Figure 3.

Circadian variation of consecutive R-R intervals (RRIs, top left panel), high-frequency (HF) power (top right panel), low frequency (LF) power (lower left panel) and the LF:HF ratio (lower right panel) during wake episodes and vigilance states of nap episodes (i.e., S0, wake during nap episode; S1, stage 1 sleep; S2, stage 2 sleep; SWS, slow wave sleep; REMS, rapid eye movement sleep). The Y axis of each HRV component represents the % deviation from the subject's mean. Results were folded every 360° and repeated over two circadian cycles for illustrative purposes. A nonlinear mixed model was applied to individual subjects' data using nlmixed SAS procedure based on equation S1. Only the significant fitted cosine functions are shown for each state. P values are reported for each state. The vertical dotted line corresponds to the minimum core body temperature (CBT). Bottom X axes represent circadian phase and top X axes represent the corresponding clock time (CBT minimum at 0° = 05:23). Black bars along the X axes represent the time of projected habitual nocturnal sleep episodes. Inverted triangles illustrate the acrophase of each significant rhythm. Peak time of adverse cardiovascular events (based on information in Muller¹) are illustrated by the horizontal bar within each panel.