Simultaneous Control of Venous Reservoir Level and Arterial Flow Rate in Cardiopulmonary Bypass

Performing a cardiopulmonary bypass (CPB) requires a well-trained perfusionist with skill and experience. In particular, operating the two occluders is difficult because it changes both the blood flow rate and reservoir level, and failure of the operation puts the patient’s life at risk. This study proposes an automatic control system with a two-degrees-of-freedom model matching controller nested in an I-PD feedback controller to simultaneously regulate the blood flow rate and the reservoir level. Experiments simulating CPB initiation and weaning were conducted using glycerin and bovine blood as perfusates. The results demonstrated that the arterial flow rate tracked the manually adjusted venous flow rate with a percentage error below 7.57%, and the reservoir level was maintained with an error below 4.89%. Then, experiments were conducted that simulated disturbances caused by venting/suction of blood from the surgical field and afterload fluctuation in the patient. The results showed that the control accuracies were not affected by afterload fluctuation; venting/suction disturbance worsened the accuracy of controlling the flow rate (3.26% error), while the reservoir level was maintained at 2.22% error. Thus, the robustness and control accuracies of the proposed system were demonstrated, and the system marks another step toward the automation of CPB.