Comparison of pulse rate variability with heart rate variability during obstructive sleep apnea

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Abstract

We investigate whether pulse rate variability (PRV) extracted from finger photo-plethysmography (Pleth) waveforms can be the substitute of heart rate variability (HRV) from RR intervals of ECG signals during obstructive sleep apnea (OSA). Simultaneous measurements (ECG and Pleth) were taken from 29 healthy subjects during normal (undisturbed sleep) breathing and 22 patients with OSA during OSA events. Highly significant (p < 0.01) correlations (1.0 > r > 0.95) were found between heart rate (HR) and pulse rate (PR). Bland–Altman plot of HR and PR shows good agreement (<5% difference). Comparison of 2 min recording epochs demonstrated significant differences (p < 0.01) in time, frequency domains and complexity analysis, between normal and OSA events using PRV as well as HRV measures. Results suggest that both HRV and PRV indices could be used to distinguish OSA events from normal breathing during sleep. However, several variability measures (SDNN, RMSSD, HF power, LF/HF and sample entropy) of PR and HR were found to be significantly (p < 0.01) different during OSA events. Therefore, we conclude that PRV provides accurate inter-pulse variability to measure heart rate variability under normal breathing in sleep but does not precisely reflect HRV in sleep disordered breathing.

Introduction

Sleep disordered breathing (SDB), which leads to an interruption of breathing during sleep, causes fragmented sleep, daytime fatigue and impaired cognitive functioning leading to memory loss. The most common is obstructive sleep apnea (OSA) which is a serious condition in which airflow from the nose and mouth to the lungs is restricted during sleep. Impaired cardiac reflexes have been demonstrated in sleep apnea patients by means of spectral heart rate variability (HRV) analysis [1]. The measurement and analysis of HRV have been valuable non-invasive method of evaluating cardiac autonomic functions which controls heart rate by means of parasympathetic and sympathetic activity.

Early in the investigation of obstructive sleep apnea it was recognized that the events of apnea and hypopnoea are accompanied by concomitant cyclic variations in heart rate [2]. Until now, this ordered variation in heart rate has been applied to the detection of sleep apnea by only a few groups [3], [4], [5]. The pattern of brady/tachycardia is closely linked to the time course of apnoeic events. As a consequence, this pattern had been used successfully to detect sleep apnea in patients with clinical symptoms for sleep apnea [2], [3], [4].

Pulse oximeter plethysmography (Pleth) (sometimes referred to simply as “pulse oximetry” or “photo-plethysmogram”) is a standard method of obtaining blood oxygenation data in a non-invasive and continuous manner. Oximeter uses two wavelengths of light to solve for hemoglobin saturation. The waveforms are created by the absorption produced by pulsatile arterial blood volume [6]. The Pleth inherently contains heart period, and the displayed pulse waves arise from heart-beat-dependent volume changes in the terminal arterial bed. Therefore, it can be used to conduct traditional HRV analyses. Pulse to pulse variability, i.e. pulse rate variability (PRV) can be calculated from peak to peak time intervals of Pleth signals. Recent study suggests that OSA and arousals induce more changes in pulse wave amplitude (PWA) of Pleth signals than changes in heart rate [7], [8].

The aims of the study are to (1) compare the HRV indices from ECG signals with PRV indices from Pleth signals during OSA event and (2) examine the effect of OSA event on PRV indices.

Section snippets

Sleep studies and SDB events

Sleep studies were collected from Institute of Breathing and Sleep (IBAS) at Austin Hospital, Melbourne, Australia. The research protocol was approved by Austin Ethics in Human Research Committee (H2008/03252).

The polysomnograms of 22 subjects with sleep apnea (age (yr) = 54.9 ± 16.3 (mean ± SD); BMI (kg m2) = 29.6 ± 4.81; AHI (number/hour) = 71.23 ± 16.39) and 29 normal subjects (age (yr) = 51.3 ± 8.5; BMI (kg m2) = 28.5 ± 6.6; AHI (number/hour) = 1.66 ± 1.0) were analyzed by Pro-Fusion software version 3 (Compumedics

Results

Fig. 3, Fig. 4 show Bland–Altman plots of PR and HR of 2-min epochs during normal breathing and OSA event. Good agreements were observed between PR and HR in both types of breathing events. In case of normal breathing events, the intraclass correlation coefficient (Pearson's coefficient) was 0.97, the mean difference was −0.0083 beat per minute (bpm), and the upper and lower limits of agreement were +1.34 and −1.36 bpm, respectively. Similarly, for disordered breathing the intraclass correlation

Discussion

Pulse oximetry technique has the tremendous potential to be readily accepted by patients due to its simplicity and comfort. In contrast to ECG, recording of Pleth requires only a single sensor, which allowed development of less expensive devices that can be used in daily life. Measures of pulse rate derived from photo-plethysmography (Pleth) have been shown to correlate well with ECG derived heart rate measures [16], [17]. Furthermore, Pleth has been successfully used as a surrogate for ECG in

Conflict of interest statement

There is no issue of conflict of interest in this manuscript.

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      Although HRV and PRV originate from similar processes, and pulse rate (PR) have been found to be a good surrogate of heart rate (HR) [6], the relationship between HRV and PRV is not straightforward, and there is still no consensus regarding the validity of using PRV as a surrogate of HRV [1]. Some researchers argue that the differences between HRV and PRV are mainly due to physiological aspects, such as changes of haemodynamics due to stress or disease [7–10], the different nature of PPG and ECG signals [1], and the effects on PRV of pulse transit time and other factors, e.g. external forces on the arterial vessels [11–13]. Moreover, PRV has been found to be present in the absence of HRV, as shown by Constant et al. [14] and Pellegrino et al. [15], and there are reports of differences in PRV due to measurement site [16,17].

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