Differences in airway responsiveness in asthma and chronic airflow obstruction.

In patients with chronic obstructive lung disease, it is difficult to distinguish clinically between asthma, chronic bronchitis, and emphysema. This is due in part to the fact that the original definitions were not mutually exclusive. Diagnosis has not been helped by the measurement of airway responsiveness to methacholine or histamine, since responsiveness seems to be increased as often in those with chronic airflow obstruction as in asthmatic patients.