MEDICONSULT

was a small consulting company for medical engineering, specialized in membrane devices,

especially dialyzers.

It was officially registered in Basel, Switzerland, 1980-1997 and operated by

Dr. Jan Erik Sigdell

The main activity was consulting to the dialysis industry for design and calculation of hollow-fiber dialyzers

and for techniques for their manufacturing.

(To day there are a few companies operating under the name Mediconsult, as a search in the Internet shows, but none of them has anything to do with this – no more existing – company. However, it looks like I may have been the first to use this company name.)

This webpage contains essential publications by Jan Erik Sigdell, who is now retired as a pensioner.

Some articles on other subjects of medical engineering are added on a separate page.

The webpage is kept to a simple form since it will be of real interest to only a handful of visitors...

Dialysis, which is the main form of treatment of chronic kidney failure by means of the artificial kidney, is based on mass exchange through a semipermeable membrane between the patient’s blood and a cleansing liquid, called the dialysate (even though, strictly speaking, the dialysate would be a linguistically appropriate designation only for what diffuses through the membrane and not for all the liquid on the dialysate side). The blood flows over one side of the membrane and the dialysate over the other side. Substances dissolved in the blood, which would normally be excreted by healthy kidneys, pass through the membrane though diffusion (driven by the concentration difference between the liquids) and are washed away by the dialysate. Certain substances, which should remain in the blood, are counterbalanced by a largely equal concentration of them in the dialysate. Other substances which need not be excreted are replaced through physiological regeneration or, if needed, by means of infusion (or their molecules are too big to be able to pass the membrane to any important amount). For the water balance, excessive water in the patient’s blood is, furthermore, extracted through ultrafiltration through the membrane (driven by a pressure difference between the two liquids), which also carries substances with it (convection). All this takes place in a device called a dialyzer (or, in British English: dialyser). It is, of course, also possible to make substances diffuse (or even filtrate) from the dialysate into the blood.

The modern form of a dialyzer is the hollow-fiber dialyzer. It has a bundle of thousands of parallel hair-thin hollow fibers, actually very thin tubings, the walls of which form the membrane. The blood flows inside the fibers and the dialysate flows between them. Even though other arrangements have been tried in the past, it is proven both theoretically and practically that the most effective configuration is that of counterflow, i.e., that the dialysate flows in a direction opposite to that of the blood flow. The basic problem for performance calculation, optimization and design is to calculate the mass transfer in such a device.

The equations for this are the same as for heat transfer in a tubular heat exchanger, having an arrangement with a multitude of parallel metal tubes. This problem has been solved long ago by Leo Graetz and his solution was published in 1885. In the case of heat exchangers, the thermal diffusion resistance of the tube wall can be neglected, being far less than in the layers of the flowing liquids. Therefore, this wall resistance is (as a good approximation) set to zero in the Graetz solution. However, in the case of hollow-fiber dialyzers, the mass-diffusion resistance of the fiber wall cannot be neglected, but its consideration is essential in this case. This calls for a generalization of the Graetz solution, which didn’t exist before. The author of this webpage set out to solve this problem in 1969-1970, about which he wrote a book A Mathematical Theory for the Capillary Artificial Kidney (Hippokrates, Stuttgart, 1974), available here* in the PDF format.

Regrettably, this theory – apparently for lack of mathematical knowledge – hasn’t found much attention in the dialysis industry. Since the theory is on an advanced level of mathematics, the common approach in the industry is rather to design by cut-and-try, experimentation and experience, based on rough estimates of the mass transfer through simpler calculations. The author has, however, applied this theory with much success in his own work, calculating, optimizing and designing various hollow-fiber dialyzers in a much more exact and appropriate manner. It is his hope that this knowledge and procedure will survive to the afterworld… And if it is spread through the Internet to the industry, to university institutions and any interested or dedicated person, it may…

The basic theoretical work is presented on this webpage in the form of publications available as PDF files. Its application in the optimization of hollow-fiber dialyzers is discussed here. A brief description of the handling of hollow fibers and assembling them to a dialyzer is given here.

The first commercially available hollow-fibers (Cuprophan ^®, cellulosic cuprammonium rayon fibers from Akzo AG in Wuppertal, Germany – earlier Enka Glanzstoff AG) had a sufficient but not very high ultrafiltration, i.e., permeability to water flow driven by the pressure difference (the transmembrane pressure). At that time, the basic design didn’t need much consideration of the effect of ultrafiltration on the mass transfer. Later, fibers with much higher ultrafiltration were developed and the need arose for also considering its effect on the mass transfer. This was done in an extended study by the author, published in an article “Calculation of combined diffusive and convective mass transfer” in The International Journal of Artificial Organs (Wichtig, Milano, Vol. 5, No. 6, pp. 361-371, 1982), available here* as a PDF file. Combining things, a review was published as Chapter 5: “Operating Characteristics of Hollow-Fiber Dialyzers” in Clinical Dialysis – Second Edition, ed. by Allen R. Nissenson et al. (Appleton & Lange, Norwalk, Connecticut, 1990, pp. 97-117), available here* as a PDF document.

The problem of reversed filtration

Using a hollow-fiber membrane with a high ultrafiltration permeability, the question about reverse filtration arises. If there is a local reversion of the transmembrane pressure, so that at some location in the dialyzer the dialysate pressure becomes higher than the blood pressure, reverse filtration will occur. This could even occur as a result of differences in the osmotic pressure. Such a situation is risky, since if dialysate filtrates into the bloodstream, pyrogens and other potentially harmful substances or even microparticles or germs could enter the bloodstream from a not perfectly sterile and pyrogen-free dialysate. Conditions under which this could occur are discussed in German in the article “Rückfiltration durch hochpermeable Membranen und grundlegende Beziehungen des Austauschvorganges”, Nieren- und Hochdruckkrankheiten, Vol. 15, No. 5, 1986, pp. 197-199, available here*.

Comparing dialyzers

In the 1980es I published a few articles with long lists of dialyzers available on the market (the lists are now outdated). In order to compare performance, it is suitable to recalculate values to a standard surface area, e.g., 1 m², since the individual dialyzers have different membrane areas. Formulae for recalculations were given as an introduction to one of these articles: “Comparison of Hollow Fiber Dialyzers”, Artificial Organs, Vol. 5, No. 4, 1981, available here*.

Optimal design of a hollow-fiber dialyzer

This review of calculation procedures and other aspects of the OPTIMAL DESIGN OF HOLLOW-FIBER DIALYZERS is based on theoretical and practical studies of the author as well as professional experience.

Some provocative texts:

Unconventional thoughts about kidney problems and dialysis

Aluminum and Alzheimer – the evidence from dialysis

In Deutsch: Aluminium und Alzheimer – Indizien aus der Dialyse

* Summary of publications available on this page:

A Mathematical Theory for the Capillary Artificial Kidney (Hippokrates, Stuttgart, 1974)
here made available with permission of MVS Medizinverlag Stuttgart in Germany, of which Hippokrates Verlag is to day a part.
Some improvements, corrections and remarks have been introduced in the text.

This is a book and takes time to download! (File size 24.5 MB.)

For those who already have the printed book: Here are some corrections.

“Calculation of combined diffusive and convective mass transfer”, The International Journal of Artificial Organs (Wichtig, Milano, Vol. 5, No. 6, pp. 361-371, 1982)
here made available with the permission of Wichtig Editore S.R.L., Milano, Italy.

“Operating Characteristics of Hollow-Fiber Dialyzers” in Clinical Dialysis – Second Edition, ed. by Allen R. Nissenson et al. (Appleton & Lange, Norwalk, Connecticut, 1990, pp. 97-117)
here made available with the permission of McGrawHill, New York, which company has acquired Appleton & Lange; no changes have been made other than a few minor corrections which were indicated in the galley proofs but not carried out.

“Rückfiltration durch hochpermeable Membranen und grundlegende Beziehungen des Austauschvorganges”, Nieren- und Hochdruckkrankheiten (Dustri-Verlag, München, Vol. 15, No. 5, 1986, pp. 197-199)
here made available with the permission of Dustri-Verlag, Oberhaching, Germany.

“Comparison of Hollow Fiber Dialyzers”, Artificial organs (Vol. 5, No. 4, 1981, pp. 401-409)
here made available with the permission of the editor-in-chief of the journal Artificial Organs.

Some minor corrections and improvements are introduced in most of these publications

NEW ADDITION: This is what we may expect more of in times of such things as a financial crisis: http://www.miamiherald.com/business/story/1413134.html

(This report is no more there, but was about a clinic in Florida that refuses dialysis for the elder or poor.)

So it is all about money, isn't it ... ?

This webpage is operated by

Dr. Jan Erik Sigdell

Dutovlje 105

SI-6221 DUTOVLJE

Slovenia

Tel. ++386 – 5 – 764 04 67

The e-mail address is displayed as a picture in the top left corner of this page.

(Presented this way, it is protected against scanning e-mail addresses for spam.)