Night-time sleep EEG changes following body heating in a warm bath

Area of Science:

• Physiology
• Sleep Science
• Thermoregulation

Background:

• Body temperature influences sleep architecture.
• The effects of acute heat exposure on sleep are not fully understood.

Purpose of the Study:

• To investigate the impact of warm water immersion on sleep patterns.
• To compare the effects of warm versus cool water immersion on sleep.

Main Methods:

• Six healthy, untrained female volunteers participated.
• Participants underwent 90-minute warm (HOT) and cool (COOL) water immersion on separate occasions.
• Rectal temperature was monitored.
• All-night sleep electroencephalograms (EEGs) were recorded post-immersion and on baseline nights.

Main Results:

• Warm water immersion (HOT) significantly increased rectal temperature by 1.8°C.
• Following HOT, participants reported increased sleepiness, more slow-wave sleep, and more stage 4 sleep.
• REM sleep duration was reduced after HOT, particularly in the first REM period.
• Cool water immersion (COOL) resulted in no significant rectal temperature change and no alterations in sleep parameters.

Conclusions:

• Acute heat exposure through warm water immersion alters sleep architecture in healthy young women.
• Increased body temperature appears to promote deeper sleep stages at the expense of REM sleep.
• Cool water immersion does not affect sleep parameters, suggesting a specific thermoregulatory effect of heat on sleep.