Effects of airway tone and volume history on maximal expiratory flow in asthma.
We assessed the difference between isovolumic maximal expiratory flows (Vmax) using maneuvers begun at mid-lung volumes, so-called partial expiratory flow-volume curves (P), vs. those begun at full inflation, so-called maximal expiratory flow-volume curves (M), in 10 asthmatic subjects before and following obstruction induced by isocapnic hyperpnea with cold air and before and after bronchodilation with a beta-agonist or antimuscarinic agent. Volume history effects were quantitated as an M-to-P ratio of Vmax at 30% vital capacity (M/P V30). Although M/P V30 was variable among patients at base line, there was a uniform increase in M/P V30 during constriction and a consistent decrease below base line after dilation. Blunting of induced obstruction with beta-agonists also diminished the increase in M/P V30. Antimuscarinics, despite equivalent bronchodilation, failed to alter the degree of obstruction induced by cold air or the increase in M/P V30 seen during obstruction. The level of airway tone, as indicated by specific resistance, related directly to the M/P V30. We conclude that the response of the asthmatic lung to a deep inhalation is relatively predictable when acute changes in airway tone are produced.
D000328:Adult; D001249:Asthma / Q000503:physiopathology*; D001285:Atropine; D003080:Cold Temperature; D005260:Female; D005540:Forced Expiratory Flow Rates; D006801:Humans; D007545:Isoproterenol; D008297:Male; D010366:Peak Expiratory Flow Rate; D012137:Respiratory System / Q000187:drug effects / Q000503:physiopathology*
D001285:Atropine; D007545:Isoproterenol