Dose-response curves to inhaled carbachol in asthma and chronic bronchitis

Dose-response curves were established in 19 asthmatic and 19 bronchitic patients by measuring changes in specific airway resistance (sRaw) induced by graded doses of aerosolized carbachol. The shape of the individual curves was classified by the least-square method according to four models: hyperbolic, exponential, linear and logarithmic (with a plateau). The dose-response curves were hyperbolic in 9 asthmatics, exponential in 9, and linear in 1; they were hyperbolic in 2 bronchitics, exponential in 4, linear in 5 and logarithmic in 5. No response could be elicited in 3 bronchitics. Carbachol responsiveness of the bronchitics who had baseline sRaw values in the same range as the asthmatics was much less than that of the asthmatics, i.e. a given dose of carbachol yielded a smaller sRaw increase in the former group. Increased responsiveness to carbachol, resembling that found in the asthmatic group, was observed in most bronchitics whose baseline sRaw values were elevated. These data suggest that bronchitics and asthmatics have different bronchial responses to carbachol, quantitatively and, in some instances, qualitatively.