Low-frequency variability in photoplethysmographic waveform and heart rate during on-pump cardiac surgery with or without cardioplegia

Figures

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  Figure 1. Schematic representation of the structure of couplings between the LF components in the signals of the systems of HR and vascular tone regulation in the normal state (a) and during cardiac surgery in CPB without cardioplegia (b) and under cardioplegia (c). Arrows indicate the directions of couplings. The dashed line is a hemodynamic coupling from HRV to BPV, the solid line indicates an autonomous regulatory influence from BPV to HRV and the thin line indicates an autonomous regulatory influence from HRV to BPV.

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  Figure 2. PPG signal (a,d), RR intervals (b,e), and their Fourier power spectra (c,f) depicted by solid line for PPG and by dashed line for RR intervals. The dashed and solid horizontal lines in (c,f) correspond to the critical power value (p = 0.05), estimated from RR intervals and PPG signals, respectively. The upper line (a–c) corresponds to patient D with low amplitude of PPG and bottom line (d–f) corresponds to patient A with a distinguishable pulse wave under CPB.

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  Figure 3. The results of the analysis of directional coupling between the HRV and PPGV signals for patient E at different values of time lags. (a) The strength of coupling from PPGV to HRV in the LF range; (b) the strength of coupling from HRV to PPGV in the LF range. Vertical lines indicate 95% confidence interval (95% CI).

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  Figure 4. The results of the analysis of the coherence function C(f) for the HRV and PPGV signals in the LF and HF bands. C(f) is shown with solid line for patients D (a) and E (b). The 95% confidence interval is shown with dashed line.

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  Figure 5. PPG signal (a) and its Fourier power spectrum (b) for patient G under cardiopulmonary bypass and cardioplegia.