Circadian chronesthesy of the airways of healthy adults to the β-agonist bronchodilator isoproterenol

We studied the circadian rhythm in airway susceptibility (chronesthesy) to an inhaled β-agonist, isoproterenol (Isuprel®, Breon Labs) at 1000, 1600, 2200 and 0400 during a single 24-hr period in 5 healthy, diurnally active (~0600-~2300), non-smoking persons. Except for 2-3 short naps (15-45 mins) during the night, participants remained awake during the study and were active continually during the 24 hours. Spirometric measures were obtained pre and post isoproterenol inhalation at each clock time test. The before-after, clock-hour differences were strung together and analyzed by cosinor analysis. Circadian rhythmicity in the effect of isoproterenol was documented for the spirometric measures of FEV_1.0 and PEF (P ≤ .05) but not FVC, FEV_1.0/FVC or FEF(25-75%).