Pressure-flow relations in the pulmonary artery during myocardial ischaemia: implications for right ventricular function in coronary disease

Abstract

Because exercise induced pulmonary hypertension may disturb optimal coupling between the right ventricle and pulmonary artery in coronary artery disease, high fidelity pulmonary artery and right ventricular pressure and electromagnetic pulmonary artery flow velocity data were recorded at rest and during supine exercise in 10 control subjects free of detectable cardiovascular disease and in 11 patients with coronary artery disease. The pulmonary artery impedance and power spectra were calculated from Fourier analysis of pressure and flow waveforms. Total hydraulic power expended per unit of forward flow was computed as an index of right ventricular-pulmonary artery coupling. In coronary artery disease exercise produced substantial increases in pulmonary artery pressure, pulmonary artery characteristic impedance, and total power per unit flow. These changes did not occur in control subjects. Despite a significant exercise increase in right ventricular end diastolic pressure and peak right ventricular dP/dt, and independent of the presence of right coronary artery involvement, the right ventricular stroke output response during exercise was significantly blunted in the coronary artery disease patients. Pulmonary vascular resistance was unchanged by exercise in either group. Exercise induced ischaemia presents an increased pulsatile hydraulic load to the right ventricle. Increased pulmonary artery input impedance impairs the hydraulic efficiency of right ventricular-pulmonary artery coupling and may contribute to the limitation of right ventricular ejection performance in coronary artery disease.