The position of the dichrotic notch in digital photoplethysmography is not affected by local vasodilation

The position of the dichrotic notch in digital photoplethysmography is not affected by local vasodilation | 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 Short Report The position of the dichrotic notch in digital photoplethysmography is not affected by local vasodilation Gerardo Tusman, Matías Nicolás, Cecilia M Acosta, Alejandro Carmona, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7445879/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Purpose The vertical position of the dichrotic notch of finger photoplethysmography (PPG) is affected by systemic vasodilation. The aim of this study was to test whether a local upper limb vasodilation would alter the position of the dichrotic notch. Methods Patients undergoing upper limb vasodilation caused by brachial plexus block (n = 8) and video-assisted bilateral sympathectomy (n = 8 with 2 measurements each) were analyzed. Continuous PPG recordings and brachial Doppler sonography were recorded before and five minutes after regional anesthesia and sympathetic ablation. The dichrotic notch of PPG was expressed as % of the PPG waveform amplitude. Results Local vasodilation after the interventions was evidenced by a decrease in Doppler’s resistive index from 0.88(0.2) to 0.79(0.2) (p = 0.021) in the regional blocks and from 0.83(0.3) to 0.80(0.3) (p = 0.003) in the sympathectomies. PPG amplitude increased from 46(24) to 59(12)% (p = 0.008) in the regional anesthesia-group and from 34(29) to 44(35)% (p = 0.010) in the sympathectomy-group. The position of the dichrotic notch was neither affected in the regional anesthesia-group before [15(12)%] and after [15(10)%;p = 0.916] nor in the sympathectomy-group before [14(21)%] and after [13(19)%;p = 0.849]. Conclusions Local vasodilation in the arm does not influence the position of the dichrotic notch in finger PPG despite increases in its amplitude. The dichrotic notch is thus a systemic phenomenon that depends on pulse wave reflections. Dichrotic notch photoplethysmography sympathectomy pulse wave wave reflection Figures Figure 1 Figure 2 Figure 3 Introduction The waveform of the pulse traveling along the vascular tree carries relevant information about the cardiovascular system and the hemodynamic status. The physiology behind the pulse waveform, including the concept of ventricular-vascular interaction, has been studied extensively since the mid-20 th century [1-4]. Based on Fourier’s analysis the decomposition of the pulse wave reveals that such waveform is composed of a number of sine waves of different frequencies travelling forward and, after rebound in arterial bifurcations, backward in the aortic wall [5-7]. The backward waves reach the heart during diastole, increase aortic diastolic pressure and participate in aortic valve closure thereby being partially responsible for the dichrotic notch observed in normal pulse waveforms (Figure 1A) [8]. The pulse pressure waveform recorded by intra-arterial catheters and the pulse wave measured by digital photoplethysmography (PPG) both adhere to the aforementioned physiological rules [9,10]. However, because PPG represents the pulse waveform in the volume or flow dimension [11], variations in arterial impedance can significantly alter its shape. This is because flow waves rebound in bifurcations and then can return upside down, in contrast to pulse pressure waveforms that always rebound in a positive fashion [4,12,13]. We reported in this journal a simple classification of the vascular tone based on this physiological behavior of this “flow” waveform, which is based on the PPG amplitude and the vertical location of the dichrotic notch (Figure 1B) [14]. A potential pitfall of this classification is that the PPG waveform may be affected by regional variations in upper limb blood flow brought about by, for example, local temperature variations. Thus, the classification could fail in case the finger PPG did not represent systemic effect on the aorta. We found some evidence for this potential shortcoming of our classification in the work of Chowienczyk et al. [15]. The authors elegantly demonstrated that the dichrotic notch of digital PPG was not affected by intra-arterial infusion of vasodilators (local effect on hand) compared to systemic iv infusion of such drugs. While local vasodilators increased PPG amplitude, the location of the dichrotic notch remained unaltered. Simply stated, the dichrotic notch is a systemic phenomenon that is independent of local variations in the vascular tone of the upper limb and is rather dependent on the reflections of the harmonics at the bifurcations of main arteries. However, a main concern of their methodology is that the intra-arterial infusion of vasodilators might have reached the systemic circulation and thus act as a confounder of their results. In this brief report, we aimed to reproduce Chowienczyk et al. [15] results using two models of vasodilation, which are strictly limited to the upper limb with no effects on the rest of the systemic vascular system. We thus hypothesized that the position of the dichrotic notch in the pulse waveform of digital photoplethysmographic represents systemic wave reflections, which are not affected by local vasodilation at the finger. The objective of this study was to test the above hypothesis inducing upper limb vasodilation by brachial plexus anesthesia and by video-assisted sympathectomy in healthy and hemodynamic stable patients. Methods The present study was performed in compliance with the Declaration of Helsinki, approved by the local ethical committee and with the corresponding written informed consent of all patients. We studied eight patients undergoing brachial plexus anesthesia for upper limb surgeries and eight patients with hyperhidrosis undergoing bilateral sympathetic ablation via uniportal video-assisted thoracoscopies (u-VATS). Since both upper limbs were independently affected by the two ablations, each patient contributed 2 data sets. We included healthy ASA I patients ≥ 20 years of age and excluded pregnant women, smokers or ex-smokers as well as patients with diabetes, obesity, arterial hypertension, peripheral vascular diseases, and emergency surgeries. Regional anesthesia for upper limb surgeries was performed under sedation with intravenous midazolam 1–3 mg. A sonography-guided supraclavicular brachial block was induced by 30 mL of bupivacaine 0.25%. General anesthesia for u-VATS was carried out with propofol 1–1,5 mg kg − 1 , fentanyl 3 µg kg − 1 and vecuronium 0.08 mg kg − 1 and maintained with sevofluorane 0.5–0.8 MAC and remifentanyl 0.5-1 µg kg − 1 min − 1 . Standard monitoring consisted of the ECG, non-invasive blood pressure (oscillometry), skin temperature and pulse oximetry of the S5 (Datex-Ohmeda, Helsinki, Finland). Pulse oximetry The tested hand was assessed by an additional pulse oximeter (Fluxmed, MBMed, Buenos Aires, Argentina). An analog front-end solution designed for pulse oximeter applications (AFE4490, Texas Instruments, Dallas, TX, USA) was used to control a custom-made transmittance pulse oximeter. It contained photodiode signal conditioning circuitry and LED driver circuitry for red (λ 660 nm) and infrared (λ 940 nm) LEDs and consisted of a 22-bit analog-to-digital converter that used a serial peripheral interface (SPI) to interact with the microcontroller while samplingthe PPG signal at 500 Hz. The system was linked via USB to a laptop running a Window operating system. Data were displayed on a custom-made user interface written in Matlab® (Mathworks, Natick, MA, USA). Figure 1 A-C show photoplethysmography waveforms in an arbitrary scale from 0-100% formed by the AC and DC components of the infrared light. The software automatically computed the perfusion index (AC/DC) of every beat [ 16 ]. All information were downloaded as .txt files on a beat-by-beat basis. (Fig. 1 near here) Doppler Brachial artery Doppler sonography of the tested hand was performed by an expert using a linear probe of 6–12 MHz (MyLab Gamma echograph; Esaote, Genova, Italy). We calculated peak systolic velocity (PSV), time average velocity (TAV), the pulsatility index (PI = systolic-diastolic velocity/mean velocity) and the resistive index (RI = systolic-diastolic velocity/systolic velocity) [ 17 , 18 ]. We displayed five spectral waveforms per screen and performed the related automatic calculations of the above variables. These measurements were done 3 times, stored in the echograph’s memory and downloaded as .jpg files on a pen-drive. The corresponding database constituted by the average value of each variable studied in these 15 pulse waveforms was built off-line. In patients undergoing regional brachial blocks, an additional Doppler sonography of the homolateral carotid artery was conducted to assess the effect of vasodilation of the arm on the systemic blood flow velocity. Protocol All patients remained supine during the protocol with standard non-invasive blood pressure and SpO 2 monitoring on the contralateral arm. An additional pulse oximeter was placed on the middle finger of the tested hand maintained at the phlebostatic level. A skin thermometer was attached on the thenar eminence of the tested hand. Under sedation (upper limb surgeries) and general anesthesia (sympathectomies) baseline PPG recordings were done during the brachial artery Doppler examination which lasted 5 to 8 minutes. Thereafter, regional anesthesia or sympathetic ablation was performed. Five minutes after these interventions we repeated the PPG and brachial Doppler in the tested arm. To track any possible effects of these procedures on the systemic vascular system, we used Doppler to evaluate the homolateral carotid artery in patients undergoing regional anesthesia but not sympathectomies, whose necks were covered by surgical sheets. PPG and Doppler measurements were stored on the laptop and the echograph, respectively, identifying the files as “before” and “after” intervention. Data analysis The stored PPG .txt files were opened in Excel (Windows 10) and 15 consecutive heartbeats corresponding with the Doppler assessment were selected. These beats were manually segmented and overlapped one beside the other (Fig. 1 C). The PPG signal, arbitrarily expressed on a 0-100% scale on the original oximeter, which allowed us to calculate the PPG amplitude and the vertical position of the dichrotic notch, both in %. Perfusion index and SpO 2 values of the 15 analyzed beats were averaged. A non-normal distribution of numerical variables was confirmed by the Shapiro-Wilk test. Continuous variables were described as median and dispersion (25th and 75th quartiles or interquartile range, IQR). Quantitative continuous variables before and after intervention were compared by the Wilcoxon test. A p value of < 0.05 was considered statistically significant for all comparisons. All analyses were performed with the statistical software Stata 15.1 (Stata Corporation, College Station, TX, USA). Results All patients completed the protocol successfully, obtaining eight complete data pairs of variables in patients undergoing regional anesthesia and sixteen data pairs in bilateral sympathectomies. Patient details are provided in Table 1 . Patients undergoing upper limb procedures were mostly male and marginally older than those undergoing u-VAT sympathectomy. Table 1 Patients’ data Regional Anesthesia (n = 8) Sympatectomies (n = 8) Age (years) 39 ± 12 27 ± 9 Sex (women/men) 1/7 5/2 Height (cm) 77 ± 11 65 ± 7 Height (cm) 173 ± 5 171 ± 6 Surgery Finger tenorrhaphy (3) -osteosynthesis (5) Uniportal video-assisted bilateral sympathectomy Doppler showed an increased blood flow velocity and decreased vascular resistance in the upper limbs. The reference brachial artery Doppler showed an increase in TAV from 27 (18) to 39 (15) cm/s (p = 0.017) after the intervention in the regional anesthesia group and from 30 (9) to 35 (9) cm/s (p = 0.001) in the sympathectomy group. This increase in mean blood flow velocity was not associated with changes in the PSV in the sympathectomy group (Table 2 ). The increase in TAV after the interventions was related to a decrease in RI from 0.88 (0.2) to 0.79 (0.2) (p = 0.021) in the regional anesthesia group and from 0.83 (0.3) to 0.80 (0.3) (p = 0.003) in the sympathectomy group. PI decreased from 2.6 (2.0) to 2.2 (1.5) (p = 0.036) in the regional anesthesia group and from 3.1 (1.6) to 2.4 (1.1) (p = 0.002) in the sympathectomy group. Figure 2 depicts the changes in brachial and carotid artery Doppler parameters for the regional anesthesia group. Regional anesthesia affected the blood flow in the brachial artery but not in the carotid artery. Table 2 Main data. Parameter Regional anesthesia (n = 8) Sympathectomies (n = 8) Before After P value Before After P value PPG Class 3 (0) 3 (0) 1.000 3 (1) 3 (1) 1.000 Amplitude (%) 46 (24) 59 (12) 0.008 34 (29) 44 (35) 0.010 Dichrotic notch (%) 15 (12) 15 (10) 0.916 14 (21) 13 (19) 0.849 Perfusion Index 5.6 (6.0) 6.8 (7.5) 0.012 4.8 (4.3) 5.2 (5.2) 0.004 Doppler PSV (cm/s) 83 (39) 90 (40) 0.012 114 (37) 100 (45) 0.983 TAV (cm/s) 27 (18) 39 (15) 0.017 30 (9) 35 (9) 0.001 RI 0.88 (0.2) 0.79 (0.2) 0.021 0.83 (0.3) 0.80 (0.3) 0.003 PI 2.6 (2.0) 2.2 (1.5) 0.036 3.1 (1.6) 2.4 (1.1) 0.002 Hemodynamics HR (bpm) 72 (15) 69 (14) 0.310 78 (15) 80 (18) 0.744 SAP (mmHg) 135 (11) 131 (19) 0.322 107 (11) 105 (12) 0.679 MAP (mmHg) 100 (12) 98 (17) 0.050 75 (7) 74 (3) 0.170 DAP (mmHg) 84 (18) 80 (18) 0.025 59 (4) 60 (3) 0.266 SpO 2 (%) 96 (1.8) 96 (2.1) 0.398 99 (0.9) 98 (1.7) 0.028 T° (Celsius) 33 (1.7) 34 (1.6) 0.292 34 (0.9) 34 (2.2) 0.122 PPG = photoplethysmography, PSV = peak systolic velocity, TAV = time average velocity, PI = pulsatility index, RI = resistive index, HR = heart rate, SAP = systolic arterial blood pressure, MAP = mean arterial blood pressure, DAP = diastolic arterial blood pressure, SpO 2 = pulse oximetry hemoglobin saturation, and T° = hand temperature. Wilcoxon test was used or pairwise comparison “before” vs “after”. A p value of < 0.05 was considered statistically significant. PPG showed vasodilation of the local limb without changes in the location of the dichrotic notch. All patients presented a PPG class 3 except for two in the sympathectomy group who had a class 4. After the interventions PPG amplitude increased from 46 (24) to 59 (12) % (p = 0.008) in the regional anesthesia group and from 34 (29) to 44 (35) % (p = 0.010) in the sympathectomy group. The perfusion index increased with the interventions in the same manner: in the group receiving regional anesthesia it increased from 5.6 (6.0) to 6.8 (7.5) (p = 0.012), and in the group receiving sympathectomy it increased from 4.8 (4.3) to 5.2 (5.2) (p = 0.004). On the other hand, the location of the dichrotic notch neither changed in the regional anesthesia group [before 15 (12) vs after 15 (10) %; p = 0.901] nor in the sympathectomy group [before 14 (21) vs after 13 (19) %; p = 0.167]. Figure 3 depicts typical examples of both groups before and after the intervention. PPG were superimposed to illustrate the effect of local limb vasodilation on the waveforms’ shape. While vasodilation increased local blood flow and PPG amplitude, the dichrotic notch remained at the same position. (Figs. 2 – 3 and Tables 1 – 2 near here) Hemodynamics, hemoglobin saturation, and local temperature at the tested hand did not change during the procedure, however there were some minor statistical differences in SpO 2 in the sympathetic group and in diastolic blood pressure in the regional anesthetic group (Table 2 ). Discussion This brief report shows that local vasodilation in the upper limb did not affect the location of the dichrotic notch of the PPG wave. The results were independent of the nature of such vasodilation as it was observed during both, a reversible anesthesia and immediately after an irreversible sympathetic ablation. Using models of pure upper limb vasodilation, we were able to replicate the findings of Chowienczyk et al. and confirm that the dichrotic notch position within the PPG waveform is a systemic phenomenon that depends on pulse wave reflections at bifurcations of main arteries [ 15 ]. In clinical practice monitoring of vascular tone at the bedside is scarce, intermittent, operator-dependent (Doppler), and invasive (pulmonary artery catheterization or invasive artery pulse waveform analysis). A straightforward, affordable, non-invasive, and ongoing vascular tone monitoring device is necessary, and PPG provides all these benefits. Because local vasodilation in the upper limb has no discernible effect on the location of the dichrotic notch, the results validate the clinical analysis of the PPG waveform to determine systemic vascular tone. The selective upper limb vasodilation by regional anesthesia and sympathectomy appears to be an adequate model to test our hypothesis because each arm represents ⁓10% of body’s vasculature. Thus, a local vasodilation in the rather-small upper limb arteries would not affect the dichrotic notch location if the wave reflections took place at bifurcations of the body’s main arteries like iliac and subclavian [ 19 ]. Figure 4 illustrates how our findings align with the aforementioned statement. Although the Doppler variables and PPG amplitude provided unequivocal evidence of local vasodilation, the position of the dichrotic notch in both, Doppler and PPG waveforms remained unchanged. Conclusions Our findings demonstrated that local vasodilation in the upper limb does not influence the position of the dichrotic notch in the waveform of digital PPG despite increases in its amplitude. The dichrotic notch is thus a systemic phenomenon that depends on pulse wave reflections. These results support the value of analyzing the position of the dichrotic notch in PPG waveforms to determine systemic vascular tone. Declarations Acknowledgment: None. Funding: The authors declare that no funds, grants, or other support was received during the preparation of this manuscript. Conflict of interest: The authors have no relevant financial or non-financial interests to disclose. Author contribution: All authors contributed to the study’s conception and design. Data collection was performed by [MN, AC, CMA, and GT ]. Material preparation, and analysis were performed by [GT].The first draft of the manuscript was written by [MN, SHB, and GT ] and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript. Ethics approval: This study was approval by the local Ethic Committee. References Remington JW, Wood EH (1956) Formation of peripheral pulse contour in man. J Appl Physiol 9:433-442. https://doi.org/10.1152/jappl.1956.9.3.433 O'Rourke MF (1970) Influence of ventricular ejection on the relationship between central aortic and brachial pressure pulse in man. Cardiovasc Res 4:291-300. https://doi.org /10.1093/cvr/4.3.291 O'Rourke MF, Kelly RP (1993) Wave reflection in the systemic circulation and its implications in ventricular function. J Hypertens 11:327-337. https://doi.org /10.1097/00004872-199303000-00001 Murgo JP, Westerhof NICO, Giolma JP, Altobelli SA (1980) Aortic input impedance in normal man: relationship to pressure wave forms. Circulation 62:105-116. https://doi.org/ 10.1161/01.CIR.62.1.105 O’Rourke MF, Gallagher DE (1996) Pulse wave analysis. J Hypertens 14:S147-S157. https://doi.org/10.1097/00004872-199612001-00025. O'Rourke MF, Avolio AP (1980) Pulsatile flow and pressure in human systemic arteries. Studies in man and in a multibranched model of the human systemic arterial tree. Circul Res 46:363-372. https://doi.org/10.1161/01.RES.46.3.363 Pythoud F, Stergiopulos N, Westerhof N, Meister JJ (1996) Method for determining distribution of reflection sites in the arterial system. Am J Physiol Heart and Circul Physiol 271:H1807-H1813. https://doi.org/10.1152/ajpheart.1996.271.5.H1807 Smith D, Craige E (1986) Mechanism of the dicrotic pulse. Br Heart J 56:531-534. https://doi.org/10.1136/hrt.56.6.531 Politi MT, Ghigo A, Fernández JM, Khelifa I, Gaudric J, Fullana JM, Lagrée PY (2016) The dicrotic notch analyzed by a numerical model. Comput Biol Med 72:54-64. https://doi.org/10.1016/j.compbiomed.2016.03.005 Shi P, Hu S, Zhu Y, Zheng J, Qiu Y, Cheang PYS (2009) Insight into the dicrotic notch in photoplethysmographic pulses from the finger tip of young adults. J Med Eng Tech 33: 628-633. https://doi.org/10.3109/03091900903150980 Korpas D, Hálek J, Dolezal L (2009) Parameters describing the pulse wave. Physiol Res 58:473-479. https://doi.org/10.33549/physiolres.931468. Van den Bos GC, Westerhof N, Randall OS (1982) Pulse wave reflection: can it explain the differences between systemic and pulmonary pressure and flow waves? A study in dogs. Circul Res 51:479-485. https://doi.org/10.1161/01.RES.51.4.479 Jones CJ, Sugawara M, Kondoh Y, Uchida K, Parker KH (2002) Compression and expansion wavefront travel in canine ascending aortic flow: wave intensity analysis. Heart & Vessels 16:91-98. https://doi.org/10.1007/s003800200002 Tusman G, Acosta CM, Pulletz S, Böhm SH, Scandurra A, Arca JM, Suarez Sipmann F (2019) Photoplethysmographic characterization of vascular tone mediated changes in arterial pressure: an observational study. J Clin Monit Comput 33:815-824. https://doi.org/10.1007/s10877-018-0235-z Chowienczyk PJ, Kelly RP, MacCallum H, Millasseau SC, Andersson TL, Gosling RG, Änggård EE (1999) Photoplethysmographic assessment of pulse wave reflection: blunted response to endothelium-dependent beta2-adrenergic vasodilation in type II diabetes mellitus. J Am Coll Cardiol 34:2007-2014. https://doi.org/10.1016/S0735-1097(99) 00473-1. Lima AP, Beelen P, Bakker J (2002) Use of a peripheral perfusion index derived from the pulse oximetry signal as a noninvasive indicator of perfusion. Crit Care Med 30:1210-1213. https://doi.org/10.1097/00003246-200206000-00006 Legarth J, Nolsoe C (1990) Doppler blood velocity waveforms and the relation to peripheral resistance in the brachial artery. J Ultrasound Med 9:449-453. https://doi.org/10.7863/jum.1990.9.8.449 Ozcan H, Oztekin PS, Zergeroglu AM, Ersöz G, Fiçicilar H, Ustüner E (2006) Doppler ultrasound evaluation of the structural and hemodynamic changes in the brachial artery following two different exercise protocols. Diagn Interv Radiol 12:80-84. https://doi.org/ 10.5152/dir.2006.12.2.80 O’Rourke MF, Adji A, Safar ME (2018) Structure and function of systemic arteries: reflections on the arterial pulse. Am J Hypertens 31:934-940. https://doi.org/10.1093/ ajh/hpy084 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted 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. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-7445879","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Short Report","associatedPublications":[],"authors":[{"id":513563569,"identity":"fe5a4991-0fe3-46f3-88cb-82086b1db978","order_by":0,"name":"Gerardo Tusman","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA0UlEQVRIiWNgGAWjYBADOQMwZWBBhFo2CGVswMAM0iJBvJbEDWAtDERokY/vMf50o+ZO+nb2/qMbfhRIMPC3dyfg1WJ4jMdMOufYs9ydPYfZbvYAHSZx5uwG/FraeMyYc9gO5264kcx2gweoxUAil6AW4885/w6nGwC13PxDjBZ5Nh4D6dy2wwkgLbeJssWALa1MOrfvsOGGM4fNbssYSPAQ9It88+HNn3O+HZY3ON747OabPzZy/O29BGw5gCbAg1c52JYGgkpGwSgYBaNgxAMAgY9FtYGFHNkAAAAASUVORK5CYII=","orcid":"","institution":"Hospital Privado de Comunidad","correspondingAuthor":true,"prefix":"","firstName":"Gerardo","middleName":"","lastName":"Tusman","suffix":""},{"id":513563570,"identity":"f24df9eb-4cf3-4615-ade2-f88a02b4b6c9","order_by":1,"name":"Matías Nicolás","email":"","orcid":"","institution":"Hospital Privado de Comunidad","correspondingAuthor":false,"prefix":"","firstName":"Matías","middleName":"","lastName":"Nicolás","suffix":""},{"id":513563571,"identity":"f9f2d735-8c26-4cdd-bfb7-891b37935f44","order_by":2,"name":"Cecilia M Acosta","email":"","orcid":"","institution":"Hospital Privado de Comunidad","correspondingAuthor":false,"prefix":"","firstName":"Cecilia","middleName":"M","lastName":"Acosta","suffix":""},{"id":513563572,"identity":"07d0a643-9a3f-4135-a7ce-51374a561a5f","order_by":3,"name":"Alejandro Carmona","email":"","orcid":"","institution":"Hospital Privado de Comunidad","correspondingAuthor":false,"prefix":"","firstName":"Alejandro","middleName":"","lastName":"Carmona","suffix":""},{"id":513563573,"identity":"7c1c8f03-1856-47a6-ab7d-59491423a902","order_by":4,"name":"Stephan H. Böhm","email":"","orcid":"","institution":"Rostock University Medical Center","correspondingAuthor":false,"prefix":"","firstName":"Stephan","middleName":"H.","lastName":"Böhm","suffix":""}],"badges":[],"createdAt":"2025-08-24 11:38:09","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7445879/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7445879/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":91309252,"identity":"15b15403-6f34-4009-ab2c-70850f5add3a","added_by":"auto","created_at":"2025-09-15 06:59:51","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1415021,"visible":true,"origin":"","legend":"\u003cp\u003eThe analysis of photoplethysmography.\u003c/p\u003e\n\u003cp\u003eA) The photoplethysmographic signal (PPG) is composed of an alternant component (AC = the pulse waveform) and a continuous component (DC = light absorption by non-pulsatile blood and tissues). The AC pulse waveform is formed by a forward systolic wave that rebounds at bifurcations of major arteries and returns in a retrograde fashion to the heart thereby creating the dichrotic notch (black arrow). B) The classification of the vascular tone using photoplethysmography is based on the waveform’s shape represented by the amplitude and dichrotic notch position (see reference #14 for more details). C) The amplitude of the PPG waveform, which spans from wave’s foot to its peak, is expressed as % of the oximeter’s 0-100% scale. The position of the dichrotic notch within the PPG waveform is calculated as the vertical distance from zero on the 0-100% scale (dotted line and black arrow).\u003c/p\u003e","description":"","filename":"Figure1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7445879/v1/5f3c04336452adc57e58600f.jpg"},{"id":91310448,"identity":"2204d53b-9d74-4c7f-9a36-7edcca9b6678","added_by":"auto","created_at":"2025-09-15 07:15:51","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1073138,"visible":true,"origin":"","legend":"\u003cp\u003eBrachial and carotid artery Doppler in patients undergoing regional anesthesia.\u003c/p\u003e\n\u003cp\u003eDoppler-based time averaged velocity (TAV), pulsatility index (PI) and resistive index (RI) was assessed in the brachial and the carotid artery before and after brachial plexus block (n = 8). Paired Wilcoxon comparison of values before and after regional anesthesia. P \u0026lt; 0.05 was considered statistically significant.\u003c/p\u003e","description":"","filename":"Figure2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7445879/v1/602c8e1a42c69452fb54983d.jpg"},{"id":91309645,"identity":"ec977e32-c75e-48f1-a772-4c2f64e07cb7","added_by":"auto","created_at":"2025-09-15 07:07:51","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":3331833,"visible":true,"origin":"","legend":"\u003cp\u003eClinical examples of Doppler and PPG waveforms before and after interventions.\u003c/p\u003e\n\u003cp\u003eDoppler spectral waveforms of the brachial artery and finger photoplethysmography (PPG) during regional anesthesia block and sympathetic ablation. Measurements were performed before and after the interventions in the representative patients. PPG waveforms before (blue) and after (red) interventions were superimposed for better comparability. Note that vasodilation increased PPG amplitude but had no influence on the vertical position of the dichrotic notch. TAV = time-averaged velocity (cm/s), RI = resistive index, and PI = pulsatility index.\u003c/p\u003e","description":"","filename":"Figure3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7445879/v1/c0e03df77a4fd877242c43db.jpg"},{"id":92214649,"identity":"bd695cfb-a326-4cf1-9250-5f370c03d62a","added_by":"auto","created_at":"2025-09-25 23:31:35","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6363086,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7445879/v1/9dbc30d6-45b9-4aa8-9fb7-b8b625ae6b22.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"The position of the dichrotic notch in digital photoplethysmography is not affected by local vasodilation","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe waveform of the pulse traveling along the vascular tree carries relevant information about the cardiovascular system and the hemodynamic status. The physiology behind the pulse waveform, including the concept of ventricular-vascular interaction, has been studied extensively since the mid-20\u003csup\u003eth\u003c/sup\u003e century [1-4]. Based on Fourier\u0026rsquo;s analysis the decomposition of the pulse wave reveals that such waveform is composed of a number of sine waves of different frequencies travelling forward and, after rebound in arterial bifurcations, backward in the aortic wall [5-7]. The backward waves reach the heart during diastole, increase aortic diastolic pressure and participate in aortic valve closure thereby being partially responsible for the dichrotic notch observed in normal pulse waveforms (Figure 1A) [8].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe pulse pressure waveform recorded by intra-arterial catheters and the pulse wave measured by digital photoplethysmography (PPG) both adhere to the aforementioned physiological rules [9,10]. \u0026nbsp;However, because PPG represents the pulse waveform in the volume or flow dimension [11], variations in arterial impedance can significantly alter its shape. This is because flow waves rebound in bifurcations and then can return upside down, in contrast to pulse pressure waveforms that always rebound in a positive fashion [4,12,13].\u003c/p\u003e\n\u003cp\u003eWe reported in this journal a simple classification of the vascular tone based on this physiological behavior of this \u0026ldquo;flow\u0026rdquo; waveform, which is based on the PPG amplitude and the vertical location of the dichrotic notch (Figure 1B) [14]. A potential pitfall of this classification is that the PPG waveform may be affected by regional variations in upper limb blood flow brought about by, for example, local temperature variations. Thus, the classification could fail in case the finger PPG did not represent systemic effect on the aorta. We found some evidence for this potential shortcoming of our classification in the work of Chowienczyk et al. [15]. The authors elegantly demonstrated that the dichrotic notch of digital PPG was not affected by intra-arterial infusion of vasodilators (local effect on hand) compared to systemic iv infusion of such drugs. While local vasodilators increased PPG amplitude, the location of the dichrotic notch remained unaltered. Simply stated, the dichrotic notch is a systemic phenomenon that is independent of local variations in the vascular tone of the upper limb and is rather dependent on the reflections of the harmonics at the bifurcations of main arteries. However, a main concern of their methodology is that the intra-arterial infusion of vasodilators might have reached the systemic circulation and thus act as a confounder of their results.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn this brief report, we aimed to reproduce Chowienczyk et al. [15] results using two models of vasodilation, which are strictly limited to the upper limb with no effects on the rest of the systemic vascular system. We thus hypothesized that the position of the dichrotic notch in the pulse waveform of digital photoplethysmographic represents systemic wave reflections, which are not affected by local vasodilation at the finger. The objective of this study was to test the above hypothesis inducing upper limb vasodilation by brachial plexus anesthesia and by video-assisted sympathectomy in healthy and hemodynamic stable patients.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003eThe present study was performed in compliance with the Declaration of Helsinki, approved by the local ethical committee and with the corresponding written informed consent of all patients. We studied eight patients undergoing brachial plexus anesthesia for upper limb surgeries and eight patients with hyperhidrosis undergoing bilateral sympathetic ablation via uniportal video-assisted thoracoscopies (u-VATS). Since both upper limbs were independently affected by the two ablations, each patient contributed 2 data sets. We included healthy ASA I patients\u0026thinsp;\u0026ge;\u0026thinsp;20 years of age and excluded pregnant women, smokers or ex-smokers as well as patients with diabetes, obesity, arterial hypertension, peripheral vascular diseases, and emergency surgeries.\u003c/p\u003e\u003cp\u003eRegional anesthesia for upper limb surgeries was performed under sedation with intravenous midazolam 1\u0026ndash;3 mg. A sonography-guided supraclavicular brachial block was induced by 30 mL of bupivacaine 0.25%. General anesthesia for u-VATS was carried out with propofol 1\u0026ndash;1,5 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, fentanyl 3 \u0026micro;g kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and vecuronium 0.08 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and maintained with sevofluorane 0.5\u0026ndash;0.8 MAC and remifentanyl 0.5-1 \u0026micro;g kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Standard monitoring consisted of the ECG, non-invasive blood pressure (oscillometry), skin temperature and pulse oximetry of the S5 (Datex-Ohmeda, Helsinki, Finland).\u003c/p\u003e\n\u003ch3\u003ePulse oximetry\u003c/h3\u003e\n\u003cp\u003eThe tested hand was assessed by an additional pulse oximeter (Fluxmed, MBMed, Buenos Aires, Argentina). An analog front-end solution designed for pulse oximeter applications (AFE4490, Texas Instruments, Dallas, TX, USA) was used to control a custom-made transmittance pulse oximeter. It contained photodiode signal conditioning circuitry and LED driver circuitry for red (λ 660 nm) and infrared (λ 940 nm) LEDs and consisted of a 22-bit analog-to-digital converter that used a serial peripheral interface (SPI) to interact with the microcontroller while samplingthe PPG signal at 500 Hz. The system was linked via USB to a laptop running a Window operating system. Data were displayed on a custom-made user interface written in Matlab\u0026reg; (Mathworks, Natick, MA, USA).\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA-C show photoplethysmography waveforms in an arbitrary scale from 0-100% formed by the AC and DC components of the infrared light. The software automatically computed the perfusion index (AC/DC) of every beat [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. All information were downloaded as .txt files on a beat-by-beat basis.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e(Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e near here)\u003c/h2\u003e\u003cdiv id=\"Sec4\" class=\"Section3\"\u003e\u003ch2\u003eDoppler\u003c/h2\u003e\u003cp\u003eBrachial artery Doppler sonography of the tested hand was performed by an expert using a linear probe of 6\u0026ndash;12 MHz (MyLab Gamma echograph; Esaote, Genova, Italy). We calculated peak systolic velocity (PSV), time average velocity (TAV), the pulsatility index (PI\u0026thinsp;=\u0026thinsp;systolic-diastolic velocity/mean velocity) and the resistive index (RI\u0026thinsp;=\u0026thinsp;systolic-diastolic velocity/systolic velocity) [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. We displayed five spectral waveforms per screen and performed the related automatic calculations of the above variables. These measurements were done 3 times, stored in the echograph\u0026rsquo;s memory and downloaded as .jpg files on a pen-drive. The corresponding database constituted by the average value of each variable studied in these 15 pulse waveforms was built off-line. In patients undergoing regional brachial blocks, an additional Doppler sonography of the homolateral carotid artery was conducted to assess the effect of vasodilation of the arm on the systemic blood flow velocity.\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\n\u003cdiv class=\"Heading\"\u003eProtocol\u003c/div\u003e\u003cp\u003eAll patients remained supine during the protocol with standard non-invasive blood pressure and SpO\u003csub\u003e2\u003c/sub\u003e monitoring on the contralateral arm. An additional pulse oximeter was placed on the middle finger of the tested hand maintained at the phlebostatic level. A skin thermometer was attached on the thenar eminence of the tested hand. Under sedation (upper limb surgeries) and general anesthesia (sympathectomies) baseline PPG recordings were done during the brachial artery Doppler examination which lasted 5 to 8 minutes. Thereafter, regional anesthesia or sympathetic ablation was performed. Five minutes after these interventions we repeated the PPG and brachial Doppler in the tested arm.\u003c/p\u003e\u003cp\u003eTo track any possible effects of these procedures on the systemic vascular system, we used Doppler to evaluate the homolateral carotid artery in patients undergoing regional anesthesia but not sympathectomies, whose necks were covered by surgical sheets. PPG and Doppler measurements were stored on the laptop and the echograph, respectively, identifying the files as \u0026ldquo;before\u0026rdquo; and \u0026ldquo;after\u0026rdquo; intervention.\u003c/p\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003eData analysis\u003c/h2\u003e\u003cp\u003eThe stored PPG .txt files were opened in Excel (Windows 10) and 15 consecutive heartbeats corresponding with the Doppler assessment were selected. These beats were manually segmented and overlapped one beside the other (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eC). The PPG signal, arbitrarily expressed on a 0-100% scale on the original oximeter, which allowed us to calculate the PPG amplitude and the vertical position of the dichrotic notch, both in %. Perfusion index and SpO\u003csub\u003e2\u003c/sub\u003e values of the 15 analyzed beats were averaged.\u003c/p\u003e\u003cp\u003eA non-normal distribution of numerical variables was confirmed by the Shapiro-Wilk test. Continuous variables were described as median and dispersion (25th and 75th quartiles or interquartile range, IQR). Quantitative continuous variables before and after intervention were compared by the Wilcoxon test. A p value of \u0026lt;\u0026thinsp;0.05 was considered statistically significant for all comparisons. All analyses were performed with the statistical software Stata 15.1 (Stata Corporation, College Station, TX, USA).\u003c/p\u003e\u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eAll patients completed the protocol successfully, obtaining eight complete data pairs of variables in patients undergoing regional anesthesia and sixteen data pairs in bilateral sympathectomies. Patient details are provided in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Patients undergoing upper limb procedures were mostly male and marginally older than those undergoing u-VAT sympathectomy.\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\u003ePatients\u0026rsquo; data\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"3\"\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\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRegional Anesthesia\u003c/p\u003e\u003cp\u003e(n\u0026thinsp;=\u0026thinsp;8)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eSympatectomies\u003c/p\u003e\u003cp\u003e(n\u0026thinsp;=\u0026thinsp;8)\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\u003eAge\u003c/b\u003e (years)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e39\u0026thinsp;\u0026plusmn;\u0026thinsp;12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e27\u0026thinsp;\u0026plusmn;\u0026thinsp;9\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eSex\u003c/b\u003e (women/men)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1/7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e5/2\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eHeight\u003c/b\u003e (cm)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e77\u0026thinsp;\u0026plusmn;\u0026thinsp;11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e65\u0026thinsp;\u0026plusmn;\u0026thinsp;7\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eHeight\u003c/b\u003e (cm)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e173\u0026thinsp;\u0026plusmn;\u0026thinsp;5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e171\u0026thinsp;\u0026plusmn;\u0026thinsp;6\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eSurgery\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFinger tenorrhaphy (3) -osteosynthesis (5)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eUniportal video-assisted bilateral sympathectomy\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\u003e\u003cem\u003eDoppler showed an increased blood flow velocity and decreased vascular resistance in the upper limbs.\u003c/em\u003e\u003c/p\u003e\u003cp\u003eThe reference brachial artery Doppler showed an increase in TAV from 27 (18) to 39 (15) cm/s (p\u0026thinsp;=\u0026thinsp;0.017) after the intervention in the regional anesthesia group and from 30 (9) to 35 (9) cm/s (p\u0026thinsp;=\u0026thinsp;0.001) in the sympathectomy group. This increase in mean blood flow velocity was not associated with changes in the PSV in the sympathectomy group (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The increase in TAV after the interventions was related to a decrease in RI from 0.88 (0.2) to 0.79 (0.2) (p\u0026thinsp;=\u0026thinsp;0.021) in the regional anesthesia group and from 0.83 (0.3) to 0.80 (0.3) (p\u0026thinsp;=\u0026thinsp;0.003) in the sympathectomy group. PI decreased from 2.6 (2.0) to 2.2 (1.5) (p\u0026thinsp;=\u0026thinsp;0.036) in the regional anesthesia group and from 3.1 (1.6) to 2.4 (1.1) (p\u0026thinsp;=\u0026thinsp;0.002) in the sympathectomy group. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e depicts the changes in brachial and carotid artery Doppler parameters for the regional anesthesia group. Regional anesthesia affected the blood flow in the brachial artery but not in the carotid artery.\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\u003eMain data.\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=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"2\" morerows=\"1\" nameend=\"c2\" namest=\"c1\" rowspan=\"2\"\u003e\u003cp\u003eParameter\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"3\" nameend=\"c5\" namest=\"c3\"\u003e\u003cp\u003eRegional anesthesia\u003c/p\u003e\u003cp\u003e(n\u0026thinsp;=\u0026thinsp;8)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"3\" nameend=\"c8\" namest=\"c6\"\u003e\u003cp\u003eSympathectomies\u003c/p\u003e\u003cp\u003e(n\u0026thinsp;=\u0026thinsp;8)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cb\u003eBefore\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u003cb\u003eAfter\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eP value\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003cb\u003eBefore\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e\u003cb\u003eAfter\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003eP value\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e\u003cp\u003e\u003cb\u003ePPG\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eClass\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3 (0)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e3 (0)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e3 (1)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e3 (1)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e1.000\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eAmplitude\u003c/p\u003e\u003cp\u003e(%)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e46 (24)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e59 (12)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.008\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e34 (29)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e44 (35)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e0.010\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eDichrotic notch (%)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e15 (12)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e15 (10)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.916\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e14 (21)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e13 (19)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e0.849\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePerfusion\u003c/p\u003e\u003cp\u003eIndex\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e5.6 (6.0)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e6.8 (7.5)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.012\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e4.8 (4.3)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e5.2 (5.2)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e0.004\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e\u003cp\u003e\u003cb\u003eDoppler\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePSV\u003c/p\u003e\u003cp\u003e(cm/s)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e83 (39)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e90 (40)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.012\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e114 (37)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e100 (45)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e0.983\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eTAV\u003c/p\u003e\u003cp\u003e(cm/s)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e27 (18)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e39 (15)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.017\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e30 (9)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e35 (9)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e0.001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRI\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.88 (0.2)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.79 (0.2)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.021\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e0.83 (0.3)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.80 (0.3)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e0.003\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePI\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2.6 (2.0)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e2.2 (1.5)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.036\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e3.1 (1.6)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e2.4 (1.1)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e0.002\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"5\" rowspan=\"6\"\u003e\u003cp\u003e\u003cb\u003eHemodynamics\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHR\u003c/p\u003e\u003cp\u003e(bpm)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e72 (15)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e69 (14)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.310\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e78 (15)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e80 (18)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e0.744\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSAP\u003c/p\u003e\u003cp\u003e(mmHg)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e135 (11)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e131 (19)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.322\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e107 (11)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e105 (12)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e0.679\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eMAP\u003c/p\u003e\u003cp\u003e(mmHg)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e100 (12)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e98 (17)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.050\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e75 (7)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e74 (3)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e0.170\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eDAP\u003c/p\u003e\u003cp\u003e(mmHg)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e84 (18)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e80 (18)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.025\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e59 (4)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e60 (3)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e0.266\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSpO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\u003cp\u003e(%)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e96 (1.8)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e96 (2.1)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.398\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e99 (0.9)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e98 (1.7)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e0.028\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eT\u0026deg;\u003c/p\u003e\u003cp\u003e(Celsius)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e33 (1.7)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e34 (1.6)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.292\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e34 (0.9)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e34 (2.2)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e0.122\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003ctfoot\u003e\u003ctr\u003e\u003ctd colspan=\"8\"\u003ePPG\u0026thinsp;=\u0026thinsp;photoplethysmography, PSV\u0026thinsp;=\u0026thinsp;peak systolic velocity, TAV\u0026thinsp;=\u0026thinsp;time average velocity, PI\u0026thinsp;=\u0026thinsp;pulsatility index, RI\u0026thinsp;=\u0026thinsp;resistive index, HR\u0026thinsp;=\u0026thinsp;heart rate, SAP\u0026thinsp;=\u0026thinsp;systolic arterial blood pressure, MAP\u0026thinsp;=\u0026thinsp;mean arterial blood pressure, DAP\u0026thinsp;=\u0026thinsp;diastolic arterial blood pressure, SpO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;pulse oximetry hemoglobin saturation, and T\u0026deg; = hand temperature. Wilcoxon test was used or pairwise comparison \u0026ldquo;before\u0026rdquo; vs \u0026ldquo;after\u0026rdquo;. A p value of \u0026lt;\u0026thinsp;0.05 was considered statistically significant.\u003c/td\u003e\u003c/tr\u003e\u003c/tfoot\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cem\u003ePPG showed vasodilation of the local limb without changes in the location of the dichrotic notch.\u003c/em\u003e\u003c/p\u003e\u003cp\u003eAll patients presented a PPG class 3 except for two in the sympathectomy group who had a class 4. After the interventions PPG amplitude increased from 46 (24) to 59 (12) % (p\u0026thinsp;=\u0026thinsp;0.008) in the regional anesthesia group and from 34 (29) to 44 (35) % (p\u0026thinsp;=\u0026thinsp;0.010) in the sympathectomy group. The perfusion index increased with the interventions in the same manner: in the group receiving regional anesthesia it increased from 5.6 (6.0) to 6.8 (7.5) (p\u0026thinsp;=\u0026thinsp;0.012), and in the group receiving sympathectomy it increased from 4.8 (4.3) to 5.2 (5.2) (p\u0026thinsp;=\u0026thinsp;0.004). On the other hand, the location of the dichrotic notch neither changed in the regional anesthesia group [before 15 (12) vs after 15 (10) %; p\u0026thinsp;=\u0026thinsp;0.901] nor in the sympathectomy group [before 14 (21) vs after 13 (19) %; p\u0026thinsp;=\u0026thinsp;0.167]. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e depicts typical examples of both groups before and after the intervention. PPG were superimposed to illustrate the effect of local limb vasodilation on the waveforms\u0026rsquo; shape. While vasodilation increased local blood flow and PPG amplitude, the dichrotic notch remained at the same position.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e(Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and Tables \u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e near here)\u003c/h2\u003e\u003cp\u003eHemodynamics, hemoglobin saturation, and local temperature at the tested hand did not change during the procedure, however there were some minor statistical differences in SpO\u003csub\u003e2\u003c/sub\u003e in the sympathetic group and in diastolic blood pressure in the regional anesthetic group (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eThis brief report shows that local vasodilation in the upper limb did not affect the location of the dichrotic notch of the PPG wave. The results were independent of the nature of such vasodilation as it was observed during both, a reversible anesthesia and immediately after an irreversible sympathetic ablation. Using models of pure upper limb vasodilation, we were able to replicate the findings of Chowienczyk et al. and confirm that the dichrotic notch position within the PPG waveform is a systemic phenomenon that depends on pulse wave reflections at bifurcations of main arteries [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eIn clinical practice monitoring of vascular tone at the bedside is scarce, intermittent, operator-dependent (Doppler), and invasive (pulmonary artery catheterization or invasive artery pulse waveform analysis). A straightforward, affordable, non-invasive, and ongoing vascular tone monitoring device is necessary, and PPG provides all these benefits. Because local vasodilation in the upper limb has no discernible effect on the location of the dichrotic notch, the results validate the clinical analysis of the PPG waveform to determine systemic vascular tone.\u003c/p\u003e\u003cp\u003eThe selective upper limb vasodilation by regional anesthesia and sympathectomy appears to be an adequate model to test our hypothesis because each arm represents ⁓10% of body\u0026rsquo;s vasculature. Thus, a local vasodilation in the rather-small upper limb arteries would not affect the dichrotic notch location if the wave reflections took place at bifurcations of the body\u0026rsquo;s main arteries like iliac and subclavian [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Figure\u0026nbsp;4 illustrates how our findings align with the aforementioned statement. Although the Doppler variables and PPG amplitude provided unequivocal evidence of local vasodilation, the position of the dichrotic notch in both, Doppler and PPG waveforms remained unchanged.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eOur findings demonstrated that local vasodilation in the upper limb does not influence the position of the dichrotic notch in the waveform of digital PPG despite increases in its amplitude. The dichrotic notch is thus a systemic phenomenon that depends on pulse wave reflections. These results support the value of analyzing the position of the dichrotic notch in PPG waveforms to determine systemic vascular tone.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgment:\u0026nbsp;\u003c/strong\u003eNone.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding:\u0026nbsp;\u003c/strong\u003e\u003cem\u003eThe authors declare that no funds, grants, or other support was received during the preparation of this manuscript.\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e\u003cstrong\u003eConflict of interest:\u003c/strong\u003e\u003c/em\u003e\u003cem\u003e\u0026nbsp;The authors have no relevant financial or non-financial interests to disclose.\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contribution:\u0026nbsp;\u003c/strong\u003e\u003cem\u003eAll authors contributed to the study\u0026rsquo;s conception and design. Data collection was performed by [MN, AC, CMA,\u0026nbsp;\u003c/em\u003eand GT\u003cem\u003e]. Material preparation, and analysis were performed by [GT].The first draft of the manuscript was written by [MN,\u0026nbsp;\u003c/em\u003eSHB, and GT\u003cem\u003e] and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval:\u0026nbsp;\u003c/strong\u003eThis study was approval by the local Ethic Committee.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eRemington JW, Wood EH (1956) Formation of peripheral pulse contour in man. J Appl Physiol 9:433-442. https://doi.org/10.1152/jappl.1956.9.3.433\u003c/li\u003e\n\u003cli\u003eO\u0026apos;Rourke MF (1970) Influence of ventricular ejection on the relationship between central aortic and brachial pressure pulse in man. Cardiovasc Res 4:291-300. https://doi.org /10.1093/cvr/4.3.291\u003c/li\u003e\n\u003cli\u003eO\u0026apos;Rourke MF, Kelly RP (1993) Wave reflection in the systemic circulation and its implications in ventricular function. J Hypertens 11:327-337. https://doi.org /10.1097/00004872-199303000-00001\u003c/li\u003e\n\u003cli\u003eMurgo JP, Westerhof NICO, Giolma JP, Altobelli SA (1980) Aortic input impedance in normal man: relationship to pressure wave forms. Circulation 62:105-116. https://doi.org/ 10.1161/01.CIR.62.1.105\u003c/li\u003e\n\u003cli\u003eO\u0026rsquo;Rourke MF, Gallagher DE (1996) Pulse wave analysis. J Hypertens 14:S147-S157. https://doi.org/10.1097/00004872-199612001-00025.\u003c/li\u003e\n\u003cli\u003eO\u0026apos;Rourke MF, Avolio AP (1980) Pulsatile flow and pressure in human systemic arteries. Studies in man and in a multibranched model of the human systemic arterial tree. Circul Res 46:363-372. https://doi.org/10.1161/01.RES.46.3.363\u003c/li\u003e\n\u003cli\u003ePythoud F, Stergiopulos N, Westerhof N, Meister JJ (1996) Method for determining distribution of reflection sites in the arterial system. Am J Physiol Heart and Circul Physiol 271:H1807-H1813. https://doi.org/10.1152/ajpheart.1996.271.5.H1807\u003c/li\u003e\n\u003cli\u003eSmith D, Craige E (1986) Mechanism of the dicrotic pulse. Br Heart J 56:531-534. https://doi.org/10.1136/hrt.56.6.531\u003c/li\u003e\n\u003cli\u003ePoliti MT, Ghigo A, Fern\u0026aacute;ndez JM, Khelifa I, Gaudric J, Fullana JM, Lagr\u0026eacute;e PY (2016) The dicrotic notch analyzed by a numerical model. Comput Biol Med 72:54-64. https://doi.org/10.1016/j.compbiomed.2016.03.005 \u003c/li\u003e\n\u003cli\u003eShi P, Hu S, Zhu Y, Zheng J, Qiu Y, Cheang PYS (2009) Insight into the dicrotic notch in photoplethysmographic pulses from the finger tip of young adults. J Med Eng Tech 33: 628-633. https://doi.org/10.3109/03091900903150980\u003c/li\u003e\n\u003cli\u003eKorpas D, H\u0026aacute;lek J, Dolezal L (2009) Parameters describing the pulse wave. Physiol Res 58:473-479. https://doi.org/10.33549/physiolres.931468.\u003c/li\u003e\n\u003cli\u003eVan den Bos GC, Westerhof N, Randall OS (1982) Pulse wave reflection: can it explain the differences between systemic and pulmonary pressure and flow waves? A study in dogs. Circul Res 51:479-485. https://doi.org/10.1161/01.RES.51.4.479\u003c/li\u003e\n\u003cli\u003eJones CJ, Sugawara M, Kondoh Y, Uchida K, Parker KH (2002) Compression and expansion wavefront travel in canine ascending aortic flow: wave intensity analysis. Heart \u0026amp; Vessels 16:91-98. https://doi.org/10.1007/s003800200002\u003c/li\u003e\n\u003cli\u003eTusman G, Acosta CM, Pulletz S, B\u0026ouml;hm SH, Scandurra A, Arca JM, Suarez Sipmann F (2019) Photoplethysmographic characterization of vascular tone mediated changes in arterial pressure: an observational study. J Clin Monit Comput 33:815-824. https://doi.org/10.1007/s10877-018-0235-z\u003c/li\u003e\n\u003cli\u003eChowienczyk PJ, Kelly RP, MacCallum H, Millasseau SC, Andersson TL, Gosling RG, \u0026Auml;ngg\u0026aring;rd EE (1999) Photoplethysmographic assessment of pulse wave reflection: blunted response to endothelium-dependent beta2-adrenergic vasodilation in type II diabetes mellitus. J Am Coll Cardiol 34:2007-2014. https://doi.org/10.1016/S0735-1097(99) 00473-1.\u003c/li\u003e\n\u003cli\u003eLima AP, Beelen P, Bakker J (2002) Use of a peripheral perfusion index derived from the pulse oximetry signal as a noninvasive indicator of perfusion. Crit Care Med 30:1210-1213. https://doi.org/10.1097/00003246-200206000-00006\u003c/li\u003e\n\u003cli\u003eLegarth J, Nolsoe C (1990) Doppler blood velocity waveforms and the relation to peripheral resistance in the brachial artery. J Ultrasound Med 9:449-453. https://doi.org/10.7863/jum.1990.9.8.449\u003c/li\u003e\n\u003cli\u003eOzcan H, Oztekin PS, Zergeroglu AM, Ers\u0026ouml;z G, Fi\u0026ccedil;icilar H, Ust\u0026uuml;ner E (2006) Doppler ultrasound evaluation of the structural and hemodynamic changes in the brachial artery following two different exercise protocols. Diagn Interv Radiol 12:80-84. https://doi.org/ 10.5152/dir.2006.12.2.80\u003c/li\u003e\n\u003cli\u003eO\u0026rsquo;Rourke MF, Adji A, Safar ME (2018) Structure and function of systemic arteries: reflections on the arterial pulse. Am J Hypertens 31:934-940. https://doi.org/10.1093/ ajh/hpy084\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"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":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Dichrotic notch, photoplethysmography, sympathectomy, pulse wave, wave reflection","lastPublishedDoi":"10.21203/rs.3.rs-7445879/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7445879/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003ePurpose\u003c/h2\u003e\u003cp\u003eThe vertical position of the dichrotic notch of finger photoplethysmography (PPG) is affected by systemic vasodilation. The aim of this study was to test whether a \u003cem\u003elocal\u003c/em\u003e upper limb vasodilation would alter the position of the dichrotic notch.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e\u003cp\u003ePatients undergoing upper limb vasodilation caused by brachial plexus block (n\u0026thinsp;=\u0026thinsp;8) and video-assisted bilateral sympathectomy (n\u0026thinsp;=\u0026thinsp;8 with 2 measurements each) were analyzed. Continuous PPG recordings and brachial Doppler sonography were recorded before and five minutes after regional anesthesia and sympathetic ablation. The dichrotic notch of PPG was expressed as % of the PPG waveform amplitude.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e\u003cp\u003eLocal vasodilation after the interventions was evidenced by a decrease in Doppler\u0026rsquo;s resistive index from 0.88(0.2) to 0.79(0.2) (p\u0026thinsp;=\u0026thinsp;0.021) in the regional blocks and from 0.83(0.3) to 0.80(0.3) (p\u0026thinsp;=\u0026thinsp;0.003) in the sympathectomies. PPG amplitude increased from 46(24) to 59(12)% (p\u0026thinsp;=\u0026thinsp;0.008) in the regional anesthesia-group and from 34(29) to 44(35)% (p\u0026thinsp;=\u0026thinsp;0.010) in the sympathectomy-group. The position of the dichrotic notch was neither affected in the regional anesthesia-group before [15(12)%] and after [15(10)%;p\u0026thinsp;=\u0026thinsp;0.916] nor in the sympathectomy-group before [14(21)%] and after [13(19)%;p\u0026thinsp;=\u0026thinsp;0.849].\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e\u003cp\u003eLocal vasodilation in the arm does not influence the position of the dichrotic notch in finger PPG despite increases in its amplitude. The dichrotic notch is thus a systemic phenomenon that depends on pulse wave reflections.\u003c/p\u003e","manuscriptTitle":"The position of the dichrotic notch in digital photoplethysmography is not affected by local vasodilation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-15 06:59:46","doi":"10.21203/rs.3.rs-7445879/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"020f74fc-51a3-49b4-8172-12f339a7f4cb","owner":[],"postedDate":"September 15th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-09-25T23:23:26+00:00","versionOfRecord":[],"versionCreatedAt":"2025-09-15 06:59:46","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7445879","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7445879","identity":"rs-7445879","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}