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.
Key words
Systolic blood pressure - spectral analysis - autonomic nervous system - respiration
