4.7 Article

Endogenous circadian rhythm of pulmonary function in healthy humans

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AMER THORACIC SOC
DOI: 10.1164/ajrccm.162.3.9911107

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Funding

  1. NATIONAL CENTER FOR RESEARCH RESOURCES [M01RR002635] Funding Source: NIH RePORTER
  2. NATIONAL HEART, LUNG, AND BLOOD INSTITUTE [R01HL062149] Funding Source: NIH RePORTER
  3. NCRR NIH HHS [MO1 RR02635] Funding Source: Medline
  4. NHLBI NIH HHS [HL62149] Funding Source: Medline

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Numerous studies have demonstrated a diurnal rhythm in indices of pulmonary function in both healthy subjects and subjects with asthma, with minima occurring during the night. To determine whether such diurnal changes are caused by an endogenous circadian rhythm or by diurnal alterations in behavior or the environment, we measured indices of pulmonary function throughout a constant routine protocol designed to unmask underlying circadian rhythms. After two acclimation days in the laboratory, 10 healthy adults maintained relaxed wakefulness in a semirecumbent posture in a constant environment with low light (10 lux) for 41 h. Measurements of FEV1, FEVC, PEF, blood cortisol, and core body temperature (CBT) were performed every 2 h. Results of cosinor analysis of group data aligned to CBT circadian minimum revealed significant circadian variations in FEV1 and FEV1/FEVC, cortisol, and CBT, and lack of significant circadian variations in FEVC and PEF. The ranges (peak to trough) of mean circadian changes in spirometric variables were 2.0-3.2% of the mesor. The circadian minima of all variables occurred within the usual sleep period (although subjects remained awake). Because of differences in phase relationships between CBT and pulmonary function among subjects, the circadian rhythms within subjects were generally larger than the group average circadian changes, being significant for FEV1/FEVC in 5 of 10 subjects and for PEF in 6 of 10 subjects. Sleep deprivation (24 h) failed to cause a significant change in any pulmonary function variable (when controlled for circadian phase). Thus, endogenous circadian rhythms contribute to diurnal changes in pulmonary function in healthy subjects.

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