A comparison of histamine, methacholine, and exercise airway reactivity in normal and asthmatic subjects.

Airway reactivity is commonly assessed by inhalation exposure to pharmacologic agents such as methacholine and histamine or by exercise challenge. To evaluate the relationship of pharmacologic challenge with exercise-induced bronchoconstriction and to determine the test that best differentiates asthmatics from normal subjects, 10 normal and 15 asthmatic subjects were studied. Allergic status was defined by the presence of one or more positive prick skin tests to 8 common allergens. Pharmacologic sensitivity was defined as the log dose of agonist producing a 20% fall in FEV1 or a 35% fall in specific conductance. Exercise consisted of 6 min of steady-state treadmill exercise at 90% of the age predicted maximal heart rate at a temperature of 22.3 ± 1.1° C (mean ± standard deviation) and humidity of 40.1 ± 13.3%. A high degree of exercise stress was achieved as documented by heart rate (171.5 ± 11.7), O2 consumption (2.19 ± 0.65 L/M), and minute ventilation (77.1 ± 24.0 L). Although histamine and methacholin...