The relationship between slow-wave activity, body temperature, and cardiac activity during nighttime sleep

Study Objectives: Recent work indicates that cardiac sympathetic activity is not influenced by the circadian system and instead decreases after steep onset. However, little is known about the pattern of change in cardiac sympathetic activity during NREM/REM sleep cycles and whether this is associated with alterations in slow-wave activity(SWA). To address these questions, we examined SWA, cardiac sympathetic activity, heart rate and rectal and foot temperatures during the first three NREM/REM sleep cycles and during transitions between NREM and REM sleep. Design: Subjects were required to maintain a constant sleep-wake cycle for at least a week and have at least one adaptation night, before their night of recording. Setting: individual temperature controlled bedrooms. Participants: 10 young healthy males and females. Interventions: NA. Measurements and Results: All variables showed the greatest change in the first NREM cycle. Specifically, SWA, sympathetic activity, heart rate and foot temperature increased white rectal temperature decreased. After the initial increase, cardiac sympathetic activity decreased across the sleep phase, in association with a decrease in heart rate. Cardiac sympathetic activity did not significantly after across NREM-REM cycles. Conclusions: The results suggest that increases in heart rate and cardiac sympathetic activity early in the sleep period are, in part, a compensatory reaction to the concomitant thermoregulatory changes observed. These results also indicate that the effect of time asleep on cardiac sympathetic activity may be greater than the influence of sleep cycles. These results are discussed with reference to the recuperative value of naps.