Abstract
The influence of intensity of coronary arterial stenosis on intramyocardial blood flow was examined by a model study. We composed a myocardial circulation model incorporating the intramyocardial pressure pump and the time varing elastance as the extravascular compressive force. The model has two myocardial layers, epimyocardial and endomyocardial layers, which consist of arteriolar, capillary and venular compartments, respectively. Stenosis was introduced into the epicardial coronary artery, and the pressure loss across stenosis was expressed by the sum of friction loss and separation loss. With increment of stenotic severity, we compared the arteriolar blood pressure and blood flow waveforms during systole and diastole between the epimyocardium and the endomyocardium. Following the simulation study, it was reveald that in the endomyocardium, the increase of systolic reverse flow and the decrease of diastolic forward flow were concomitantly progressd with the severity of stenosis, leading to remarkable reduction of total volume flow. On the other hand, despite the decrease of diastolic forward flow, systolic reverse flow did not develop in the epimyocardium until stenosis was severe enough to cause extreme pressure drop. Thus, epimyocardial ischemia was not apparent until stenosis became very severe, i. e., about 97% area stenosis. In coclusion, the endomyocardium is susceptible to ischemia due to the reduction of diastolic forward flow with the concomitant increment of systolic reverse flow, whereas the epimyocardium is tolerant to ischemia, resulted from the relative lack of systolic reverse flow disturbance along the progression of stenosis.
