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HANDBOOK OF PHYSIOLOGY ^ CIRCULATION II 



lar distention on cardiac energetics and coronary flow 

 can also be gauged (in the dog) by inserting into the 

 left ventricle a balloon inflated to different degrees of 

 fullness (328). The blood may be oxygenated by 

 passing it through a mechanical oxygenator system, an 

 autogenous lung, or through a donor, human or 

 animal. It is believed that isolated hearts generally are 

 in varying degrees of failure (performance character- 

 istics less than those of a normal heart within the chest) 

 and that this can be prevented by a continued inter- 

 change of its blood with that of a supporting dog or 

 human. The latter arrangement has been used by 

 Sarnoff (335) and by Garcia-Ramos, Rosenblueth, 

 and their associates (126, 313). A possible explanation 

 for this phenomenon is the loss of myocardial cate- 

 cholamines in the isolated heart preparation and its 

 replenishment by the cross-perfusion technique (201). 

 In any case, in these varying types of isolated hearts 

 doing work, the coronary vascular bed is largely di- 

 lated, for the coronary flow is greatly increased and 

 the coronary A-V oxygen difference greatly decreased 

 over the values for hearts working within the chest. 

 Finally, it is of considerable interest that the heart 

 beat and carbohydrate metabolism of the isolated dog 

 heart can be maintained for prolonged periods by per- 

 fusion of the coronary circulation, not with blood, but 

 with gaseous oxygen (55). 



Wiggers (796) was one of the first to study the hemo- 

 dynamics of the coronary circulation and energetics 

 of the heart beating and working in situ in the anes- 

 thetized open-chest dog, in which the coronary vessels 

 were naturally perfused from the aorta. By right heart 

 bypass, the extracoronary sinus venous drainage can 

 be quantitated. In this, systemic venous return by- 

 passes the right atrium and ventricle into a reservoir 

 from which it is pumped into the peripheral portion 

 of the pulmonary artery. The coronary venous drain- 

 age can be collected by a tube in the right atrium or in 

 the central portion of the divided pulmonary artery 



(3 9)- 



While in some of these preparations the coronary 

 circulation is naturally perfused from the aorta at its 

 prevailing pressure, for many investigations it is 

 desirable to have coronary artery perfusion at constant 

 controlled flow rates or at constant perfusion pressures, 

 or both, the pressures being different from the pre- 

 vailing aortic pressure. Various expedients have been 

 devised to achieve these ends. The simplest arrange- 

 ment is to connect the peripheral end of a coronary 

 artery or a branch to a blood reservoir at an appro- 

 priate elevation so that it drains into the artery by 

 gravity (249). In another arrangement, air expansion 



chambers are used to permit constant pressure per- 

 fusion (153). Similarly, one end of a pump may be 

 connected to a local arterial source and the other end 

 of the pump to the coronary artery. Either the per- 

 fusion pressure or flow rate can be varied separately. 

 For more complicated systems, pump or pump 

 oxygenator systems such as already indicated for 

 right heart and total heart bypass are used, in which 

 the coronary perfusion pressure is constant. These ap- 

 proaches have the important advantage that they 

 enable the investigator to study separately the periph- 

 eral and myocardial factors that regulate flow. As a 

 further separation of those peripheral parameters 

 which determine flow and metabolism in the myo- 

 cardium, the coronary arteries of the isolated heart, 

 heart-lung preparation, and of the open-chest dog, 

 may be perfused at constant pressure or flow rate, 

 first while the heart is beating, and then while it is in 

 prolonged diastole as the result of stoppage from pro- 

 longed cervical vagal stimulation or intracoronary 

 injection of acetylcholine, potassium chloride or 

 citrate (17, 249, 311, 323). 



Finally, with the advent of methodologies not re- 

 quiring use of anticoagulants or the insertion into a 

 vessel of a flow metering device, reasonably satis- 

 factory measurements have been made in the resting 

 and active dog (159, 212) and the resting human 

 (9 2 . 3 r 9)- 



Coronary Flow Methods (Animals) 



phasic flow. These were designed with the hope of 

 analyzing the factors affecting coronary flow which 

 are too rapid in action to be studied effectively by 

 mean flow measurements. They record the instan- 

 taneous flow at the point of their insertion into a blood 

 vessel. The vascular bed of the heart is made up not 

 only of vessels within the myocardial wall, but also of 

 vessels lying on the surface of the heart. Since the 

 change in mean vessel bore during a cardiac cycle in 

 the superficial vessels (in which the flow measurement 

 is made) is presumably different from that of the 

 deeper vessels, such a device measures a combination 

 of "intramural" and ''extramural" flow. It does not, 

 therefore, necessarily indicate correctly the intramural 

 flow at all times. Comparison, however, of the arterial 

 blood pressure with the flow in late diastole in such 

 recordings is the only means known to the author by 

 which change in the active vasomotor state of the 

 coronary bed can be estimated when the coronary 

 arteries are naturally perfused from the aorta. 



Some of the major earlier phasic flow methods 



