Effects of Hypoxia on the Circadian Patterns in Men

Abstract

We tested the hypothesis that acute hypoxia may alter the circadian pattern of body temperature in adult humans. Six healthy subjects were studied in normoxia, hypoxia (approximately 13% inspired O(2)), and again normoxia, each session lasting >24 h and spaced a few days apart, with a constant routine protocol of sustained wakefulness and minimal activity. Some parameters (e.g., tympanic and abdominal temperatures, heart rate) were recorded continuously; others (e.g., oxygen consumption and pulmonary ventilation) were monitored for approximately 10 min every 2 h. The amplitudes of the circadian oscillation of tympanic, abdominal, and calf skin temperatures were reduced in hypoxia, averaging, respectively, 61%, 80% and 50% of the normoxic amplitude. Oxygen consumption and pulmonary ventilation, which presented a circadian pattern in normoxia, had no longer significant oscillations during hypoxia, whereas the opposite was the case for heart rate and diastolic pressure. Therefore, acute hypoxia can disturb the normal circadian patterns and, specifically, depress those of body temperature. These effects, qualitatively similar to those observed in chronically hypoxic animals and humans, could contribute to sleep disturbances at high altitude.

Breathing around the clock: an overview of the circadian pattern of respiration

“…In human subjects, the amplitude of the circadian oscillation of temperatures monitored at some skin locations varied between high altitude and sea level, and the tympanic temperature had a significantly lower oscillation at high altitude (Vargas et al 2001). Similar qualitative differences between normoxia and hypoxia were found in lowlanders studied in normobaric conditions either for several days under the normal wake-sleep cycles (Guagnano et al 1986) or for about 30 h with the constant routine methodology (Bosco et al 2003).…”

Autonomic Nervous System under Ketamine/xylazine and Pentobarbital Anaesthesia in a Wistar Rat Model: A Chronobiological View

“…Similar, but probably more pronounced rhythm alterations occur in rats anaesthetized with pentobarbital. Other explanations for the modulation of daily rhythmicity may be found in the studies by Mortola and Seifert (2000), Bishop et al (2001), Bosco et al (2003), Kaplan et al (2003) and Mortola (2007). The fact that hypoxia modifies the circadian oscillation of important variables, such as body temperature and metabolism, may lead to the expectation that the daily rhythms of many functions are disrupted by hypoxia according to their relationships and connection with the primary variables.…”

Heart-rate changes in asphyxic preconditioning in rats depend on light-dark cycle

“…The spontaneously breathing rats under ketamine/xylazine anaesthesia were in an asphyxic condition independent of the LD cycle from the start of experiment in vivo [31]. Thus, the disruptive effect of hypoxia on the LDdependent differences in the HR-response curve was not affirmed, as suggested by other authors [32][33][34][35]. One of the main conclusions from our study was that the HR was statistically significantly and systematically higher in the dark part of the regimen day than in the light part of the day, including under asphyxic conditions, even though the HR-response curves practically paralleled each other (Figure 1).…”