Biomedical subjects
Publications and source records attributed to M Papadimitriou.
Experiments have been performed upon the absorption of ammonia and hydrazine from different solutions instilled into a human ileal sac with an exteriorized stoma. Ammonia and hydrazine absorption was greater from solutions of higher pH. It is concluded that non-ionic diffusion plays an important role in ammonia absorption from the human ileum.
Two out of four patients who had severe ischaemic E.C.G. changes when first accepted on to the dialysis programme showed much improvement after six months. From an analysis of 40 electrocardiograms (20 before and 20 after dialysis) of a further 17 patients it was found that the height of the T wave is a good index of the plasma potassium level. The tolerance of higher plasma potassium levels by these patients compared with patients with acute renal failure may be explained by the fact that the former do not have a hypercatabolic process and have a lesser degree of acidosis.
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A 5-megacycle Doppler flow meter, calibrated in-vitro, was found to give a linear response to blood flow in the ranges commonly encountered in haemodialysis. With this, blood flow through artificial kidneys could be measured simply and with a clinically acceptable error. The method is safe, as blood lines do not have to be punctured or disconnected and hence there is no risk of introducing infection. Besides its value as a research tool the flow meter is useful in evaluating new artificial kidneys. Suitably modified it could form the basis of an arterial flow alarm system.
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The detection of lymphoid cells by routine examination of the urine after renal allotransplantation has proved to be a useful early indication of rejection. In a study of 36 rejection episodes, 20 (56%) were associated with a significant number of lymphocytes in the urine. The incidence was much higher when rejection occurred during the first month after operation (76%); lymphocytes were rarely found when rejection occurred after three months. The appearance of lymphocytes in the urine was of particular value for detecting rejection in patients with prolonged oliguria after transplantation.
Total white cell, neutrophil, and lymphocyte counts were compared in patients with chronic renal failure treated successively by conservative means (low-protein diet), regular haemodialysis, and renal allotransplantation. The lowest total white cell and neutrophil counts and the highest lymphocyte counts were found in patients on regular haemodialysis. A rapid fall in neutrophil count during the first half-hour of dialysis and a more gradual fall between the first and sixth hours were observed. Adherence of neutrophils and mononuclear cells to the cuprophane (PT 150) dialysis membrane has been shown.
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Episodes of clotting that occurred in 22 patients on regular haemodialysis were studied over a six-month period. The venous pressure during dialysis and the radiology of the Teflon-Silastic arteriovenous shunt were found to be satisfactory guides for the management of the shunt. The failure of the shunt during the early stage was mainly due to technical reasons. Histological study of the excised vessels in removed long-term shunts showed that these had failed because of rigidity and thickening of the vessel wall due to calcium and iron deposits or chronic inflammation, or both.
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The different permeability of high-flux and low-flux dialysis membranes results in different removal capacity, particularly for uremic toxins of middle and large molecular weight. High-flux dialysers have been evaluated in clinical and epidemiological studies for their effect on mortality, morbidity, dialysis-related amyloidosis, nutritional status, response to erythropoietin treatment, dialysis tolerance and the preservation of residual renal function. Many of these studies, however, lack a prospective design and randomised treatment allocation, or have too few patients and too short a follow-up. Therefore, this clinical trial was designed to prospectively investigate the long-term effect of membrane permeability on clinical outcome in a larger number of patients. The primary objective is to compare the effect of membrane permeability on mortality of patients on bicarbonate hemodialysis and treated with a minimum dialysis dose. Patients included in the study should have been on hemodialysis for no longer than one month and have serum albumin 4 g/dl or lower. Patients will be randomised to either the experimental or the control group. During the four-week run-in period the treatment parameters will be established in order to achieve the required dialysis dose. During the maintenance period of three to five years regular visits are scheduled to record clinical and laboratory parameters, to measure Kt/V and to adapt the treatment parameters. Altogether a minimum of 660 patients should be enrolled within a two-year recruitment period.
To determine the role of the renin-angiotensin-aldosterone system in the maintenance of hypertension in patients with end stage renal disease, twenty four hypertensive patients were studied on regular haemodialysis treatment (RDT) and after successful kidney transplantation. The first group consisted of nine patients on RDT with their own kidneys in situ, and the second group consisted of nine kidney transplants. All 18 patients were given spironolactone 300 mg daily for three weeks following a control period of the same duration. In addition, three anephric patients on RDT were studied with the above protocol and three other patients on RDT were given the same dose for only six days. Blood pressure (BP), body weight, plasma K-Na, aldosterone and renin activity in all patients, and Na and aldosterone in urine in the second group were measured. In the first group of patients on RDT plasma potassium and renin activity increased significantly but BP remained unchanged. In the second group of transplanted patients plasma potassium, renin activity, and aldosterone were increased and BP diminished significantly. In the group of three anephric patients plasma potassium increased but plasma renin activity remained very low. Finally, in the patients on dialysis who received spironolactone for only six days there was a parallel increase of serum potassium and plasma renin activity. These findings suggest that in patients on RDT spironolactone stimulates renin secretion and potassium retention possibly by an effect on the remaining nephrons and/or the intestinal wall. On the contrary, in the transplanted patients the effect of spironolactone on the renal tubule is capable of producing sodium depletion and fall in BP.
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