FIBREOPTIC COLONOSCOPE

998 PLASMA-PHOSPHATE AND TUBULAR REABSORPTION OF PHOSPHATE SIR,-It is perhaps unfortunate that in your leader on this subject (April 18, p. 820) you did not quote the paper1 in which we advocated (a year before Bijvoet et al.2) the expression of phosphate excretion in mg. per 100 ml. of glomerular filtrate (PE) instead of as a phosphate/creatinine clearance ratio (Cp/Ccr), and showed that this was related to plasma-phosphate concentration in normal persons. (PE is easily calculated by dividing urine-phosphate by urine-creatinine and multiplying by plasma-creatinine [all concentrations in mg. per 100 ml.]). We suggested that the deviation of any observed PE value from the normal mean for the prevailing plasma-phosphate concentration might be termed an " index of phosphate excretion " (I.P.E.) to distinguish it from the original " phosphate excretion index " of Nordin and Fraser,3 and we showed that this index yielded a very satisfactory separation on one estimation between the diagnostic groups studied-95 normal subjects, 31 cases of primary hyperparathyroidism, 100 cases of renal-stone disease, and 10 cases of hypoparathyroidism. We rely on the same basic data as Bijvoet-the simultaneous concentrations of phosphate and creatinine in plasma and urine-which we originally introduced in 1954.4 The difference between our I.P.E. and the Tm*/ G.F.R. calculated by the method of Bijvoet is the difference between an observable fact and an extrapolation from that fact. Our calculation simply indicates the extent to which an observed value of PE differs from the mean value in normal persons with the same plasma-phosphate concentration. This is like measuring a child’s height and comparing it with the mean height of normal children of the same age. Bijvoet’s analysis extrapolates from the observed point along a theoretical line to the point where Tm phosphate should be reached, which is rather like measuring a child’s height and then predicting his final stature from growth charts. Bijvoet and his colleagues have frequently complained that our indices have no " physiological meaning ". It is, however, difficult to see what physiological meaning can be attached to an imaginary Tm. We do not of course question the value of an actual Tm measurement,but as far as quick methods go, our approach involves fewer assumptions than theirs. Needless to say, it also has the two " attractive features " which you find in Bijvoet’s method -namely, the possibility of easily repeating the observation and the fact that it corrects for changes in the filtered load of phosphate. In practice, there will be found to be little, if any, difference in the diagnostic or physiological value of these two approaches, since they use the same basic data, but for clinical purposes at least, our I.P.E. (which it might be more appropriate to call APE) can be calculated by mental arithmetic at the bedside, and does not require the use of a nomogram. Blood and urine are collected in the fasting state and the calculation is performed as follows: Subtract 2’5 (the mean normal plasma-phosphate threshold) from the observed plasma-phosphate concentration in mg. per 100 ml. and halve the remainder. The result represents the mean normal PE in mg. per 100 ml. of G.F. The APE is the difference between the observed and predicted PE value, and its normal range is ±0-5 mg. per 100 ml. of G.F. * Maximum tubular reabsorption capacity. M.R.C. Mineral Metabolism Research Unit, General Infirmary, Leeds.

B. E. C. NORDIN L. BULUSU.

1. 2.

Nordin, Bijvoet,

B. E. C., Bulusu, L. Postgrad. med.J. 1968, 44, 93. O. L., Morgan, D. B., Fourman, P. Clinica chim. Acta,

3. 4.

1969, 26, 15. Nordin, B. E. C., Fraser, R. Lancet, 1960, i, 947. Nordin, B. E. C., Fraser, R. Clin. Sci. 1954, 13, 477.

EFFECT OF INSULIN ON RENAL TUBULAR REABSORPTION SIR,-A leading article in your issue of April 18 (p. 820) refers to some work I reported to the Medical Research Society. Unfortunately the quotation is not quite accurate.

By maintaining

a

constant

arterial-blood-glucose

con-

centration during insulin infusion in a group of diabetics, it was possible to show that insulin reduces the amount of glucose in the urine independently of any changes it may produce in blood-glucose levels. These results demonstrate a previously unrecognised direct effect of insulin on the kidney, and would be in keeping with the idea that insulin increases (and not, as you say, reduces) the renal tubular reabsorption of glucose. The Middlesex Hospital, London W.1.

G. S. SPATHIS.

AIR POLLUTION BY NOISE SIR,-In your otherwise excellent editorial (May 2, p. 928), you express surprise that trade-unions lack enthusiasm for tests to identify those most liable to ear damage from industrial noise. When you have identified all those who are accident-prone, who are susceptible to industrial dermatitis, who are liable to fits, or whose hearing is most at risk-who, then, is to employ them ? In South Wales, at least, sheltered employment on a living wage is almost non-existent for an unskilled manual labourer with one of these disabilities. Doctors are accustomed to think of health as beyond price, but unfortunately most people cannot afford to think this. They will prefer to risk their health for the sake of wages and job-security, until the rehabilitation and reemployment of the disabled become a serious social priority. In the meantime we should support unions which press for the elimination of bad working conditions, rather than the exclusion from employment of high-risk workers.

J. TUDOR HART.

FIBREOPTIC COLONOSCOPE

SlR,—Iwas interested in the article by Mr. Dean and Dr. Shearman (March 14, p. 550). I too have been using the Olympus’CF-SB’ colonoscope (I am currently using the

modification). I would take issue with the Edinon the distance of insertion. In my experiworkers burgh ence the instrument can be inserted to 40 cm. in virtually every case, and the majority tolerate it to the full depth of 75 cm. My technique differs slightly from that of Mr. Dean and Dr. Shearman. new

The patient takes threeDulcolax ’ tablets the night before the procedure. A high saline enema is given 75 minutes before the examination, and this is repeated 30-45 minutes later. Meperidine hydrochloride (pethidine) 50-100 mg. and, if necessary’Valium’ (diazepam) 1-10 mg. are given intravenously immediately before achieve relaxation and sedation. The instrument is a speculum. Once the rectum is entered, air is introduced to distend the lumen and the instrument is advanced using distal-tip manipulation, gentle pressure, and rotation of the probe. At between 20 and 30 cm. the tip commonly abuts against the sigmoid wall.’ At this point " persuasive pressure " is brought into play. With this technique, steady pressure slides the instrument along the curve of the colon. It is essential for the mucosa to be observed to slip slowly by the tip of the scope. If this does not occur, the fibreoptic colonoscope is withdrawn several centimetres, the lumen identified, and advancement again attempted. As in conventional sigmoidoscopy, the tip is directed towards and around the valve or angulus " of the colon to find the lumen. Rolling the patient onto his abdomen, and occasionally to his right side, often facilitates insertion. intubation

to

passed through

"

Fibreoptic colonoscopes

add

considerably

to

diagnostic

999 acumen

nique is

in colon disease. A fuller description of our techto appear shortly in the Southern Medical,7ournal.

Knoxville Gastroenterology Group,

Knoxville, Tennessee

37920.

B. F. OVERHOLT.

ASSISTING VENOUS RETURN Roberts has shown in dogs (May 2, p. 948), and others have shown in man, that raising the legs increases the venous return (blood-flow in femoral veins). The words used suggested that venous return was assisted by using gravity to encourage blood to drain from the limbs. This may indeed happen, and the elevated limb may diminish in volume accordingly. However, it is obvious that the increase in venous flow which will thus result cannot be more than transitory and cannot represent, even momentarily, more than a tiny fraction of total venous flow, nowhere near approaching the increase demonstrated. Unless associated with progressive change in limb volume, altered venous blood-flow must, of course, indicate correspondingly altered arterial inflow. I suggest that what has really been demonstrated on leg-raising is an increase in cardiac output associated with increased central venous pressure. This could be readily demonstrated by observing the effect of leg-raising on arterial flow. H. DAINTREE JOHNSON.

SIR,-Mr.

HIP DISEASE IN AFRICANS

SIR,-I was interested in the short communication of Dr. Wittman and Mr. Fellingham (April 18, p. 842) on the unusual hip disease in Zululand. Their findings of joint-space narrowing, subarticular sclerosis, large osteophytes, protrusio acetabuli, and deformity of the femoral head with medial subluxation are not too unlike those observed here in sickle-cell disease (figs. 1, 2, and 3). Dr. Wittman and Mr. Fellingham expect to find an environmental cause " in view of the very high incidence in a small area ", but I would make bold to suggest that they keep in mind hereditary disease. The " confined area " would suggest intermarriage, and hence a high incidence of the disease. Assuming that this was hereditary, then an environmental factor which might be expected to produce clinical signs (or exacerbate them) would be excessive activity, just as playing football or running exacerbates hip necrosis of sickle-cell disease in Ghana. From the South African figures, twice as many females seemed to be affected as men. Are the women the bread-winners ? Do they farm ? Other environmental factors which tend to bring on hip necrosis quickly in Ghana are (i) severe infection, and (ii) confinement, labour, and childbirth. It is not unusual to discover hip necrosis for the first time in a sickle-cell-disease patient convalescing from severe

Fig. 1-Subluxation old

man

of left hip in 18-yearwith sickle-cell disease.

Fig.2-Destruction of Ghanaian

man

typhoid fever. Is the onset of hip trouble in the Bantus often preceded by a febrile illness ? Several of the female sickle-cell-disease patients in Accra had their first hip trouble after confinement. 66% of the 667 women examined by Dr. Wittman and Mr. Fellingham had hip trouble. Perhaps a careful obstetric history together with haemoglobin electrophoresis and tests to unmask inborn errors of metabolism should also be added to the list of investigations being planned. But, of course, the very high proportions afflicted would seem to cast doubt on the hereditary aetiology of the disease. Finally, tactful questioning of the adults about sex life would be valuable. Some of my sickle-cell-disease male patients with hip involvement find coitus impossible because body movement of any sort produces agonising pain, while some women with bilateral disease have no sex life at all, due to inability to part the legs (fig. 3). It seems to me this is one further means Nature has devised to limit dissemination of the sickle-cell gene. University of Ghana Medical School, Korle Bu Teaching Hospital, F. I. D. KONOTEY-AHULU. Accra, Ghana.

HÆMOGLOBIN AND SERUM-CHOLESTEROL SiR,-The observation by Dr. Elwood and his colleagues (March 21, p. 589) that anaemia is associated with a decreased serum-cholesterol is an important one. However, the conclusion that mild anaemia may have a beneficial effect on atherosclerotic vascular disease is possibly premature, particularly since the serum-cholesterol concentration did not increase significantly after correction of anaemia in the patients studied. In a pluricausal disease such as atherosclerosis, occurring in a complex biological system such as the human body, it may be fallacious to assume that factors which affect a single facet of the disease will influence the process as a whole. For example, it has been shown that the production of hypothyroidism is frequently not helpful in patients with intractable angina pectoris, even though the hypothyroid state is associated with decreased cardiac work. Furthermore, although data are still forthcoming, clinical trials with anticoagulant drugs, and with diets low in saturated fats and cholesterol, have shown conflicting results in patients with ischxmic heart-disease. Treatment with oestrogens appears to have aggravated the process in some instances. I do not mean to suggest that the study of the association between anaemia and serum-cholesterol concentration and between anaemia and intravascular thrombosis should not be pursued. The point is that patients with mild anaemia, whether it be due to iron deficiency or to some other cause, should be treated, and should not be allowed to remain anaemic because of the assumption that anaemia may retard the progress of atherosclerotic vascular disease. The

left hip in

46-year-old

with sickle-cell ansemia.

Fig. 3-Bilateral hip necrosis in 26-yearold housewife with sickle-cell disease.