Airway narrowing associated with inhibition of deep inspiration during methacholine inhalation in asthmatics

Reduced bronchodilatation in response to deep inspiration (DI) has been dem onstrated in asthmatics. We have previously shown that inhibition of DI for 10 min or more during methacholine inhalation increases airway narrowing i n normals. We tested the hypothesis that inhibition of DIs during methachol ine inhalation in asthmatics would not affect the magnitude of airway narro wing. We administered the PC15 dose of methacholine to eight asthmatics eve ry 5 min for 5 doses and measured spirometry after each dose. On four separ ate days, subjects received either 2, 3, 4, or 5 doses selected randomly, b ut Dis were inhibited during the challenge and spirometry was measured only at the start and after the final dose. Geometric mean PC15 was 1.6 mg/ml. Mean values for FEV1 (+/- SEM) after Doses 2 through 5 were 84 +/- 4, 78 +/ - 6, 79 +/- 5, and 81 +/- 3% of baseline, respectively, when Dis were allow ed. During inhibition of DIs, they were 73 +/- 6, 67 +/- 5, 64 +/- 6, and 6 1 +/- 7% of baseline values. Decreases in FEV1 after Doses 4 and 5 were sig nificantly greater when Dis were inhibited (p < 0.05). We conclude that in this group of asthmatics, inhibition of DI for 15 min is associated with in creased airway narrowing in response to methacholine inhalation, and theref ore, DI may be an important factor limiting induced airway narrowing in ast hmatics as well as in normal subjects.