Genetic factors in nonspecific bronchial hyperreactivity. An epidemiologic study.

We tested bronchial reactivity to carbachol in 50 asthmatics, healthy parents of 40 asthmatic children, and 70 healthy subjects with no personal or family history of asthma. Stepped doses of carbachol (0.1%) aerosol were given until a 50% drop in forced expiratory flow rate from 25% to 75% was observed, or until the subject had inhaled 80 of his or her own vital-capacity equivalent volumes of the aerosol.