low-pressure BOO: a history of anti-incontinence or pelvic organ prolapse surgery, a V/S ratio\u0026thinsp;\u0026gt;\u0026thinsp;1, age\u0026thinsp;\u0026lt;\u0026thinsp;70 years, or a mean flow rate\u0026thinsp;\u0026lt;\u0026thinsp;10 mL/s. These indicators should prompt clinicians to consider further evaluation with VUDS to prevent missed diagnoses. While these findings provide a practical screening approach, the retrospective nature and subjective interpretation of imaging in this study necessitate future prospective, multi-center trials to validate these clinical clues in broader populations.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNone\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e:\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThis work was supported by the Yan Ching-Ling Medical Foundation (Grant No. CI-112-20).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of Interest\u003c/strong\u003e:\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe authors declare no conflict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical Approval\u003c/strong\u003e:\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe protocol for this research project has been approved by the Research Ethics Committee of Taipei Veterans General Hospital (approval No. TPEVGH-IRB 2021-02-007BC) and it conforms to the provisions of the Declaration of Helsinki.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eInformed Consent\u003c/strong\u003e:\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThis retrospective study used existing medical records, and individual informed consent was waived by the Institutional Review Board.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e:\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe datasets analyzed during this study are available from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eY.F: conceptualization, data curation, writing-review and editing\u003c/p\u003e\n\u003cp\u003eL.Y.: formal analysis,\u0026nbsp;writing-review and editing\u003c/p\u003e\n\u003cp\u003eC.L.: data curation\u003c/p\u003e\n\u003cp\u003eM.K.:\u0026nbsp;data curation\u003c/p\u003e\n\u003cp\u003eE.Y.H: supervision\u003c/p\u003e\n\u003cp\u003eW.C.: conceptualization, formal analysis, writing-review and editing\u003c/p\u003e\n\u003cp\u003eC.Y.: project administration, supervision\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAbrams PH, Griffiths DJ (1979) The assessment of prostatic obstruction from urodynamic measurements and from residual urine. Br J Urol 51:129-134. https://doi.org/10.1111/j.1464-410x.1979.tb02846.x\u003c/li\u003e\n\u003cli\u003eMalde S, Solomon E, Spilotros M et al (2019) Female bladder outlet obstruction: Common symptoms masking an uncommon cause. Low Urin Tract Symptoms 11:72-77. https://doi.org/10.1111/luts.12196\u003c/li\u003e\n\u003cli\u003ePang KH, Campi R, Arlandis S et al (2022) Diagnostic Tests for Female Bladder Outlet Obstruction: A Systematic Review from the European Association of Urology Non-neurogenic Female LUTS Guidelines Panel. Eur Urol Focus 8:1015-1030. https://doi.org/10.1016/j.euf.2021.09.003\u003c/li\u003e\n\u003cli\u003eHaylen BT, de Ridder D, Freeman RM et al (2010) An International Urogynecological Association (IUGA)/International Continence Society (ICS) joint report on the terminology for female pelvic floor dysfunction. Int Urogynecol J 21:5-26. https://doi.org/10.1007/s00192-009-0976-9\u003c/li\u003e\n\u003cli\u003eChow PM, Hsiao SM, Kuo HC (2021) Identifying occult bladder outlet obstruction in women with detrusor-underactivity-like urodynamic profiles. Sci Rep 11:23242. https://doi.org/10.1038/s41598-021-02617-0\u003c/li\u003e\n\u003cli\u003eOkamura K, Nojiri Y, Osuga Y, Tange C (2009) Psychometric analysis of international prostate symptom score for female lower urinary tract symptoms. Urology 73:1199-1202. https://doi.org/10.1016/j.urology.2009.01.054\u003c/li\u003e\n\u003cli\u003eBlaivas JG, Groutz A (2000) Bladder outlet obstruction nomogram for women with lower urinary tract symptomatology. Neurourol Urodyn 19:553-564. https://doi.org/10.1002/1520-6777(2000)19:5\u0026lt;553::aid-nau2\u0026gt;3.0.co;2-b\u003c/li\u003e\n\u003cli\u003eNitti VW, Tu LM, Gitlin J (1999) Diagnosing bladder outlet obstruction in women. J Urol 161:1535-1540. \u003c/li\u003e\n\u003cli\u003eTran H, Rutman M (2018) Female Outlet Obstruction After Anti-incontinence Surgery. Urology 112:1-5. https://doi.org/10.1016/j.urology.2017.08.041\u003c/li\u003e\n\u003cli\u003eDunn JS, Jr., Bent AE, Ellerkman RM, Nihira MA, Melick CF (2004) Voiding dysfunction after surgery for stress incontinence: literature review and survey results. Int Urogynecol J Pelvic Floor Dysfunct 15:25-31; discussion 31. https://doi.org/10.1007/s00192-003-1114-8\u003c/li\u003e\n\u003cli\u003eRoss J, Avvakoumova L, Yassein A et al (2023) Prevalence and Predictors of Bladder Outlet Obstruction in Women With Chronic Urinary Symptoms and a History of Urethral Sling Surgery. J Urol 209:384-390. https://doi.org/10.1097/JU.0000000000003068\u003c/li\u003e\n\u003cli\u003eChang YH, Siu JJ, Hsiao PJ, Chang CH, Chou EC (2018) Review of underactive bladder. J Formos Med Assoc 117:178-184. https://doi.org/10.1016/j.jfma.2017.09.006\u003c/li\u003e\n\u003cli\u003eEvangelos S, Michail S, Vasileios S, Aikaterini S, Charalampos K (2025) Average flow rate (Qave): Current role and clinical value of a neglected urodynamic parameter in predicting diagnosis of bladder outlet obstruction in males. J Urol 213:e1207. \u003c/li\u003e\n\u003cli\u003eWu PC, Hsiao SM, Lin HH (2024) Age-specific prevalence, clinical and urodynamic findings of detrusor underactivity and bladder outlet obstruction in female voiding dysfunction. Int J Gynaecol Obstet 167:797-803. https://doi.org/10.1002/ijgo.15705\u003c/li\u003e\n\u003cli\u003eRajasekaran MR, Fu J, Nguyen ML et al (2019) Age and multiparity related urethral sphincter muscle dysfunction in a rabbit model: Potential roles of TGF-beta and Wnt-beta catenin signaling pathways. Neurourol Urodyn 38:607-614. https://doi.org/10.1002/nau.23889\u003c/li\u003e\n\u003cli\u003ePerucchini D, DeLancey JO, Ashton-Miller JA, Galecki A, Schaer GN (2002) Age effects on urethral striated muscle. II. Anatomic location of muscle loss. Am J Obstet Gynecol 186:356-360. https://doi.org/10.1067/mob.2002.121090\u003c/li\u003e\n\u003cli\u003eLau HH, Su TH, Huang WC (2021) Effect of aging on lower urinary tract symptoms and urodynamic parameters in women. Taiwan J Obstet Gynecol 60:513-516. https://doi.org/10.1016/j.tjog.2021.03.022\u003c/li\u003e\n\u003cli\u003eChoi YS, Kim JC, Lee KS et al (2013) Analysis of female voiding dysfunction: a prospective, multi-center study. Int Urol Nephrol 45:989-994. https://doi.org/10.1007/s11255-013-0475-2\u003c/li\u003e\n\u003cli\u003eHsiao SM, Lin HH, Kuo HC (2013) International Prostate Symptom Score for assessing lower urinary tract dysfunction in women. Int Urogynecol J 24:263-267. https://doi.org/10.1007/s00192-012-1818-8\u003c/li\u003e\n\u003cli\u003eGolbidi S, Laher I (2010) Bladder dysfunction in diabetes mellitus. Front Pharmacol 1:136. https://doi.org/10.3389/fphar.2010.00136\u003c/li\u003e\n\u003cli\u003eCao N, Gu B, Gotoh D, Yoshimura N (2019) Time-Dependent Changes of Urethral Function in Diabetes Mellitus: A Review. Int Neurourol J 23:91-99. https://doi.org/10.5213/inj.1938050.025\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"world-journal-of-urology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"wjur","sideBox":"Learn more about [World Journal of Urology](https://link.springer.com/journal/345)","snPcode":"345","submissionUrl":"https://submission.nature.com/new-submission/345/3","title":"World Journal of Urology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"age, bladder outlet obstruction, low-pressure bladder outlet obstruction, mean flow rate, videourodynamics","lastPublishedDoi":"10.21203/rs.3.rs-8890223/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8890223/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003ePurpose\u003c/h2\u003e \u003cp\u003eFemale bladder outlet obstruction is typically characterized by high-pressure, low-flow patterns. However, low-pressure, low-flow variants are frequently overlooked by conventional urodynamic studies. This study aims to identify clinical predictors of low-pressure bladder outlet obstruction in women categorized as non-obstructed by standard criteria.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eWe retrospectively reviewed women with lower urinary tract symptoms who underwent videourodynamics between 2012 and 2020. Conventional obstruction was defined as maximal flow rate of less than 12 milliliters per second combined with a detrusor pressure at maximal flow of greater than 20 centimeters of water. Patients not meeting these parameters were evaluated for low-pressure obstruction, confirmed via fluoroscopic evidence during videourodynamics.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eAmong 419 women classified as non-obstructed by conventional urodynamics, 128 (30.5%) demonstrated low-pressure bladder outlet obstruction on videourodynamics. Multivariable logistic regression identified a history of anti-incontinence or pelvic organ prolapse surgery and an International Prostate Symptom Score voiding-to-storage subscore ratio greater than 1 as significant independent predictors. Conversely, age 70 years or older and a mean flow rate of 10 milliliters per second or greater served as independent negative predictors.\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e \u003cp\u003eApproximately 30% of women deemed non-obstructed by conventional urodynamics exhibit low-pressure bladder outlet obstruction. Clinicians should prioritize further evaluation with videourodynamics in patients with prior anti-incontinence surgery, a high voiding-to-storage ratio, younger age, or low mean flow rates to prevent misdiagnosis.\u003c/p\u003e","manuscriptTitle":"Diagnostic Clues for Low-Pressure Female Bladder Outlet Obstruction Overlooked by Conventional Urodynamics","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-03 16:41:55","doi":"10.21203/rs.3.rs-8890223/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-04-27T15:34:37+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-21T14:32:44+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"177150287093250609377753746330748239466","date":"2026-04-19T15:44:32+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-19T02:53:46+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"23655656687462965984007213442223069141","date":"2026-04-14T08:28:51+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"299074244373813280830549850038092793475","date":"2026-04-02T01:51:49+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"119671764294127863930430615803216228542","date":"2026-03-03T20:07:48+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-02-26T06:36:14+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-02-17T23:28:32+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-02-17T15:39:29+00:00","index":"","fulltext":""},{"type":"submitted","content":"World Journal of Urology","date":"2026-02-16T06:17:17+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"world-journal-of-urology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"wjur","sideBox":"Learn more about [World Journal of Urology](https://link.springer.com/journal/345)","snPcode":"345","submissionUrl":"https://submission.nature.com/new-submission/345/3","title":"World Journal of Urology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"2e499c91-75d8-47bc-8ff2-88beb0c7a1e6","owner":[],"postedDate":"March 3rd, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-11T06:23:28+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-03 16:41:55","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8890223","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8890223","identity":"rs-8890223","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}