IMPORTANCE OF METABOLIC FUNCTION OF THE NATURAL LUNG EVALUATED BY PROLONGED EXCLUSION OF THE PULMONARY CIRCULATION

It is generally considered that the natural lung metabolizes various v asoactive substances through the pulmonary circulation. However, the i nfluences of bypassing or eliminating the pulmonary circulation have n ot been fully elucidated, especially for prolonged periods. In this st udy, we performed total cardiopulmonary bypass and exclusion of the pu lmonary circulation for up to 336 hr in awake goats to clarify the imp ortance of the metabolic function of the lung. In seven adult goats, b iventricular bypass with a pulsatile ventricular assist system was fir st established. After 2 weeks, the biventricular bypass was converted to total cardiopulmonary bypass without anesthesia. Adequate gas excha nge and perfusion support were achieved in all animals. However, the i nstitution of total cardiopulmonary bypass led to marked decreases in the mean aortic pressure and systemic vascular resistance, and they re mained low thereafter. The arterial levels of prostaglandin E(2) and n orepinephrine, which are inactivated naturally through the pulmonary c irculation, increased remarkably. These results indicate that the natu ral lung plays an important role in controlling systemic circulation b y metabolizing various vasoactive substances. Understanding the non re spiratory function of the natural lung is of prime importance for adva ncement of lung and heart-lung support.