Differences in responsiveness to hyperventilation and methacholine in asthma and chronic bronchitis.
In a previous study on 27 patients with chronic bronchitis we found that only three developed bronchoconstriction in response to hyperventilation of cold, dry air despite an increased responsiveness to methacholine inhalation. We therefore investigated bronchial responsiveness to hyperventilation with cold, dry air and methacholine in 27 patients with stable asthma who had a similar range of baseline FEV1 values but who developed bronchoconstriction that could be reversed to give an FEV1 more than 70% of the predicted value. Baseline FEV1 was 0.88-3.98 l (37-114% predicted). All but one subject developed bronchoconstriction in response to hyperventilation. There was a linear relationship between baseline FEV1 and response to methacholine (r2 = 0.37, p less than 0.001) and the relationship was significantly different from that found in the bronchitic subjects (F2.50 = 24.94, p less than 0.001). In general, the response to methacholine was greater in the asthmatic than in the bronchitic subjects for any baseline FEV1. The results suggest that there are different mechanisms underlying the increased responsiveness to methacholine in asthma and chronic bronchitis.