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P Ahrenholz

Publications and source records attributed to P Ahrenholz.

14 recordsLinked to original sources
PubMed1991

Theoretical basis and experimental verification of the impact of ultrafiltration on dialyzer clearance.

Dialyzer clearance K is usually presented as K = K0 + Tr Qu, were Qu is ultrafiltration rate, K0 is clearance for Qu = 0, and Tr is transmittance coefficient. Although a simple and accurate mathematical description of K0 is widely used, only a somewhat inaccurate formula for Tr that predicts a linear relationship between Tr and K0 has been proposed before. In this study the detailed investigation of Tr using a one-dimensional theory of a dialyzer is presented. In general, the application of a one-dimensional theory requires sophisticated numerical methods, but for small and middle molecular weight solutes an analytical formula for K can be derived. Tr predicted by the developed theory in comparison to Tr predicted by the previous linear formula is higher for small molecular weight solutes and lower for middle and large molecular weight solutes. These theoretical results were confirmed in experiments carried out in vitro for hollow-fiber dialyzers and small molecular weight solutes (urea, creatinine, sodium, TcO4) as well as middle molecular weight solutes (vitamin B12).

Hemofiltration↗
PubMed1990

Measurements of plasma colloid osmotic pressure, total protein and sodium concentration during haemodialysis: can single-pool sodium modelling explain the results?

Considering the plasma colloid osmotic pressure (COP) as a possible parameter for the monitoring of dialysis treatment compatibility, a characteristic time course was found. The COP and the total protein concentration very often do not increase significantly during the first treatment hour in spite of ultrafiltration. An increase in the plasma sodium concentration, which was higher than expected, was found to be the reason for a plasma dilution effect. This can be explained by a transcapillary sodium transfer coefficient which is not infinitely high as assumed in single-pool sodium modelling. From a 2-pool model considering the plasma volume as a separate pool and including capillary filtration time courses for plasma sodium, total protein concentration and COP could be calculated, which was very similar to the measured curves.

Blood Proteins↗
PubMed1990

[Precision of data from models of sodium kinetics in hemodialysis].

The 1-pool-model of sodium kinetics during hemodialysis is based upon the assumption of an immediate compensation of osmotic shifts. This assumption is not supported by measurements of plasma sodium, total protein concentration and colloid osmotic pressure kinetics. When a high dialysate sodium concentration is applied, an inflow of sodium into the plasma space occurs, which results in an osmotic suction and thus a plasma dilution. These conditions can be represented by a 2-pool-model taking into consideration capillary filtration. The results indicate that following the first treatment period the sodium kinetics are sufficiently explained by a 1-pool-model with the total body water as distribution volume. Both the plasma sodium concentration and the eliminated sodium at the end of a hemodialysis treatment can be described to an acceptable level by the 1-pool-model. The input of the measured in-vivo sodium dialysance value (or alternatively the urea clearance) is necessary.

Blood Proteins↗
PubMed1988

[Determination of clearance for urea-controlled hemodialysis].

Through a simple variant of the urea model the qualitative influence of the dialyzer-clearance on the individual dialysis guidance is elucidated. Realization of the respective Kdtd/V-value require an exact knowledge of the in-vivo-urea-clearance of all available dialyzer types and their manipulation with the aid of blood flow. The theoretical connections are explained and possible parameters affecting the in-vivo-clearance are discussed. The results concerning the dependence of urea-clearance on the blood flow are presented in an urea-guided dialysis patient pool for all in the GDR customary in the trade or temporary available dialyzers. It is shown, that in MLW-dialyzers an influence on the urea-clearance about the blood flow is small because of their relatively thick-walled membrane. Therefore, the development of dialysis membranes with superior diffusible permeability is necessary.

Blood Flow Velocity↗
PubMed1988

A simplified procedure to compute dialysis time and frequency by means of urea kinetics.

A simplified urea model is presented based on the concept of the time-averaged deviation (TAD) of the blood urea concentration and the introduction of an effective urea generation rate. The increase in the interdialytic blood urea concentration delta c is specific for the individual patient and includes the urea generation rate, distribution volume and residual kidney clearance. By measuring delta c of the largest interdialytic interval of the week the treatment frequency and duration can be calculated. Even for larger residual clearances Kr less than or equal to 5 ml/min this calculated treatment time does not differ by more than 5 min from the result of the exact urea kinetics. In vivo estimation of the urea clearances versus blood flow for the dialyzer types used is necessary for the application of urea modelling in clinical practice.

Blood Flow Velocity↗
PubMed1986

[Current status and future perspectives of extracorporeal blood purification].

After the description of the main indications for an extracorporeal blood purification the authors enter the at present existing and applied detoxication methods on the basis of membranes and absorbents, respectively. A short characterization of the most important membrane separation techniques peritoneal dialysis, haemodialysis, haemofiltration, haemodiafiltration and membrane plasma separation, respectively, is given. Moreover, an estimation of the cascade methods is given, i.e. the application of several separation filters. As adsorptive methods the haemoperfusion and the plasma perfusion, respectively, are assessed with their advantages and disadvantages and the authors enter the possibility of the combination of the procedures mentioned. As problems which are to be solved still in the first place the deficient blood compatibility, selectivity, individualization and continuity are discussed and ways of solution are shown which up to now are entered upon for the improvement and optimization, respectively, of the problems mentioned. In this case particularly the surface modification of materials and the search for new materials, respectively, as well as the use of special models is emphasized as important for future. In the field of selectivity adsorptive methods are to be developed in the first place which without danger of complications remove relevant metabolites from the organism. For the future is above all to be reckoned with the further development of so-called hybrid organs, since such organs may best repeat biological processes.

Acute Kidney Injury↗
PubMed1982

Tc-99m-DTPA--a new test substance for detoxification devices.

Tc99m labeled diethylenetriaminepentaacetic acid (Tc-99m-DTPA) is an appropriate in vivo test solute for all extracorporeal detoxification procedures. The molecular weight of the Tc-99m-DTPA complex is within the biologically relevant middle molecular range of 400 to 700 daltons. Tc-99m-DTPA is distributed in the extracellular space in the same way as inulin. Regarding its localization in the gel filtration spectra and plasma clearance, Tc-99m-DTPA corresponds to middle molecule peak 2. The evaluation of elimination rate and plasma clearance CP of Tc-99m-DTPA is possible by measuring the pulse rates before and after the detoxification device. Taking into account the corrections for Ht and UFR, the Tc-99m-DTPA plasma clearances were calculated for different dialyzers, high flux dialyzers, hemofilters and a hemoperfusion device. The continuous measurement of pulse rates and the use of a UFR-controller (A2008) allow an exact tracking of CP vs. time, the estimation of CP (QB), CP(UFR) and of the sieving coefficient. Examples are given for these cases. It was shown that an increase in plasma clearance to more than about 100 ml/min does not greatly increase the Tc-99m-DTPA elimination rate.

Humans↗
PubMed1982

Volumetrically controlled ultrafiltration. Current experiences and future prospects.

Exact control of ultrafiltration (UF) is a prerequisite for high flux dialysis and hemodiafiltration. Volumetric dialysate balancing is the best current method for the use of dialyzers with high water permeabilities. The precision of UF control by volumetric dialysate balancing is in agreement with all medical requirements. A positive influence of volumetric UF control on patients undergoing chronic hemodialysis can be shown by the frequencies of dialysis side effects. Volumetric UF control is only a first step towards an intelligent UF module to correlate water removal, solute removal and sodium balance.

Body Water↗
PubMed1981

Continuous measurement of DTPA-clearance in extracorporeal detoxification circuits.

A new method for investigating clearances is described. DTPA labelled with technetium 99m (MW: 496 daltons) is used as an agent to be measured. Continuous determination of the DTPA-clearance is possible in extracorporeal detoxification circuits including dialyzers, hemofilters and hemoperfusion columns. As an example, DTPA-clearances are given for two different dialyzers. In comparison to clearance measurements of peak 7, DTPA-clearance was very similar to that obtained for peak 7.

Autoanalysis↗
PubMed1980

[Developmental tendencies of hemadsorption in uremia treatment].

After at first having dealt with the present stage of haemoperfusion in the therapy of chronic renal insufficiency, the developmental tendencies for the haemoadsorbers to be expected are mentioned which in future allow to think of a diminution of the artificial kidney. Own results concerning the behaviour of blood compatibility and the effectivity of different active charcoals show that it is to be reckoned with the further development of unstratified adsorbents or such ones with ultra-thin layer. Comparative examinations of 4 patients from the chronic haemodialytic programme, who were treated for 4 months with the CDAK 1.8 and then for 4 months with the sorbent dialyser 1.3, could not show any essential differences in the behaviour of the low-molecular substances urea, creatinine and uric acid and of the clinical condition of the patients.

Creatinine↗
PubMed1980

[Technics and indications for hemofiltration treatment].

Technique, possibilities of application, advantages and disadvantages of haemofiltration are described. A convective mass transport underlies the method. By this means the elimination of molecules of different size takes place with the same speed and the removal of so-called middle molecules is performed more effectively than in the usual method of dialysis.

Acute Kidney Injury↗