Spectral analysis of AC and DC components of the pulse photoplethysmograph at rest and during induction of anaesthesia

Abstract

We examined spectral components of beat to beat variability in AC and DC signals of the reflectance photoplethysmograph at finger and earlobe sites in 20 resting volunteers and 20 patients during propofol, alfentanil, isoflurane, nitrous oxide anaesthesia. We observed that at rest, the majority of spectral power at both sites and in both signals was in the low 'thermoregulatory' frequency band (0.01-0.08 Hz). These fluctuations were greater in the finger than in the earlobe and in the AC signal compared to the DC. With anaesthesia, low as well as mid (0.08-0.15 Hz) frequency variability decreased at both sites and in both signals whereas high frequency 'ventilatory' power (0.15-0.45 Hz) was maintained. During anaesthesia we found no significant differences between the spectral components of the AC or DC signals or between the finger and the earlobe sites. At all frequencies, the fluctuations in the AC and DC signals were out of phase with each other.

Fingertip photoplethysmographic waveform variability and systemic vascular resistance in intensive care unit patients

“…With prior studies demonstrating variations in the spectral powers of PPG waveform variability under conditions associated with sympathetic changes [5,7,10,11,16,17,26], this study is the first to establish a significant relationship between the spectral pattern of fingertip PPGV with a quantitative estimation of vascular tone by SVR. Mild but significant positive correlations (r ranged from 0.53 to 0.56) were obtained between the normalized LF powers of PPGV and SVR in a cohort of post cardiac surgery ICU patients, despite the understandably high degree of variation in pathological status and drug usage within this group.…”

“…The HF band of PPGV represents the respiratory fluctuation in peripheral blood volume, secondary to the modulation of venous return and stroke volume by intrathoracic pressure change [5,6,11,18,26]. The LF band generally represents peripheral vasomotor activities, including those mediated by sympathetic control mechanisms [5,10,11,13,16,17,20,22,26]. The power in each band, which reflects the strength or amplitude of the oscillations, was calculated by integration of the power spectrum over the specified frequency range.…”

“…While previous studies have demonstrated clear links between PPGV and conditions associated with sympathetic changes [5,7,10,11,16,17,26], no study has ever been performed to establish a relationship between the spectral pattern of PPGV and a quantitative measure of vascular tone. In addition, since the suppression of sympathetic vascular tone could lead to a relative dominance of HF over LF power in PPGV [11,26], we also examined whether the PPGV spectral powers were useful for the categorical identification of patients in highly vasodilated states (indicated by the low SVR). This is of considerable importance from diagnostic and therapeutic purposes [14].…”

“…Similar to BPV, the frequency spectrum of PPG variability (PPGV) consists of both low frequency (LF) vasomotor waves, and high frequency (HF) respiratory fluctuations [5,10,11,16,17,23,26]. Sympathetic activation induced by active standing has been shown to augment normalized LF power of PPGV [5,17], whereas suppression of basal sympathetic tone by induction of anesthesia leads to a relative reduction in LF and enhancement of HF fluctuations [11,26]. Recent studies by our group have highlighted the potential of PPGV for identifying changes in sympathetic vascular control associated with various critical conditions in the clinical setting, including blood volume loss, sepsis, and endotoxic shock [7,10,16,31], and raised the exciting possibility of detecting these complications at an early stage using an easy-to-measure non-invasive PPG signal.…”

“…Infrared light can penetrate deep into the skin and subcutaneous tissue and is relatively insensitive to blood oxygenation [8,12], thus the resultant PPG signal reflects total blood volume change in the fingertip circulation, under the combined influences of central perfusion pressure and local sympathetic vascular control [2]. Similar to BPV, the frequency spectrum of PPG variability (PPGV) consists of both low frequency (LF) vasomotor waves, and high frequency (HF) respiratory fluctuations [5,10,11,16,17,23,26]. Sympathetic activation induced by active standing has been shown to augment normalized LF power of PPGV [5,17], whereas suppression of basal sympathetic tone by induction of anesthesia leads to a relative reduction in LF and enhancement of HF fluctuations [11,26].…”