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Severity of cicatricial R.L.F. in two time periods.

Surveillance of the results of intensive care and a search foradditional factors leading to R.L.F. are possible, when all in-fants affected are recognised.

In the time period studied increased survival of very smallpreterm infants did not seem to play a role in the greater inci-dence of R.L.F. However, in the last year of the study (1976)the survival-rate of such infants rose to 44%.Our findings strongly support the recommendation that, for

all infants at risk of R.L.F., ophthalmological examination withindirect fundoscopy with or without scleral depression shouldbe done both in the neonatal intensive-care unit and withinthree months of discharge.

McGill University-Montreal Children’s Hospital,Montreal, Quebec, Canada

TANIA R. GUNN

JACOB V. ARANDAJOHN LITTLE

POSSIBLE ROLE FOR ENZYME INHIBITION INCONTROLLING KIDNEY CYSTS

SIR,-Multiple cysts in patients with cystic disease of thekidney are usually associated with the destruction of func-tional parenchyma, and they can lead to renal insufficiency.Growth of cysts is a major hazard for surrounding paren-chyma. Microscopy suggests that cysts enlarge mainly becauseof increased hydrostatic pressure. Active transport of solutes,and the resulting osmotic imbalance, might increase the pres-sure of fluid in the cavity against the tension of the cyst walland surrounding structures. Enzyme inhibitors and cytostaticdrugs as potential inhibitors of biological activity of the cystwall might suppress growth.We have measured the hydrostatic pressure of cyst fluid in

sixteen patients with multiple or solitary cystic lesions of thekidney. Pressure was determined by needle puncture in thelumbar region and measurement of the height of the fluidcolumn. Pressures were on average 22 cm H2O (range 16-31).The pressure seemed greater in patients with multiple cyststhan in those with solitary ones. There seemed to be no corre-lation between cyst volume and fluid pressure. The osmolarityof cystic fluid was 315-321 mosmol/1. Unusually high concen-trations of urate, creatinine, and potassium in some fluidssuggest active transport in the cyst wall. Such an active trans-port mechanism might be an inheritance of cystic-wallepithelium originating from parts of the nephron during cystformation.’ Nevertheless we could not attribute the pressure ofcyst fluid to its osmotic activity.One approach to suppression of cyst growth might be to

decrease the active transport of cyst-wall epithelium and its"pumping" effect-for example, by inhibiting the activity of

1. Ostanondh, V., Potter, E. Archs Path. 1964, 77, 510.

enzymes which play a part in active transport. Dichlorphena-mide lowers intraocular pressure, probably by acting againstcarbonic anhydrase in the ciliary body as well as by its diureticeffect. Cytostatics also deserve consideration as agents directedagainst the activity of cyst-wall epithelium.

Polycystic disease of the kidneys usually means a long andinconstant course, so assessment of the proposed therapeuticapproach will be difficult. Unfortunately, we know of noanimal model with which to study the effects of enzyme inhibi-tors and cytostatic drugs on the growth of kidney cysts.Department of Urology,University of Zagreb,YU-41000, Zagreb, Yugoslavia

DANIEL DEREŻIĆLJUBOMIR CECUK

PULSATILE PUMPS FOR OPEN-HEART SURGERY

SIR,-Following recent meetings of the American, Scan-dinavian, and British Thoracic Surgeons and ExtracorporealTechnologists, it is apparent that there is considerable interestin the use of pulsatile pumps in open-heart surgery. This is ahighly commendable development since the experimental andclinical evidence favouring pulsatile blood-flow over non-pulsa-tile blood-flow is substantial.The many advantages of pulsatile flow include more uni-

form tissue perfusion, 1.2 more efficient use of energy,3 greatermovement of tissue fluids and higher rates of tissue metabo-lism.5 These factors are probably responsible for lower peri-pheral vascular resistance higher rates of oxygen use,’ im-proved kidney function,8 and better preservation of thebrain9,lO and heart" during pulsatile perfusions than duringnon-pulsatile perfusions. These advantages can be obtained ifthe pump produces arterial pressure and flow waveforms simi-lar to those produced by the natural heart. An accurate de-scription of these waveforms requires harmonic analysis ofrecords made with measuring systems which have linear high-frequency responses.12 Coupling the pressure transducer to thepatient’s artery with a long catheter reduces the frequency re-sponse below that necessary to record the highest frequencycomponents. Also, simultaneous recording of blood-flow is

rarely possible, so that the ideal recording situation is difficultto achieve in human subjects. However, a normal range ofvalues can be established very crudely by measuring the ejec-tion phase, rise time, and peak values on the systemic arterialpressure and flow records.13 It is not known which of these fea-tures is responsible for the proven advantages of pulsatile flow.More accurate records can be obtained in laboratory ani-

mals or with a model circulation in vitro. If the measuredvalues are used to define pulsatile flow, it can be seen that themodified roller pumps currently being offered as pulsatilepumps produce pressure and flow waveforms that are far fromnormal (fig. 1). We have measured the flow waveforms pro-duced by the Stockert pulsatile pump and found that, com-pared with normal flow waveforms, the rise times are close tothe normal range but their peak flow is very low and the ejec-

1. Nonoyama, A. Archs jap. Chir. 1960, 29, 1381.2. Ogata, T., Ida, Y., Nonoyama, A., Sasaki, H. ibid. 59.3. Shepard, R. B., Simpson, D. C., Sharp, J. F. Archs Surg. 1966, 93, 730.4. McMaster, P. D., Parsons, R. J. J. exp. Med. 1938, 68, 377.5. Trinkle, J. K., Helton, N. E., Wood, R. E., Bryant, L. R. J. thorac. cardio-

vasc. Surg. 1969, 58, 562.6. Nakayama, K., Tamiya, T., Yamanoto, K., Izumi, T., Akimoto, S., Hashi-

zumi, S., Iimori, T., Odaka, M., Yazawa, C. Surgery, St. Louis, 1963, 54,694.

7. Shepard, R. B., Kirklin, J. W. J. thorac. cardiovasc. Surg. 1969, 58, 694.8. Many, M., Soroff, H. S., Birtwell, W. C., Giron, F., Wise, H., Deterling,

R. A. Archs Surg. 1967, 95, 762.9. Sanderson, J. M., Wright, G., Sims, F. W. Thorax, 1972, 27, 275.

10. Wright, G., Sanderson, J. M. ibid. 1972, 27, 738.11. Habal, S. M., Weiss, M. B., Spotnitz, H. M., Parodi, E. N., Wolff, M., Can-

non, P. J., Hoffman, B. F., Malm, J. R. J. thorac. cardiovasc Surg. 1976,72, 742.

12. McDonald, D. A., Blood Flow in Arteries; p. 162. London, 1974.13. Sanderson, J. M., Morton, P. G., Tolloczko, T. S., Vennart, T., Wright, G.

Med. Biol. Eng. 1973, 182.