Über die Interferenz temperaturregulatorischer und kreislaufregulatorischer Vorgänge in den Extremitäten des Menschen

A relationship between heat loss and sleepiness: effects of postural change and melatonin administration

Both the pineal hormone melatonin (Mel) and postural changes have thermoregulatory sequelae. The purpose of the study was to evaluate their relationship to subjective sleepiness. Eight healthy young men were investigated under the unmasking conditions of a constant routine protocol. Heart rate, rectal temperature (Tre), skin temperatures (foot, Tfo; and stomach), and subjective sleepiness ratings were continuously recorded from 1000 to 1700. Mel (5 mg po) was administered at 1300, a time when Mel should not phase shift the circadian system. Both the postural change at 1000 from upright to a supine position (lying down in bed) and Mel administration at 1300 reduced Tre and increased Tfo in parallel with increased sleepiness. These findings suggest that under comfortable ambient temperature conditions, heat loss via the distal skin regions (e.g., feet) is a key mechanism for induction of sleepiness as core body temperature declines.

Thermoregulatory responses of rhesus monkeys during spaceflight

This study examines the activity, axillary temperature (T(ax)), and ankle skin temperature (Tsk) of two male Rhesus monkeys exposed to microgravity in space. The animals were flown on a Soviet biosatellite mission (COSMOS 1514). Measurements on the flight animals, as well as synchronous flight controls, were performed in the Soviet Union. Additional control studies were performed in the United States to examine the possible role of metabolic heat production in the T(ax) response observed during the spaceflight. All monkeys were exposed to a 24-h light-dark cycle (LD 16:8) throughout these studies. During weightlessness, T(ax) in both flight animals was lower than on earth. The largest difference (0.75 degree C) occurred during the night. There was a reduction in mean heart rate and Tsk during flight. This suggests a reduction in both heat loss and metabolic rate during spaceflight. Although the circadian rhythms in all variables were present during flight, some differences were noted. For example, the amplitude of the rhythms in Tsk and activity were attenuated. Furthermore, the T(ax) and activity rhythms did not have precise 24.0 hour periods and may have been externally desynchronized from the 24-h LD cycle. These data suggest a weakening of the coupling between the internal circadian pacemaker and the external LD synchronizer.

The dependence of onset and duration of sleep on th circadian rhythm of rectal temperature

The sleep-wake cycle and the circadian rhythm of rectal temperature were recorded in subjects who lived singly in an isolation unit. In 10 subjects, the freerunning rhythms remained internally synchronized, 10 other subjects showed internal desynchronization. Times of onset and end of bedrest ("sleep") were determined in each cycle and referred to the phase of the temperature rhythm. In the synchronized subjects, onset of sleep occurred, on the average, 1.34 h before the minimum of temperature, and end of sleep 6.94 h thereafter, with narrow distributions. The desynchronized subjects had a broad bimodal distribution of sleep onsets (peaks 6.3 and 1.3 h before the minimum); the duration of sleep varied between more than 15 h when sleep began about 10 h before the temperature minimum, and less than 4 h when sleep began several hours after the minimum. The dependence of sleep duration on body temperature is interpreted as a continuing action of the coupling forces between the two rhythms after mutual synchronization is lost.