Effect of angiotensin converting enzyme inhibition on airway conductance during hypocapnic hyperventilation in normal subjects.

In nine normal subjects, specific airway conductance was measured by whole body plethysmography before and immediately after hypocapnic hyperventilation. This procedure, forced expiratory manoeuvres and arterial blood pressure measurements were carried out before and 4 h after placebo and the angiotensin converting enzyme inhibitor, enalapril, in a double-blind, randomized study design. Bronchoconstriction to hypocapnic hyperventilation was shown by a reduction in specific airway conductance on all occasions (P < 0.001). A reduction in mean blood pressure was obtained after enalapril compared to placebo (P < 0.05). No significant change attributable to enalapril was observed in any lung function measurement either at rest or immediately after hypocapnic hyperventilation, despite an expected enhancement of endogenous angiotensin converting enzyme activity by alkalosis. Inhibition of angiotensin converting enzyme revealed no effect of the endogenous activity of this enzyme on airway calibre either at rest or during the bronchoconstrictor response to hypocapnic hyperventilation.