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REDISTRIBUTION OF REGIONAL BLOOD FLOW IN HYPOTHERMIA
REDISTRIBUTION OF REGIONAL BLOOD FLOW IN
HYPOTHERMIA
N. Anders Delin, M.D.*
Kjartan B. Kjartansson,
Lawrence Pollock, M.D., and Worthington Buffalo, N.
U
M.D.,
G. Schenk, Jr.,
M.D.,
Y.
conditions of hypotension from blood loss it has beeen found that a preferential shift of blood flow to the kidneys occurs which has been interpreted as a physiological response of protective nature. In hypothermia there is also hypotension with reduction in blood flow, and one might ask whether a similar preferential shift occurs. Search of available reports in the literature indicates that contrary to this assumption there is a shift of blood flow away from the kidneys toward the splanchnic bed during hypothermia of a moderate degree. However, this information is gathered from reports of study of either one but not both of the blood flow regions mentioned. This study presents measurements during progressive hypothermia of abdominal inflow, splanchnic flow, renal flow, and flow below renal arteries by means of a triple-probe electromagnetic flow measurement technique described earlier. 7 NDER
METHOD
Ten adult mongrel dogs of both sexes, weighing 15.9 to 27.2 kilograms (average 21.1 Kg.), were anesthetized with sodium pentobarbital intravenously, (26 mg. per kilogram) intubated, and ventilated with a positive-negative pres sure ventilator with a tidal volume and frequency that kept them somewhat hyperventilated. Shivering was prevented with additional amounts of sodium pentobarbital if needed. Through a retroperitoneal but intrapleural approach, with the dorsal parts of the eleventh and twelfth ribs taken, the abdominal aorta was exposed. All vessels leaving the aorta in this area were localized, the celiac axis, the superior mesenteric artery, and the renal arteries were saved, all others were divided to accommodate one electromagnetic flow-probe t above the celiac axis, one below the superior mesenteric but above the renal arteries, and one below the renal arteries. The probes were connected via a switch-box From the Department of Surgery, State University of New York at Buffalo, and the Edward J. Meyer Memorial Hospital, Buffalo, N. Y. Supported in part by a grant-in-aid from the National Heart Institute (HE-03181) of the U. S. Public Health Service. Received for publication July 15, 1964. •Research Fellow of the United Health Foundation of Buffalo and Erie County. tElectromagnetic Probe Co., Winston-Salem, N. C. 511
J. Thoracic and Cardiovas. Surg.
D E L I N ET AL.
512
to a square-wave electromagnetic flowmeter* which made flow determinations possible from the three probes in rapid sequence. The meter zero position Mas determined by downstream vessel occlusion. Pressure was measured with a Sanborn inductance-type transducer con nected to a catheter introduced via the right brachial artery to the aortic arch. Temperature was measured in mid or low esophagus with a thermistor probe, f Blood stream cooling was used. One shunt, consisting of 1.5 to 2 M. PE-360 polyethylene tubing interposed between carotid artery and jugular vein, and a similar shunt between the femoral artery and vein were coiled and immersed in ice water. Measurements were made before cooling and at intervals during cooling, always with both shunts closed. The experiment was ended when ven tricular fibrillation occurred.
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Pig. 1.—Scattergram of aortic mean pressure versus esophageal temperature in 10 dogs. The regression curve is part of a parabola which statistically nts better than a straight line. Fig. 2.—Scattergram of flow in the aorta above the celiac axis versus esophageal tempera ture. No tendency to a deviation from a straight line relationship is evident.
RESULTS
The rate of fall of temperature was 0.3° C. per minute at higher tempera tures, falling to 0.15° C. per minute at lower temperatures—a relatively slow cooling which did not produce temperature gradients exceeding 3° C. any where between the esophagus, intracranial space, aortic blood, rectum, or front and hind leg muscles. Ventricular fibrillation occurred at an average esophageal temperature of 21° C. The flow measurements from the three probes were used to obtain, directly, the abdominal inflow, by subtraction, the splanchnic flow (less renal), by sub•Carolina Medical Electronics, Winston-Salem, N. C. fYellow Springs Instrument Co., Yellow Springs, Ohio.
REGIONAL BLOOD FLOW IN HYPOTHERMIA
Vol. 49, No. 3 March, 1965
313
traction, the renal flow, and, directly, flow below the renals. The flow values on a body-weight basis were plotted on rectilinear coordinates as functions of esophageal temperature. There was in no instance any obvious nonlinearity in the plots obtained, although one might for theoretical reasons expect an ex ponential relationship. Regression lines for each set of data points were cal culated on an IBM 1620 computer by means of the least squares method. Blood pressure values were treated similarly with the addition of the calculation of a regression equation of the second order. Figs. 1-5 show the results in graphic form. Aortic mean pressure was reduced a small amount down to 30° C , then
•
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Fig. 3.—Scattergram of splanchnic flow versus esophageal temperature. Pig. 4.—Scattergram of renal flow versus esophageal temperature. Note the much more rapid rate of decline in this function as compared with that in Fig. 3.
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Fig. 5.—Scattergram of aortic flow below renal arteries versus esophageal temperature.
J. Thoracic and Cardiovas. Surg.
DELIN ET AL.
514
PRESSURE AND FLOWS IN PERCENT OF NORMOTHERMIC
100-
Z U
o tr
50 SPLANCHNIC FLOW AORTIC PRESSURE ABDOMINAL INFLOW FLOW BELOW RENAL RENAL FLOW
40
—I—
—i—
35 25 30 20 ESOPHAGEAL TEMPERATURE "c
Pig. 6.—Superimposed regression lines of all measured parameters In the 10 dogs. All have been expressed as per cent of normothermic. Note the considerable difference between splanchnic and renal flow, the first being above and the second below the lines representing the other two measured flows.
fell more rapidly. All the flows measured fell with the temperature in an ap parently linear fashion, but with different slopes, which are illustrated in Table I and Fig. 6. In Table I a series of fixed temperatures are chosen and the value of the dependent variable, flow or pressure, is found in each instance from the calculated regression line. This value is expressed both in absolute terms and as a percentage of the normothermic value. The per cent values have then been plotted in Fig. 6 to permit a visual comparison between the rate of fall of the various parameters. It is obvious that there is a shift of blood flow toward the splanchnic bed and away from the kidneys as cooling progresses. DISCUSSION
The method used for flow determinations measures directly the flow to large samples of the regions mentioned, the splanchnic, the renal, and the area TABLE
38° c. PARA METERS
NO. OF POINTS
Aortic arch mean pres sure Abdominal inflow Splanchnic flow Eenal flow
66 66
C.C./MIN.
%
107.3 ± 17.5 S.D.
100
I*
30 ' c . 20 ' c. 25 ' c. 35 ' c. c.c./ % O F c.c./ % O F c.c./ % O F c.c./ % O F M I N . 38° c. M I N . 38° c. M I N . 38° c. M I N . 38° c. 105.0 98.0 93.8 87.5 71.5 66.2 37.8 35.2
69.8 ± 100 61.5 88.2 12.6 S.D. 37.6 ± 100 33.8 90.0 66 11.7 S.D. 19.5 ± 100 66 16.5 84.7 4.4 S.D. Flow below 66 12.1 ± 100 10.5 86.9 3.6 S.D. renal •Alteration in regional blood flow with progressive absolute terms (cc./min.) and as percentage of control
47.4
67.8
33.4
47.8
19.8
28.4
27.5
73.2
21.3
56.7
15.0
40.0
11.5
59.1
6.5
33.3
1.54
8.0
66.1
5.4
45.1
2.97 24.5
7.9
hypothermia. Values expressed both in (38°C.)
Vol. 49, No. 3
March, 1965
REGIONAL BLOOD FLOW I N H Y P O T H E R M I A
515
supplied by the distal part of the aorta. It has the disadvantage of requiring a subtraction for the calculation of splanchnic and renal flow, the error in measurement of these two regions being, therefore, possibly double that of the error of the individual measurements. This error should not, however, tend to give any higher or lower average values, but rather widen the distribution of the measurements. The advantages of the method are (1) that the same mea surement technique is used to determine flow to the regions involved in the study as opposed to the clearance techniques which have to be different for different organ system, (2) that the measurement does not depend on organ function, as in the case of clearance techniques, and (3) the flowmeter sensi tivity, and therefore the calibration factor, does not vary with the temperature of the vessel on which the probe is fitted.9 The splanchnic flow region comprises, with our technique, all of the in testinal tract from the stomach down to the left colic flexure and the liver, spleen, and pancreas. The renal region measures kidney flow plus a possible very small contribution to adrenal inflow. The region supplied by the aorta below the renal arteries comprises the lower part of the body, mostly bone, muscle, and skin, but also the descending colon, rectum, bladder, and genitalia. In plotting the data from this study is was realized that flow would be an exponential function of temperature if flow varied directly with the speed of one or more chemical reactions in the tissues. However, under these experi mental conditions, blood flow appeared to be roughly a linear function of temperature reduction. The results of earlier studies are shown in Table II, in which the original information, as far as possible, has been treated in the same manner as in the present study, accepting 38° C. as the normothermic level and expressing the flows as percentages of this level at 35°, 30°, and 25°. As can be seen, both in this presentation of data from earlier investigations and in the present study, the splanchnic flow is relatively less rapidly decreased with temperature than is renal flow, indicating a shift of blood flow away from the kidneys toward the splanchnic region. A comparison of the per cent figures in Table I with the values for ascending aorta flow obtained in another study in this laboratory 2 further substantiates this observation—ascending aorta flow, per cent of normoTABLE I I . COMPILATION OF F L O W DETERMINATIONS BY EARLIER INVESTIGATORS: F L O W S AT T H R E E LEVELS OF HYPOTHERMIA AS P E R C E N T OF NORMOTHERMIC (38° C.)
AUTHOR
REGION STUDIED
METHOD
NO. EXPTS.
38° C. 35° c. 30° c. 25° C.
(%)
(%)
(%)
Morris et al., 1954c Miles & ChurchillDavidson, 1955 5 Mover et al., 1956? Blatteis & Horvath, 19581 ' Westin et al., 1 9 6 1 "
Renal Renal
PAH-elearance PAH-clearance
6
100 100
Renal Renal
PAH-clearance PAH-clearance
6
100 100
Renal
8
100
75
Hallett, 19543 Heimburger et al., 1960* Teramoto, 1962io
Splanchnic Portal
Electro-magnetic flowmeter BSP-clearance Portal vein drain
8 10
100 100
65 78
Splanchnic
Hepatic vein drain
10
100
67
74
50 54 53 53
(%) 30 30
31
516
D E L I N E T AL.
J. Thoracic and Cardiovas. Surg.
thermic (38° C.) : 35° C. (87 per cent), 30° C. (67 per cent), 25° C. (45 per cent), 20° C. (24 per cent). The abdominal inflow and the flow below the renal arteries show similar changes with temperature, whereas splanchnic flow shows less reduction at low temperatures while renal flow shows more reduction. Information was not elicited in this study as to whether the demonstrated shift in blood flow distribution was advantageous or detrimental. SUMMARY
1. Blood flow to the splanchnic region, the kidneys, and to the area sup plied by the aorta below the renal arteries has been measured in normothermia and during progressive hypothermia with an electromagnetic flowmeter. 2. As hypothermia progresses, there is a shift of blood flow away from the kidneys toward the splanchnic region. 3. The splanchnic flow is 40 per cent of normothermic at 20° C. 4. The renal flow is 8 per cent of normothermic a t 20° C. 5. Abdominal inflow and flow in the aorta below the renal arteries are both around 26 per cent of normothermic at 20° C. REFERENCES 1. Blatteis, C. M., and Horvath, S. M.: Renal, Cardiovascular and Respiratory Responses and Their Interrelations During Hypothermia, Am. J . Physiol. 192: 357, 1958. 2. Delin, N . A., Pollock, L., Kjartansson, K. B., and Schenk, W. G., J r . : Cardiac Per formance in Hypothermia, J . THOKACIO & CARDIOVAS. SURG. 4 7 : 774, 1964.
3. Hallett, E . B . : Effect of Decreased Body Temperature on Liver Function and Splanchnic Blood Flow in Dogs, S. Forum 5 : 362, 1954. 4. Heimburger, I., Teramoto, S., and Shumacker, H . B . : Influence of General Hypothermia and Local Gastric Cooling on Portal Blood Flow, Surgery 47: 534, 1960. 5. Miles, B . E., and Churchill-Davidson, H . C : T h e Effect of Hypothermia on the Renal Circulation of the Dog, Anesthesiology 16: 230, 1955. 6. Morris, G. C , Moyer, J . H., Cooley, D. A., and Brockman, H . L . : The Renal Hemodynamic Response to Hypothermia and to Clamping of t h e Aorta With and With out Hypothermia, S. Forum 5 : 219, 1954. 7. Moyer, J . H., Morris, G. C , and De Bakey, M. E . : The Physiology of Induced Hypo thermia, edited b y R. D. Dripps, Publication No. 451, Washington, D. C , National Academy of Sciences, National Research Council, p . 199. 8. Schenk, W. Or., J r . , McDonald, K . E., Camp, F . A., and Pollock, L . : The Measurement of Regional Blood Flow, J . THORACIC & CARDIOVAS. SURG. 46: 50, 1963.
9. Spencer, M. P . , and Denison, A. B . , J r . : Square Wave Electromagnetic Flowmeter for Surgical and Experimental Applications, edited b y H . D. Bruner, m Methods in Medical Research, Chicago, 1960, The Year Book Publishers, Inc., vol. 8, p . 335. 10. Teramoto, S., and Shumacker, H . B., J r . : Hepatic Blood Flow in the Moderately Hypothermic State, J . Surg. Res. 2 : 3, 1962. 11. Westin, B., Sehgal, N., and Assali, N . S.: Regional Blood Flow and Vascular Resistance During Hypothermia in Dog, Am. J . Physiol. 201: 485, 1961.
HYPOTHERMIA
N. Anders Delin, M.D.*
Kjartan B. Kjartansson,
Lawrence Pollock, M.D., and Worthington Buffalo, N.
U
M.D.,
G. Schenk, Jr.,
M.D.,
Y.
conditions of hypotension from blood loss it has beeen found that a preferential shift of blood flow to the kidneys occurs which has been interpreted as a physiological response of protective nature. In hypothermia there is also hypotension with reduction in blood flow, and one might ask whether a similar preferential shift occurs. Search of available reports in the literature indicates that contrary to this assumption there is a shift of blood flow away from the kidneys toward the splanchnic bed during hypothermia of a moderate degree. However, this information is gathered from reports of study of either one but not both of the blood flow regions mentioned. This study presents measurements during progressive hypothermia of abdominal inflow, splanchnic flow, renal flow, and flow below renal arteries by means of a triple-probe electromagnetic flow measurement technique described earlier. 7 NDER
METHOD
Ten adult mongrel dogs of both sexes, weighing 15.9 to 27.2 kilograms (average 21.1 Kg.), were anesthetized with sodium pentobarbital intravenously, (26 mg. per kilogram) intubated, and ventilated with a positive-negative pres sure ventilator with a tidal volume and frequency that kept them somewhat hyperventilated. Shivering was prevented with additional amounts of sodium pentobarbital if needed. Through a retroperitoneal but intrapleural approach, with the dorsal parts of the eleventh and twelfth ribs taken, the abdominal aorta was exposed. All vessels leaving the aorta in this area were localized, the celiac axis, the superior mesenteric artery, and the renal arteries were saved, all others were divided to accommodate one electromagnetic flow-probe t above the celiac axis, one below the superior mesenteric but above the renal arteries, and one below the renal arteries. The probes were connected via a switch-box From the Department of Surgery, State University of New York at Buffalo, and the Edward J. Meyer Memorial Hospital, Buffalo, N. Y. Supported in part by a grant-in-aid from the National Heart Institute (HE-03181) of the U. S. Public Health Service. Received for publication July 15, 1964. •Research Fellow of the United Health Foundation of Buffalo and Erie County. tElectromagnetic Probe Co., Winston-Salem, N. C. 511
J. Thoracic and Cardiovas. Surg.
D E L I N ET AL.
512
to a square-wave electromagnetic flowmeter* which made flow determinations possible from the three probes in rapid sequence. The meter zero position Mas determined by downstream vessel occlusion. Pressure was measured with a Sanborn inductance-type transducer con nected to a catheter introduced via the right brachial artery to the aortic arch. Temperature was measured in mid or low esophagus with a thermistor probe, f Blood stream cooling was used. One shunt, consisting of 1.5 to 2 M. PE-360 polyethylene tubing interposed between carotid artery and jugular vein, and a similar shunt between the femoral artery and vein were coiled and immersed in ice water. Measurements were made before cooling and at intervals during cooling, always with both shunts closed. The experiment was ended when ven tricular fibrillation occurred.
120ISOCO
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35 30 25 20 15 ESOPHAGEAL TEMPERATURE ' C
<
0
40
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1
35 30 25 20 15 ESOPHAGEAL TEMPERATURE *C
Pig. 1.—Scattergram of aortic mean pressure versus esophageal temperature in 10 dogs. The regression curve is part of a parabola which statistically nts better than a straight line. Fig. 2.—Scattergram of flow in the aorta above the celiac axis versus esophageal tempera ture. No tendency to a deviation from a straight line relationship is evident.
RESULTS
The rate of fall of temperature was 0.3° C. per minute at higher tempera tures, falling to 0.15° C. per minute at lower temperatures—a relatively slow cooling which did not produce temperature gradients exceeding 3° C. any where between the esophagus, intracranial space, aortic blood, rectum, or front and hind leg muscles. Ventricular fibrillation occurred at an average esophageal temperature of 21° C. The flow measurements from the three probes were used to obtain, directly, the abdominal inflow, by subtraction, the splanchnic flow (less renal), by sub•Carolina Medical Electronics, Winston-Salem, N. C. fYellow Springs Instrument Co., Yellow Springs, Ohio.
REGIONAL BLOOD FLOW IN HYPOTHERMIA
Vol. 49, No. 3 March, 1965
313
traction, the renal flow, and, directly, flow below the renals. The flow values on a body-weight basis were plotted on rectilinear coordinates as functions of esophageal temperature. There was in no instance any obvious nonlinearity in the plots obtained, although one might for theoretical reasons expect an ex ponential relationship. Regression lines for each set of data points were cal culated on an IBM 1620 computer by means of the least squares method. Blood pressure values were treated similarly with the addition of the calculation of a regression equation of the second order. Figs. 1-5 show the results in graphic form. Aortic mean pressure was reduced a small amount down to 30° C , then
•
75-
SD- 11.7
SD-4-.39
50.
•
25-
^
0 40
<
^
35 30 25 20 15 ESOPHAGEAL TEMPERATURE *C
40
35
30
25
20
15
ESOPHAGEAL TEMPERATURE *C
Fig. 3.—Scattergram of splanchnic flow versus esophageal temperature. Pig. 4.—Scattergram of renal flow versus esophageal temperature. Note the much more rapid rate of decline in this function as compared with that in Fig. 3.
SD-3.58
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25-
4
-I
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20
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°. " * ° 10 o
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—i— —r— 30 20 15 225 5 ESOPHAGEAL TEMPERATURE *C 35
Fig. 5.—Scattergram of aortic flow below renal arteries versus esophageal temperature.
J. Thoracic and Cardiovas. Surg.
DELIN ET AL.
514
PRESSURE AND FLOWS IN PERCENT OF NORMOTHERMIC
100-
Z U
o tr
50 SPLANCHNIC FLOW AORTIC PRESSURE ABDOMINAL INFLOW FLOW BELOW RENAL RENAL FLOW
40
—I—
—i—
35 25 30 20 ESOPHAGEAL TEMPERATURE "c
Pig. 6.—Superimposed regression lines of all measured parameters In the 10 dogs. All have been expressed as per cent of normothermic. Note the considerable difference between splanchnic and renal flow, the first being above and the second below the lines representing the other two measured flows.
fell more rapidly. All the flows measured fell with the temperature in an ap parently linear fashion, but with different slopes, which are illustrated in Table I and Fig. 6. In Table I a series of fixed temperatures are chosen and the value of the dependent variable, flow or pressure, is found in each instance from the calculated regression line. This value is expressed both in absolute terms and as a percentage of the normothermic value. The per cent values have then been plotted in Fig. 6 to permit a visual comparison between the rate of fall of the various parameters. It is obvious that there is a shift of blood flow toward the splanchnic bed and away from the kidneys as cooling progresses. DISCUSSION
The method used for flow determinations measures directly the flow to large samples of the regions mentioned, the splanchnic, the renal, and the area TABLE
38° c. PARA METERS
NO. OF POINTS
Aortic arch mean pres sure Abdominal inflow Splanchnic flow Eenal flow
66 66
C.C./MIN.
%
107.3 ± 17.5 S.D.
100
I*
30 ' c . 20 ' c. 25 ' c. 35 ' c. c.c./ % O F c.c./ % O F c.c./ % O F c.c./ % O F M I N . 38° c. M I N . 38° c. M I N . 38° c. M I N . 38° c. 105.0 98.0 93.8 87.5 71.5 66.2 37.8 35.2
69.8 ± 100 61.5 88.2 12.6 S.D. 37.6 ± 100 33.8 90.0 66 11.7 S.D. 19.5 ± 100 66 16.5 84.7 4.4 S.D. Flow below 66 12.1 ± 100 10.5 86.9 3.6 S.D. renal •Alteration in regional blood flow with progressive absolute terms (cc./min.) and as percentage of control
47.4
67.8
33.4
47.8
19.8
28.4
27.5
73.2
21.3
56.7
15.0
40.0
11.5
59.1
6.5
33.3
1.54
8.0
66.1
5.4
45.1
2.97 24.5
7.9
hypothermia. Values expressed both in (38°C.)
Vol. 49, No. 3
March, 1965
REGIONAL BLOOD FLOW I N H Y P O T H E R M I A
515
supplied by the distal part of the aorta. It has the disadvantage of requiring a subtraction for the calculation of splanchnic and renal flow, the error in measurement of these two regions being, therefore, possibly double that of the error of the individual measurements. This error should not, however, tend to give any higher or lower average values, but rather widen the distribution of the measurements. The advantages of the method are (1) that the same mea surement technique is used to determine flow to the regions involved in the study as opposed to the clearance techniques which have to be different for different organ system, (2) that the measurement does not depend on organ function, as in the case of clearance techniques, and (3) the flowmeter sensi tivity, and therefore the calibration factor, does not vary with the temperature of the vessel on which the probe is fitted.9 The splanchnic flow region comprises, with our technique, all of the in testinal tract from the stomach down to the left colic flexure and the liver, spleen, and pancreas. The renal region measures kidney flow plus a possible very small contribution to adrenal inflow. The region supplied by the aorta below the renal arteries comprises the lower part of the body, mostly bone, muscle, and skin, but also the descending colon, rectum, bladder, and genitalia. In plotting the data from this study is was realized that flow would be an exponential function of temperature if flow varied directly with the speed of one or more chemical reactions in the tissues. However, under these experi mental conditions, blood flow appeared to be roughly a linear function of temperature reduction. The results of earlier studies are shown in Table II, in which the original information, as far as possible, has been treated in the same manner as in the present study, accepting 38° C. as the normothermic level and expressing the flows as percentages of this level at 35°, 30°, and 25°. As can be seen, both in this presentation of data from earlier investigations and in the present study, the splanchnic flow is relatively less rapidly decreased with temperature than is renal flow, indicating a shift of blood flow away from the kidneys toward the splanchnic region. A comparison of the per cent figures in Table I with the values for ascending aorta flow obtained in another study in this laboratory 2 further substantiates this observation—ascending aorta flow, per cent of normoTABLE I I . COMPILATION OF F L O W DETERMINATIONS BY EARLIER INVESTIGATORS: F L O W S AT T H R E E LEVELS OF HYPOTHERMIA AS P E R C E N T OF NORMOTHERMIC (38° C.)
AUTHOR
REGION STUDIED
METHOD
NO. EXPTS.
38° C. 35° c. 30° c. 25° C.
(%)
(%)
(%)
Morris et al., 1954c Miles & ChurchillDavidson, 1955 5 Mover et al., 1956? Blatteis & Horvath, 19581 ' Westin et al., 1 9 6 1 "
Renal Renal
PAH-elearance PAH-clearance
6
100 100
Renal Renal
PAH-clearance PAH-clearance
6
100 100
Renal
8
100
75
Hallett, 19543 Heimburger et al., 1960* Teramoto, 1962io
Splanchnic Portal
Electro-magnetic flowmeter BSP-clearance Portal vein drain
8 10
100 100
65 78
Splanchnic
Hepatic vein drain
10
100
67
74
50 54 53 53
(%) 30 30
31
516
D E L I N E T AL.
J. Thoracic and Cardiovas. Surg.
thermic (38° C.) : 35° C. (87 per cent), 30° C. (67 per cent), 25° C. (45 per cent), 20° C. (24 per cent). The abdominal inflow and the flow below the renal arteries show similar changes with temperature, whereas splanchnic flow shows less reduction at low temperatures while renal flow shows more reduction. Information was not elicited in this study as to whether the demonstrated shift in blood flow distribution was advantageous or detrimental. SUMMARY
1. Blood flow to the splanchnic region, the kidneys, and to the area sup plied by the aorta below the renal arteries has been measured in normothermia and during progressive hypothermia with an electromagnetic flowmeter. 2. As hypothermia progresses, there is a shift of blood flow away from the kidneys toward the splanchnic region. 3. The splanchnic flow is 40 per cent of normothermic at 20° C. 4. The renal flow is 8 per cent of normothermic a t 20° C. 5. Abdominal inflow and flow in the aorta below the renal arteries are both around 26 per cent of normothermic at 20° C. REFERENCES 1. Blatteis, C. M., and Horvath, S. M.: Renal, Cardiovascular and Respiratory Responses and Their Interrelations During Hypothermia, Am. J . Physiol. 192: 357, 1958. 2. Delin, N . A., Pollock, L., Kjartansson, K. B., and Schenk, W. G., J r . : Cardiac Per formance in Hypothermia, J . THOKACIO & CARDIOVAS. SURG. 4 7 : 774, 1964.
3. Hallett, E . B . : Effect of Decreased Body Temperature on Liver Function and Splanchnic Blood Flow in Dogs, S. Forum 5 : 362, 1954. 4. Heimburger, I., Teramoto, S., and Shumacker, H . B . : Influence of General Hypothermia and Local Gastric Cooling on Portal Blood Flow, Surgery 47: 534, 1960. 5. Miles, B . E., and Churchill-Davidson, H . C : T h e Effect of Hypothermia on the Renal Circulation of the Dog, Anesthesiology 16: 230, 1955. 6. Morris, G. C , Moyer, J . H., Cooley, D. A., and Brockman, H . L . : The Renal Hemodynamic Response to Hypothermia and to Clamping of t h e Aorta With and With out Hypothermia, S. Forum 5 : 219, 1954. 7. Moyer, J . H., Morris, G. C , and De Bakey, M. E . : The Physiology of Induced Hypo thermia, edited b y R. D. Dripps, Publication No. 451, Washington, D. C , National Academy of Sciences, National Research Council, p . 199. 8. Schenk, W. Or., J r . , McDonald, K . E., Camp, F . A., and Pollock, L . : The Measurement of Regional Blood Flow, J . THORACIC & CARDIOVAS. SURG. 46: 50, 1963.
9. Spencer, M. P . , and Denison, A. B . , J r . : Square Wave Electromagnetic Flowmeter for Surgical and Experimental Applications, edited b y H . D. Bruner, m Methods in Medical Research, Chicago, 1960, The Year Book Publishers, Inc., vol. 8, p . 335. 10. Teramoto, S., and Shumacker, H . B., J r . : Hepatic Blood Flow in the Moderately Hypothermic State, J . Surg. Res. 2 : 3, 1962. 11. Westin, B., Sehgal, N., and Assali, N . S.: Regional Blood Flow and Vascular Resistance During Hypothermia in Dog, Am. J . Physiol. 201: 485, 1961.