Respiration differentially modulates HRV obtained from arterial pressure wave and electrocardiogram

We assessed the variability of the series resulting from the subtraction of the RR intervals from the pulse intervals (PI-RR) and examined how it was affected by two maneuvers that modify the cardiac autonomic status. The RR, PI, PI-RR and respiratory series of 20 healthy subjects were computed during three 5-min conditions: supine, standing and exercise. High frequency (HF) and low frequency (LF) components and coherence were computed using spectral and cross-spectral analysis. In the three conditions power spectra of the PI-RR series were distributed exclusively in the HF band and were highly coherent with the respiratory spectra. The HF_PI-RR to HF_RR ratio was 14% in supine, 34% in standing and 262% in exercise. The spectral measures obtained from the RR intervals and PI are not equivalent since the subtraction PI-RR yields a residual series with only HF power due to the greater respiratory effect on PI, exerted by a non-neural mechanism which is subtle in supine, relevant in standing and very important in exercise.