EFFECT OF LUNG-VOLUME MAINTENANCE DURING SLEEP IN NOCTURNAL ASTHMA

Previous studies have shown that lung volume decreases and airway resi stance increases during sleep in patients with nocturnal asthma. To de termine whether the fall in lung volume per se causes the overnight de crement in forced expiratory volume in 1 s (FEV1) and/or increase in b ronchial responsiveness, we investigated the effect of preventing this nocturnal decrease in lung volume. The mean volume change on a baseli ne night was -16.3 +/- 1.6% from presleep values and on the volume mai ntenance night +7.1 +/- 3.0% (P = 0.0001). However, this maintenance o f lung volume did not alter the overnight decrement in FEV1 (-29.6 +/- 5.2% baseline vs. -30.2 +/- 5.8% volume maintenance). Similarly, the increase in bronchial responsiveness was also unaltered from baseline to volume maintenance nights, with presleep provocative concentrations of methacholine producing a 20% decrement in FEV1 of 0.28 +/- 0.15 vs . 0.22 +/- 0.7 mg/ml, respectively, and postsleep values of 0.07 +/- 0 .03 vs. 0.04 +/- 0.02 mg/ml, respectively. Thus the fall in lung volum e during sleep in the nocturnal asthmatic patient is a result, not a c ause, of the overnight worsening of lung function.