blood through a dog's kidney either in situ or removed from (From the Physiology Institute, Cardiff.)

Transcription

1 6i x SOME OBSERVATIONS ON THE PERFUSION OF THE ISOLATED KIDNEY BY A PUMP. BY A. HEMINGWAY. (From the Physiology Institute, Cardiff.) MANY endeavours to perfuse the kidney by a pump have been unsuccessful judged by two standards. In the first place there has been difficulty in securing an adequate blood flow through the kidney, since the organ may respond to the artificial conditions of the circulation by a considerable constriction of its vessels; and secondly, the kidney with blood flowing through it may not form urine. Cushny [1926] states that the rate of blood flow through the mammalian kidney is in the region of 2 c.c. per g. of tissue per minute, and this opinion is supported by many observers who have reported figures for renal blood flow in the intact animal, chiefly the cat and the dog. Starling and Verney [1925] in many experiments with the heart-lung-kidney preparation recorded flows much in excess of this estimate. But in very few experiments where the kidney has been perfused by a pump have flows of a similar magnitude been obtained, as is noted by Eichholtz and Verney [1924], who themselves were unable to perfuse in this way any defibrinated blood through a dog's kidney either in situ or removed from the body. One explanation of the difficulty of maintaining an adequate flow of blood through the kidney (or any other organ) by artificial means is that defibrinated blood rapidly develops vaso-constrictor properties. Passage of such blood through lung tissue results in loss of the "toxic " properties [Eichholtz and Verney, 1924; Herrick and Markowitz, 1929], and for this reason the heart-lung preparation is so successful when used as a perfusing agent. But a perfusion carried on by a pump and employing lung tissue to oxygenate the blood should, besides having other advantages, avoid this difficulty. In the experiments to be described this problem of the development of vaso-constrictor properties in defibrinated blood and the part played by the lungs in " detoxicating " such blood has been re-investigated. In them the perfused kidney is supplied with blood by a pump, the per- PH. LXXI. 14

2 202 A. HEMINGWAY. fusion rate being measured, while venous blood is collected and perfused under hydrostatic pressure through isolated lungs. By this arrangement E Fig. 1. Diagram of perfusion apparatus. Description in text. Details of Dixon pump and flow recorder are not shown. the pulmonary flow must be equal to the flow in the kidney, and the disadvantage inherent in methods in which a second pump is used for the pulmonary circuit [Dale and Schuster, 1928; Jacoby, 1928] is avoided.

3 KIDNEY PERFUSION. 203 DESCRIPTION OF APPARATUS. (a) General arrangement. The arrangement of the apparatus is shown in Fig. 1. A is a glass reservoir containing blood and kept in a water bath maintained at a suitable temperature. Blood from the reservoir is taken by the pump B, and after passing through the flow recorder D (to be described later) is perfused through the kidney. The kidney may however be short-circuited by passing blood directly to the lungs through the tube C. Venous blood, collected in a funnel placed above the reservoir, is oxygenated by perfusion through lungs placed in the reservoir chamber. The lungs are removed from the animal supplying the kidney after perfusion of this organ has been commenced. Inflation and deflation of the lungs is caused by varying a negative pressure inside the chamber A, and inspired and expired air separated by Muller valves V1, V2. The funnel supporting the kidney and the tube leading from the reservoir to the pump have water jackets supplied with warm water from the main bath by an "Autopulse " E. (b) The pump. The pump consists of a T-shaped glass chamber; the head 9 cm. in length and 1*5 cm. internal diameter; the leg 7 cm. in length and 2 cm. internal diameter. Blood passes along the direction of the head which is furnished with valves. The seating of these consists of shallow cylinders of rubber, the ends being cut at right angles to the central hole while the rubber is spun in the lathe. Circular discs of thin sheet rubber 1 cm. in diameter are cemented under pressure along 5 mm. of their periphery to the seating. If the latter is cut true a perfectly fitting valve is obtained. The leg of the T contains a rubber finger-stall held in place by a rubber stopper. Connection is made through the stopper to the syringe of a Dix o n pump [Dixon, 1922]. The piston of the syringe (Record type) is carefully ground to avoid leakage, and so movements of the pump alternately inflate and deflate the finger-stall with air. Considerable elasticity is given to the vascular circuit by employing this type of pump, which further possesses a certain measure of adjustment to changes in the conditions of circulation. For instance, an increased resistance to perfusion such as that brought about by vasoconstriction leads to a slight diminution in the output of the pump due to compression of air in the transmission system, and so the rise in perfusion pressure is smaller than it would be if a rigid pump system with 14-2

4 204 A. HEMINGWAY. a constant output was employed. This adjustment to circulatory changes coupled with ability to alter the stroke of the pump while it is working make it easily possible to maintain a constant perfusion pressure throughout an experiment. If this is done, then changes in the vascular pathway of the kidney may be recorded solely as changes in flow. Alternatively, the rate of blood flow may be kept constant against changing resistances. (c) The flow recorder. The flow recorder is a modification of the original St o lni ko v type adapted for automatic reversal of the flow through the stromuhr by electro-magnetic clamping of the tubes. Such a device is not new, and an automatic method of control was described by Pavlov [1887]. Recently, Montgomery and Lipscomb [1929] have introduced a new method of alternating the direction of flow in the chambers of the stromuhr. Instead of placing the two chambers in direct communication with each other, a U-tube is interposed between them, each limb of the tube being similar in shape and capacity to the stromuhr chambers. The lower half of the U-tube is filled with saturated copper sulphate solution, while each upper half and corresponding portions of the stromuhr are filled with liquid paraffin. Movement of blood in the stromuhr causes a corresponding movement of paraffin and sulphate solution. The excursion of the latter limits the extent of the movement, for, by coming into contact with electrodes, electrical circuits are completed which control the position and movement of the stromuhr clamp and reverse the direction of flow. Since no description of the original model demonstrated by the authors appears to be available, certain constructional details and points in working are here given. Four stromuhr chambers of the shape shown in Fig. 2 are employed. They have a capacity of 40 c.c. Two form the stromuhr proper and are connected at their lower ends to the tubes passing to the electromagnetic clamp. The details of such a clamp are given by Barcroft; [1929]. The other two chambers are connected to form the U-tube. Three electrodes of 20 B.W.G. copper wire are introduced into the U-tube, one at the lowest point and one in each of the upper shoulders. As oil is displaced from one stromuhr chamber by the entry of blood, the copper sulphate solution rises in one limb of the U-tube, and eventually makes contact with the upper electrode. A small current of the order of 15 milliamps. passes through the copper sulphate column and energizes one pole of a G.P.o. double pole polarized type relay. Working through

5 KIDNEY PERFUSION. 205 a secondary relay the G.P.O. relay breaks the current on one side of the electro-magnet clamp and energizes the other, so that the clamp is changed over and the stromuhr flow reversed. A signal wired in series with the windings of one of the secondary relays marks the point of change on the kymograph tracing. The polarized relay keeps the secondary relay and clamp magnets in action until the opposing contact is made in the stromuhr. Polarization of electrodes is prevented by using Fig. 2. Diagram of Montgomery-Lipscomb flow recorder with arrangements for working directly on 200 V. D.C. supply. the copper/copper sulphate system, and electrolysis and disappearance of the electrodes take place very slowly with the small current passed. By adjustment of the amount of copper sulphate solution in the apparatus the rate of reversal of the stromuhr may be made suitable to the magnitude of the flow. Current for the relays and the magnets is most conveniently taken from the mains and limited by resistances placed in series with the coils. Suitable values for working from D.C. mains are given in the diagram.

6 206 A. HEMINGWAY. (d) Perfusion of the lungs. Blood which issues from the kidney through the cut end of the renal vein is collected into a funnel which communicates with a cannula in the pulmonary artery. A sufficient head of pressure for the perfusion of the lungs is obtained by placing the funnel 80 cm. above the cannula. It is necessary to maintain blood in the funnel and prevent it emptying, otherwise air bubbles would be introduced into the pulmonary stream. This is achieved by interposing a regulating clamp on the tube between funnel and cannula. Its action will be made clear by reference to Fig. 1. The level of blood in the funnel is balanced by a mercury manometer, and any increase in height above a pre-fixed point completes an electrical circuit. This, acting through a relay, releases the clamp, which is of an electro-magnetic type and permits blood to leave the funnel and flow through the lungs. The actual perfusion pressure is about 24 cm. saline. In use, the alternate opening and closing of the clamp set up oscillations of the mercury in the manometer. These movements minimize any disadvantages due to the lag of the mercury column and its small range of movement compared with the blood level in the funnel, and, increasing the rate at which the electrical circuit is made and broken, set up a rhythmic alternation in the pulmonary flow. METHOD OF SETTING UP THE PREPARATION. One dog weighing kg. is sufficient to supply the blood, lungs and kidney requisite for the experiment. The animal after being anmesthetized with chloroform and ether mixture is bled. About 350 c.c. of blood are usually taken and whipped. After filtering through double thicknesses of muslin, the blood, which has been kept warm, is introduced into the apparatus, the stromuhr filled and the clamp for regulating the pulmonary flow brought into operation with blood passing from funnel to reservoir by tube R. While this is being done about 400 c.c. of saline are injected intravenously and diuresis induced. The left kidney is then excised following the technique of Starling and Verney, but without cleaning the renal artery, and the perfusion is commenced. Provided the operations are performed rapidly, so that the time available for the development of toxic properties in the standing blood is minimal, a considerable blood flow through the kidney may be established and maintained until the lungs can be added to the circuit and detoxication performed. The lungs are next prepared for perfusion. The chest is opened and

7 KIDNEY PERFUSION. 207 a cannula introduced into the pulmonary artery through a slit in the base of the right ventricle. After washing out the lungs with saline so that very little stagnant blood remains, the cannula is clamped and the apex of the heart cut across to permit the escape of blood from the left auricle. A tracheal cannula is inserted and lungs, trachea and heart are removed from the thorax. Both the pulmonary arterial cannula and the tracheal cannula pass through a rubber bung which fits the mouth of the blood reservoir, making it airtight and available for negative pressure ventilation. The lungs are transferred to the reservoir and, avoiding introduction of air bubbles, perfusion of the lungs is commenced by clamping tube R and opening tube S. A gas mixture containing about 5 p.c. CO2 is used for ventilating the lungs. Any small clots or particles which may try to circulate are caught up on muslin filters placed in the funnel and the base of the reservoir. EXPERIMENTAL. (a) The r6le of the lungs in "detoxicating" defibrinated blood. Preliminary experiments demonstrated that defibrinated blood, which had been standing, caused vaso-constriction if added to blood already perfusing lungs and kidney. The action lasted for 5 or 10 minutes before detoxication took place, depending upon the intensity of the reaction and the original rate of blood flow. There was no difference between the action of blood which had been merely allowed to stand since withdrawal from the animal and that which had been circulated in the perfusion system prior to standing. Toxic properties develop gradually, and a slight reaction may usually be demonstrated after about 2 minutes' stagnation. Since the lungs are able to remove the vaso-constrictor principles, experiments were performed to determine whether or not defibrinated blood had a constrictor action on the pulmonary vessels themselves. The lungs were fixed in the reservoir chamber but, instead of perfusing by the gravity feed, the pulmonary cannula was attached to the pump and the lungs perfused at a pressure of 26 cm. saline and a flow of about 300 c.c. per minute. Defibrinated blood either from the animal or from the perfusion system, after being allowed to stand, showed a vasoconstrictor action on the pulmonary vessels when added to the blood in the reservoir. But the effect was not of long duration. For instance, 140 c.c. of blood which had been standing in a thermos flask for 30 minutes, when added to 250 c.c. of perfusing blood, caused a constriction which lasted for only 2 minutes. From these experiments it would seem

8 208 A. HEMINGWAY. likely that the lungs alone might be responsible for the removal of toxic properties. But the possibility of the kidney playing some part is not excluded, although it is impossible to make any good comparison between the two tissues because of the differences they present in resistance to perfusion and in the degree of their response to other vaso-constrictor substances. Perfusion at a low pressure is sufficient to set up a large flow through the lungs, which is only slightly reduced by defibrinated blood. Thus a large volume of blood can be circulated through the lungs and "detoxicated" in a short time. A tissue, such as the kidney, if it possesses a considerable resistance, may have little detoxicating power because of its relatively small blood flow. It is perhaps for this reason that the lungs are regarded as the chief detoxicating agent for defibrinated blood. But in the early phases of some experiments when a large kidney (40-50 g.) was being perfused, the renal blood flow began to increase before the lungs were incorporated in the circuit. Thus, in one experiment, when the kidney had been perfused for 2 minutes at a pressure of 90 mm. Hg the flow was 132 c.c. per minute. Two minutes later it had increased to 160 c.c. per minute, and 6 minutes later was over 190 c.c. per minute. At this point the lungs were added to the circuit, and there was a diminution in renal flow due no doubt to the presence of small quantities of stagnant blood in the lungs. The flow then increased and ultimately became steady between 177 and 184 c.c. per minute, the pressure being constant all the time. The increase in flow through the kidney before the lungs were added to the circuit might have been due in part to the removal of toxic materials, and in part to the production and accumulation of CO2 in the blood, as is suggested by the smaller flow with the lungs in circuit and the blood aerated. It shows definitely, however, that the kidney can be perfused in the absence of any circulation through lung tissue. But, though the blood might be oxygenated by other means, the incorporation of the lungs brings many advantages. In the preparation here described, and in the heart-lungkidney preparation, the blood supply to the kidney may be shunted and the blood rapidly detoxicated if necessary by passing through the lungs many times before any portion reaches the kidney. (b) Effect of removing the lungs from the perfusion circuit. In ten experiments the lungs were removed from the perfusion circuit after a steady renal blood flow had been established, and on no occasion did the blood develop toxic properties.

9 KIDNEY PERFUSION. To cut out the lungs, blood was diverted from tube S and the pulmonary cannula into tube R (Fig. 1) which led directly to the reservoir. Results from two typical experiments are given in Table I and Fig. 3. TABLE I. Effect of removing lungs from circulation. Lungs out Weight of kidney 52 g. C0) in expired air 2*3 p.c. Temperature of perfusing blood 38 C. Blood Blood flow, A Time (c.c./min.) 0, P.C. CO2 P.C Lungs out of circuit * Lungs in circuit During the first experiment samples of blood for estimation of 02 and CO2 were taken immediately before and during the period when the lungs were excluded from the circulation. Both experiments demonstrate that there is no immediate change in the renal blood flow following the removal of the lungs beyond a slight vaso-constriction due to blood which has been standing in the connecting tubes being washed into the reservoir and circulated. After about 5 minutes and until the end of the period there is a slight increase in blood flow indicating a fall in resistance. This is also additionally demonstrated in Fig. 3 by a slight fall in blood-pressure. Anoxeemia and accumulation of C02 are no doubt the cause of the vaso-dilatation, for the blood becomes much darker in colour within 5 minutes, and the blood estimations given in Table I show that, in this experiment, the 02 content fell from 18-4 vols. p.c. to 14'5 while the C02 content rose from 31*2 vols. p.c. to FORMATION OF URINE BY THE KIDNEY. Over forty experiments have been performed in which the kidney has excreted a fluid which is undoubtedly urine. The specimens obtained in the early phases of an experiment are straw coloured, but the later ones are paler. At the commencement the urine is acid (ph 6.8) but gradually becomes alkaline (ph 8.0). There is no protein present. In a

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11 KIDNEY PERFUSION. 211 few experiments where there was delay in establishing the renal circulation or where the blood flow was interrupted, traces of albumin and haemoglobin have occurred in late specimens, but this is exceptional I "600_ Z c 800 Q ] I120 B 100mm.Hg 120 Blood flow 1 00 c.c./min.,_t ~~~- OBlood chloride \ Urine chloride Urine urea s = 12-0 or 10 _ H 1-0j?:- - 8 cj - I 0 1' Minutes Fig. 4. Effect of adding urea to circulating blood. 1 g. of urea in 5 c.c. of saline added to blood at point shown by arrow. The rate of urine formation varies as expected with changes in the pressure of the perfusing blood. Chlorides (estimated by Volhard's method) are present usually in a concentration lower than that in the plasma, although in four experiments, including the one described below, it has been higher. The chloride concentration gradually falls away during an experiment,

12 212 A. HEMINGWAY. though it does not appear to do so as rapidly as in the urine obtained in the heart-lung-kidney preparation. Urea (estimated by the urease method) is present in the urine in a higher concentration than in the plasma. Fig. 4 depicts the course of a typical experiment and shows the diuresis consequent upon the addition X1 30[ * *150r IPressure increased 6 500,0740 L / Z 300 L Jf Minutes Fig. 5. Action of pituitary extract. 005 c.c. Parke Davis's "Pituitrin" added to 400 c.c. blood. Pressure controlled by adjustment of pump. Weight of kidney 30 g. Temp. 380 C. of 1 g. of urea in 5 c.c. of saline to the circulating blood. During the diuresis there is an increase in the concentration and total amount of chloride excreted. The action of pituitary extract. The response of the perfused kidney to this should be a good test of its viability. Since the concentration of chloride in the urine formed by this preparation never falls so low as it does in the urine from the heartlung-kidney preparation, pituitary extract has not so good a background

13 KIDNEY PERFUSION. on which to show its action. Nevertheless, the addition of small quantities (0.05 c.c. Parke Davis's "Pituitrin") of the extract has always caused a diminution in blood flow, a diminution in the rate of urine formation and an increase in the chloride concentration of the urine. The results of an experiment are shown in Fig. 5. The perfusion pressure was kept constant by adjustment of the stroke of the pump. SUMMARY. 1. A method of perfusing the isolated dog's kidney with a pump is described. 2. The part played by the lungs in "detoxicating" defibrinated blood is discussed and experiments described in which the kidney has been perfused in the absence of lung tissue. 3. The kidney forms urine and responds to urea and pituitary extract. REFERENCES. Barcroft, H. (1929). J. Phy8iol. 67, 402. Cushny, A. R. (1926). Secretion of the Urine, p. 43. Dale, H. H. and Schuster, E. H. J. (1928). J. Phy8iol. 64, 356. Dixon, W. E. (1922). J. Phy8iol. 56, Proc. p. xl. Eichholtz, F. and Verney, E. B. (1924). J. Physiol. 59, 340. Herrick, J. F. and Markowitz, J. (1929). Amer. J. Phy8iol. 88, 698. Jacoby, C. (1928). Arch. exp. Path. Pharmak. 136, 203. Montgomery, M. L. and Lipscomb, T. H. (1929). Amer. J. Phy8iol. 90, 454. Pavlov, I. P. (1887). Arch. Anat. Pharmak. 7, 452. Starling, E. H. and Verney, E. B. (1925). Proc. Roy. Soc. B, 97,