Cyclical Reduction in Blood Flow of Partially Constricted Coronary Artery in Dogs Ii. An Arteriographic Study

Mechanisms for cyclical reduction in peripheral blood pressure and flow of partially constricted coronary artery of anesthetized dogs has been examined. In 64 of 97 preparations, cyclical reduction in coronary blood pressure and flow developed 3 to 32 min after the beginning of constriction. Period duration of the cyclical reduction ranged from 1 to 32 min. The cyclical reduction was frequently associated with elevation of the ST segment of surface electrocardiogram, systolic bulge of the left ventricle and excitation of afferent cardiac sympathetic nerve fibers. In the preparations in which cyclical reduction was not produced by constriction, a brief stretching of the constricted portion provoked the cyclical reduction. Segmental or diffuse narrowing of the constricted coronary artery which occurred during the reduction in pressure and flow was demonstrated by selective arteriography. Also, segmental spasm in the constricted coronary artery was demonstrated by photography. No obvious difference in the constricted of the artery was observed histologically between the preparations in which cyclical reduction developed and those in which cyclical reduction was not produced. The results indicate participation of vasospasm in the cyclical reduction of blood pressure and flow in partially constricted coronary artery.