COMPUTER-SIMULATION OF THE PROPAGATION OF CONTRAST-MEDIUM IN A CORONARY-ARTERY DURING ONE CARDIAC CYCLE

In some angiographic methods for measurement of mean coronary flow in ml/min, a threshold is applied to 'concentration-distance' curves obta ined from a constant rate injection by computing the intravascular con trast medium concentration along the main coronary branches. If the sh ape of the velocity profile would remain parabolic throughout the card iac cycle, the correct threshold value would be '50% of the concentrat ion at the injection site'. But, coronary flow being strongly pulsatil e, the shape of the velocity profile must be expected to vary apprecia bly within the cardiac phase. In order to investigate if a single, app ropriate threshold value nevertheless exists for a great variety of co ronary flow pulses and velocity profiles, the spreading of contrast me dium injected continuously in a tube perfused by a time varying flow Q (t) was studied by computer simulation. While the particular time cour ses of flow and velocity profile appear to be of secondary importance, the ratio 'injection rate to peak coronary flow' has a major impact. If it is equal to or greater than 1, a threshold value of 47% is the b est choice. If the ratio is markedly less than 1, no appropriate thres hold exists and use of the 47% threshold will result in considerable f low underestimations. This was fully confirmed by measurements of abso lute coronary flow performed in patients.