Reflex effects of left heart and pulmonary vascular distension on airways of dogs.

Two types of experiments were performed in anesthetized dogs on cardiopulmonary bypass to see if pulmonary vascular congestion and left heart distension would induce reflex bronchoconstriction. First we distended the isolated left heart and lung vessels with blood while ventilating the lungs and measuring airflow, tidal volume, and transpulmonary pressures. Congestion reduced dynamic compliance and increased inspiratory resistance. Vagotomy increased compliance and decreased resistance but did not alter the effects of congestion. Then we measured changes in tracheal wall tension while we separately distended the pulmonary vessels and left heart. Left heart distension increased tracheal tension, whereas pulmonary congestion increased tension in some dogs but decreased it in others. All effects were eliminated by vagotomy. We concluded that although left heart distension and pulmonary vascular congestion may reflexly increase airway tone, pulmonary congestion may at some times reflexly reduce tone. None of these reflex changes, however, appear to be important in the modest (approximately 20%) changes in airflow dynamics observed during combined left heart and pulmonary vascular distension.