Estimation of coronary flow reserve with the instantaneous coronary flow velocity versus pressure relation: a new index of coronary flow reserve independent of perfusion pressure.

Our goal was to develop a new method to evaluate coronary flow reserve independent of perfusion pressure by equipping dogs with a Doppler flow probe in the left anterior descending artery. The slope of the linear portion of the velocity-pressure loop in the late diastolic phase was defined as VP slope; the hyperemic:basal ratio of the VP slope was defined as VP slope ratio, and the hyperemic:basal ratio of the mean coronary blood flow velocity was defined as coronary flow reserve (CFR). We measured VP slope ratio and CFR, altering aortic pressure by aortic banding and inferior vena cava occlusion. VP slope ratio was independent of aortic pressure, but CFR increased with increments in aortic pressure. The VP slope ratio and CFR decreased in the presence of coronary stenoses. In conclusion, VP slope ratio is considered to be a physiologic index of the severity of coronary stenosis, which is independent of perfusion pressure. This measure is easily applicable in clinical practice.