Effect of acute experimental aortic stenosis on coronary circulation.

• The effect of aortic stenosis on the coronary circulation warrants further investigation because the few previous studies led to conflicting conclusions based on small series of experiments. Moreover, aortic stenosis presents a unique situation for a study of the determinants of coronary blood flow. On the one hand, the location of the stenosis, between the left ventricle and the aortic origin of the coronary arteries, creates a systolic pressure gradient unfavorable for coronary flow. This flow-reducing factor is augmented by the increase in extravascular compression resulting from the prolonged systolic ejection phase in aortic stenosis. Indeed, a decrease in coronary blood flow was noted by Green when he produced aortic stenosis by inflating a balloon in the aortic orifice. On the other hand, it has generally been observed that coronary blood flow increases whenever the load on the left ventricle is increased. It would seem logical that a similar increase in load would result from constriction of the outflow tract, whether it be proximal or distal to the coronary ostia. It has been repeatedly demonstrated that aortic constriction distal to the coronary ostia results in an increase in coronary blood flow. Moreover, Gregg and Shipley noted an increase in coronary blood flow in a modified preparation of aortic constriction that was analogous to aortic stenosis. In their preparation, the ascending aorta was constricted,