Non-ventilatory functions of the lung- Influence on the cardiovascular system

Although concerned primarily with gas exchange, the lungs have other functions which are unrelated to ventilation. The cells and enzyme systems of the pulmonary vascular bed change the biological activity of a variety of substances presented to them via the pulmonary circulation. The lungs have the ability to clear certain vasoactive hormones from the pulmonary blood and to synthesize or activate others, which then enter the blood leaving the pulmonary circulation. Thus, the lungs can alter arterial blood concentration of vasoactive compounds. Evidence for the role of the lung in modifying circulating vasoactive substances can be found in the literature dating back to the first quarter of this century. Starling and Verney1 recognized the metabolic role of the lung, as indicated by their experiments on the formation of urine in which an isolated lung was included in the system to prevent vasoconstriction in the isolated perfused kidney. Page 2 later demonstrated that extracts of lung tissue could inactivate a "serum vasocon-