A history of natural membranes in dialysis

The scientific principles and technological determinants of haemodialysis membranes

In most biological or industrial (including medical) separation processes, a membrane is a semipermeable barrier that allows or achieves selective transport between given compartments. In haemodialysis (HD), the semipermeable membrane is in a tubular geometry in the form of miniscule pipes (hollow fibres) and separation processes between compartments involve a complex array of scientific principles and factors that influence the quality of therapy a patient receives. Several conditions need to be met to accomplish the selective and desired removal of substances from blood in the inner cavity (lumen) of the hollow fibres and across the membrane wall into the larger open space surrounding each fibre. Current HD membranes have evolved and improved beyond measure from the experimental membranes available in the early developmental periods of dialysis. Today, the key functional determinants of dialysis membranes have been identified both in terms of their potential to remove uraemic retention solutes (termed ‘uraemic toxins’) as well subsidiary criteria they must additionally fulfill to avoid undesirable patient reactions or to ensure safety. The production of hundreds of millions of kilometres of hollow fibre membranes is truly a technological achievement to marvel, particularly in ensuring that the fibre dimensions of wall thickness and inner lumen diameter and controlled porosity—all so vital to core solute removal and detoxification functions of dialysis—are maintained for every centimetre length of the fragile fibres. Production of membranes will increase in parallel with the increase in the number of chronic kidney disease (CKD) patients expected to require HD therapies in the future. The provision of high-quality care entails detailed consideration of all aspects of dialysis membranes, as quality cannot in any way be compromised for the life-sustaining—like the natural membranes within all living organisms—function artificial dialysis membranes serve.

The use of the kidneys in secular and ritual practices according to ancient Greek and Byzantine texts

The use of kidneys in secular and spiritual practices was very common for centuries. In this article we present some references on their employment as sacrificial offers, as plain food or as a source for medicaments. Our material derives from Greek texts of the Classical, Hellenistic, Roman, and Byzantine eras. Relevant extracts from the Old Testament are also included, as they have become part of a common cultural heritage in that period of syncretism, when Jews were Hellenized and Greeks orientized. From the fragments cited in this article, it is obvious that the practical use of kidneys by priests, doctors, and lay persons in the periods under discussion was widespread. The sacrificial offering was based on the religious significance of the organ. The dietary consumption of the kidneys was limited by their function as urine producers. Their medicinal use was dictated first, by the abundance of the adipose tissue surrounding them, which was an ideal warming and binding substance. Second, it may be explained by the deeply rooted conviction that eating a particular organ led to the incorporation of its strength, thus protecting the corresponding eater's organs. Those practices should not surprise us in view of their corresponding modern use. Currently, kidney donors offer their organs in a sacrificial gesture, kidneys are consumed as a delicacy worldwide, and renal tissue is therapeutically used in transplantations and, until very recently, as a source for hormonal substances.

Substitution of renal function through skin catharsis: evidence from the classical period to the Middle Ages

The skin's cleansing capacity has been known for centuries and has been used therapeutically and extensively for a great number of diseases. We studied the historical evolution of the methods used for catharsis through the skin, particularly for those in renal failure, by reviewing most of the existing ancient Greek and Byzantine codices dealing with the skin's cleansing capacity. From the fragments cited in this article, it is evident that the ancient medical writers were well aware of the mechanism of perspiration, and through this process the excretion of several body toxins, they knew about renal failure as well as the influence of environmental temperature on blood purification via the skin. To validate their views, we reviewed the seasonal variation of the average values for blood urea, creatinine, and electrolytes for 161 regular dialysis treatment (RDT) patients in four dialysis units in southern Greece. The estimations were carried out during the winter/summer 1997, 1998, and 1999 terms and included three winter months and three summer months. We traced an unexpectedly large number of references in the ancient and medieval Greek medical literature concerning detoxification through the skin, mainly regarding patients in renal failure. This seasonal variation hypothesis is supported by the results of our retrospective study: there was a difference of 16 mg/dL in the average blood urea (mean winter urea 182 mg/dL, mean summer urea 166 mg/dL). We suggest that the ancients had a vivid idea about the substitution of renal function by the skin's cleansing ability in renal failure. The previously mentioned phenomenon may be due to the elimination of blood urea through excessive perspiration. Our clinical results seem to verify their notions, and hence, the skin (like the peritoneum) may be considered a natural membrane for dialysis. We were unable to trace a similar report in the literature on the seasonal fluctuation of blood urea in dialysis patients.