Abstract
We studied the properties of low-frequency (LF) heart rate variability (HRV) and photoplethysmographic waveform variability (PPGV) and their interaction under conditions where the hemodynamic connection between them is obviously absent, as well as the LF regulation of PPGV in the absence of heart function. The parameters of HRV and finger PPGV were evaluated in 10 patients during cardiac surgery under cardiopulmonary bypass (on-pump cardiac surgery) with or without cardioplegia. The following spectral indices of PPGV and HRV were ertimated: the total spectral power (TP), the high-frequency (HF) and the LF ranges of TP in percents (HF% and LF%), and the LF/HF ratio. We assessed also the index S of synchronization between the LF oscillations in finger photoplethysmogram (PPG) and heart rate (HR) signals. The analysis of directional couplings was carried out using the methods of phase dynamics modeling. It is shown that the mechanisms leading to the occurrence of oscillations in the LF range of PPGV are independent of the mechanisms causing oscillations in the LF range of HRV. At the same time, the both above-mentioned LF oscillations retain their activity under conditions of artificial blood circulation and cardioplegia (the latter case applies only to LF oscillations in PPG). In artificial blood circulation, there was a coupling from the LF oscillations in PPG to those in HR, whereas the coupling in the opposite direction was absent. The coupling from the LF oscillations in PPG to those in HR has probably a neurogenic nature, whereas the opposite coupling has a hemodynamic nature (due to cardiac output).
Highlights
Despite the relatively widespread use of photoplethysmography to assess the state of peripheral blood flow[1,2], the question of the physiological interpretation of the frequency components of photoplethysmographic waveform variability (PPGV) remains largely debatable
Since blood flow through the distal arteries contributes to the formation of the finger PPG12, the autonomic regulation of blood pressure (BP) can be indirectly assessed by the PPG signal
The parameters of heart rate variability (HRV) and finger PPGV were evaluated in patients during cardiac surgery under cardiopulmonary bypass with or without cardioplegia
Summary
Despite the relatively widespread use of photoplethysmography to assess the state of peripheral blood flow[1,2], the question of the physiological interpretation of the frequency components of photoplethysmographic waveform variability (PPGV) remains largely debatable. The aim of this work was to study the properties and interaction of LF oscillations in HR and PPG under conditions where the hemodynamic coupling between them is certainly absent, and to study the LF regulation of PPGV in the absence of heart function For this purpose, the parameters of heart rate variability (HRV) (if available) and finger PPGV were evaluated in patients during cardiac surgery under cardiopulmonary bypass (on-pump cardiac surgery) with or without cardioplegia. The parameters of heart rate variability (HRV) (if available) and finger PPGV were evaluated in patients during cardiac surgery under cardiopulmonary bypass (on-pump cardiac surgery) with or without cardioplegia Such an approach allows us to understand better the principles of the functional organization of the autonomic regulation of blood circulation and increases the reliability of the analysis of biological signals in the experimental studies of cardiovascular system
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