Cardiac Activity and Sympathovagal Balance During Sleep

Various techniques have demonstrated that NREM sleep is associated with reduced sympathovagal tone (vagal dominance). The effect is characterized by lowered sympathetic vasomotor tone, downward resetting of the baroreflex, marginally increased BRS, and elevated parasympathetic activity. Because it has not been possible to isolate sympathetic effects on the heart during sleep, the central role of the SNS remains uncertain. It remains unclear whether the change in sympathovagal balance reflects an influence of sleep mechanisms over the ANS, or the reverse; the most likely scenario is that there are reciprocal influences. Sleep deprivation appears to have only minor effects on sympathovagal balance. However, the effects of OSA are substantial and are likely to mediate many pathophysiological processes associated with the disorder.