Pulmonary regurgitation: the effects of varying pulmonary artery compliance, and of increased resistance proximal or distal to the compliance.

BACKGROUND: Pulmonary regurgitation is common after repair of tetralogy of Fallot, predisposing to right ventricular dilatation and potentially fatal arrhythmias. Magnetic resonance studies of such patients led us to hypothesize that the amount of regurgitation, in the absence of an effective valve, depends on pulmonary arterial compliance and on the location of resistance relative to the compliance. METHODS AND
RESULTS: Using a pre-existing mathematical model representing the cardiovascular system, removal of the virtual pulmonary valve gave a triphasic pulmonary artery flow curve similar in shape to those recorded in patients with free regurgitation, with a regurgitant fraction of 30%. There was no reversal of flow at pulmonary capillary level, the regurgitant volume originating entirely from the compliance of the virtual pulmonary arteries and arterioles. Doubling their compliance increased regurgitation to 35%, whereas halving it decreased regurgitation to 23%. Doubling the total pulmonary vascular resistance by increasing arteriolar resistance increased regurgitation to 46%, whereas doubling it by simulating pulmonary annular stenosis proximal to the compliance limited regurgitation to 10%, but at the cost of a 32 mmHg peak systolic pressure drop.
CONCLUSIONS: The model supported our hypotheses, indicating the relevance to pulmonary regurgitation of previously overlooked variables. The virtual pulmonary regurgitation was exacerbated by pulmonary artery compliance and by elevated resistance distal to it, but was limited by more proximal resistance. These relationships merit careful clinical investigation as they would have implications for the initial management, subsequent investigation and decisions on re-intervention in patients with pulmonary regurgitation.