title: Circadian rhythms in the chemoreflex control of breathing.
abstract: Mechanisms underlying the circadian rhythm in lung ventilation were investigated. Ten healthy male subjects were studied for 36 h using a constant routine protocol to minimize potentially confounding variables. Laboratory light, humidity, and temperature remained constant, subjects did not sleep, and their meals and activities were held to a strict schedule. Respiratory chemoreflex responses were measured every 3 h using an iso-oxic rebreathing technique incorporating prior hyperventilation. Subjects exhibited circadian rhythms in oral temperature and respiratory chemoreflex responses, but not in metabolic rate. Basal ventilation [i.e., at subthreshold end-tidal carbon dioxide partial pressure (PET(CO(2)))] did not vary with time of day, but the ventilatory response to suprathreshold PET(CO(2)) exhibited a rhythm amplitude of approximately 25%, mediated mainly by circadian variations in the CO(2) threshold for tidal volume. We conclude that the circadian rhythm in lung ventilation is not a simple consequence of circadian variations in arousal state and metabolic rate. By raising the chemoreflex threshold, the circadian timing system may increase the propensity for respiratory instability at night.
authors.affiliation: Respiratory Research Group, University of Toronto, Toronto, Ontario, Canada M5S 1A1. rstephsn@zoo.utoronto.ca
authors.forename: R
authors.initials: R
authors.lastname: Stephenson
authors.forename: R M
authors.initials: RM
authors.lastname: Mohan
authors.forename: J
authors.initials: J
authors.lastname: Duffin
authors.forename: T M
authors.initials: TM
authors.lastname: Jarsky
mesh_terms: D000328:Adult; D001831:Body Temperature / Q000502:physiology; D002245:Carbon Dioxide; D002628:Chemoreceptor Cells / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D006801:Humans; D008297:Male; D009055:Mouth / Q000502:physiology; D010313:Partial Pressure; D012018:Reflex / Q000502:physiology*; D012143:Respiratory Physiological Phenomena; D012892:Sleep Deprivation / Q000503:physiopathology; D013990:Tidal Volume
chemical_list: D002245:Carbon Dioxide