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. 2021 Aug 16;3:721919. doi: 10.3389/fdgth.2021.721919

Figure 4.

Figure 4

(A) Conduction system of the heart. (B) Schematic for ECG recording of electrical activity. (C) High vs. low heart rate variability (HRV). (D) Schematic depicting various factors influencing HR and HRV. (E) Correlation between R-R interval from ECG trace to P-P interval from PPG trace.