BLOOD SUPPLY TO 1 UK HEART 



[ 537 



anemia to marked polycythemia so that the myo- 

 cardial extraction coefficient (A-V), A is constant. 



In addition to patterns of myocardial metabolism in 

 the normal heart, other metabolic changes have been 

 reported in some pathological and diseased states. 

 Patients with heart failure and decreased cardiac 

 work due to valvular disease show an increased carbo- 

 hydrate uptake by the heart with a normal extraction 

 of lactate and pyruvate and increased glucose exti ac- 

 tion. The heart in the patient with diabetes appears 

 to derive most of its energy from fat even in mild 

 cases with a postabsorptive respiratory quotient ol 

 about 0.7 and an increased uptake of fatty acids and 

 a decreased carbohydrate uptake. 



Thus, the heart demonstrates broad flexibility in 

 the utilization of substrate for energy production 

 without a change in work performance or work 

 capacity. This makes it largely independent of fluctua- 

 tions in its chemical environment. There is no evi- 

 dence that substrate lack occurs in any clinical 

 situation to the extent that it embarrasses the cardiac 

 work capacity. Similarly, the metabolic disturbances 

 such as diabetes mellitus which alter the fuel mixture 

 available to the heart do not also alter cardiac func- 

 tion. It is, however, well to defer detailed considera- 

 tion of other data because an interpretation must be 

 based on the assumption that oxidation of foodstuffs 

 to carbon dioxide and water is the sole factor in the 

 determination of the myocardial respiratory quotient 

 and of the myocardial extraction and uptake of these 

 compounds including oxygen. Without doubt, stor- 

 age of and or conversion into other compounds is 

 occurring concurrently, and these activities are 

 expecially prominent in the presence of a changing 

 cardiac level of activity or changing levels of blood 

 substrate (16, 32, 33, 74, 1 16, 133, 169, 278, 279). 



BASAL DATA 



In the resting state, the coronary data for dog and 

 man agree. With the left ventricular cardiac work 

 index approximating 3.0 to 4.6 kg-m, left coronary- 

 flow approximates 72 to 85 ml per 100 g of left 

 ventricle per min (118, 153, 307). In the anesthetized 

 open-chest dog, values as high as 600 ml per 100 g 

 left ventricle per min have been recorded when the 

 left heart has been stressed by a combination of 

 catecholamine injection and aortic constriction (344). 

 Left coronary flow values in the unanesthetized dog 

 during maximal natural stresses are not yet available 

 but during moderate treadmill exercise and following 



excitement, the coronary flow has approximated 

 that in the open-chest dog (212). As indicated under 

 physical determinants of coronary flow, the frac- 

 tionation of the volume flow between systole and 

 diastole is somewhat variable, but in the left coronary- 

 artery of the unanesthetized dog the systolic volume 

 flow very often approximates 25 to 30 per cent of the 

 diastolic flow under semibasal conditions, as well as 

 during excitement, exercise, and reactive hyperemia 



(i59 a )- 



In the anesthetized dog, the circulation time from 

 the central coronary artery to the coronary sinus 

 approximates 4.5 sec (260). In normal patients, the 

 coronary transit time (with I 131 injection) varies from 

 6.5 to 1 1 sec. Exercise and nitroglycerin, which in- 

 crease coronary flow (nitrous oxide method), decrease 

 the transit time (increased coronary flow velocity) 

 while the Valsalva maneuver, which increases the 

 circulation time, decreases coronary flow (135). 



Flow values for the right coronary artery in a good- 

 sized open-chest dog approximate 10 to 15 ml per 

 min. In the resting, unanesthetized dog, the values 

 are similar (unpublished observations). The volume of 

 systolic flow generally exceeds the diastolic volume 

 flow for an equivalent time period and very often ex- 

 ceeds total diastolic flow (153, and unpublished obser- 

 vations). Values per gram of myocardium and the 

 flow responses to natural stresses of everyday life are 

 not known. 



Although each ventricle can remove essentially all 

 oxygen from the coronary blood in its passage through 

 the myocardium, normally, for the left ventricle 

 (also the right), about two-thirds is extracted with an 

 arteriovenous difference of 1 1 to 14 ml, and a coro- 

 nary sinus value of 5 to 6 ml. This extraction changes 

 little, i.e., less than 10 to 20 per cent with increased 

 stress (except following catecholamine injection, 

 anoxia, and anemia, in which it decreases), indicating 

 that the oxygen supply is well balanced with metabolic 

 demands (208). 



Oxygen uptake per 100 g left ventricle (coronary 

 flow X coronary A-V 2 difference) is 8 to 10 ml 

 per min in the open-chest dog, the anesthetized closed- 

 chest dog with normal blood pressure and cardiac 

 output, and in the resting unanesthetized dog and 

 human. Maximum values calculated in the open- 

 chest dog approximate 60 ml per 100 g per min. In 

 the unanesthetized active dog under the influence of 

 mild exercise and excitement, values are not avail- 

 able. 



With present poor methodology, separation of oxy- 

 gen usage between systole and diastole can only be 



