Angiographic changes in the coronary artery associated with cyclical reductions of coronary blood pressure

Morphological changes associated with cyclical reductions of blood pressure in the partially constricted coronary artery of anesthetized dogs have been examined. In the constricted coronary segments, smooth and diffuse spasm, rosary-like spasm, a localized narrowing indicating a platelet aggregate or thrombus, and no obvious change were observed during the pressure reductions in 3, 5, 2 and 5 of 15 trials of 12 preparations, respectively. In the distal segments of the same preparations, segmental spasm and diffuse spasm were observed during the pressure reductions in 8 and one trials, respectively. The changes in the constricted and distal segments appeared simultaneously or independently. The change which indicates obstruction of the distal segments with platelet aggregates or thrombi was observed in none. The results indicate that spasm, but not platelet aggregates or thrombi, in the constricted segments and/or distal segments plays the major role in the cyclical reductions of blood pressure in the partially constricted coronary artery.