Compensations of cardiac output and other circulatory functions in areflex dogs with large A-V fistulas

Abstract

In ten dogs made areflex by administration of total anesthesia, opening large A-V fistulas with flows equal to the control cardiac output caused an instantaneous average increase in cardiac output of 75%. Obviously, therefore, the circulation can compensate for most of the fistula flow in the complete absence of all circulatory reflexes. In the same number of animals with intact reflexes, the compensation was 82%. Most of the compensation in both the areflex and the reflex dogs occurred literally with the next few heartbeats after opening the A-V fistulas, though, in the animals with the intact reflexes, an additional small degree of compensation occurred during the ensuing 15–30 sec; this additional effect was ascribed to reflexes. The nonreflex portion of the compensation can be explained by a) increased venous return caused by decreased peripheral resistances and b) cardiac adaptation in accordance with Starling's principle.