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Masking Effects of Posture and Sleep Onset on Core Body Temperature Have Distinct Circadian Rhythms: Results from a 90-Min/Day Protocol

Department of Psychiatry, University of Pittsburgh School of Medicine, Western Psychiatric Institute and Clinic, Pittsburgh, PA 15213, USA; Sleep and Chronobiology Center, Western Psychiatric Institute and Clinic, 3811 O'Hara Street, Pittsburgh, PA 15213, USA; moulde{at}msx.upmc.edu

Hernando Ombao

Department of Psychiatry, University of Pittsburgh School of Medicine, Western Psychiatric Institute and Clinic, Pittsburgh, PA 15213, USA; Department of Statistics, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA

Timothy H. Monk

Department of Psychiatry, University of Pittsburgh School of Medicine, Western Psychiatric Institute and Clinic, Pittsburgh, PA 15213, USA

Qingxia Chen

Department of Biostatistics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27514, USA

Daniel J. Buysse

Department of Psychiatry, University of Pittsburgh School of Medicine, Western Psychiatric Institute and Clinic, Pittsburgh, PA 15213, USA

Both recumbency and sleep affect core body temperature (CBT). To characterize their circadian effects and interactions, the authors examined the bedtime temperature drops (TDs) of nine men and eight women (aged 20 to 30) who repeated 90-min sleep-wake cycles over 2.5 days. While awake, subjects were exposed to 50 to 250 lux; while asleep, lights were off. Electroencephalogram-monitored time in bed lasted 30 min during each cycle. Cosinor nonlinear mixedeffects regressions modeled the circadian rhythm of TDs. The circadian maximum of TDs occurred approximately 4 h before the time of circadian CBTminimum, in a model that included the effects of baseline expected CBT, deviations from baseline CBT, time in study, and gender-dependent 24- and 12-h adjustments. Rates of temperature drops were faster during initial periods of lying awake than during periods of initially sleeping. Both rates followed separate circadian rhythms. The circadian maximum of TDs was located near customary nocturnal bedtimes, suggesting its role in fostering sleep during a normal bedtime routine. The apparent deceleration of temperature dropping at sleep onset supports the notion that the sleep onset period has complicated circadian neuroregulatory dynamics. These findings confirm the need for nonlinear models of temperature responses to postural changes and sleep that incorporate circadian variability in these masking effects.

Key Words: circadian • sleep • posture • temperature • masking • cosinor • nonlinear mixed effects

Journal of Biological Rhythms, Vol. 17, No. 5, 447-462 (2002)
DOI: 10.1177/074873002237139


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