Spectral and coherence analysis of the variabilities of heart rate, stroke volume, and systolic blood pressure in exercise stress tests

Stress-induced changes in the cardiovascular parameters have been found to carry valuable information for predicting cardiovascular diseases (CVD). To investigate the influence of exercise on the cardiovascular system, in this paper, we analyzed the spectral distributions of the variabilities of heart rate (HRV), stroke volume (SVV), and systolic blood pressure (SBPV) for the at-rest, during-exercise and post-exercise conditions, respectively. Coherence spectrums were also calculated to quantify the degree of coupling between these variabilities. The results showed that, the power of HRV, SVV, and SBPV was all concentrated in two bands, i.e., low frequency (LF 0.04-0.15Hz) and high frequency (HF 0.15-0.4Hz). During the exercise, the LF component of HRV decreased slightly while the HF component decreased significantly in most subjects, resulting in an increased LF/HF ratio, which indicated a change in the balance of sympathetic and vagal activities. For SVV, the LF, HF and LF/HF components all increased during exercise. No consistent change patterns were found in SBPV for different individuals. Significant coherences were found in the HF components between these variability signals for the under-rest condition (HRV~SBPV: 0.72±0.25, HRV~SVV: 0.50±0.22, SVV~SBPV: 0.54±0.28). By contrast, the coherences of these variability signals in the LF components were insignificant (<;0.5) for all the conditions. These phenomena may indicate that HF components in the variability of these variables reflect the influence of some common impact factors while the LF components mainly reflect the different mechanisms of the cardiovascular functions measured by each individual variable.