RESUMEN
The intrinsic period tau of the circadian pacemaker in humans was investigated by means of forced desynchrony. In this protocol, during 6 scheduled days, the sleep-wake alternation was forced to a period of 20h (i.e., 13.5h for wakefulness and 6.5h for sleep). Light intensity was kept below 10 lux. Three experiments were performed. In experiment 1, 12 subjects were free to spend the available time studying, watching videos, and reading books. In experiment 2, at 2h intervals, 11 subjects spent 6 half-hour sessions per subjective day cycling with minimal effort on a cycle trainer, resulting in an average increase of heart frequency of less than 10 beats per minute. In experiment 3, 11 subjects spent the same intervals of time cycling, but now during 20 minutes per session at an average heart rate of between 140 and 150 beats per minute. Core body temperature was measured continuously. A deconvolution technique discriminated the impact of the circadian pacemaker on body temperature from the impact of activities related to sleeping and waking. From this analysis, the period of the pacemaker was derived. We found the following results: experiment 1, tau = 24.30 +/- 0.36h; experiment 2, tau = 24.17 +/- 0.45h; experiment 3, tau = 23.98 +/- 0.42h. The trend of shorter tau at higher levels of physical activity was not statistically significant. We conclude that tau in humans, determined under conditions of forced desynchrony, is very close to 24h. The suggestion from the literature that single activity pulses would predominantly yield phase delays of the circadian pacemaker is not confirmed by these multiple pulse experiments because no lengthening of tau with increasing effort was observed.
Asunto(s)
Relojes Biológicos/fisiología , Esfuerzo Físico/fisiología , Adulto , Temperatura Corporal , Humanos , Masculino , Sueño , VigiliaRESUMEN
Core body temperature is predominantly modulated by endogenous and exogenous components. In the present study we tested whether these two components can be reliably assessed in a protocol which lasts for only 120 h. In this so-called forced desynchrony protocol, 12 healthy male subjects (age 23.7 +/- 1.4 y) were subjected one by one to an artificial light/dark cycle of 20 h (10 lux vs. darkness). Core body temperature was measured continuously. The temperature data were analysed by an iterative method based on the assumption that the endogenous and exogenous components contribute to body temperature in an additive way. The results show that the average temperature curve is an almost perfect addition of the two components. The endogenous component differs from a sinusoid, and the relative contributions of the endogenous and exogenous components to the raw temperature curves differ substantially between the subjects. The average amount of unexplained variance in the individual data was 17%. Averaging of the body temperature curves over subjects reduced the unexplained variance to only 2%. This reduction in unexplained variance upon averaging over subjects must be due to the fact that most of the variance is either differently dependent on circadian phase for the various subjects or not dependent on circadian phase at all. The circadian pacemaker component revealed an average value of tau of 24.30 +/- 0.36 h, which is consistent with recent findings in the literature. We conclude that a short forced desynchrony protocol is sufficient for the distinction between the masking and pacemaker components of core body temperature. The same protocol can be used to study the influence of these components on all kinds of other physiological and psychological signals.