THE HEART BEAT. 557 



efficient heart is determined the variations in reaction ma}' be 

 used to estimate different degrees of inefficiency.* 



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 

 b}' 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 semilimar valves is incorrect, t Records of pressure changes 

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

 Sedgwick and by Porter show that they are substantially identical 



Fig. 237.— Simultaneous record of the blood-pressure (A) and the blood-velocity (B) 

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

 (there is a rise in pressure and in velocity) ; 6, marks a second rise of pressure {A) diie to 

 the closure of the coronary capillaries bv the contracting ventricle (at this moment m B 

 the velocity falls off rapidly); c, curve (B) sh9ws 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 Rebate) show that at the beginning of systole 

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



* For details see works on clinical medicine; also Crampton, "New York 

 Med. Journal," 98, 916, 1913, for the Crampton index, and Schneider, "Journal 

 of the Amer. Med. Assoc," May 29, 1920, for the point method. 



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

 cussion and literature. 



