Journal of Applied Physiology, Vol 62, Issue 3 1133-1140, Copyright © 1987 by American Physiological Society

ARTICLES

Effects of airway tone and volume history on maximal expiratory flow in asthma

B. M. Pichurko and R. H. Ingram Jr

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.

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