Photoplethysmographic Pulse Research Articles

In-ear photoplethysmography for central pulse waveform analysis in non-invasive hemodynamic monitoring

Abstract In recent years, the analysis of the photoplethys-mographic (PPG) pulse waveforms has attracted much research focus. However, the considered signals are primarily recorded at the fingertips, which suffer from reduced peripheral perfusion in situations like hypovolemia or sepsis, rendering waveform analysis infeasible. The ear canal is not affected by cardiovascular centralization and could thus prove to be an ideal alternate measurement site for pulse waveform analysis. Therefore, we developed a novel system that allows for highly accurate photoplethysmographic measurements in the ear canal. We conducted a measurement study in order to assess the signal-to-noise ratio of our developed system Hereby, we achieved a mean SNR of 40.65 dB. Hence, we could show that our system allows for highly accurate PPG recordings in the ear canal facilitating sophisticated pulse waveform analysis. Furthermore, we demonstrated that the pulse decomposition analysis is also applicable to in-ear PPG recordings.

PP.09.31] CALCULATION OF CENTRAL BLOOD PRESSURE BY ANALYZING THE CONTOUR OF THE PHOTOPLETHYSMOGRAPHIC PULSE MEASURED AT THE FINGER WITH THE POPMÈTRE® DEVICE

Objective: Analysis of the contour of the peripheral pulse to assess arterial properties was first described in the nineteenth century. The reference technique to estimate central blood pressure (CBP), non-invasively, is by analyzing the radial pressure pulse acquired using a tonometer and then to establish a transfer function relating the radial pressure to the CBP. An alternative technique utilizes a volume pulse. This may conveniently be acquired optically from a finger (digital volume pulse obtained with the photodiode of the pOpmètre® device- Axelife SAS- France). The objective is to establish a transfer function estimating the central blood pressure (CBP), calibrated with a brachial pressure cuff and using the parameters obtained with the contour analysis of the photoplethysmographic pulse measured at the finger with the pOpmètre® system. Design and method: We positioned the photodiode sensor on the finger, insuring that the sensor's lens is in contact with the pulp. Brachial blood pressure measurement was performed with a cuff adapted to the arm circumference and an oscillometric device (Omron M10 -IT). The central blood pressure values measured with Sphygmocor used as the reference values, with similar calibrating pressures. Multiple regression analysis was done to establish the transfer functions. Pearson's correlation and Bland Altman graph were performed for agreement. Results: 69 subjects were included: 24 healthy subjects and 45 patients with essential hypertension aged 33 ± 8 years and 59 ± 17 years respectively. The correlation between the estimated central systolic pressure (CSP) and the reference one, was good and significant (r2 = 0.94; p < 0.0001). A better correlation was found in terms of central diastolic pressure (CDP) (r2 = 0.95; p < 0.0001). The Bland and Altman analysis, mean difference was 4 mmHg p < 0.0001 (CSP) versus 3 mmHg p < 0.0001 (CDP), the standard deviation of the difference was 5 mmHg (CSP) versus 4 mmHg (CDP), classifying the estimation as good agreement. Conclusions: The estimation of the central blood pressure with the finger pulse qualifies as good agreement with the reference technique for the central systolic and diastolic pressure estimation.

Quantification of vascular function changes under different emotion states: A pilot study.

Recent studies have indicated that physiological parameters change with different emotion states. This study aimed to quantify the changes of vascular function at different emotion and sub-emotion states. Twenty young subjects were studied with their finger photoplethysmographic (PPG) pulses recorded at three distinct emotion states: natural (1 minute), happiness and sadness (10 minutes for each). Within the period of happiness and sadness emotion states, two sub-emotion states (calmness and outburst) were identified with the synchronously recorded videos. Reflection index (RI) and stiffness index (SI), two widely used indices of vascular function, were derived from the PPG pulses to quantify their differences between three emotion states, as well as between two sub-emotion states. The results showed that, when compared with the natural emotion, RI and SI decreased in both happiness and sadness emotions. The decreases in RI were significant for both happiness and sadness emotions (both P< 0.01), but the decreases in SI was only significant for sadness emotion (P< 0.01). Moreover, for comparing happiness and sadness emotions, there was significant difference in RI (P< 0.01), but not in SI (P= 0.9). In addition, significant larger RI values were observed with the outburst sub-emotion in comparison with the calmness one for both happiness and sadness emotions (both P< 0.01) whereas significant larger SI values were observed with the outburst sub-emotion only in sadness emotion (P< 0.05). Moreover, gender factor hardly influence the RI and SI results for all three emotion measurements. This pilot study confirmed that vascular function changes with diffenrt emotion states could be quantified by the simple PPG measurement.

Comparison between heart rate variability and pulse rate variability during different sleep stages for sleep apnea patients

The usefulness of heart rate variability (HRV) in the clinical research has been verified in numerous studies. However, it is controversy that using pulse rate variability (PRV) as a surrogate of HRV in different clinical applications. We aimed to investigate whether PRV extracted from finger pulse photoplethysmography (Pleth) signal could substitute HRV from ECG signal during different sleep stages by analyzing the common time-domain, frequency-domain and non-linear indices. Seventy-five sleep apnea patients were enrolled. For each patient, ECG and Pleth signals were simultaneously recorded for the whole night using Alice Sleepware Polysomnographic System and the sleep stage signals were automatically calculated by this System. Time-domain, frequency-domain and non-linear indices of both HRV and PRV were calculated for each sleep stage. Mann-Whitney U-test showed that for both time-domain and frequency-domain indices, there were no statistical differences between HRV and PRV results during all four sleep stages. For non-linear indices, sample entropy reported statistical differences between HRV and PRV results for N1, N2 and REM sleeps (all P< 0.01) whereas fuzzy measure entropy only reported statistical differences for REM sleep (P< 0.05). SDNN, LF and LF/HF indices decreased for both HRV and PRV with the sleep deepening while HF and non-linear indices increased. In addition, there were strong and significant correlation between HRV and PRV indices during all four sleep stages (all P< 0.01). PRV measurement could present the similar results as HRV analysis for sleep apnea patients during different sleep stages.

Abstract 160: Multiscale Entropy of Photoplethysmographic Pulse Amplitudes of Bilateral Fingertips Varies by Hand Dominance and Diabetes Status

Objective: Multiscale entropy (MSE) of photoplethysmographic (PPG) pulse amplitudes may reflect cardiovascular health. In addition, poor glycemic control and weak handgrip strength are related to microvascular dysfunction in diabetes. We hypothesized that MSE of PPG pulse amplitudes between dominant and non-dominant hand may differ by diabetes status. Methods: Of a middle-to-old aged and right hand-dominant population free of prior cardiovascular disease, we matched age, sex, and weight to select the unaffected (no type 2 diabetes, n =36), the well-controlled diabetes (HbA1c &lt;8%, n =22), and the poorly-controlled diabetes (HbA1c ≥8%, n =22) groups. MSEs were calculated from simultaneous consecutive 1,500 resting PPG pulse amplitudes of bilateral index fingers. The small- and large-scale MSEs were defined as the average of scales 1 to 3 (MSE 1-3 ) and scales 4 to 10 (MSE 4-10 ), respectively. Intra- and inter-groups comparisons were performed by 1- and 2-sample t tests. Results: The inter- and intra-groups mean pulse amplitudes did not differ. In contrast, the pulse wave velocity was higher in the two diabetes groups, but was similar between two hands in each group. The dominant hand MSE 4-10 was lower in the poorly-controlled diabetes compared with the unaffected and well-controlled diabetes groups (1.25 vs. 1.52 and 1.49, p=0.001 and 0.017, respectively); whereas the non-dominant hand MSE 4-10 was lower in the well- and poorly-controlled diabetes groups than the unaffected (1.31 and 1.26 vs. 1.54, p=0.007 and 0.002 respectively). There was no intra-groups difference in MSE 4-10 , but a higher MSE 1-3 of dominant hand than that of non-dominant hand in the well-controlled diabetes (1.30 vs. 1.07, p=0.05). Conclusion: Diabetes status and hand activity are related to the MSE of PPG pulse amplitudes. The MSE indexes differed between two hands with euglycemia indicated that local physical inactivity might be an independent contributor to diabetic microvascular dysfunction.

Multiscale Cross-Approximate Entropy Analysis of Bilateral Fingertips Photoplethysmographic Pulse Amplitudes among Middle-to-Old Aged Individuals with or without Type 2 Diabetes

Multiscale cross-approximate entropy (MC-ApEn) between two different physiological signals could evaluate cardiovascular health in diabetes. Whether MC-ApEn analysis between two similar signals such as photoplethysmographic (PPG) pulse amplitudes of bilateral fingertips can reflect diabetes status is unknown. From a middle-to-old-aged population free of prior cardiovascular disease, we selected the unaffected (no type 2 diabetes, n = 36), the well-controlled diabetes (glycated hemoglobin (HbA1c) &lt; 8%, n = 30), and the poorly- controlled diabetes (HbA1c ≥ 8%, n = 26) groups. MC-ApEn indexes were calculated from simultaneous consecutive 1500 PPG pulse amplitudes signals of bilateral index fingertips. The average of scale factors 1–5 (MC-ApEnSS) and of scale factors 6–10 (MC-ApEnLS) were defined as the small- and large-scales MC-ApEn, respectively. The MC-ApEnLS index was highest in the unaffected, followed by the well-controlled diabetes, and then the poorly-controlled diabetes (0.70, 0.62, and 0.53; all paired p-values were &lt;0.05); in contrast, the MC-ApEnSS index did not differ between groups. Our findings suggested that the bilateral fingertips large-scale MC-ApEnLS index of PPG pulse amplitudes might be able to evaluate the glycemic status and detect subtle vascular disease in type 2 diabetes.

Gaussian modelling characteristics changes derived from finger photoplethysmographic pulses during exercise and recovery

Gaussian modelling method has been reported as a useful method to analyze arterial pulse waveform changes. This study aimed to provide scientific evidence on Gaussian modelling characteristics changes derived from the finger photoplethysmographic (PPG) pulses during exercise and recovery.65 healthy subjects (18 female and 47 male) were recruited. Finger PPG pulses were digitally recorded with 5 different exercise loads (0, 50, 75, 100, 125W) as well as during each of 4minute (min) recovery period. The PPG pulses were normalized in both width and amplitude for each recording, which were decomposed into three independent Gaussian waves with nine parameters determined, including the peak amplitude (H1, H2, H3), peak time position (N1, N2, N3) and half-width (W1, W2, W3) from each Gaussian wave, and four extended parameters determined, including the peak time interval (T1,2, T1,3) and amplitude ratio (R1,2, R1,3) between 1st Gaussian wave and 2nd, 3rd Gaussian waves. These derived parameters were finally compared between different exercise loads and recovery phases.With gradually increased exercise loads, the peak amplitude H2, peak time position N1, N2, N3, and half-width W1, W2 increased, peak amplitude H3 decreased significantly (all P<0.05). The peak time interval T1,2 and T1,3 increased significantly from 10.6±1.2 and 36.0±4.4 at rest to 14.4±2.3 and 45.1±6.5 at 100W exercise load, respectively (both P<0.05). The amplitude ratio R1,2 also increased from 1.07±0.2 at rest to 1.22±0.2 at 100W, and the amplitude ratio R1,3 decreased from 1.10±0.3 at rest to 0.42±0.2 at 125W (all P<0.05). An opposite changing trend of these parameters was observed during recovery phases.In conclusion, this study has quantitatively demonstrated significant changes of Gaussian modelling characteristics derived from finger PPG pulse with exercise and during recovery, providing scientific evidence for the physiological mechanism that exercise increases cardiac ejection and vasodilation, and reduces the total peripheral vascular resistance.

Discrepancies between Conventional Multiscale Entropy and Modified Short-Time Multiscale Entropy of Photoplethysmographic Pulse Signals in Middle- and Old- Aged Individuals with or without Diabetes

Multiscale entropy (MSE) of physiological signals may reflect cardiovascular health in diabetes. The classic MSE (cMSE) algorithm requires more than 750 signals for the calculations. The modified short-time MSE (sMSE) may have inconsistent outcomes compared with the cMSE at large time scales and in a disease status. Therefore, we compared the cMSE of 1500 (cMSE1500) consecutive and 1000 photoplethysmographic (PPG) pulse amplitudes with the sMSE of 500 PPG (sMSE500) pulse amplitudes of bilateral fingertips among middle- to old-aged individuals with or without type 2 diabetes. We discovered that cMSE1500 had the smallest value across scale factors 1–10, followed by cMSE1000, and then sMSE500 in both hands. The cMSE1500, cMSE1000 and sMSE500 did not differ at each scale factor in both hands of persons without diabetes and in the dominant hand of those with diabetes. In contrast, the sMSE500 differed at all scales 1–10 in the non-dominant hand with diabetes. In conclusion, autonomic dysfunction, prevalent in the non-dominant hand which had a low local physical activity in the person with diabetes, might be imprecisely evaluated by the sMSE; therefore, using more PPG signal numbers for the cMSE is preferred in such a situation.

Glycemic Control, Hand Activity, and Complexity of Biological Signals in Diabetes Mellitus

Both glycemic control and handgrip strength affect microvascular function. Multiscale entropy (MSE) of photoplethysmographic (PPG) pulse amplitudes may differ by diabetes status and hand activity. Of a middle-to-old aged and right-handed cohort without clinical cardiovascular disease, we controlled age, sex, and weight to select the unaffected (no type 2 diabetes,n=36),the well-controlled diabetes (HbA1c &lt; 8%,n=22), and the poorly controlled diabetes (HbA1c ≥ 8%,n=22) groups. MSEs were calculated from consecutive 1,500 PPG pulse amplitudes of bilateral index fingertips. Thesmall-, medium-,and large-scale MSEs were defined as the average of scale 1 (MSE1), scales 2–4 (MSE2–4), and scales 5–10 (MSE5–10), respectively. Intra- and intergroups were compared by one- and two-samplet-tests, respectively. The dominant handMSE5–10was lower in the poorly controlled diabetes group than the well-controlled diabetes and the unaffected (1.28 versus 1.52 and 1.56,p=0.019and 0.001, resp.) groups, whereas the nondominant handMSE5–10was lower in the well- and poorly controlled diabetes groups than the unaffected group (1.35 and 1.29 versus 1.58,p=0.008and 0.005, resp.). TheMSE1of dominant hand was higher than that of nondominant hand in the well-controlled diabetes (1.35 versus 1.10,p=0.048). In conclusion, diabetes status and hand dominance may affect the MSE of PPG pulse amplitudes.

Increase in the effectiveness of identifying peaks and feet of the photoplethysmographic pulse to be reconstructed it using adaptive filtering

To improve the identification of peaks and feet in photoplethysmographic (PPG) pulses deformed by myokinetic noise, through the implementation of a modified fingertip and applying adaptive filtering. PPG signals were recordedfrom 10 healthy volunteers using two photoplethysmography systems placed on the index finger of each hand. Recordings lasted three minutes andwere done as follows: during the first minute, both handswere at rest, and for the lasting two minutes only the left hand was allowed to make quasi-periodicmovementsin order to add myokinetic noise. Two methodologies were employed to process the signals off-line. One consisted on using an adaptive filter based onthe Least Mean Square (LMS) algorithm, and the other includeda preprocessing stage in addition to the same LMS filter. Both filtering methods were compared and the one with the lowest error was chosen to assess the improvement in the identification of peaks and feet from PPG pulses. Average percentage errorsobtained wereof 22.94% with the first filtering methodology, and 3.72% withthe second one. On identifying peaks and feet from PPG pulsesbefore filtering, error percentages obtained were of 24.26% and 48.39%, respectively, and once filtered error percentageslowered to 2.02% for peaks and 3.77% for feet. The attenuation of myokinetic noise in PPG pulses through LMS filtering, plusa preprocessing stage, allows increasingthe effectiveness onthe identification of peaks and feet from PPG pulses, which are of great importance for medical assessment.

Association between uterine artery Doppler blood flow changes and arterial wall elasticity in pregnant women

Introduction: Uterine artery (UtA) Doppler velocimetry changes and increased arterial stiffness are associated with preeclampsia. We aimed to investigate the relation between UtA velocimetry changes and arterial stiffness in pregnant women.Methods: Doppler velocimetry and photoplethysmographic digital pulse wave analysis (DPA) were performed in 173 pregnant women in the second or the third trimester, where UtA Doppler pulsatility index (PI), diastolic notching, and UtA score (UAS) combining notching and high PI were calculated. DPA stiffness parameters representing large arteries were ejection elasticity index (EEI) and b/a, small arteries dicrotic index (DI) and d/a, and global stiffness the aging index (AI).Results: One hundred and thirty women had normal Doppler and 43 had diastolic notching, of whom nine had high PI. DI indicated increased stiffness in small arteries when notching was present (p = 0.044) and showed a significant but weak correlation to UAS (p = 0.025, tau 0.12). EEI and b/a indicated increased large artery stiffness (p ≤0.014), d/a small artery stiffness (p = 0.023), and AI a systemic stiffness (p = 0.040) when high PI.Conclusion: High UtA PI was associated with increased systemic arterial stiffness, whereas notching was related to increased stiffness in small arteries only. This indicates pathophysiological differences between the two Doppler parameters.

Relative peripheral blood volume changes induced by premature ectopic beats and their role in hemodialysis

Hemodialysis patients often suffer from cardiovascular disorders and uremic neuropathy, increasing the propensity to homeostatic imbalance that, in turn, may result in intradialytic complications like cramp, nausea, and, worse, hypotension. Ectopic beats, being abundant in such patients, may lead to imbalance through repeated, sudden drops in blood pressure. By exploring the properties of postectopic peripheral circulation recovery, treatment sessions prone to intradialytic complications may be better identified. This paper introduces a novel method for quantifying changes in peripheral blood volume due to ventricular or supraventricular premature beats (VPBs or SVPBs). Using the fingertip photoplethysmographic pulse waveform, VPB and SVPB-induced changes in relative peripheral blood volume are quantified by the postectopic pulse amplitude. Two parameters are proposed for characterizing (i) the initial drop in peripheral blood volume following an ectopic beat, and (ii) the degree of postectopic peripheral circulation recovery. A small set of data from 16 hemodialysis sessions in 9 hypotension-prone patients are used to illustrate the method. In asymptomatic sessions, the first parameter was found to be 8 ± 13% (mean ± std), whereas, in symptomatic sessions, it increased to 32 ± 13%, suggesting that postectopic pulse amplitude recovery is related to intradialytic complications; similar results were obtained for the second parameter. Postectopic pulse amplitude recovery may also be of interest in other applications where relative changes in peripheral blood volume play a role.

Photoplethysmographic waveform characteristics of newborns with coarctation of the aorta.

Fetal echocardiography, physical examination and pulse oximetry detect only half of coarctation of aorta (CoA) cases. We aimed to quantify delayed arrival and diminished amplitude of lower extremity photoplethysmographic (PPG) pulses relative to the right hand in affected patients. We studied 8 CoA infants and 32 healthy controls. The pulse arrival time difference between foot and hand (f-hTD) and pulse amplitude ratio (F/H) were measured on PPG signal waveforms by digitally-determining maxima and minima of systolic decrease of light transmission. Mann-Whitney test was used for group comparisons. In comparison to healthy newborns, CoA infants' PPG waveforms demonstrated prolonged f-hTD (mean±s.d. of 73.2±26.6 versus 35.2±8.3 ms, P<0.001) and lower F/H (0.57±0.26 versus 0.99±0.58, P=0.014). F-hTD and F/H are quantifiable from hand- and foot-derived PPG waveforms and are significantly different in CoA versus healthy newborns. Larger studies are needed to validate PPG for improved critical congenital heart disease screening.

Parameters of Overnight Pulse Wave under Treatment in Obstructive Sleep Apnea

Background: Sleep-related breathing disorders may promote cardiovascular (CV) diseases. A novel and differentiated approach to overnight photoplethysmographic pulse wave analysis, which includes risk assessment and measurement of various pulse wave characteristics, has been evaluated in obstructive sleep apnea (OSA). Objectives: The purpose of this study was to assess if and which of the differentiated pulse wave characteristics might be influenced by OSA treatment with positive airway pressure (PAP). Methods: The study included two protocols. In the case-control study (group A), pulse wave-derived CV risk indices recorded during PAP therapy were compared with those obtained in age, body mass index, and CV risk class-matched patients with untreated OSA (n = 67/67). In the prospective PAP treatment study (group B), 17 unselected patients undergoing a full-night sleep test at baseline and after 23 ± 19 weeks of treatment were analyzed. Results: In untreated OSA patients (group A), the overnight hypoxic load was increased (SpO₂ index 38.7 ± 17.5 vs. 24.0 ± 11.1, p < 0.001) and the pulse wave attenuation index (PWA-I) was lower (29.4 ± 9.2 vs. 33.5 ± 11.8, p = 0.022) than in treated patients. In group B, PAP therapy reduced the hypoxic load and increased the PWA-I significantly. The composite CV risk index was slightly but not significantly reduced. Conclusions: PAP therapy modified the hypoxic load and pulse wave-derived markers. The PWA-I - associated with sympathetic vascular tone - was most prominently modified by PAP. This novel approach to markers of CV function should be further evaluated in prospective studies.

Diagnostic Performance of a Smartphone-Based Photoplethysmographic Application for Atrial Fibrillation Screening in a Primary Care Setting.

BackgroundDiagnosing atrial fibrillation (AF) before ischemic stroke occurs is a priority for stroke prevention in AF. Smartphone camera–based photoplethysmographic (PPG) pulse waveform measurement discriminates between different heart rhythms, but its ability to diagnose AF in real‐world situations has not been adequately investigated. We sought to assess the diagnostic performance of a standalone smartphone PPG application, Cardiio Rhythm, for AF screening in primary care setting.Methods and ResultsPatients with hypertension, with diabetes mellitus, and/or aged ≥65 years were recruited. A single‐lead ECG was recorded by using the AliveCor heart monitor with tracings reviewed subsequently by 2 cardiologists to provide the reference standard. PPG measurements were performed by using the Cardiio Rhythm smartphone application. AF was diagnosed in 28 (2.76%) of 1013 participants. The diagnostic sensitivity of the Cardiio Rhythm for AF detection was 92.9% (95% CI] 77–99%) and was higher than that of the AliveCor automated algorithm (71.4% [95% CI 51–87%]). The specificities of Cardiio Rhythm and the AliveCor automated algorithm were comparable (97.7% [95% CI: 97–99%] versus 99.4% [95% CI 99–100%]). The positive predictive value of the Cardiio Rhythm was lower than that of the AliveCor automated algorithm (53.1% [95% CI 38–67%] versus 76.9% [95% CI 56–91%]); both had a very high negative predictive value (99.8% [95% CI 99–100%] versus 99.2% [95% CI 98–100%]).ConclusionsThe Cardiio Rhythm smartphone PPG application provides an accurate and reliable means to detect AF in patients at risk of developing AF and has the potential to enable population‐based screening for AF.

Hemodynamic Monitoring for the Evaluation and Treatment of Shock: What Is the Current State of the Art?

Hemodynamic monitoring has become a fundamental and ubiquitous, if not defining, aspect of critical care medicine practice. Modern monitoring techniques have changed significantly over the past few years and are now able to rapidly identify shock states earlier, define the etiology, and monitor the response to therapies. Many of these techniques are now minimally invasive or noninvasive. Basic hemodynamic monitoring and evaluation usually includes a focused physical examination and static hemodynamic vital signs: temperature, heart rate, respiratory rate, mean arterial pressure, and arterial hemoglobin oxygen saturation, typically measured with pulse photoplethysmography. When available, measurement of urinary output is often included. Advanced hemodynamic monitoring incorporates both noninvasive and invasive continuous hemodynamic monitoring. Noninvasive ultrasound has emerged as a fundamental hemodynamic evaluation tool and its use is now rapidly increasing. Invasive monitoring from arterial and central venous catheters, and occasionally pulmonary artery catheters, provides measurement of arterial pressure, intracardiac filling pressures, arterial and venous blood gases, and cardiac index. Minimally invasive and noninvasive measure of arterial pressure and cardiac output are also possible and often remain as accurate as invasive measures. Importantly, such advanced monitoring provides the foundation for goal-directed therapies for the treatment of shock. When coupled with functional hemodynamic monitoring analyses, these measures markedly extend the diagnostic and therapeutic potential of all monitoring modalities by defining preload reserve, vasomotor tone, cardiac performance, and tissue perfusion.

Detection of cardiovascular risk from a photoplethysmographic signal using a matching pursuit algorithm.

Cardiovascular disease is the main cause of death in Europe, and early detection of increased cardiovascular risk (CR) is of clinical importance. Pulse wave analysis based on pulse oximetry has proven useful for the recognition of increased CR. The current study provides a detailed description of the pulse wave analysis technology and its clinical application. A novel matching pursuit-based feature extraction algorithm was applied for signal decomposition of the overnight photoplethysmographic pulse wave signals obtained by a single-pulse oximeter sensor. The algorithm computes nine parameters (pulse index, SpO2 index, pulse wave amplitude index, respiratory-related pulse oscillations, pulse propagation time, periodic and symmetric desaturations, time under 90% SpO2, difference between pulse and SpO2 index, and arrhythmia). The technology was applied in 631 patients referred for a sleep study with suspected sleep apnea. The technical failure rate was 1.4%. Anthropometric data like age and BMI correlated significantly with measures of vascular stiffness and pulse rate variability (PPT and age r=-0.54, p<0.001, PR and age r=-0.36, p<0.01). The composite biosignal risk score showed a dose-response relationship with the number of CR factors (p<0.001) and was further elevated in patients with sleep apnea (AHI≥15n/h; p<0.001). The developed algorithm extracts meaningful parameters indicative of cardiorespiratory and autonomic nervous system function and dysfunction in patients suspected of SDB.

Arteries Stiffen With Age, but Can Retain an Ability to Become More Elastic With Applied External Cuff Pressure.

It is accepted that arterial compliance decreases with age, with changes in the arterial pulse shape measured at the periphery. The aim of this study was to determine the relationship between arterial transmural pressure changes and changes in peripheral finger pulse shape characteristics for both older and younger subjects.Finger photoplethysmographic pulses were recorded noninvasively from the right index fingers of 100 healthy normotensive subjects. Their median age was 43 years (range 20–71 years) allowing two distinct age groups to be compared (older group ≥45 and younger group < 45 years). Arterial transmural pressures on the whole right arm were reduced with a 50 cm long cuff inflated to 10, 20, 30, and 40 mmHg. Pulse maximum amplitude and rise time were calculated for each age group, and for each cuff pressure level.Gradual and significant decreases in both pulse maximum amplitude and rise time were found with increasing cuff pressure for both age groups. With an external cuff pressure of 40 mmHg, there was an average maximum amplitude and rise time decrease of 27.1% (P < 0.001) and 7.5% (P < 0.001) respectively. The changes in the older group were significantly greater than those in the younger group for maximum amplitude (30.3% vs 24.4%, P = 0.006), but not for rise time (8.0% vs 6.7%, P = 0.23).Our results show that arterial compliance of the arm artery increases with reduced transmural pressure for both older and younger groups, and demonstrate that the aged arm artery can become more elastic with applied external cuff pressure.

Athletic Differences in the Characteristics of the Photoplethysmographic Pulse Shape: Effect of Maximal Oxygen Uptake and Maximal Muscular Voluntary Contraction

This study aimed to investigate the athletic differences in the characteristics of the photoplethysmographic (PPG) pulse shape. 304 athletes were enrolled and divided into three subgroups according to a typical sport classification in terms of the maximal oxygen uptake (MaxO2_low, MaxO2_middle and MaxO2_high groups) or the maximal muscular voluntary contraction (MMVC_low, MMVC_middle, and MMVC_high groups). Finger PPG pulses were digitally recorded and then normalized to derive the pulse area, pulse peak time T p, dicrotic notch time T n, and pulse reflection index (RI). The four parameters were finally compared between the three subgroups categorized by MaxO2 or by MMVC. In conclusion, it has been demonstrated by quantifying the characteristics of the PPG pulses in different athletes that MaxO2, but not MMVC, had significant effect on the arterial properties.

Pulse oximetry: fundamentals and technology update.

Oxygen saturation in the arterial blood (SaO2) provides information on the adequacy of respiratory function. SaO2 can be assessed noninvasively by pulse oximetry, which is based on photoplethysmographic pulses in two wavelengths, generally in the red and infrared regions. The calibration of the measured photoplethysmographic signals is performed empirically for each type of commercial pulse-oximeter sensor, utilizing in vitro measurement of SaO2 in extracted arterial blood by means of co-oximetry. Due to the discrepancy between the measurement of SaO2 by pulse oximetry and the invasive technique, the former is denoted as SpO2. Manufacturers of pulse oximeters generally claim an accuracy of 2%, evaluated by the standard deviation (SD) of the differences between SpO2 and SaO2, measured simultaneously in healthy subjects. However, an SD of 2% reflects an expected error of 4% (two SDs) or more in 5% of the examinations, which is in accordance with an error of 3%–4%, reported in clinical studies. This level of accuracy is sufficient for the detection of a significant decline in respiratory function in patients, and pulse oximetry has been accepted as a reliable technique for that purpose. The accuracy of SpO2 measurement is insufficient in several situations, such as critically ill patients receiving supplemental oxygen, and can be hazardous if it leads to elevated values of oxygen partial pressure in blood. In particular, preterm newborns are vulnerable to retinopathy of prematurity induced by high oxygen concentration in the blood. The low accuracy of SpO2 measurement in critically ill patients and newborns can be attributed to the empirical calibration process, which is performed on healthy volunteers. Other limitations of pulse oximetry include the presence of dyshemoglobins, which has been addressed by multiwavelength pulse oximetry, as well as low perfusion and motion artifacts that are partially rectified by sophisticated algorithms and also by reflection pulse oximetry.