THE HEART BEAT. 563 



The Coronary Circulation during the Heart Beat. The 



condition of the blood-flow in the coronary vessels during the phases 

 of the heart beat has been the subject of much speculation and 

 experiment, since it has entered as a factor in the discussion of 

 several mechanical and nutritive problems that are connected with 

 the physiology of the heart. According to a view usually attributed 

 to Thebesius (1708), the flaps of the semilunar valves are thrown 

 back during systole and shut off the coronary circulation, and 

 therefore the coronary vessels, unlike those of other organs, are 

 filled during diastole. In modern times this view has been revived 

 by Briicke, who made it a part of his theory of the " self-regulation " 

 of the heart beat. According to this view, the coronaries are shut 

 off from the aorta during systole by the flaps of the semilunar valves, 

 so that the contraction of the ventricle is not opposed by the 

 distended arteries, while, on the other hand, the reinjection of these 

 vessels from the aorta during diastole aids in the dilatation of the 

 ventricular cavities. Experimental work has shown decisively that 

 the part of this theory relating to the closure of the coronary arteries 

 by the semilunar valves is incorrect.* Records of pressure changes 

 in the coronary arteries during the heart beat made by Martin and 

 Sedgwick and by Porter show that they are substantially identical 



Fig. 235. Simultaneous record of the blood-pressure (A) and the blood-velocity (B) 

 ill the coronary arteries (Chauveau and Rebatel): a, Marks the beginning of the systole 

 (there is a rise in pressure and in velocity) ; b, marks a second rise of pressure (A) due to 

 the closure of the coronary capillaries by the contracting ventricle (at this moment in B 

 the velocity falls off rapidly) ; c, curve (B) shows an increase in velocity due to the open- 

 ing of the small coronary vessels at the beginning of diastole. 



with those in the carotid or aorta, and records of the velocity of the 

 blood-flow made by Rebatel show that at the beginning of systole 

 the flow in the coronaries suffers a sudden systolic acceleration as in 

 the case of other arteries. During systole, therefore, the mouths of 

 the coronary arteries are in free communication with the aorta. 

 But the coronary system arteries, capillaries, and veins is in 

 part imbedded in the musculature of the ventricles, and we should 



*See Porter, " American Journal of Physiology," 1, 145, 1898, for dis- 

 cussion and literature. 



