Numerical simulation of hemodynamic parameters and coronary blood flow during beating-heart coronary bypass surgery

Hemodynamic instability, mostly due to vertical lifting of the heart, is usually observed during beating heart surgical procedures. When it happens, it is important to evaluate hemodynamic parameters, such as coronary blood flow or ventricular volumes, that are not routinely measured in the clinic. The primary aim of this work is to develop a tool, based on a digital computer model of the circulation, to supply information to clinicians to estimate hemodynamic changes during beating heart surgery. A lumped parameters model of the circulation was applied to analyze data obtained from both beta-blocked and not beta-blocked pigs underwent beating heart surgery. The circulatory model includes both ventricles, pulmonary and systemic circulation and a simple model of coronary circulation. After a tuning with basal experimental data, the model was used to estimate hemodynamic parameters during heart lifting and the Trendelenburg maneuver. The results confirmed a drop of cardiac output and coronary flow during heart lifting and a rise of both variables after the Trendelenburg maneuver for beta-blocked animals. In not beta-blocked pigs, the analysis was more complex but the model reproduced experimental data and permitted to estimate coronary flow. In both cases, the model gave an estimate of other variables including ventricular volumes. These results showed the possibility to use numerical simulation for specific circulatory conditions encountered during beating heart surgery. The model will be improved and transformed into a tool to be used both in the operating theater and in the intensive care unit as a bedside help.