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HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



various latter maneuvers, protection in large part, 

 and in many instances, is probably afforded by the 

 augmented collateral circulation. For example, with 

 an aorta-coronary sinus shunt, the backflow of i o to 

 12 ml of arterial blood exceeds that calculated to be 

 necessary for viability and persists for at least a year 

 and even after loss of function of the shunt (95). But 

 since most hearts following coronary artery ligation 

 die within 24 hours, since the usual retrograde flow 

 observed with these procedures is not large, and since 

 sham operation involving manipulation of the heart 

 at times increases collateral flow or gives sustained 

 protection against coronary occlusion, or both, the 

 possibility must be entertained that there may be no 

 specific effect of some of the maneuvers; they may 

 act by raising the ventricular fibrillation threshold 

 thus giving time for collaterals to develop. 



In some procedures that apply extracardiac tissue 

 to the heart, such as a pedical skin flap (271), or an 

 internal mammary artery ligation (99) or its myo- 

 cardial implantation (324), the collateral flow does 

 not increase. These studies, however, are incomplete. 

 Further work should be done to determine, in 

 addition to the usual arterial collateral flow measure- 

 ments, whether blood actually flows from the extra- 

 cardiac tissue through the capillary bed of the 

 myocardium into the coronary sinus or other coronary 

 venous outflow channels. Despite some positive find- 

 ings, no firm conclusion can be drawn (372, 373). 



ATTEMPTS TO IMPROVE THE COLLATERAL CIRCULATION 

 AFTER CORONARY ARTERY OBSTRUCTION IN ANIMALS 



and man. As already indicated, immediate or early 

 augmentation of the coronary collateral circulation, 

 beyond that occurring naturally following marked 

 coronary constriction or occlusion, has not been 

 demonstrated. Neither experimental estimation of a 

 favorable delayed or chronic collateral response 

 (decrease in infarct size and increased injectable 

 collateral bed or collateral flow) to drugs has been 

 demonstrated (379, 412). However, the following 

 evidence of positive benefit has been reported : a) 

 Treadmill exercise, when added to a pre-existing 

 coronary insufficiency, appears to increase the 

 collateral flow to a level greater than with coronary 

 constriction alone (98). b) In the presence of aneroid- 

 induced chronic left coronary insufficiency and 

 epicardectomy, the addition of a mammary artery 

 implant or application of an Ivalon sponge is stated to 

 greatly extend the survival time of the dog and to 

 increase the functional communications of the 

 ischemic bed with the left ventricular cavity and 



extracardiac arteries. This benefit does not follow the 

 use of cardiopneumopexy or the applications of 

 various other irritants to the myocardium (374). c) 

 Experimental attempts have been made to improve 

 the blood supply to the normal heart and the heart 

 with infarction (intracoronary injection of plastic 

 microspheres) by altering the time of arrival of the 

 arterial pressure pulse so that the systolic pulse 

 arrives during diastole, the period of greater flow (59, 

 188, 203). The procedure is reported to greatly 

 reduce the mortality rate from the myocardial in- 

 farction and to increase the injectable collateral bed. 

 d) When a pulmonary artery to left atrial shunt is 

 added to an already existing chronic occlusion of the 

 left circumflex branch, coronary angiograms and 

 vinyl acetate casts show a more rapid collateral 

 filling and a greater vascularity, respectively, than 

 following coronary artery occlusion alone (30). 



Most of the procedures designed to promote 

 collateral development, including the sham opera- 

 tion, have been applied to the heart of man suffering 

 from coronary artery disease. All appear to increase 

 to some extent the work and exercise tolerance and to 

 decrease cardiac pain (19, 178, 374). The summary of 

 over 600 patients on whom the Beck operation was 

 performed may serve as an example (51). These 

 observations are not necessarily explained on the 

 same basis of the improvement in the collateral 

 circulation of the dog which follows such procedures. 

 This is because in the dog most surgery precedes 

 coronary artery ligation and is designed to promote 

 collaterals in the presence of a normal coronary 

 circulation, whereas, in the human, surgery follows 

 coronary artery occlusion and is designed to promote 

 collateral circulation after the coronary insufficiency 

 has been naturally established. In man, hypoxia, the 

 greatest known vessel dilator, and a natural stimulus 

 to collateral development, has already been working 

 for many months. Since human coronary surgery 

 which follows coronary occlusion has as yet little 

 counterpart in animal experiments, attempts should 

 not be made to interpret these human coronary 

 experiments on a physiological basis. 



The explanation of the results in man is not clear. 

 Patients treated surgically by epicardial phenoliza- 

 tion, poudrage, cardiopneumopexy, and bilateral 

 internal mammary artery ligation, although showing 

 marked relief of angina, do not show electrocardio- 

 graphic improvement or an increase in coronary flow, 

 or a decrease in coronary vascular resistance following 

 nitroglycerin (44). Undoubtedly, some subjects are 

 protected and live longer because of the known experi- 



