A model of phasic arterial and venous blood flow in the coronary circulation

Abstract

A numerical model of the coronary circulation was developed which simultaneously addresses both the arterial and venous sides of the circulation. The model is based upon the concept of an intramyocardial pump rather than the vascular waterfall mechanism and utilizes only phasic pressures as input. The left ventricular myocardium was modelled as three equal and parallel compartments, each consisting of fixed arterial and venous resistances on either side of a lumped arterial and venous intramyocardial capacitance. A time-varying intramyocardial pressure, P i ( t), different for each compartment, was applied through the capacitance. Input pressures were obtained from direct measurements of phasic aortic, right atrial and intramyocardial pressures in six open-chest anesthetized dogs. The model accurately predicted the phasic waveforms of coronary arterial inflow and venous outflow and the nearly 180° phase shift between coronary inflow and outflow. The predicted magnitudes of mean systolic coronary arterial inflow (4.7 ± 1.0 ml/min), mean diastolic coronary inflow (38.4 ± 0.5 ml/min) and mean total coronary arterial inflow (27.7 ± 1.0 ml/min) in the left anterior descending coronary artery were not significantly different from those measured in dogs. The measured values were 5.2 ± 1.0, 28.1 ± 4.2, and 22.2 ± 3.0 ml/min, respectively. The model also predicted a transmural gradient of coronary arterial blood flow which favors the subepicardial layers during systole and the subendocardial layers during diastole. The latter is consistent with experimental observations in the beating canine left ventricular myocardium.