CHAPTER XIX 

 THE NUTRITION OF THE HEART 



THE BLOOD SUPPLY 



In cold-blooded animals, such as the frog, the heart muscle is nourished 

 by blood soaking into it from the heart chambers, which indeed do not 

 form definite cavities as in the mammalian heart, but exist as an inter- 

 lacement of muscular tissue. In the hearts of higher animals, the muscu- 

 lature is supplied by special arteries (the coronary), although a certain 

 amount of blood may still pass directly from the cardiac cavities into 

 the musculature through the veins of Thebesius. 



The relative importance of the various branches of the coronary artery 

 in maintaining an adequate nutrition of the heart has been studied by 

 observing the effect of occlusion of one or more of them (W. T. Porter 9 .) 

 Occlusion of the circumflex branch of the left coronary artery caused 

 arrest of the heartbeat in about 80 per cent of cases, the arrest being 

 usually accompanied by fibrillary contraction. Occlusion of the right 

 coronary arrested the ventricular contraction in about 20 per cent of 

 the cases. Smaller branches may be occluded without any evident 

 change in the heartbeat. 



These results indicate that the capillary areas supplied by the branches 

 of the coronary artery do not freely anastomose with one another. They 

 are more or less terminal arteries ; that is, each branch supplies a distinct 

 region of the cardiac muscle. If one of the smaller branches of the coro- 

 nary is occluded, although there is 110 immediate stoppage of the heart- 

 beat, yet after some time the area supplied by that branch usually under- 

 goes necrosis, again indicating that collateral circulation can not have 

 become established. It is interesting, however, to note in this connection 

 that anatomic studies have shown that a certain amount of anastomosis 

 does occur between capillaries of different branches, although it is evi- 

 dent, from the above observations, that no adequate collateral circulation 

 becomes established through this anastomosis. 



PERFUSION OF HEART OUTSIDE THE BODY 



In order that the blood supply through the coronary arteries may 

 adequately maintain the normal nutrition of the cardiac muscle, certain 



161 



