Balance of blood flow and gas exchange during partial heart-lung bypass

¹ Department of Physiology, Emory University, Atlanta, Georgia

During partial heart-lung bypass, O₂ uptake and CO₂ elimination occur simultaneously at two sites: in the natural lung and in an artificial gas-exchange device. The total amount of arterialized blood distributed to the body tissues is the sum of pulmonary blood flow plus extracorporeal flow. When the extracorporeal flow rate is increased, the pulmonary blood flow decreases in proportion, provided the body blood content remains constant. Therefore, the total tissue perfusion during partial heart-lung bypass is not significantly different from the control value. The decrease in pulmonary blood flow is accompanied by a less marked decrease in pulmonary ventilation and gas exchange. Partial heart-lung bypass permits diminishing the pulmonary blood flow while maintaining normal metabolic conditions for the organism.