Effects of different stresses on cardiac autonomic control and cardiovascular coupling

The objective of this study was to investigate the impacts of different stresses on time varying autonomic reactivity and cardiovascular coupling. In total, 25 male subjects were recruited. RR intervals (RRI), systolic and diastolic blood pressure (SBP, DBP), stroke volume (SV), cardiac output (CO) and systemic vascular resistance (SVR) values were collected during rest, mental arithmetic task (MAT) and cold pressor test (CPT). Baroreflex sensitivity (BRS) was derived using the transfer function method. Continuous wavelet transform of RRI was used to describe the time variant patterns of autonomic neural activities. Wavelet cross-correlation and phase synchronization were used to estimate the amplitude and phase coupling between RRI and SBP. MAT was characterized by increased HR, SBP, DBP and CO with decreased BRS due to prolonged parasympathetic withdrawal. Moreover, cardiovascular coupling was disrupted in MAT. These results indicated that baroreflex was depressed, and the top-down system started to take action under mental stress. In CPT, SBP, DBP and SVR increased significantly, whereas HR and BRS remained unchanged. The increase of sympathetic activity was transient, and cardiovascular coupling did not change in CPT. Intriguingly, the frequency of the maximum cross-correlation coefficient in the LF band (0.04-0.15 Hz) was significantly decreased in CPT, which may be due to the change of resonance frequency of the baroreflex loop.