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 exercise, but there are only few studies on blood pressure (BP) variability with exercise loads and the effect of breathing pattern has never been investigated. Thus, we studied HR and systolic blood pressure (SBP) signals by spectral analysis (FFT), in 9 healthy subjects, at different breathing frequencies (0.15, 0.2, 0.3, 0.4, 0.5, 0.6 Hz), at rest and during 3 exercise loads (25, 50 and 75% VO2max). BP was measured with a non-invasive device (Finapres) and continuously recorded. The power spectrum of R-R period significantly decreased with exercise loads in the low frequency band (LF: 0.04-0.128 Hz) and in the high frequency band (HF: 0.128-0.65 Hz), but with breathing frequency only in the HF part of the spectrum. The power spectrum of SBP significantly increased with exercise loads in LF and HF bands, and decreased in HF band with increasing breathing frequency. R-R and SBP HF peaks were centered on breathing frequency peaks. Therefore, spectral analysis of HR and SBP confirm the withdrawal of vagal control during exercise, while mechanical effect of respiration on SBP persists. LF/HF ratio of R-R spectral components decreased with increasing load, whereas cardiovascular sympathetic activity is known to rise, suggesting that this ratio is not a good indicator of cardiovascular autonomic modulation during exercise.