Circulatory responses from lung inflation in anesthetized dogs.

HAINSWORTH, R. Circulatory YeSponSeS from hng in.ation in anesthetized dogs. Am. J. Physiol. 226(2) : 247-255. 1974.-Responses from inflation of one lung with different pressures were studied L using a) relatively intact dogs, b) dogs with denervated aortic baroreceptors and a controlled pressure to the carotid baroreceptors, and c) dogs with open chests and the inflated lung artifiSally perfused. Reflex tachycardia u sually resulted from inflation of normally perfused lungs with lo-20 cm Hz0 pressure. Reflex bradycardia usually occurred during a) inflation of normally perfused lungs with pressure of 30-40 cm Hz0 provided arterial baroreceptor input was controlled, b) inflation with 20 cm Hz0 immediately following hyperinflation, and c) inflation with 10-4-O cm Hz0 of an artificially perfused lung. Hindlimb vascular resistance usually showed a small increase during inflation at the lower pressures. At the higher inflation pressures vasomotor responses were variable and vasodilatation sometimes occurred. Although the mechanisms responsible are not known, these experiments define the conditions favoring different responses and help to explain the differing reports of previous investigators.