Pulmonary alveolar-vascular reflex

¹ Department of Medicine, University of Sydney, Sydney, N. S. W., Australia

Lung mechanics and pulmonary circulation were studied in lightly anesthetized, spontaneously breathing, supine sheep. Aerosol atropine restored lung compliance (Cl) in animals after fluid inhalation. Ventilation-perfusion relationship was studied by comparing Cl and effective pulmonary capillary blood flow (Qe = 100 minus venous admixture in per cent of cardiac output). The relation between Cl and Qe in unpremedicated sheep before and after fluid inhalation suggested homeostatic redistribution of blood flow away from nonventilated areas. Compensation for nonventilated areas was enhanced by severe pulmonary hypertension and abolished by atropine or isoproterenol; vagotomy had no effect. Homeostasis therefore appears to depend on a local reflex response of the parasympathetic nervous system— "alveolar-vascular reflex." Pulmonary hypertension of generalized alveolar hypoxia was a different reaction not blocked by atropine. Consistent with this analysis, an infusion of acetylcholine increased pulmonary arterial resistance. The increase in Cl which followed atropine or isoproterenol indicated that in addition to surface forces, smooth muscle contraction may result in closure of lung units.

Submitted on March 25, 1963