Computer simulation of circulation in patient with total cavo-pulmonary connection: inter-relationship of cardiac and vascular pressure, flow, resistance and capacitance.

The aim is to develop a computer model representative of the circulation in a patient with a uni-ventricular heart surgically palliated by a total cavo-pulmonary connection (TCPC). The effects of known hazardous exposures on this type of circulation are investigated. A model of the cardiovascular system is built using standard components such as transmission lines, restrictors and capacitances. The chamber of the heart consists of a volume connected to checkvalves, and an oscillating source flow connected to the volume represents the pumping of the heart. The following are simulated: exposure to cold, heat, high altitude, accelerating forces, blood loss, reduction in ventricular function, atrioventricular-valve regurgitation and treatment with afterload-reducing agents. During simulations, all the parameters can be changed, independently of each other, and the resulting changes in flow, resistance and pressure are recorded. Exposure to cold, reduced ventricular function and atriventricular-valve regurgitation result in a decrease in cardiac output (14, 58 and 45%, respectively). At high altitude, an increase of 18% is noted in the central venous pressure. Afterload-reducing agents increase the cardiac output by 8% and reduce central aortic pressure by 23%. Blood loss results in a marked reduction in perfusion pressure. It is concluded that the computer model is a useful instrument for simulation of a TCPC or Fontan circulation. The original criteria for this surgical procedure are those showing the most marked haemodynamic responses to different stimulus.