Characteristics of airway tone during exercise in patients with asthma.

In 10 nonasthmatic subjects and 11 patients with asthma, we measured pulmonary resistance (RL), functional residual capacity (FRC), and specific conductance (sGaw) before, during, and after submaximal treadmill exercise. Nonasthmatic subjects did not change RL, FRC, or sGaw from base-line resting values during or after exercise. In patients with asthma, RL decreased significantly during exercise, both when exercise was begun from the control resting state and from conditions of elevated RL after a preceding period of exercise. When asthmatic patients inhaled a standardized dose of aerosolized histamine, the increase in RL during exercise was significantly less than the increase in RL when they breathed histamine at rest. When patients hyperventilated at rest with tidal volumes, breathing frequencies, and end-tidal CO2 tensions similar to those during exercise conditions, bronchodilatation also occurred, and the increase in RL following inhaled histamine during isocapnic hyperventilation was also less than at rest. Since bronchodilatation and inhibition of histamine-induced bronchoconstriction occur during both exercise and isocapnic hyperventilation, we suggest that the mechanism of bronchodilatation during exercise may not necessarily be related to metabolic factors associated with exercise.