The effect on airway function of inspired air conditions after isocapnic hyperventilation with dry air.

The magnitude of postexercise or posthyperventilation bronchoconstriction in patients with asthma is related to the temperature and the water content of the inspired air during the exercise or hyperventilation period. Recent studies have suggested that the inspired air conditions during recovery from exercise may also be important in determining the magnitude of postexercise airway narrowing. In the present study, normal subjects (n = 8) and patients with asthma (n = 12) were studied on separate days. On day 1 the subjects performed isocapnic hyperventilation with warm dry air and recovered breathing warm dry air. On the second day, an identical warm dry air challenge was administered, but recovery occurred while they were breathing warm humid air. There was no significant bronchoconstriction in the normal subjects, irrespective of the inspired air conditions during recovery. The patients with asthma showed greater bronchoconstriction during recovery in warm, humid air (maximal decrease in FEV1 31% +/- 17%) than in dry air (maximal decrease in FEV1 19% +/- 20%; p less than 0.05). These results suggest that the inspired air condition during recovery from isocapnic hyperventilation of dry air is also a determinant of the magnitude of the bronchoconstrictor response.