The effect of sleep upon human circadian rhythms

Area of Science:

• Chronobiology
• Human Physiology
• Sleep Science

Background:

• Circadian rhythms govern numerous physiological processes, including body temperature and excretion patterns.
• Understanding how sleep, particularly fragmented or restricted sleep, affects these rhythms is crucial for maintaining health.

Purpose of the Study:

• To investigate the effects of a split sleep schedule (4 hours at night, 4 hours distributed during the day) on rectal temperature and urinary excretion of various substances.
• To compare these effects with those observed in wakeful subjects and analyze endogenous rhythms using Cosinor analysis.

Main Methods:

• Subjects underwent a split sleep schedule (4h + 4h) while rectal temperature and urinary excretion of water, potassium, sodium, chloride, phosphate, creatinine, calcium, and urate were continuously monitored.
• Data were analyzed using Cosinor analysis to assess circadian rhythms and compared between sleeping and wakeful states.
• A case study of an air pilot with irregular sleep was included to observe free-running rhythms.

Main Results:

• Rectal temperature was generally lower during sleep, except between 1000 and 1200, with the maximal difference preceding midnight.
• Potassium excretion was consistently lower, and phosphate excretion higher, during sleep.
• Phosphate excretion showed a significant exogenous component, decreasing after 8 hours of sleep but not after 4 hours.

Conclusions:

• Split sleep schedules significantly alter circadian rhythms of temperature and urinary excretion.
• Endogenous rhythms can adapt to external influences like sleep, but irregular sleep can lead to free-running rhythms.
• Phosphate excretion is particularly sensitive to sleep duration, suggesting a direct impact of sleep on its regulation.