SUMMARY A large-scale model of the coronary circulation, instrumented to permit detailed pressure and velocity measurements, has been used to study flow through isolated stenotic elements in large coronary arteries. Pulsatile aortic pressure and instantaneous peripheral resistance were simulated with servo valves. A variety of axisymmetric and asymmetric stenoses were studied and flow separation was found to occur for all but very mild stenoses. Pressure recovery downstream of the stenosis throat was limited and, in some cases, no recovery was observed. Pressure drop was primarily dependent upon the minimum area of the stenosis and relatively independent of stenosis geometry. Flow was quasi-steady at normal heart rates, and simple steady flow theory proved adequate to describe the pressure drop through the stenosis. The theory yielded results that agreed well with published data for dogs and appears promising for predicting effects of hemodynamic variables on a given stenotic lesion. Thus, principal findings of the study are that a relatively severe stenosis behaves essentially like an orifice and that a simple quasi-steady theory appears adequate to predict effects of a stenosis on coronary flow.IT HAS BEEN known for some time that a relatively severe constriction of a coronary artery is required to alter mean resting coronary flow significantly. Studies in open-chested dogs 1 "5 have delineated the following characteristics. An area occlusion of approximately 80-85% (corresponding to a diameter reduction of 60-80%) is required to reduce resting coronary flow. This value has been referred to as a "critical" occlusion. As this critical occlusion is approached, reactive hyperemia is almost entirely abolished indicating that full peripheral vasodilation has already occurred. For smaller degrees of occlusion, reactive hyperemia is reduced in comparison to the control state indicating partial vasodilation. Similar results were obtained in steady flow in vitro experiments conducted using postmortem coronary arteries with partial occlusion." In this study, in which perfusion pressure and downstream resistance could be independently controlled, it was found that at low flow rates stenotic resistance (ratio of pressure drop to flow) was essentially constant, suggesting fully developed laminar flow. At high flows resistance increased with flow, indicating the importance of turbulence, flow separation, or entrance effects. It was further observed that the resistance of the stenosis was primarily dependent on its minimum cross-sectional area rather than its length.The foregoing studies have been confined to a description of the overall behavior of coronary flow in the presence of a stenosis. Because of the small size of the arteries, it is very difficult to make any detailed pressure or flow measurements to describe in detail the flow mechanism responsible for stenotic resistance. In order to study the flow in detail, it is necessary to develop large scale laboratory models. Most studies of flow through an isolated area of...

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