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HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



mental animal, these are concerned with measure- 

 ments of the effects of various prophylactic and, 

 occasionally, postcoronary occlusion procedures on 

 the electrocardiogram, mortality, size of infarcts, 

 exercise tolerance, the coronary artery pressure be- 

 yond a region of coronary artery occlusion (the 

 so-called peripheral coronary pressure), and finally, 

 on the injectable and functional collaterals in the 

 presence of coronary insufficiency or occlusion. All 

 are difficult to evaluate because of the considerable 

 variability in the size of the naturally occurring 

 collateral circulation. The latter difficulty can be 

 significantly reduced but not eliminated by using 

 only animals showing large T-wave inversion and 

 S-T segment depression during temporary coronary 

 artery ligation. Experimental indications are that the 

 size of the injectable collateral bed and the level of 

 the peripheral coronary pressure correlate well with 

 direct collateral flow measurements (95). The latter 

 measurement has been widely used and has given 

 considerable information (9, 15:3). The collateral 

 flow (retrograde or backflow) is determined by 

 collecting the volume of blood flowing externally 

 from a tube inserted into the peripheral end of a 

 centrally occluded coronary artery. This is flow- 

 before it has passed through a capillary bed, i.e., it is 

 fully oxygenated, and is presumably somewhat too 

 large because, in the measurement, it drains against 

 atmospheric pressure whereas, functionally, the 

 collateral blood must flow against the peripheral 

 coronary resistance beyond the occlusion. Collateral 

 flow can also be measured under selected circum- 

 stances as it enters the myocardium, or after it has 

 passed through a capillary bed and appears in the 

 coronary sinus. This can be done when extracardiac 

 tissue with a vascular stalk has been previously 

 applied to the heart to stimulate collateral develop- 

 ment. The collateral inflow can be measured acutely 

 in the open-chest dog by interposing a rotameter in 

 the vascular stalk, or chronically by applying an 

 electromagnetic flowmeter to the extracardiac arterial 

 pedicle. The collateral contribution to the coronary 

 sinus is estimated by measuring the decrease in sinus 

 flow after clamping the potential extracardiac source 

 of collateral flow. 



Recent investigations indicate caution in the use of 

 the directly measured collateral flow. 0) Rb 86 

 clearance studies estimate collateral flow as two to 

 three times the directly measured backflow, thus 

 suggesting that in addition to functioning inter- 

 arterial channels, other vessels communicate with the 

 ischemic zone at the arteriolar and capillary levels 



(235, 247). This method, however, cannot be used for 

 estimating changes in collateral flow because of the 

 unknown and variable extraction ratio of this sub- 

 stance in the ischemic area, b) The small portion 

 (possibly 15%) of left coronary artery inflow not 

 recoverable in the coronary sinus or anterior cardiac 

 veins has been largely accounted for by drainage of 

 the septal artery and some branches of the left 

 descendens into the right ventricular cavity (265). 

 Thus, in the presence of coronary artery occlusion, 

 some blood might perfuse portions of the septum 

 retrogradely during systole when the pressure gradient 

 might be favorable. 



Tests of coronary collateral function in life in the 

 normal and diseased heart of man have been largely 

 restricted to monitoring changes in the electro- 

 cardiogram to exercise tolerance and angina and, 

 after death, to injection of the coronary collateral 

 circulation at autopsy with opaque viscous material 

 (338). In those individuals with an occluded coronary 

 artery ramus and undergoing a coronary operation, 

 it would appear feasible to use as an index of collateral 

 flow the coronary pressure beyond the occlusion, 

 which can be measured by simple needle insertion. 

 This technique used so successfully in animals has not 

 been attempted in man. Finally, coronary angio- 

 graphic studies by Sones (352), and others, have 

 demonstrated collaterals in both normal and ab- 

 normal hearts. Whether this technique has a future 

 in the study of the development and regression of 

 collaterals and atheromatous lesions remains to be 

 seen (184). 



From the preceding it can be seen that, because of 

 our poor methodology, and especially because the 

 direct or indirect measurement of collateral flow has 

 not as yet been made in man, objective evidence of 

 positive benefit to the heart cannot come primarily 

 from observations after experimental or surgical 

 maneuvers or coronary surgery in man, but must 

 come from the effect of various procedures on coronary 

 collateral function in other animals. 



NATURAL RESPONSES OF THE CORONARY COLLATERAL 



circulation. The natural responses of the coronary 

 circulation of animals during experimental coronary 

 artery constriction and occlusion, which, presumabh , 

 also happen in the heart of man, have been studied 

 extensively. 



Considerable reduction in the lumen of a coronary 

 artery can occur with minimal or no permanent 

 change in coronary flow. This is so because the 

 coronary resistance to flow measured beyond a point 



