BLOOD SUPPLY TO THE HEART 



! 529 



which were used on isolated hearts or anesthetized 

 animals have been: a) estimation of the phasic dif- 

 ference between the central and peripheral coronary 

 pressure curves during a cardiac cycle (151, 153); 

 b ) the recording of movement of the free end of a 

 bristle mounted in the wall of a tube of fixed diameter 

 through which coronary flow occurs (302); c) meas- 

 urement of cooling by air of a heated platinum wire 

 mounted in the neck of a bottle partially filled with 

 blood, the lower part of which is connected to the 

 coronary circulation (10); d) measurement of cyclic 

 movement of various foreign substances (toluene, 

 mercury droplet) inserted into a coronary artery (10); 

 e) recording of the small pressure drop in a pressurized 

 air-blood chamber as blood flows from the base of the 

 reservoir into a coronary artery (93, 153);/) measure- 

 ment of the lateral pressure difference above and 

 below an area of constriction (orifice) in a metal tube 

 inserted into a coronary artery (153); g) recording of 

 the upstream and downstream pressure difference in 

 a metal tube inserted into the coronary sinus (196). 



Finally, the electromagnetic flowmeter has been 

 successfully applied to the coronary circulation in the 

 dog (217, 395). A square-wave type of electromag- 

 netic flowmeter has been found quite useful in coro- 

 nary flow studies in open-chest sacrifice dogs (81 ), but 

 because of their necessary size, they have not yet been 

 chronically implanted on the coronary arteries. The 

 sine-wave type can be miniaturized, and flow trans- 

 ducers of aspirin-tablet size or smaller have been suc- 

 cessfully applied for periods of weeks to the right 

 coronary artery, the main left coronary artery and its 

 major branches, of the conscious and active dog (212). 

 For further discussion of flowmeters see Chapter 38 

 in this Handbook. 



mean flow. The most accurate measurement of mean 

 coronary venous outflow is by its collection in a 

 graduate, and of coronary arterial inflow by reading 

 the graduations on a calibrated reservoir. More 

 sophisticated devices have been developed and applied 

 to dog and man. Some of the more important in the 

 dog are: a) timing visually or photoelectrically the 

 passage of an air bubble through a glass tube of known 

 length and volume which is placed between the cut 

 ends of a coronary artery through which flow is being 

 measured [bubble flowmeter (90)]; b) recording the 

 position of a '"float" in a vertical tapered tube through 

 which coronary blood is flowing [rotameter (153, 

 345)]; c ) recording the temperature difference of two 

 thermojunctions mounted in a plastic sleeve of con- 

 stant cross section through which coronary blood is 



flowing (thermostromuhr — though its ultimate re- 

 liability in many circumstances has been questioned) 

 (153); d) recording the heat clearance or the tempera- 

 ture difference of a reference cold thermocouple and 

 an electrically heated thermocouple inserted into the 

 myocardium ( 14;^ ). 



Coronary Flow (Man and Animals) 



Variations of the Fick principle and coronary cine- 

 angiography have been used to attack the coronary 

 blood flow problem in man. The first major advance 

 came with the use of nitrous oxide inhalation for 

 determining blood flow draining into the coronary 

 sinus. As compared to direct measurement of coronary 

 blood flow, the method [see previously cited reviews: 

 (35, 92, 154, 319)] shows a reasonable accuracy, and 

 in humans has furnished almost all our information 

 regarding coronary blood flow. Another variation of 

 the Fick principle has been used to estimate myo- 

 cardial blood flow in the animal and in man. Studies 

 in the rat and dog have indicated that when intra- 

 venous slug injections of the radioisotopes K 42 or Rb 8B 

 are made, the following occurs: the isotopes have a 

 large volume of distribution within the myocardium, 

 and, for at least 1 min after a single intravenous 

 injection of the isotope, their coronary venous drain- 

 age is negligible compared with their initial deposi- 

 tion; the extraction ratios of the heart and whole body 

 for the isotope are identical. By determining cardiac 

 output by means of this isotope injection, and at the 

 same time determining the fraction of the injected 

 isotope taken up by the myocardium (animal sacrifice 

 and direct counting) within this minute, it is possible 

 to estimate total myocardial blood flow in the dog 

 and rat (185, 234, 330). By comparing the isotope 

 concentrations in different myocardial areas, the 

 regional flow distribution can also be estimated. These 

 results could have a reasonable accuracy. The obsta- 

 cles, however, to the use of such a method in man 

 without coronary sinus catheterization are formidable. 

 While the isotope is being infused intravenously at a 

 rate designed to keep a constant arterial concentration, 

 it might be possible to estimate, by radiation detection 

 over the precoidium and by direct counts on the 

 blood, the increments in myocardial Rb 86 content and 

 its concentration in the coronary sinus blood. How- 

 ever, the isotope extraction at different coronary 

 blood flow rates is not constant (reported extractions 

 vary from 40 to 70%) and may vary with duration of 

 the perfusion. As yet, these difficulties have not been 

 resolved (245, 274). 



