Vascular determinants of univentricular support.

The dynamic coupling between cardiac pump performance and vascular arterial-venous capacitive and resistive properties was examined analytically and experimentally to determine the feasibility of maintaining systemic and pulmonary circulation, devoid of the right heart. Analysis of the cardiovascular system (excluding neurohumoral factors), used a mathematical representation of the major determinants involved in cardiac output and demonstrated that change in pump flow output has reciprocal effects on the venous and arterial pressures. Independent of the pump's performance characteristics, cardiac output reserve was restricted, reaching a critical plateau (50% of normal) because of the rapidly depleting pulmonary venous pressure, concurrent with the translocation of the venous stressed volume to the arterial side of the circulation. Animal experiments aided by computer modeling confirmed that near normal flow can be sustained by actively mobilizing or augmenting blood volume, or by reducing selectively the unstressed volume and venous pooling. A single blood pump, in a form of a mechanical substitute, or the biologic left heart acting alone, can support the entire circulation. The right heart is not essential for normal pulmonary circulation, but serves to maintain low systemic venous pressure and a relatively high left heart flow reserve state. Peripheral vascular parameters, i.e., stressed volume and venous capacitance, serve a vital role in preserving the mechanical self regulation of cardiac output.