Influences of exclusion of pulmonary circulation on systemic circulatory conditions

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The pulmonary arterial blood flow (PAF), which plays an important role in metabolizing various vesoactive substances, is reduced during venoarterial bypass (VAB) including cardiopulmonary bypass and ECMO.The influence of reduced PAF during VAB on hemodynamic and humoral conditions ws investigated in a series of chronic animal experiments. A biventricular bypass system with two pulsatile ventricular assist devices (VADs) was first installed in adult goats. After two weeks of convalescent period, VAB was conducted using the right uptake and left-return cannular and a VAD,in combination with a compact artificial lung interposed in the return cannula. The PAF was reduced stepwise from 100% to 50,25,10, and 0% of total systemic blood flow by occluding the pulmonary artery with a baloon catheter. The animals' respiration was sufficiently maintained with the native and artificial lungs at any time of the experiments. The mean aortic pressure and the systemic vascular resistance decreased from 111(]SY.+-。[)12 to 62(]SY.+-。[)6 mmHg, and from 1089(]SY.+-。[)95 to 650(]SY.+-。[)150 dyne・sec・cm-5, respectively, in proportion to the decrease in PAf from 100 to 0%. The prostaglandin E2 concentration increased from 2.1(]SY.+-。[)1.6 to 12.5(]SY.+-。[)2.1 pg/dl in proportion to the decrease in PAF from 100 to 0%. Such proportional change to the PAF was also observed for plasma renin activity and angiotensin I and II.In contrast, the epinephrine and norepinephrine concentrations (60(]SY.+-。[)28 and 307(]SY.+-。[)194 pg/dl, respectively, at 100% of PAF) did not change appreciably even at 10% of PAF (49(]SY.+-。[)34 and 217(]SY.+-。[)141 pg/dl), but drastically elevated to 442(]SY.+-。[)285 and 628(]SY.+-。[)519 pg/dl when the PAF was completely shut off. The similar mode of change was also noted for antidiuretic hormone. In conclusion, the decrease in PAF during VAB exerts dignificant influences on hemodynamics in a proportional manner, and on vasoactive humoral factors in diverse manners.