José Marı́a Vergara

Photoplethysmography pulse rate variability as a surrogate measurement of heart rate variability during non-stationary conditions

In this paper we assessed the possibility of using the pulse rate variability (PRV) extracted from the photoplethysmography signal as an alternative measurement of the HRV signal in non-stationary conditions. The study is based on analysis of the changes observed during a tilt table test in the heart rate modulation of 17 young subjects. First, the classical indices of HRV analysis were compared to the indices from PRV in intervals where stationarity was assumed. Second, the time-varying spectral properties of both signals were compared by time-frequency (TF) and TF coherence analysis. Third, the effect of replacing PRV with HRV in the assessment of the changes of the autonomic modulation of the heart rate was considered. Time-invariant HRV and PRV indices showed no statistically significant differences (p > 0.05) and high correlation (>0.97). Time-frequency analysis revealed that the TF spectra of both signals were highly correlated (0.99 +/- 0.01); the difference between the instantaneous power, in the LF and HF bands, obtained from HRV and PRV was small (<10(-3) s(-2)) and their temporal patterns were highly correlated (0.98 +/- 0.04 and 0.95 +/- 0.06 in the LF and HF bands, respectively) and TF coherence in the LF and HF bands was high (0.97 +/- 0.04 and 0.89 +/- 0.08, respectively). Finally, the instantaneous power in the LF band was observed to significantly increase during head-up tilt by both HRV and PRV analysis. These results suggest that although some differences in the time-varying spectral indices extracted from HRV and PRV exist, mainly in the HF band associated with respiration, PRV could be used as a surrogate of HRV during non-stationary conditions, at least during the tilt table test.

Detection of decreases in the amplitude fluctuation of pulse photoplethysmography signal as indication of obstructive sleep apnea syndrome in children

Abstract In this paper, a methodology for using pulse photoplethysmography (PPG) signal to automatically detect sleep apnea is proposed. The hypothesis is that decreases in the amplitude fluctuations of PPG (DAP), are originated by discharges of the sympathetic branch of autonomic nervous system, related to arousals caused by apnea. To test this hypothesis, an automatic system to detect DAP events is proposed. The detector was evaluated using real signals, and tested on a clinical experiment. The overall data set used in the studies includes the polysomnographic records of 26 children which were further subdivided depending on the evaluation of interest. For real signals, the sensitivity and positive predictive value of the DAP detector were 76% and 73%, respectively. An apnea detector has been developed to analyze the relationship between apneas and DAP, indicating that DAP events increase by about 15 % when an apnea occurs compared to when apneas do not occur. A clinical study evaluating the diagnostic power of DAP in sleep apnea in children was carried out. The DAP per hour ratio r DAP was statistically significant ( p = 0.033 ) in classifying children as either normal r DAP = 13.5 ± 6.35 (mean ± S.D.) or pathologic r DAP = 21.1 ± 8.93 . These results indicate a correlation between apneic events and DAP events, which suggests that DAP events could provide relevant information in sleep studies. Therefore, PPG signals might be useful in the diagnosis of OSAS.

PTT Variability for Discrimination of Sleep Apnea Related Decreases in the Amplitude Fluctuations of PPG Signal in Children

In this paper, an analysis of pulse transit time variability (PTTV) during decreases in the amplitude fluctuations of pulse photoplethysmography signal (PPG) (DAP) events for obstructive sleep apnea syndrome (OSAS) screening is presented. The temporal evolution of time-frequency PTTV parameters during DAP was analyzed. The results show an increase in the sympathetic activity index low-frequency component (LF) during DAP for PTTV (85%) significantly higher than for heart rate variability (HRV) (33%), (¿ < 10^-13). However, decreases in parasympathetic activity produce lower decrements in high-frequency component (HF) indexes for PTTV (18%) than for HRV (22%). Thus, PTTV reflects sympathetic changes more clearly than HRV. A clinical study was carried out. DAP events were classified as apneic or nonapneic using a linear discriminant analysis from the PTTV indexes. The ratio of DAP events per hour <i>r</i> _DAP, the ratio after filtering based on HRV indexes <i>r</i> ^HRV _DAP, or on PTTV indexes <i>r</i> ^PTTV _DAP, were computed. The results show an accuracy of 75% for <i>r</i> ^PTTV _DAP (14% increase with respect to <i>r</i> _DAP and 5% increase with respect to <i>r</i> ^HRV _DAP), a sensitivity of 81.8%, and a specificity of 73.9% when classifying 1-h polysomnographic excerpts as OSAS or normal. These results suggest that the combination of DAP and PTTV could be better alternative for sleep apnea screening using PPG with the added benefit of its low cost and simplicity.

Discrimination of Sleep-Apnea-Related Decreases in the Amplitude Fluctuations of PPG Signal in Children by HRV Analysis

In this paper, an analysis of heart rate variability (HRV) during decreases in the amplitude fluctuations of photopletysmography (PPG) [decreases in the amplitude fluctuations of photopletysmography (DAP)] events for obstructive sleep apnea syndrome (OSAS) screening is presented. Two hundred and sixty-eight selected signal segments around the DAP event were extracted and classified in five groups depending on SaO2 and respiratory behavior. Four windows around each DAP are defined and temporal evolution of time-frequency HRV parameters was analyzed for OSAS screening. Results show a significant increase in sympathetic activity during DAP events, which is higher in cases associated with apnea. DAP events were classified as apneic or nonapneic using a linear discriminant analysis from the HRV indexes. The ratio of DAP events per hour r DAP and the ratio of apneic DAP events per hour r alpha DAP were computed. Results show an accuracy of 79% for r alpha DAP (12% increase with respect to r DAP), a sensitivity of 87.5%, and a specificity of 71.4% when classifying 1-h polysomnographic excerpts. As for clinical subject classification, an accuracy of 80% (improvement of 6.7% ), a sensitivity of 87.5%, and a specificity of 71.4% are reached. These results suggest that the combination of DAP and HRV could be an improved alternative for sleep apnea screening from PPG with the added benefit of its low cost and simplicity.

Pulse Rate Variability Analysis for Discrimination of Sleep-Apnea-Related Decreases in the Amplitude Fluctuations of Pulse Photoplethysmographic Signal in Children

A technique for ambulatory diagnosis of the obstructive sleep apnea syndrome (OSAS) in children based on pulse photoplethysmographic (PPG) signal is presented. Decreases in amplitude fluctuations of the PPG signal (DAP) events have been proposed as OSAS discriminator, since they are related to vasoconstriction associated to apnea. Heart rate variability (HRV) analysis during these DAP events has been proposed to discriminate between DAP events related or unrelated to an apneic event. The use of HRV requires electrocardiogram (ECG) as an additional recording, meaning a disadvantage that takes more relevance in sleep studies context where the number of sensors is tried to be minimized in order not to affect the physiological sleep. This study proposes the use of pulse rate variability (PRV) extracted from the PPG signal instead of HRV. Polysomnographic registers from 21 children (aged 4.47 ±2.04 years) were studied. The subject classification based on DAP events and PRV analysis obtained an accuracy of 86.67% which represents an improvement of 6.67% with respect to the HRV analysis. These results suggest that PRV can be used in apnea detectors based on DAP events, to discriminate apneic from nonapneic events avoiding the need for ECG recordings.

Pulse Photopletismography Amplitude Decrease Detector for Sleep Apnea Evaluation in Children

A method for automatic detection of sleep apnea using pulse photoplethysmography signal (PPG) is proposed. This method is based on a detection of decreases on PPG amplitude fluctuations. The proposed detector is composed of three stages: pre-processing, envelope detection, based on root mean square series or Hilbert transform, and decision algorithm based on an adaptive threshold. The detector has been evaluated using simulated and real signals. Sensibility and positive predictive value of the detector where 76% and 73% for real signals. A clinical study to sleep apnea diagnosis in children based on this detector has been carried out. PPG attenuation events per hour ratio E h has statistical significance (p < 0.05) to classify children as normal 13.5 plusmn 6.35 Eh (mean plusmn SD) or pathologic 21.1 plusmn 8.93 Eh

Study of the relationship between Pulse Photopletismography amplitude decrease events and sleep apneas in children

In this work, a method to analyse the effects of an apnea on the pulse photopletismography signal (PPG) is proposed. Therefore, an apnea detector based on respiratory signals has been developed and a decreases in amplitude of PPG (DAP) detector developed in a previous study was used. The apnea detector was tested using real signals. S and +PV of the detector were 95.3% and 94.4%, respectively. For each of the apneic events, we analyzed the presence of DAP in a window previous to the apnea event and another during/following the apnea. An increase of about 15% in DAP events in the window during/following the apnea with respect to the previous to apnea window is produced. These results shows an association between apneic events and DAP events, which indicates that DAP events provide useful information in sleep research and PPG signals might be useful in the diagnosis of OSAS

Time-varying spectral analysis for comparison of HRV and PPG variability during tilt table test

In this work we assessed the possibility of using the pulse rate variability (PRV) extracted from photoplethysmography signal as an alternative measurement of the HRV signal in non-stationary conditions. The study is based on the analysis of the changes observed during tilt table test in the heart rate modulation of 17 young subjects. Time-varying spectral properties of both signals were compared by time-frequency (TF) and TF coherence analysis. In addition, the effect of replacing PRV with HRV in the assessment of the changes of the autonomic modulation of the heart rate was considered. Time-frequency analysis revealed that: the TF spectra of both signals were highly correlated (0.99 ± 0.01); the difference between the instantaneous power, in LF and HF bands, obtained from HRV and PRV was small (<10−3 s−2) and their temporal patterns were highly correlated (0.98±0.04 and 0.95±0.06 in LF and HF bands respectively); TF coherence in LF and HF bands was high (0.97±0.04 and 0.89±0.08, respectively). Finally, the instantaneous power in LF band was observed to significantly increase during head-up tilt by both HRV and PRV analysis. These results suggest that, although some small differences in the time-varying spectral indices extracted from HRV and PRV exist, mainly in the HF band associated with respiration, PRV could be used as an acceptable surrogate of HRV during non-stationary conditions, at least during tilt table test.

Obstructive Sleep Apnea Syndrome analysis in children by Decreases in the Amplitude Fluctuations of Pulse Photoplethysmography: role of recording duration and Heart Rate Variability

Heart rate variability (HRV) during decreases in the amplitude fluctuations of pulse photopletysmography signal events (DAP) is studied. The DAP duration and the time span of the polysomnography (PSG) recording under study are also considered for identification of obstructive sleep apnea events in children. Oxygen desaturation is used as reference. The study involves recordings of 21 children. Periods of time associated with a drop in SaO2 of 3% from baseline during at least 5% of the time were labeled as pathologic. DAP events were detected using an automatic detector, HRV signal processing using the Smooth pseudo Wigner-Ville distribution was carried out in order to obtain several time and frequency HRV indexes. T-test was used to analyze differences between groups. The results show discrimination power between groups that increases as the duration of the time period under analysis, becomes shorter, and so more tune to the apneic episodes. Also HRV increase the discrimination power helping in discriminating DAP event non related to apnea.

Detection of obstructive sleep apnea in children using decreases in the amplitude fluctuations of PPG signal and HRV

An analysis of the HRV during decreases in the amplitude fluctuations of PPG (DAP) events, and their utility in OSAS screening is presented. The overall data set used in the study includes the polysomnographic records of 21 children. DAP events were automatically detected by an algorithm based on the envelope attenuations of the PPG. DAP events were classified as apneic or non apneic by a linear discriminant analysis. The features used by the linear discriminant come from the temporal and spectral parameters of the heart rate obtained by Smooth Pseudo Wigner Ville Distribution. Two indexes were defined: the number of DAP events per hour ratio rDAP and the number of apneic DAP events per hour ratio rDAPα. Results show a 12% increase in accuracy for rDAPα with respect to rDAP in classifying 1 hour polysomnographic segments, reaching values of 72.7% and 80% for sensitivity and specificity, respectively. As for subject classification, the improvement in accuracy is 6.7% obtaining values of 87.5% and 71.4% for sensitivity and specificity respectively. These results suggest that the combination of DAP and HRV could be an alternative for sleep apnea screening with the added benefit of low cost and simplicity.