Effects of Pulmonary Embolism on the Pulmonary Circulation With Special Reference to Arteriovenous Shunts in the Lung

Abstract

Pulmonary embolism using glass beads was investigated in anesthetized dogs. The instantaneous bradycardia and apnea immediately following the injection is a reflex mediated by the vagus. The subsequent respiratory stimulation is also reflex in nature mediated not only by the sensory vagus but also by the thoracic sympathetics and the aortic and carotid body chemoreceptors. The latter are activated by anoxemia which appears to be due to opening of arteriovenous communications in the embolized lungs. In the perfused lungs, the hypertension of embolization is the outcome of mechanical obstruction by the emboli plus reflex vasoconstriction which is partly mediated by the extrinsic pulmonary nerves.