Post-exercise recovery of autonomic cardiovascular control: a study by spectrum and cross-spectrum analysis in humans

The recovery of the baseline autonomic control of cardiovascular activity a fter exercise has not been extensively studied. In 12 healthy subjects, we assessed the time-course of recovery by autoregressive spectrum and cross-s pectrum analysis of heart period and systolic blood pressure during the 3 h after the end of 20 min of steady-state exercise at 50% (light workload, L W) and 80% (moderate workload, MW) of the individual's anaerobic threshold. The electrocardiogram and noninvasive blood pressure were simultaneously r ecorded during 10 min periods in the sitting position, at rest before exerc ise, and at 15, 60 and 180 min of recovery after exercise. At 15 min we obs erved a persistent tachycardia and relative hypotension; after MW, at 60 mi n heart rate was still slightly higher. Spectrum and cross-spectrum analysi s showed, at 15 min, an increase in the low frequency component of systolic blood pressure, a reduction in the high frequency component of heart rate (larger in MW), and a decrease in baroreceptor sensitivity. After 60 and 18 0 min none of these parameters was significantly different from those at re st, although, in MW, some subjects still displayed signs of sympathetic act ivation after 1 h. We concluded that, after 15 min of recovery, the cardiov ascular reflexes were blunted? that sympathetic nerve activity was still en hanced, and that the tone in the vagus had not fully recovered. Only the pe rsistent vagal restraint seemed to be exercise intensity-dependent. For com plete restoration of autonomic control after LW Ih of rest was sufficient, and just enough after MW.