Patterns of response to inhaled methacholine.

Fifty-two patients with unexplained pulmonary symptoms were tested using inhaled methacholine. Of the 32 who reacted 11 had a greater than 20% decrease in FEV1 (with or without an associated change in FEF25-75%) as the end-point, 15 had a greater than 25% decrease in FEF25-75% as their initial response while 6 had an initial greater than 25% decrease in FEF200-1200. In some but not all subjects in the latter two groups a decrease in FEV1 occurred with increased methacholine concentrations. Changes in FEF25-75% and FEF200-1200 should be considered in documentation of airway hyperreactivity in some patients.