The site of pulmonary vasomotor activity during hypoxia or serotonin administration.

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Abstract
The measurements of pressure, flow, and volumes of the pulmonary circulation permit localization of the site of action of a vasoactive agent. In this study carried out in dogs, hypoxia or serotonin administration was investigated. During hypoxia, either a rise or fall in pulmonary vascular resistance may occur. The rise in pulmonary vascular resistance is associated with a significant decrease in pulmonary arterial blood volume, and, hence, constriction of the greater portion if not the entire pulmonary arterial tree must take place. There probably is concomitant venous vasodilation, which might be of an active nature. A fall in pulmonary vascular resistance during hypoxia was associated with passive dilatation of the pulmonary arterial tree. An analysis of the pressure-volume and the conductance-volume relationships of the pulmonary circulation indicates that pulmonary arterial vasoconstriction occurs in both types of responses. Serotonin produced pronounced arterial vasoconstriction and probably a lesser amount of venous constriction. These studies indicate that significant vasomotor activity is present throughout the pulmonary arterial tree, rather than confined to the arterioles as in the systemic circulation.

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