The effect of increased abdominal pressure on cardiac output was analyzed by constructing cardiac function and venous return curves in anesthesized, ventilated dogs. Increasing abdominal pressure to 40 mm Hg by infusing fluid into the abdomen decreased cardiac output by 53% in hypervolemic dogs and by 17% in normovolemic dogs, but increased cardiac output by 50% in hypervolemic dogs. Left ventricular cardiac function curves were shifted downward with increased abdominal pressure, due, at least in part, to increased total peripheral resistance. Venous return curves were constricted by using a right heart bypass. Venous resistance rose from 8 to 17 mm Hg/liter/min with increase at high right atrial pressures. The effect of increased abdominal pressure on cardiac output results from the combined effects of changes in cardiac function and venous return, the direction and magnitude of which depend on intravascular volume and the level of abdominal pressure.
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