BLOOD SUPPLY TO THE HEART 



1 555 



SPONTANEOUS EXCITEMENT 

 CONTROL I 25 SEC 



HEART 

 RATE 



MEAN 

 ART B P 



MEAN COR 

 FLOW/MIN 



STROKE COR 

 FLOW (cc) 



DIASTOLIC 

 FLOW/MIN 



SYSTOLIC 

 FLOW/MIN 



98 

 115 

 94 

 1.0 

 76 



250 

 122 

 314 

 13 

 258 

 56 



117 

 137 

 340 

 29 

 276 

 64 



77 

 126 

 200 

 2.6 

 177 

 23 



72 

 113 

 74 

 10 

 66 

 85 



fig. 1 2. Reproduction of sections from a continuous record in a conscious dog some days post- 

 operative, showing effect of excitement on mean arterial blood pressure and stroke left circumflex 

 flow, using strain gauge and electromagnetic flowmeter as in fig. 6. [Rayford et al. (301).] 



experiments of a long-term chronic nature. It is not 

 known, therefore, what application to the clinical 

 situation can be made of present experiments. 



AORTIC STENOSIS, PULMONARY HYPERTENSION, PUL- 

 MONARY EMPHYSEMA AND COR PULMONALE. In the 



past, the coronary effects of stenosis of the aortic 

 valves, cor pulmonale, pulmonary emphysema, and 

 pulmonary hypertension associated with mountain 

 sickness have not been studied in humans, largely for 

 lack of an adequate method. Our information on 

 these events thus comes largely from the dog. 



In experiments with the isolated heart, elevation of 

 right ventricular pressure by constriction of the 

 pulmonary artery or elevation of left ventricular 

 pressure by aortic constriction (coronary perfusion 

 pressure kept constant) has been demonstrated to 

 cause a reduction in blood flow to the myocardium 

 of the right and left heart, respectively (153, 205). 

 The flow decrease is attributed to the dominant 

 effect of the direct mechanical inhibitive action of the 

 increased vigor of the heart or the establishment of 

 an unfavorable pressure gradient for right coronary 

 drainage or both. In studies of the isolated supported 

 dog heart, when coronary perfusion pressure (aortic) 

 is kept constant, elevation of the resistance to right 



ventricular output (an increase in cardiac work) 

 does not affect total coronary outflow (313). This 

 means that either the heart is performing the work 

 much more economically or there is a large safety 

 factor in the oxygen to be extracted. The latter is, of 

 course, true in the isolated heart in which the ex- 

 traction may be only 20 per cent, but in the normal 

 heart no such wide margin of safety is available, 

 extraction being of the order of 75 per cent. Therefore, 

 it remains to be seen whether this dissociation of 

 cardiac work and coronary flow in the isolated heart 

 applies to a normal situation. 



Acute elevation of right ventricular pressure by 

 pulmonary artery constriction in the open-chest dog 

 with constant heart rate is followed by a maintained 

 increase up to 4 hours in systolic as well as diastolic 

 blood flow in the right coronary artery in the presence 

 of the same or some lowering of the aortic or central 

 coronary artery pressure. In addition, venous outflow 

 in the anterior cardiac veins increases greatly (1 53). 

 During the sustained response, both right ventricular 

 work and metabolism increase, the former being a 

 result of the increased pulmonary arterial pressure 

 and a small decrease in cardiac output, the latter 

 elevation resulting from a combination of an increase 

 in right coronary flow and a greater oxygen extrac- 



