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The Hypothermic Heart* Work Potential and Coronary Flow by 1 Thorax: first published as 10.1136/thx.12.3.208 on 1 September 1957. Downloaded from Thorax (1957), 12, 208. THE HYPOTHERMIC HEART* WORK POTENTIAL AND CORONARY FLOW BY 1. K. R. McMILLAN,t R. B. CASE,+ W. N. STAINSBY, AND G. H. WELCH, JR. From the National Heart Institute, National Institutes of Health, Md., U.S.A. Surgery of the heart and great vessels of eously recorded on a Sanborn direct-writing oscillo- necessity imposes a burden on an already graph. Clotting was prevented with " treburon." diseased heart. Whether hypothermia as an Blood increments of 50 to 100 ml. were added to the a load femoral vein at regular intervals resulting in increases ancillary technique adds further to the in all flows and pressures. In this way, data were heart is of fundamental importance and therefore gathered for the calculation of left ventricular func- the effect of cooling on myocardial contractility tion curves. was investigated. This was determined by the Left ventricular stroke work in gram-metres was use of modified Starling curves (relation of stroke calculated by multiplying stroke volume in cubic work to filling pressure) as described by Sarnoff centimetres by the difference between mean arterial and Berglund (1954). The behaviour of coronary and mean left atrial pressure in cm. of water and flow and filling pressures in relation to other dividing by 100. Left ventricular function curves physiological variables was also studied. were obtained by plotting the stroke work of the leftcopyright. ventricle against its simultaneous mean left atrial pressure over the whole range of atrial pressures. METHOD After this information had been obtained at 37' C., Dogs premedicated with morphine (2 mg./kg.) were the animal was cooled to 28 C. by passing blood anaesthetized with a 1:10 chloralose-urethane solu- from the femoral artery to the femoral vein through tion given intravenously. The chest was opened in a coil immersed in ice water (Delorme, 1952). the fifth left interspace, occasionally with the resection Measurements were not made while this shunt was of the fifth rib, and respiration was maintained by functioning. Rewarming was accomplished by im- http://thorax.bmj.com/ constant volume, intermittent positive pressure from mersing the coil in water at 45' C. Temperature was a Starling pump. The circulation was rearranged measured by a standardized mercury thermometer in- according to the method of Sarnoff and Berglund serted into the aortic blood stream. The data for (1954), with the addition of measurement of coronary ventricular function curves were then gathered at flow (Case, Berglund, and Sarnoff, 1954). Blood leav- 28' C. as previously described and again after ing the left ventricle enters the aorta from which it rewarming. flows through a Potter electroturbinometer (Sarnoff In three dogs, complete A-V dissociation was ob- and Berglund, 1953) to the descending aorta and tained by ligation of the bundle of His three weeks before performing the experiments described herein. brachiocephalic artery. A side arm proximal to the on October 1, 2021 by guest. Protected electroturbinometer leads blood through a recording The ligation is a modification by Borst (personal com- rotameter (Shipley and Wilson, 1951) from which it munication) of the technique of Starzl, Gaertner, and flows into a modified Gregg coronary cannula. The Baker (1955). In these dogs heart rate was controlled tip of this has been passed into the aorta via the left by electrical stimulation of the left ventricular myo- subclavian artery and then tied in the left main cardium. coronary artery. Thus the total cardiac output was RESULTS measured except for blood entering the right coronary were artery. Nine successful preparations obtained. Pressures were measured in the left and right atria, Left main coronary flow was measured in two and in the pulmonary artery and aortic arch by means and the rate was controlled by electrical stimu- of electromanometers, and, with the coronary flow lation in three. and cardiac output, were continuously and simultan- COOLING CURVES.-Results obtained during *Presented in part at the Second European Congress of cooling, which are typical of the data obtained Cardiology, Stockholm, 1956. in all animals, are presented in Fig. 1. Filling tVisiting scientist, National Heart Institute, 1954-1955. Present address: St. Thomas's Hospital, London. pressures remained essentially the same while tPresent address: St. Luke's Hospital, New York City, N.Y. stroke volume rose. Other values fell as expected, Thorax: first published as 10.1136/thx.12.3.208 on 1 September 1957. Downloaded from THE HYPOTHERMIC HEART 209 37 36 35 34 33 32 31 30 29 28 27 left coronary flow decreasing relatively more than 2.0 aortic pressure. For example, in the experiment shown in Fig. 1, heart rate fell 46%, aortic pres- LO - sure 55 %, cardiac output 31 %, while coronary CARDIAC OUTPUT L./M. flow fell 77% and stroke volume rose 25%. 10 - VENTRICULAR FUNCTION CURVES.-AS blood was loo - transfused, aortic pressure rose to approximately the same levels at 280 C. as at 370 C. at equiva- 50 - AORTA MM. HG. lent filling pressures. However, cardiac output 0- i .. rose relatively less at 280 C., presumably due to 60 - the lower heart rates at the lower temperature. 40- In Fig. 2, for example, heart rate at 370 C. fell 20- LEFT CORONARY RLOW C.CO/MI. from 200 to 140 during blood transfusion, while 0- at 280 C. it fell from 115 to 100. Coronary flow 15- rose less during hypothermia. Ventricular func- 10- tion curves were approximately the same, or occa- 5- STROKE VOLUME C.C. U . - sionally higher at 280 C., as compared with those 120 - obtained at 370 C. in the same dog, indicating 90 - an equal or greater contractility of the myo- 60 - cardium in the hypothermic state (Fig. 2). 30 - HEART RATE 0- FIG. I.-Simultaneous and continuous measurement of: (1) cardiac 20 - output, (2) mean aortic pressure, (3) left coronary artery flow, - PA. (4) stroke volume of the heart, (5) heart rate, (6) pulmonary 10 - - --- LL A. arterial and left and right atrial pressures in a 25-kg. dog during RHA. cooling from 370 C. to 280 C. CM. H20 copyright. FIG. 2.-Left ventricular function curve of a 25 kg. dog plotted at 0 _ I 370 C. and 280 C. Abscissa shows left atrial mean pressure in 37 36 35 34 33 32 31 30 29 28 27 cm. water. Otdinate shows left ventricular stroke work in BLOOD TEMPERATLRE °C. gram-metres. FIo. 1 701I I I I 60 http://thorax.bmj.com/ LVSW = so5 on October 1, 2021 by guest. Protected 30 // X ~~~~~~~X370C 20 0 0 0 280C l0 LA MEAN Cm.H 20 I I 0l,;,'u 3U l40 FIG. 2 Thorax: first published as 10.1136/thx.12.3.208 on 1 September 1957. Downloaded from 210 1. K. R. MCMILLAN, R. B. CASE, W. N. STAINSBY, and G. H. WELCH, Jr. c 5 10 15 20 25 30 35 40 45 50 CORONARY FLOw.-Fig. 5 is a plot of left i 1 --A I I ventricular minute work against left main coro- nary flow as measured during transfusions at 70 - 370 C. and 28° C. It may be seen that at lower work levels the performance of a given amount 60 of work is accompanied by lowered coronary 50 flows at reduced temperature. The third curve shows no appreciable drift after 40- hypothermia to 28.70 C. has been maintained for 40 minutes. 30 RUN TEMP RATE DISCUSSION 20 - 1 360 72 2 28.5" 72 A. COOLING CURVES.-The simultaneous, con- 10 - 3 35S 72 REWARMED tinuous recording of the seven variables pre- t-A 4 285" 72 RECOOLED sented in Fig. 1 gives a composite picture of the 0-i physiological changes occurring during the induc- 140 - 120 - tion of hypothermia. Regardless of the number 100 - of points taken from the recordings there were no 80 - sudden changes in these values during cooling, 60 - 40 - KEAN L.A.-CM. H20 20 - 0 2 4 6 8 10 12 14 16 18 2022242628 3032 34363840 0 ~IIII II JII II II I 40- = 70 - 30 - copyright. 20 10 60 - 10o- 0 50 - - I . A I I I I I 0 5 10 15 20 25 30 35 40 45 50 40 - FIG. 3.-Top: Left ventricular stroke work in gram-metres. Middle: Mean aortic pressure in mm. Hg. Bottom: Stroke volume in c.c. All three plotted against left atrial mean pressure. This 30 - figure shows four separate curves plotted from the same dog at http://thorax.bmj.com/ different temperatures with the heart rate held constant. 20 - 10 - 371C. Curves obtained at identical heart rates (Fig. 3) show that the function curve is virtually the same 0- at 28° C. and 370 C. under these conditions and that increases in stroke volume and aortic mean 70 - pressure were also similar. 70 60 - The upper part of Fig. 4 shows the effect of heart rate on the ventricular function curve at 50 - 4l* on October 1, 2021 by guest. Protected 370 C. In this experiment, heart rate was con- trolled and maintained constant throughout each 40- curve at 70, 100, and 125 beats per minute. The curve is seen to be depressed slightly as the rate 30- / is increased, as has been previously observed 20- (Berglund, Duff, and Borst, to be published). 28"C. The lower half of Fig. 4 shows curves obtained 10- . at similar rates but at 28° C. in the same animal. 0- I I I I II II II The curve is seen to fall off slightly at a rate of 0 2 4 6 8 10 12 14 16 I8 202224 2628303234363840 100, and to fall severely at a rate of 125.
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