[Relationship between the initial dimensions of bronchial ring and its contraction after acetylcholine (author's...

Contractions produced by comulative doses of acetylcholine were studied in isolated canine bronchical rings from 2 to 10 mm internal diameter. The maximal active tension achieved was directly related to the initial caliber of the ring and to the amount of smooth muscle. The maximal decrease in caliber was relatively greater (--39%) in the smaller than in the larger bronchi (--17%). However the corresponding increase in airway resistance may be predicted to be more important in the larger resistive bronchi.