A closed-circuit heart-lung preparation.—Effect of alterations in the peripheral resistance and the capacity of the circulation

Abstract

In the closed-circuit heart-lung preparation, a diminution in capacity of the systemic circulation produces the same qualitative and quantitative effects as an increase in the volume of circulating blood, namely, a rise in pressure in both auricles, the aorta and the pulmonary artery, and an increase in the cardiac output. An increase in peripheral resistance causes a fall of pressure in both auricles and in the pulmonary artery, and a diminution in the cardiac output. These changes are due to the raised aortic pressure distending the arterial system, pooling the blood therein, and reducing the inflow to the right heart. The extent of these alterations is dependent upon the "potential capacity increment" possessed by the arterial system. By the simultaneous production of a resistance increase and a capacity diminution, the pressures in the left auricle, right auricle or pulmonary artery, or the output of the heart, can be maintained constant. When the systemic resistance and capacity of the systemic circulation are balanced so that the output of the heart remains constant, the pulmonary arterial pressure is unaltered or only slightly elevated.. This is in confirmation of Anrep and Bulatao. "Resistance," "capacity," and blood redistribution effects are interdependent, their relative effects being determined by the physical constants of the circulation.