Changes in compliance in rabbits subjected to acute bronchoconstriction

¹ Department of Physiology, Dartmouth Medical School, Hanover, New Hampshire

The pulmonary mechanics of anesthetized rabbits were studied during induced acute bronchoconstriction. The bronchoconstricting agent was acetyl-ß-methylcholine which, when injected intravenously as in these experiments, appeared to act via the pulmonary circulation. In spontaneously breathing animals functional residual capacity increased with bronchospasm, and dynamic compliance decreased. This decrease correlated in magnitude with the severity of the bronchoconstriction. Frequency changed in random direction. Dynamic compliance recovered more slowly than conductance after bronchoconstriction unless the lungs were inflated just prior to each recovery measurement, in which case the two variables recovered equally quickly. This observation suggested that airway occlusion accounted for part of the decrease in dynamic compliance. Bronchoconstriction reduced semistatic compliance in paralyzed artificially ventilated animals and also static compliance, which was measured by arresting breathing with phrenic stimulation, in spontaneously breathing animals. These observations supported the above hypothesis.