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TRIAL OF UNSATURATED-FAT DIET
1191
having individual secretaries who know the work will be given up in favour of a pool of secretaries. The question arises as to how far the smooth running and efficiency of a hospital should be subservient
to
small economies.
St. Peter’s
Hospital, Chertsey, Surrey.
J. S. PHILLPOTTS.
VASECTOMY FOR VOLUNTARY MALE STERILISATION Alderman’s monumental series of nearly SIR,-Dr. Philip 2000 vasectomies (Nov. 23, pp. 1137) represents an experience with which most of us cannot compete. The significant figures are the failure-rate of 0-68% and a positive sperm-count at three months in 20% of men. My own experience is only some 50 cases, but I have learnt two things. First, excision of 1 cm. of vas under local anaesthesia, which is the operation I used to do, resulted in one case of proved " leakage " of sperms across the gap-proved in that six months after operation the sperm-count was still 100,000 per ml. and a second operation under general anxsthesia removed about 5 cm. of vas, microdissection of which showed recanalisation on one side. Secondly, since using general anaesthesia and removing 5 cm. of vas, I have had no positive sperm count at three months. My figures are quite insignificant statistically but I do suggest that a failure-rate of 0-68% is not acceptable, that it is due to " leakage " across too small a gap, and that it can be reduced by a I find my more radical resection under general anxsthesia. patients are only too willing to accept the anxsthetic and the irreversibility of this method in exchange for a lower failurerate.
Leicester.
PAUL HICKINBOTHAM.
DEFENCE MECHANISMS OF THE BLADDER SIR,-Your leaderstated that " Hinman2 has shown that distension of the female urethra can produce such turbulent flow that the peripheral part of the stream is reversed and organisms close to the meatus are carried into the bladder ". Hinman’s paper2 in fact only suggested this-but no theoretical or experimental evidence was given to substantiate it. His suggestion has been taken up by several other workers 3-5
recently. Fluid flow may be either laminar or turbulent; for urine the urethra the main determining factor is the stream velocity. This, in all but extreme degrees of obstruction, is such that the stream is always turbulent.67However, at the edge of the stream there is a thin layer whose velocity is so reduced by shearing forces caused by the stationary urethral wall that the flow in this layer is actually laminar.8 This layer is, of course, the only part of the urinary stream that is in contact with bacteria that may be present on the urethral wall. It is also inconceivable on theoretical grounds that retrograde eddies would take the paths depicted by Hinman. Cox 9 has shown that bacteria are often present in the proximal centimetre of the urethra of normal woman. How then might disturbances of micturition carry these bacteria into the bladder ? Consideration of normal micturating cystourethrograms shows that at cessation of micturition the female urethra empties from its mid-point: the contents of the part proximal to this pass retrogradely into the bladder. This occurs whether the bladder is empty or not, and about 1-2 ml. of urine that has been in contact with the potentially infected urethral wall is returned to the bladder on each occasion.
flowing along
1. 2. 3. 4. 5. 6. 7. 8. 9.
Lancet, 1968, i, 1183. Hinman, F. Jr. J. Urol. 1966, 96, 546. Halverstadt, D. B., Leadbetter, G. W. ibid. 1968, 100, 297. Hinman, F. Jr. ibid. 1968, 99, 811. Kedar, S. S. Br. J. Urol. 1968, 40, 441. Bryndorf, J., Sandøe, E. Dan. med. Bull. 1960, 7, 65. Smith, J. C. Invest. Urol. 1963, 1, 477. Bayley, F. J. Introduction to Fluid Dynamics; p. 99. London, 1958. Cox, C. E. Sth. med. J., Nashville, 1966, 59, 621.
In addition many females often void with an interrupted and this is more common with painful minor vulval and urethral conditions. This may well be due to detrusor inhibition, as described by Pompeius.1o Obviously factors which increase the number of interruptions of flow, such as simple frequency, as in the " urethral syndrome ", or multiple interruptions of voidings of normal quantity and frequency, will considerably increase the quantity of bacteria carried into the bladder, and this " rate of inoculation " may be sufficient to exceed the natural defence mechanisms of the bladder.4 In young girls episodes of vulval discomfort are common and are usually due to simple intertrigo or faecal contamination. In the adolescent chafing by external sanitary pads is often responsible. These conditions should be considered a real factor in the causation of recurrent urinary infections and care should be taken to eliminate them. Department of Urology, Newcastle General Hospital, ROGER HOLE. Newcastle upon Tyne NE4 6BE. stream
TRIAL OF UNSATURATED-FAT DIET a blind trial those being observed do not know whether or not they are getting the substance being tested, because the substitute given to the controls is indistinguishable from the tested material. In a double-blind trial the investigators also do not know. In the trial of diets reported by Dr. Dayton and his colleagues (Nov. 16, p. 1060) the treated group got a high unsaturated-fat diet and the controls a conventional diet. The two groups must have had to collect separate rations in the canteen, the controls getting butter more liberally, the others receiving corn-oil preparations, and so on. Surely most of the men knew who was in each group. Moreover the doctors presumably provided the men with dietary instructions and perhaps special cooking fats for their periods at home, and in doing this and in monitoring dietary adherence in the canteen they must often have known which group men were in. The authors write of this trial that " being a double-blind trial in randomised subjects it had the virtue of freedom from bias ". Is this quite accurate ? However free from bias it may have been, would not the expression " half blind " be more suitable than " double blind " to describe the nature of the trial ? RICHARD ASHER. London W.I.
SIR,-In
SMOKING AND PREGNANCY SIR,-My disappointment at your annotation (Oct. 26, p. 905) has made me wonder how much I was responsible for not underlining sufficiently the evidence that regular smoking in pregnancy is a danger to the life of the foetus. In our series 11 of over 2000 pregnancies the overall mortality (abortions, stillbirths, and neonatal deaths taken together) was 53 per 1000, but that of the smokers was 79 per 1000 against 41 for the non-smokers. Reduced to simple terms this difference means that the risk to the foetus of maternal smoking was about 8 per 1000.12 Perhaps unwisely we chose to give a final estimate as half this because we had included in our series rather a large proportion of abnormal cases. Which risk-rate to choose, the 8/1000 or 4/1000, may depend on whether one accepts 53 per 1000 as representative of the community as a whole. But does it matter ? The risk is there, and it may be formulated in a still more practical way: out of every 10 unsuccessful pregnancies due to abortions, stillbirths, or neonatal deaths, 1 or 2 would have been successful if the mother had not been a regular smoker. Surely such evidence is enough for action, and I cannot do better than quote the leader in the British Medical Journal of Nov. 9, which said: " It seems that the time has come when 10. Pompeius, R. Acta chir. scand. 1966, suppl. 361. 11. Russell, C. S., Taylor, R., Law, C. E. Br. J. prev. 12. Russell, C. S., Taylor, R., Maddison, R. N. Commonw. 1966, 73, 746.
soc. Med. 1968, 22, 119. J. Obstet. Gynœc. Br.
having individual secretaries who know the work will be given up in favour of a pool of secretaries. The question arises as to how far the smooth running and efficiency of a hospital should be subservient
to
small economies.
St. Peter’s
Hospital, Chertsey, Surrey.
J. S. PHILLPOTTS.
VASECTOMY FOR VOLUNTARY MALE STERILISATION Alderman’s monumental series of nearly SIR,-Dr. Philip 2000 vasectomies (Nov. 23, pp. 1137) represents an experience with which most of us cannot compete. The significant figures are the failure-rate of 0-68% and a positive sperm-count at three months in 20% of men. My own experience is only some 50 cases, but I have learnt two things. First, excision of 1 cm. of vas under local anaesthesia, which is the operation I used to do, resulted in one case of proved " leakage " of sperms across the gap-proved in that six months after operation the sperm-count was still 100,000 per ml. and a second operation under general anxsthesia removed about 5 cm. of vas, microdissection of which showed recanalisation on one side. Secondly, since using general anaesthesia and removing 5 cm. of vas, I have had no positive sperm count at three months. My figures are quite insignificant statistically but I do suggest that a failure-rate of 0-68% is not acceptable, that it is due to " leakage " across too small a gap, and that it can be reduced by a I find my more radical resection under general anxsthesia. patients are only too willing to accept the anxsthetic and the irreversibility of this method in exchange for a lower failurerate.
Leicester.
PAUL HICKINBOTHAM.
DEFENCE MECHANISMS OF THE BLADDER SIR,-Your leaderstated that " Hinman2 has shown that distension of the female urethra can produce such turbulent flow that the peripheral part of the stream is reversed and organisms close to the meatus are carried into the bladder ". Hinman’s paper2 in fact only suggested this-but no theoretical or experimental evidence was given to substantiate it. His suggestion has been taken up by several other workers 3-5
recently. Fluid flow may be either laminar or turbulent; for urine the urethra the main determining factor is the stream velocity. This, in all but extreme degrees of obstruction, is such that the stream is always turbulent.67However, at the edge of the stream there is a thin layer whose velocity is so reduced by shearing forces caused by the stationary urethral wall that the flow in this layer is actually laminar.8 This layer is, of course, the only part of the urinary stream that is in contact with bacteria that may be present on the urethral wall. It is also inconceivable on theoretical grounds that retrograde eddies would take the paths depicted by Hinman. Cox 9 has shown that bacteria are often present in the proximal centimetre of the urethra of normal woman. How then might disturbances of micturition carry these bacteria into the bladder ? Consideration of normal micturating cystourethrograms shows that at cessation of micturition the female urethra empties from its mid-point: the contents of the part proximal to this pass retrogradely into the bladder. This occurs whether the bladder is empty or not, and about 1-2 ml. of urine that has been in contact with the potentially infected urethral wall is returned to the bladder on each occasion.
flowing along
1. 2. 3. 4. 5. 6. 7. 8. 9.
Lancet, 1968, i, 1183. Hinman, F. Jr. J. Urol. 1966, 96, 546. Halverstadt, D. B., Leadbetter, G. W. ibid. 1968, 100, 297. Hinman, F. Jr. ibid. 1968, 99, 811. Kedar, S. S. Br. J. Urol. 1968, 40, 441. Bryndorf, J., Sandøe, E. Dan. med. Bull. 1960, 7, 65. Smith, J. C. Invest. Urol. 1963, 1, 477. Bayley, F. J. Introduction to Fluid Dynamics; p. 99. London, 1958. Cox, C. E. Sth. med. J., Nashville, 1966, 59, 621.
In addition many females often void with an interrupted and this is more common with painful minor vulval and urethral conditions. This may well be due to detrusor inhibition, as described by Pompeius.1o Obviously factors which increase the number of interruptions of flow, such as simple frequency, as in the " urethral syndrome ", or multiple interruptions of voidings of normal quantity and frequency, will considerably increase the quantity of bacteria carried into the bladder, and this " rate of inoculation " may be sufficient to exceed the natural defence mechanisms of the bladder.4 In young girls episodes of vulval discomfort are common and are usually due to simple intertrigo or faecal contamination. In the adolescent chafing by external sanitary pads is often responsible. These conditions should be considered a real factor in the causation of recurrent urinary infections and care should be taken to eliminate them. Department of Urology, Newcastle General Hospital, ROGER HOLE. Newcastle upon Tyne NE4 6BE. stream
TRIAL OF UNSATURATED-FAT DIET a blind trial those being observed do not know whether or not they are getting the substance being tested, because the substitute given to the controls is indistinguishable from the tested material. In a double-blind trial the investigators also do not know. In the trial of diets reported by Dr. Dayton and his colleagues (Nov. 16, p. 1060) the treated group got a high unsaturated-fat diet and the controls a conventional diet. The two groups must have had to collect separate rations in the canteen, the controls getting butter more liberally, the others receiving corn-oil preparations, and so on. Surely most of the men knew who was in each group. Moreover the doctors presumably provided the men with dietary instructions and perhaps special cooking fats for their periods at home, and in doing this and in monitoring dietary adherence in the canteen they must often have known which group men were in. The authors write of this trial that " being a double-blind trial in randomised subjects it had the virtue of freedom from bias ". Is this quite accurate ? However free from bias it may have been, would not the expression " half blind " be more suitable than " double blind " to describe the nature of the trial ? RICHARD ASHER. London W.I.
SIR,-In
SMOKING AND PREGNANCY SIR,-My disappointment at your annotation (Oct. 26, p. 905) has made me wonder how much I was responsible for not underlining sufficiently the evidence that regular smoking in pregnancy is a danger to the life of the foetus. In our series 11 of over 2000 pregnancies the overall mortality (abortions, stillbirths, and neonatal deaths taken together) was 53 per 1000, but that of the smokers was 79 per 1000 against 41 for the non-smokers. Reduced to simple terms this difference means that the risk to the foetus of maternal smoking was about 8 per 1000.12 Perhaps unwisely we chose to give a final estimate as half this because we had included in our series rather a large proportion of abnormal cases. Which risk-rate to choose, the 8/1000 or 4/1000, may depend on whether one accepts 53 per 1000 as representative of the community as a whole. But does it matter ? The risk is there, and it may be formulated in a still more practical way: out of every 10 unsuccessful pregnancies due to abortions, stillbirths, or neonatal deaths, 1 or 2 would have been successful if the mother had not been a regular smoker. Surely such evidence is enough for action, and I cannot do better than quote the leader in the British Medical Journal of Nov. 9, which said: " It seems that the time has come when 10. Pompeius, R. Acta chir. scand. 1966, suppl. 361. 11. Russell, C. S., Taylor, R., Law, C. E. Br. J. prev. 12. Russell, C. S., Taylor, R., Maddison, R. N. Commonw. 1966, 73, 746.
soc. Med. 1968, 22, 119. J. Obstet. Gynœc. Br.