Effects of exercise load and breathing frequency on heart rate and blood pressure variability during dynamic exercise

It is known that heart rate (HR) variability decreases with dynamic exercis e, but there are only few studies on blood pressure (BP) variability with e xercise loads and the effect of breathing pattern has never been investigat ed. Thus, we studied HR and systolic blood pressure (SBP) signals by spectr al analysis (FFT), in 9 healthy subjects, at different breathing frequencie s (0.15, 0.2, 0.3, 0.4, 0.5, 0.6 Hz), at rest and during 3 exercise loads ( 25, 50 and 75 % (V) over dot O(2)max). BP was measured with a non-invasive device (Finapres) and continuously recorded. The power spectrum of R-R peri od significantly decreased with exercise loads in the low frequency band (L F: 0.04-0.128 Hz) and in the high frequency band (HF: 0.128-0.65 Hz), but w ith breathing frequency only in the HF part of the spectrum. The power spec trum of SEP significantly increased with exercise loads in LF and HF bands, and decreased in HF band with increasing breathing frequency. R-R and SEP HF peaks were centered on breathing frequency peaks. Therefore, spectral an alysis of HR and SEP confirm the withdrawal of vagal control during exercis e, while mechanical effect of respiration on SEP persists. LF/HF ratio of R -R spectral components decreased with increasing load, whereas cardiovascul ar sympathetic activity is known to rise, suggesting that this ratio is not a good indicator of cardiovascular autonomic modulation during exercise.