Respiratory modulation on the time span and amplitude indices of Electrocardiogram and Photoplethysmogram

The fluctuation of heart rate within each respiratory cycle that called respiratory sinus arrhythmia (RSA) is often observed in healthy persons. The present study investigated the respiratory modulation on the time span and amplitude indices of Electrocardiogram (ECG) and Photoplethysmogram (PPG). Totally 25 time span and amplitude indices from ECG of lead V5 and PPG of left finger were extracted from 32 healthy subjects during a controlled respiration test with breathing frequency at 0.09 Hz, 0.17 Hz, 0.25 Hz and 0.32 Hz in orderly sequence, and a respiratory effort signal was simultaneously recordings by inductance Plethysmography. The fundamental respiratory frequency (FRF) during the breathing-controlled sections was obtained from the spectrum of respiratory effort signal. Then the mean absolute error between FRF and the estimated respiratory frequency (ERF) derived from the 25 indices was calculated. The mean absolute errors of diastole-related indices between ERF and FRF from all subjects were smaller than 1 mHz during the breathing-controlled sections, which were smaller than that of PTT-related indices and amplitude indices, as the first seven indices with smallest estimated error of respiratory frequency were all diastole-related indices. In conclusion, both time span and amplitude indices of ECG and PPG are modulated by respiration. And the respiratory modulation on diastole-related indices is more prominent than that on PTT-related indices and amplitude indices.