Estimation of Venous Blood Flow Rate in Cardiopulmonary Bypass Using Occluder Opening Ratio, Centrifugal Pump Speed and Height Difference Between Venous Drainage Site and Reservoir

Cardiopulmonary bypass (CPB) is the temporary replacement of the heart and lungs during heart surgery. Its operation varies significantly depending on the surgical procedure and requires the operator to manage several parameters. One such parameter is the control of an occluder, which has been investigated for automated regulation. Previous studies, however, have not accounted for variations in the speed of the centrifugal pump and the height difference between the venous drainage site and the reservoir, both of which vary during surgery. In this study, we propose a model for estimating the blood flow rate based on the occluder opening ratio, incorporating the effects of pump speed and height difference. Perfusion experiments with a glycerol solution were performed to characterize the pressure-flow rate and pressure-occluder opening ratio relationships. These characteristics were modelled using fluid dynamics theory for sudden contraction and expansion in tubing and showed strong agreement with experimental measurements (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$R^{2}=0.9975$</tex> and 0.9969; <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$p&lt;0.0001$</tex>). By integrating the identified characteristics, the proposed model accurately estimated blood flow rate, with Bland-Altman analysis confirming high agreement with measured values and minimal systematic bias.