Effects of high ambient temperature on sleep in young men

Each of 10 normal subjects had 4 nights of laboratory-monitored sleep, consisting of adjustment, baseline, high blanket temperature (HBT), and recovery nights. EEG-EOG recordings were made on each night; rectal temperature, heart rate, body weight, and ambient temperatures were monitored throughout the last 2 nights. On the HBT night, subjects had less total sleep time, more frequent and longer awakenings, greater shifting among sleep stages, decreased amounts of stage 1 REM and stages 3 + 4, and delayed onset of deep sleep (stages 3 and 4). Body temperature was elevated to a relatively constant level of 37 degrees C on the HBT night, but gradually decreased from 36 degrees C to 34.5 degrees C across the recovery night. Heart rate decreased at a linear rate on both the HBT and recovery nights, but was 15 beats/min faster on the former. Subjects experienced liquid loss of 1.25 kg on the HBT night, but had a full recovery by the following evening.