Barnard, C.N.

de Villiers, D.R.

Mckenzie, M.B.

English

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S.A. TYDSKRIF VIR GENEESKUNDE10 Oktober 1959I wish to thank the Medical Superintendent of the EmestOppenheimer Hospital, Dr. T. Leontsinis, for helpfulsuggestions and criticism in the preparation of this paper, andam indebted to him and to the Medical Consultant of theAnglo American Corporation for permission to publish thesecases. My thanks are also due to the medical staff and thelaboratory technologists of the hospital for their cooperation andassistance.859REFERENCESt. Kollf, W. J. (1957): Circulation, 2, 285.2. Joekes, A. M. (1958): Proc. Roy. Soc. Med., 12, 1069.3. KoHl', W. J. and Watsehinger, B. (1956): J. Lab. Clin. Med., 6, 969.4. Merrill, J. (1955): TTearmem af Renal Failure. ew York: Grune andStratton.5. Moore, J. (1958): Brit. Med. J., 2, 120t.6. Jackson, R. C. (1958): Proc. Roy. Soc. Med., 21, 107t.7. Seldinger, S. J. (1953): Acta. radiol., 39, 368.8. Ludbrook, J. (1958): Brit. Med. J., 2, 523. ~9. Indar, R. (1959): Lance!, 1, 284.THE ELECTRICAL PULSE DUPLICATOR-ITS USE IN TESTING VALVE PROS-THESES WITH SPECIAL REFERENCE TO THE AORTIC AND MITRAL VALVESc. . BARNARD, M.D., M.MED. (CAPE TOWN), M.S., PH.D. (MlN fESOTA); M. B. MCKENZIE, M.B., CH.B. (CAPE TovVN);and D. R. DE VILLIERS, M.Sc., M.B., CH.B. (CAPE Tow. ,) Department of Surgery, University of Cape Towno1Fig. 1. Diagram of the electrical pulse-duplicator.perfusion fluid for photographic purposes, and the waterpressure in the tap provides inexpensive power for thepulsator. The second limb leads off to a drain through asecond solenoid valve C, of similar diameter.The two solenoid valves are electrically activated. Therate, and systole-diastole ratio corresponding to differentrates, are controlled by two switches on control box D.This control system is constructed in such a manner thatthe one solenoid valve is open while the other is shut andvice versa. The third limb of the metal tube is connectedto the testing chamber, which varies with each valve to betested and the type of test done.Testing Chambers for Aortic-valve ProsthesesIn order to test an aortic-valve prosthesis, the duplicatoris connected to two chambers, A and B, manufactured fromquarter-inch-thick plexiglass (Fig. 2). These two chambersare separated by a disc C, in which the valve to be tested isinserted. It is possible to unscrew chamber A from chamberB, and also to unscrew the lid of chamber B, thus allowinginsertion of the valve and operation on the valve once it isin position.purpose is illustrated in Fig. 1. This apparatus consists ofa T-tube A, 1 inch in diameter. One limb of this tube isconnected through a solenoid valve B, 1 inch in diameter,to a water tap. Water was found to be the most satisfactoryProgress in modem open heart surgery and the use ofcardioplegic drugs,loa retrograde perfusion of the coronarysinus; or other means of supporting the myocardium duringcross-clamping' of the ascending aorta, has made directsurgery on any of the four valves of the heart possible. Atpresent there appears to be general agreement that the idealcorrection of acquired valvular defects awaits the developmentof suitable prosthetic valves.Before a prosthesis of any design can be used for thecorrection of a valvular defect in patients it should fulfil thefollowing criteria:(a) The prosthesis should be of such design that it can beinserted and secured in the limited space that exists in theannulus of the valve to be corrected.(b) It should function freely under the conditions whichexist at that particular point of the circulation and continueto function for many years.(c) It should be tolerated within the circulation; that is tosay, it should not be extruded as a foreign body.(d) It should not damage the elements of the blood orthe heart itself, or promote clotting of the blood with em-bolization.Part of the work in testing fabricated prosthetic valvesthus necessitates the study of valvular mechanics by dynamicdemonstration of the action of these valves. ·If this is doneunder hydrodynamic conditions, similar to those presentduring life, such an investigation will determine whether thevalve being tested will function freely and adequately whenused for the correction of valvular insufficiency. By leavingthe prosthetic valve to function under these conditions forlong periods of time at speeds of 120 -150 cycles per minute,fatigue can be studied, giving useful information on how thevalve will withstand the systolic and diastolic forces through-out life.The purpose of this paper is to describe a method by whichprostheses for the correction of regurgitant aortic and mitralvalves can be tested in a pulse duplicator to determine whetherthey fulfil some of the criteria listed above.APPARATUSThe Electrical Pulse DuplicatorThe 0 important part of an apparatus used in testingprosthetic valves for the left side of the heart is a pulseduplicator capable of producing a pulsatile flow of fluidcomparable in volume and pressure to the stroke of the leftventricle, An electrical pulse duplicator used by us for this860 S.A. MEDICAL JOURNAL 10 October 1959A3Abase of aorta""sa-<::~Ivalon strip~~~~r------'---..L...,oIn order to observe whether the valve to be tested can besecured in the root of the aorta and whether it will functionfreely, the base of the aorta together with the aortic valveand half an inch of ventricular muscle and the aortic leafletof the mitral valve are excised from a post-mortem humanheart (preferably from a patient who died of aortic regurgi-tation) and attached between two strips of Ivalon as shownin Fig. 3A. When the purpose of the test is to see howlong the prosthesis will last when subjected to forces similar\~=~from duplicatorSink 2Fig. 2. Diagram of the testing chamber for studying theaortic valve.to those in the circulation, it is set up as shown in Fig. 3Battached to a strip of Ivalon overlying an opening approxi-mately the size and shape of the aortic valve in mid-cycle.After the chambers have been screwed together with avalve in position the only connection between them isthrough the valve.An inverted plastic V-tube D, 1 inch in diameter, is attachedto the top chamber (Fig. 2). The length of the ascendinglimb of this tube can be adjusted so that, when filled withwater, the desired pressure is exerted on the valve. Thedescending limb is connected by way of a compressiblerubber tube to the water drain. The pressure in this tubecan thus be adjusted further by partially clamping the rubbertube. This, in conjunction with the air trapped in the descend-ing limb, will allow of elastic resistance simulating theperipheral resistance in the human circulation.Testing Chambers for Mitral-valve ProsthesesWhen testing a mitral-valve prosthesis for strength anddurability, the assembly is the same as for the aortic valveexcept that chamber A now has an outlet which leads to thedrain (the aortic outflow) and chamber B, instead of theinverted U tube, has an adjustable water supply (pulmonaryveins supplying left atrium)-Fig. 4A. The valve to beFig. 3. Diagram showing the method of fixation of the aorticvalve in the testing chamber: (A) For studying valve action.(B) For studying durability of the valve.tested is secured in the manner described above in a pieceof Ivalon. In order to see whether the prosthesis can besecured in the mitral annulus and whether it will functionfreely, the apparatus is set up as shown in Fig. 4B. A freshhuman heart is removed at post-mortem (preferably from apatient who died of mitral regurgitation). The roof of theleft auricle is excised below the entrance of the pulmonaryveins. The left auricular appendage is ligated at its baseand a linen purse-string suture is placed around the circum-Ato drain",.\~~~from duplicator 4AFig. 4A. Diagram of testing chamber as used for the study ofthe durability of a mitral prosthesis.Fig. 4B. Diagram showing the apparatus used for the studyof the mitral valve.S.A. TYDSKRIF VIR GENEESKUNDE10 Oktober 1959 861rand the system filled with water, expelling all the air. Whenthis is complete the control box is switched on and the speedand systole-diastole ratio adjusted to give the desired rhythmof pulsation. The pressure changes in the two chambers(left ventricle and aorta) are measured by connecting tapsa 1 and bI to a pressure-recording device. By adjusting theFig. 6. Cycle of normal aortic-valve movements showing theopening and subsequent closure.water inflow, the height of the ascending limb of the invertedV-tube, and the resistance in the descending limbs, the outputper minute and pressure changes closely simulating those inthe human circulation can be obtained (Fig. 5). The actionof the valve can be observed and photographed through thetop of chamber B (Fig. 6).Mitral valve. The testing chambers are connected asdescribed and connected to the pulse duplicator. The systemis filled with water as for the aortic valve, systole and diastoleadjusted, and pressures recorded in the top and bottomchambers (left auricle and left ventricle). The diastolic lossof fluid from the viewing chamber into the ventricles iscompensated for, by the constant addition of water via thewater supply f (Fig. 4B). It is essential to maintain the fluidlevel in this chamber during photography of the valve in-... ... ..III~I~II'" ,..l ... ~ ,. ,.. ,.. ,.. r ,.. ......IChamber 8.5150-F···+!·~f+-+-~~~.. ~~~-+:-lI 25 - b:-HHr-:-iH-:-tt-:-H~tHt:-:ilr-lt:-:iH+-*:-c-IIt--iH100- ~~::. ':75-···· f·50_8;::~~Itt;:"..ttmJ.tJtJ1IiiWt;ftJtm25 - r.-:-:t+:-':-:-1"~~I:±:=t:-:-:"+'~"'~:::~'+--+~g:'o-~:: .Fig. 5. Pressure tracings recorded while studying a competentaortic valve.Chamber A.150-125-100-75-50-25 -0-ference of the auricular defect, through which the plexiglassviewing chamber V is attached. The roof of the aorta isdissected free from the pulmonary artery and the vessel istransected approximately 2 inches from its origin. A purse-string suture is placed about its circumference just proximalto the line of transection, to which the ascending limb of aninverted plastic V-tube A is attached.The apex of the left ventricle is amputated so as to affordentry to the ventricular cavity and a thick linen purse-stringsuture is placed around this opening. A metal tube whichpasses through a cylindrical plexiglass block P is screwedthrough the hole in the apex into the left ventricular cavityand secured in position by tying the purse-string. The heartrests on the cup-shaped upper surface of the plexiglassblock; the other end of the metal tube is connected to theduplicator. The heart. and tubes attached are supported bysuitable stands. The test can now be started. By unscrewingthe lid of the viewing chamber V, the valve to be tested canbe secured in the annulus of the heart.METHOD OF TESTING VALVESAorTic valve. The testing chambers and valve to be testedare set up as described above and connected to the pulseduplicator. Inlet valve B, is opened, the water tap turned on,862 S.A. MEDICAL JOURNAL 10 October 1959Fig. 7. Cycle of normal mitral-valve movements showing the opening and subsequent closure.order to avoid the presence of bubbles or a receding water system enables one to study and photograph the action ofmeniscus, which may impair visibility. The action of the normal and abnormal valves and also to study and testvalve can be carefully observed and photographed through prosthetic valves under conditions of pressure and volumethe top chamber (Fig. 7). flow similar to those existing in the normal circulation...CONCLUSIONThe use of the artificial pulse duplicator makes it possibleto study the action of normal and abnormal aortic and mitralvalves under conditions of pressure and flow similar to thosepresent in the beating heart. Intrinsic valvular action, however,cannot be evaluated in such a system, but despite thesedisadvantages the apparatus has proved to be of great valuefor the study of the action of prostheses designed to correctincompetent valves, and, in addition, such a system maybe used to test the durability of a prosthesis under conditionssimilar to those found during life.SUMMARYThe construction and method of operation of a simpleinexpensive artificial pulse duplicator is descrIbed. Such aWe are most grateful to the United States Public Health Depart-ment, the South African Council for Scientific and IndustrialResearch, and the University of Cape Town Research Grants, forvaluable financial assistance. We should also like to thank Mr. C.C. Goosen, technician to the Department of Surgery, Universityof Cape Town, for the photography of diagrams and figuresincluded in this article, and Mr. J. Linney, representative ofMessrs. A. Lalieu (Pty.) Ltd., for making a film of the openingand closing of the valve, from which we have taken Fig. 7.REFERE CESI. Melrose, D. G., Dreyer, B., Bentall, H. H. and Baker, J. B. E. (1955): Lancet2,21 .2. Lam, C. R. (1956): J. Thorac. Surg., 32, 370.3. Efller, D. B., Groves, K. L., Sones, F. M. and Kollf, M.J.(I956): ClevelandCIin. Quan., 23, 105.4. Got!, V. L., GonzaIes, J. L., Zulidi, M. N., Varco, R. L. and Lillehei, C. w.(1957): Surg. Gynec. Obstet., 104,319.THE TUMBU FLY, CORDYLOBIA ANTHROPOPHAGA (BLANCHARD), INSOUTHER AFRICA*F. ZUMPT, Department ofEntomology, South African Institl/te for lvledical Research, JohannesburgCordylobia anthropophaga, the 'Tumbu fly' or 'skin maggotfly' is widespread over the Ethiopian region, i.e. Africasouth of the Sahara, but it does not occur in any other zoo-geographical region of the world. In West and CentralAfrica it is a very common pest; the larvae affect mainlyhumans, dogs and various kinds of rats, but they are alsooccasionally found in other wild and domesticated mammals.* Paper read at the National Meeting of the DermatologicalSub-group of the Venereology and Dermatology Group (M.A.S.A.),Pretoria, 28 March 1959.In the Union of South Africa this parasite has become ofgreater importance only in recent times. Drs. Annie Porterand Heymann, l who submitted a paper on this fly at a meetingof the Medical Association in Johannesburg on 19 December1929, 30 years ago, said that 'in the Union of South Africasuch cases are relatively uncommon'. They presented a caseof a 9-months-old European girl who had contracted theinfection during a short stay in the Bulawayo district,S. Rhodesia.De Meillon and Gear, 2 in 1947, said that the Tumbu

The electrical pulse duplicator-its use in testing valve prostheses with special reference to the aortic and mitral valves

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The electrical pulse duplicator-its use in testing valve prostheses with special reference to the aortic and mitral valves

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