Pattern and mechanism of airway response to hypocapnia in normal subjects.
We examined the bronchoconstriction produced by airway hypocapnia in normal subjects. Maximal expiratory flow at 25% vital capacity on partial expiratory flow-volume (PEFV) curves fell during hypocapnia both on air and on an 80% helium- 20% oxygen mixture. Density dependence also fell, suggesting predominantly small airway constriction. The changes seen on PEFV curves were not found on maximal expiratory flow-volume curves, indicating the inhalation to total lung capacity substantially reversed the constriction. Pretreatment with a beta-sympathomimetic agent blocked the response, whereas atropine pretreatment did not, suggesting that hypocapnia affects airway smooth muscle directly, not via cholinergic efferents.
D000328:Adult; D000403:Airway Resistance; D001285:Atropine; D001980:Bronchi / Q000503:physiopathology*; D002245:Carbon Dioxide; D003251:Constriction, Pathologic; D005540:Forced Expiratory Flow Rates; D006371:Helium; D006801:Humans; D007528:Isoetharine; D008297:Male; D008448:Maximal Expiratory Flow Rate; D010100:Oxygen; D012120:Respiration Disorders / Q000503:physiopathology*; D014797:Vital Capacity
D002245:Carbon Dioxide; D006371:Helium; D001285:Atropine; D010100:Oxygen; D007528:Isoetharine