ESTIMATION OF AIRWAY RESPONSES TO PHYSIOLOGICAL STIMULI AND DRUGS

Abstract

Intermittent positive pressure insufflation of the lungs of anesthetized, thoracotomized, curarized dogs was maintained with the Burns valve. During each respiratory cycle, the duration of the insufflation phase with this instrument is determined by the rate of rise of intratracheal air pressure to the selected value at which the valve will close; passive expiration is then triggered. Narrowing or occlusion of a bronchus shortens the cycle; an increase in available lung volume prolongs it. The respiratory cycle was found to be shortened after administration of serotonin, histamine, or acetylcholine; the cycle was prolonged by Aminophylline, TEAC, or vagotomy. The responses increased with the amount given. These results suggest that the drugs used modify the pulmonary air space available for insufflation, presumably by an action on the bronchiolar musculature. Thus, the data suggest that bronchoconstriction results from serotonin, histamine, or acetylcholine, while bronchodilatation follows TEAC, Aminophylline, or vagotomy. Hypoxia, hypercapnia, tachycardia, occlusions of branches of the pulmonary arteries or veins, and rapid infusion or removal of fluid from the circulation, all had no significant effect on respiratory cycle length. These studies provide a new approach for testing agents or physiological conditions which modify ventilatory lung volume.