Effects of Body Heating During Sleep Interruption

Abstract

Summary: This study assessed the effects that elevating body temperature had on sleep structure in the third and fourth sleep cycles, cycles typically characterized by a high propensity for REM sleep and diminished levels of delta amplitude and incidence. The sleep of eight women and two men was interrupted for 30 min on each of 3 consecutive nights following an undisturbed adaptation night. The subjects were awakened each night following the end of the second REM sleep period. On 2 nights, subjects were immersed to midthorax in water at either 34°C (TW condition) or 41°C (HW condition) for 20 min. A third interruption without immersion (NW condition) was performed to provide a second type of baseline condition. The HW condition induced a mean tympanic temperature rise of 2.SoC, that returned to baseline levels in ~60 min. Analysis of sleep patterns focused on the two sleep cycles following interruption. The mean of the two baseline conditions (TW + NW/2) was compared with the HW condition. Sleep onset latency, REM latency, REM duration, and eye movement activity in REM were unaffected by heating. Heating evoked increases in both total NREM and slow wave sleep, though these increases were delayed until the second cycle following sleep onset (i.e., appearing in the fourth, but not the third, NREM period). These were paralleled by increases in two objective measures of delta activity: integrated slow-wave amplitUde (33% increase) and slow-wave density (10% increase). Key Words: Body temperature-Sleep--Passive heating-Interrupted s1eep--Slow wave sleep--REM sleep--REM propensity.In a previous study (1), exercise imposed during a period of sleep interruption resulted in suppression of both the phasic (eye movement activity) and tonic (duration) components of the REM period that followed (by contrast, NREM sleep was unaffected). The effects of exercise that were hypothesized to contribute to this REM suppression were (a) an increase in central noradrenergic turnover or (b) increased body temperature. While an inverse relationship between REM propensity and the normal body temperature rhythm is well established (2), it is unclear whether a reduction in REM propensity should follow an induced elevation of body temperature.Two studies (3,4) sought to test the effects of elevating body temperature during sleep. Body temperature was elevated by pyrogens (3) in one case and by use of an electric blanket (4) in the second. While both studies reported reductions in REM sleep, a considerable sleep disturbance and reduction of NREM sleep as well suggested that the effects

Effects of a Nocturnal Environment Perceived as Warm on Subsequent Daytime Sleep in Humans

“…When individuals were passively warmed before nighttime sleep, SWS increased, either over the entire night or over its first part only. 8,9,23,29,30,32,47 The difference in SWS changes observed between daytime and nighttime sleep may be due to their circadian placements, which discourage its occurrence in the former condition. The propensity of REMS to occur is high at the end of the night and in the early hours of the day.…”

“…In the case of nocturnal sleep, it was reported that REMS proportions remained unaltered by a previous passive warming. 8,9,23,29,47,32 The invariance of REMS could be related to the fact that the short-term thermal loads used induced only transient hyperthermia whose effects never reached the end of the night (the time zone favorable for REMS occurrence). Hence, it could be interesting to see whether or not human nocturnal REMS could not be altered (nay enhanced) by a diurnal thermal stress prolonging its influence until the end of the night.…”

“…INDIVIDUALS EXPOSED TO A THERMAL LOAD BEFORE 8,9,23,29,30,32,47 OR DURING 6,13,25,33,35,38,39,46 BED-TIME present alterations in their nocturnal sleep. Several adverse effects, which are known to reduce the subsequent vigilance level, have been determined, such as partial sleep deprivation and/or sleep fragmentation.…”

Effects of a moderate nocturnal cold stress on daytime sleep in humans

“…The after-effects of a passive thermal stress on nighttime sleep have been widely investigated, but exclusively under warm exposure. Passive warming occurring before bedtime provoked SWS increases over the entire night and/or over its first part (Bunnell and Horvath 1985;Bunnell et al 1988;Di Nisi et al 1989;Horne and Reid 1985;Jordan and Montgomery 1990;Shapiro et al 1989). The difference in SWS changes reported between daytime and nighttime sleep may be related to their circadian placements, which refrain SWS occurrence in the former condition.…”

Selective SWS suppression does not affect the time course of core body temperature in men

“…Induced elevations of core body temperature by 2°C or more (Horne and Staff 1983;Horne and Reid 1985;Shapiro et al 1989) have been shown to increase SWS in the subsequent sleep episode, provided that this heat stress does not occur too close to sleep onset (Bunnell et al 1988). SWS can be induced to occur in the second half of a sleep episode by elevating core body temperature in the middle of the night (Bunnell and Horvath, 1985). Furthermore a positive correlation between core body temperature at the beginning of sleep and Correspondence: Dr D. G .…”