'53° 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



The indicator dilution technique for coronary blood 

 flow in man is based on the fact that, when cardiac 

 output is being estimated by means of a device placed 

 over the precordium to pick up the specific activity of 

 a tracer substance such as I 131 following rapid intra- 

 venous injection, the curve produced during the first 

 circulation of the radioactivity, in addition to having 

 two well-defined peaks representing passage of radio- 

 activity through the right and left sides of the heart, 

 respectively, may also have a third small peak closely 

 following that attributed to left ventricular activity. 

 This appears at a time which could represent myo- 

 cardial blood flow (343, 381 ). Unfortunately, because 

 of an insufficient time lag, it is difficult to differentiate 

 the peak of precordial radioactivity related to myo- 

 cardial flow from other rapid changes in precordial 

 activity, such as that resulting from the preceding 

 passage of blood through the left side of the heart, or 

 that due to subsequent recirculation from the most 

 rapid noncoronary circuits (252). Until the true 

 coronary precordial peak in radioactivity can be more 

 sharply defined, it is difficult to place reliance on data 

 obtained with this method as representing coronary 

 flow. A variation of the application of the isotope 

 dilution technique to the problem arises from the 

 observation in both humans and dogs that concentra- 

 tion curves of radioactivity recorded over the heart, 

 following rapid intravenous injection of small boluses 

 of I 131 , have slower disappearance rates than those 

 obtained by sampling directly from a peripheral 

 artery, such as the femoral (260), the difference being 

 due presumably to the coronary flow. 



Finally, special techniques have been developed 

 for selective catheterization of individual coronary 

 arterial branches in intact closed-chest dogs and 

 unanesthetized human subjects by means of special 

 catheters which permit intracoronary injection of 

 radiopaque materials and roentgenological visualiza- 

 tion of the coronary vessels (352, 393). Coronary cine- 

 angiography is, at the present time, in a somewhat 

 embryonic stage of development as a research or 

 diagnostic method. Perfusion with the media in ap- 

 propriate volume and concentration apparently does 

 not result in development of anginal pain, EGG evi- 

 dence of myocardial ischemia, or photographic evi- 

 dence of coronary vasoconstriction. However, funda- 

 mental hazards in the application of this technique 

 lie in the possibility of inadvertent mechanical occlu- 

 sion of a coronary artery with the catheter tip and the 

 known moderate vasodilator and cardiotoxic proper- 

 ties of the contrast media. From an investigative point 

 of view, coronary arteriography, even when recorded 



continuously by motion picture photography of the 

 fluorescent screen, does not provide a measure of 

 coronary flow and vascular resistance. Such data can, 

 however, provide evidence of change in size and 

 number of visible arterial vessels after administration 

 of various physiological and pharmacological agents. 

 In the presence of a constant blood pressure, such 

 changes would indicate local changes in the vasomo- 

 tive states although it cannot be currently determined 

 whether these alterations are active or passive. In 

 addition, it is used to study the existence of and change 

 in intercoronary arterial collateral channels in life, 

 since the origin and distribution of collateral channels 

 as small as 100 ju can be well demonstrated. From a 

 diagnostic point of view, selective opacification of 

 individual coronary arteries provides information on 

 the length and exact location of partial and complete 

 occlusive lesions in major vessels as small as 1 mm in 

 diameter. 



DISTRIBUTION OF MYOCARDIAL BLOOD FLOW' 



Arterial Circuit 



As blood is ejected from the left ventricle, it simul- 

 taneously enters both coronary ostia and flows via the 

 epicardial coronary arteries to their respective myo- 

 cardial beds. By direct measurement in open-chest 

 dogs, the left coronary and right coronary arterial 

 inflow approach 85 and 15 percent, respectively ( 1 53)- 

 The same relationship also exists in the dog heart-lung 

 preparation and perfused, fibrillating heart, lending 

 physiologic support to the anatomically designated 

 left coronary artery dominance in dogs. While the 

 direct measurement of coronary arterial distribution 

 in man is unknown, coronary arteriography in un- 

 anesthetized patients has demonstrated variations in 

 volume of the various coronary arterial beds which 

 correspond quite well with postmoitem anatomic 

 studies (84). 



Utilizing the bubble flowmeter (90) in both open- 

 and closed-chest acute experiments in dogs, an average 

 left coronary inflow of 65 ml per 100 g left ventricular 

 tissue per minute was found with no significant dif- 

 ference between the two groups. The left circumflex 

 was found to supply an average of 40 per cent, and the 

 anterior descendens about 26 per cent by weight of the 

 left ventricle. Similar values have been obtained with 

 rotameters and in the intact unanesthetized dog with 

 electromagnetic flowmeters. Figures for the contribu- 

 tion of the anterior septal artery flow in the dog can 



