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Biomedical subjects

D Falkenhagen

Publications and source records attributed to D Falkenhagen.

At least 73 records · Page 4Linked to original sources
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↗
PubMed1988

[Hemocompatibility testing in the rat model by noninvasive blood flow measurement using an arteriovenous shunt].

The flowing periods of blood through biomaterial shunts were measured by means of a noninvasive sensor with sufficient reliability. Falsifications of the measuring results by foreign influences as roller pumps, punctures, changes of the cross section, or the coupling of different materials were avoided extensively. The accomplishment of the test is possible routinely without a great display of apparatus.

Animals↗
PubMed1988

[Hemorheological/hemodynamic study on miniaturized capillary filters in the concept of an implantable artificial kidney].

The conception of an implantable kidney provides the substitute of the non-functioning kidney by a technical-biological system. The filtration function is to be performed by a capillary hemofilter. The results obtained in an open test circulation on 3 filters produced by optimum aspects were represented and compared with the physiological performance parameters of the kidney. The special importance of the construction of the flow conditions in the single capillary is accentuated as the fundamental aspect for additional optimization. An optimized capillary filter produced the necessary filtration rate for maintaining the homeostasis on condition of a low-protein diet and an increased level of blood urea. The changes of the hemorheologic parameters is to come up by an adequate absorption of fluid in the colon.

Capillaries↗
PubMed1988

[Modelling and simulation of urea balance in a rat model on the condition of large intestine infusion analogous to the ultrafiltrate as a contribution to the development of an implantable intestinal hybrid kidney].

The urea kinetics in blood plasma is discussed for the animal model in rats in the development conception of an implantable artificial kidney, in which the filtration process is received energetically endogenically by a technical hemofilter whereas the ultrafiltrate procedure takes place by intestinal reabsorption and elimination of the end-products. The underlying monocompartment model contains the elements plasma, hemofilter, intestine including their urea turnover rates. Further on a special model conception is developed for the animal experimental designation of the selective urea reflecting power of the intestinal mucosa. The hemofilter-intestine-hybrid kidney-system has chanced to be in order if the experimentally ascertained quantities of the preliminary experiments will be inserted simultaneously for essential parameters in the model experiment.

Animals↗
PubMed1988

[The selective elimination function of the colon in a rat model for the substances water and urea in long-term experiments as a contribution to the development of an implantable hemofilter-intestine-hybrid kidney].

The investigations on the selective elimination and preservation function of the colon represented one of the numerous problems in the development of an implantable hemofilter-intestine-hybrid kidney. The assumption of an ideal reflection of urea on the intestinal mucosa and the ability of water absorption of the colon had to be checked. A fluid which is nearly analogous to the ultrafiltrate with different urea concentrations was infused into the colon of rats by a cecocutaneous catheter fistula during two-phasic long-term experiments. The renal and enteral urea elimination rates were defined. The apparent reflection coefficient for urea of the colon amounted 0.5 to 0.6 in an infusion rate of 80 ml/day. The ability of water absorption of the colon in rats of nearly 300 g of weight could be increased up to 200 ml/day during slow and continuous adaptation in the infusion quantity.

Animals↗
PubMed1988

[Extracorporeal blood circulation in the unanesthetized free-moving rabbit--an animal model for biocompatibility studies].

The rabbit is suitable as a basis model for the extracorporal circuit (ECC) in long-term test (20 days). A decrease of the leucocytes and platelets is established already in the blank test qualified by catheter material and pumping influence. This effect can be compensated by the rabbit in long-term test. The typical decrease of the leucocytes and platelets does not show any significant alteration during many test days independent of the number of tests which were carried out in one rabbit (blank test and hemoperfusion). A hemoperfusion across activated carbon--independent of the albumin coating--leads to a significant decrease of the leucocytes in comparison to the blank test. This rabbit model is well-suitable for biocompatibility investigations respectively also for effective investigations of detoxication techniques taken as a basis of our results.

Animals↗
PubMed1987

In vitro investigations with selective adsorbents for IgE and IgM.

In vitro studies were carried out with IM-T. This adsorbent consists of polyvinyl alcohol joined with tryptophan side chains and was delivered by ASAHI Medical Co., Ltd., Tokyo/Japan. It was found that IM-T binds immunoglobulins G and M and also immune complexes only moderately but IgE was adsorbed in remarkable amounts. A clear dose-dependent was adsorbed in remarkable amounts. A clear dose-dependent manner of the IgE adsorption could be stated. Kinetic studies revealed that the binding was only slow and gradual.

Animals↗
PubMed1987

A clinical study on different cellulosic dialysis membranes.

A controlled clinical study was performed over a period of 8 weeks in two dialysis centres (Rostock, GDR, and Munich, FRG). The aim was to compare a dialysis membrane made of modified cellulose (Hemophan) with classical regenerated cellulose (Cuprophan). Dialysers containing these membranes, together with a cellulose acetate dialyser, were therefore incorporated in a cross-over programme and clinical and biochemical investigations undertaken. The efficacy of the modified cellulosic membrane with respect to urea and creatinine clearance was shown to be comparable to that of regenerated cellulose and cellulose acetate. However, modified cellulose showed an increased clearance for inorganic phosphate, significantly different from that demonstrated by both regenerated cellulose and cellulose acetate. Blood compatibility studies, which included the assessment of C3a activation and the reduction of white blood cell (WBC) and platelet count, clearly demonstrated that in comparison to regenerated cellulose, modified cellulose resulted in significantly less complement activation and WBC reduction. Similarly in comparison to cellulose acetate, modified cellulose showed reduced complement-activating and WBC-reducing properties. The reason for the improved blood compatibility of modified cellulose is not, as was originally assumed, related to binding of complement-inhibiting heparin, but appears instead to be due to the substitution of hydroxyl groups of regenerated cellulose.

Biocompatible Materials↗
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↗
PubMed1986

Preclinical evaluation of haemosorbents.

The selection of assessment procedures for the preclinical evaluation of haemosorbents and the relationship between such procedures and the intended application are exemplified by examination of the design and utilization of procedures based on the rat. Procedures are described for haemoperfusion and for membrane plasma separation followed by on-line sorbent treatment of plasma (plasma perfusion). These procedures are suitable for single or repeated use, with the animal in an unrestrained and conscious state. The relevance to the intended application is demonstrated with respect to artificial liver support by the ability of rat extracorporeal circuits to provide information on the relationship between sorbent properties and liver regeneration as determined by the proliferative response following partial hepatectomy.

Adsorption↗
PubMed1986

Experiments with continuous hemofiltration and hemofiltrate regeneration in the rat.

Experimental studies were made with continuous hemofiltration treatment for bilaterally nephrectomized rats and initial observations regarding the effects of such treatment on leukocyte and thrombocyte counts are reported. Hemofiltration of unanesthetized rats able to move freely within their cage could be continued for up to 30 h using a pump-driven ECC system. Blood parameters recorded during this treatment indicate that the detoxification was effective. In another series of experiments the water and electrolyte reabsorption capacity of the colon ascendens of healthy rats was tested by continuously supplying NaCl solution into the colon via a fistula. A large proportion, if not all, of the hemofiltrate can be discharged into the colon without diarrhoea. A final series of experiments showed that the three-stage operation (implantation of permanent catheters, connection of a permanent intestinal fistula and bilateral nephrectomy) is possible with the rat.

Animals↗
PubMed1985

Cell electrophoretic investigations of peripheral blood lymphocytes during hemodialysis with different membranes.

Determining the relative percentage of LMC in PBL histograms of RDT patients during hemodialysis we observed a temporary decrease of the LMC proportion during the first 15 minutes of hemodialysis using Cuprophan in contrast to AN 69S and MC Cellulose. These results correlate with the increase of C3a plasma concentration and the decrease of total count of granulocytes. In all investigated RDT patients higher proportions of LMC could be found in relation to healthy donors already before dialysis treatment. Our study therefore seems to indicate that the application of cell electrophoresis is a useful method for the characterization of lymphocytes during extracorporeal circulation as an additional parameter of blood compatibility.

Acrylic Resins↗
PubMed1985

[Effects of the hemodialyzer on blood gases and acid-base equilibrium].

During bicarbonate and acetate dialysis the blood gas parameters and the acid-base balance values were measured before and after the dialyzer. Significant changes of these values are revealed after the dialyzer passage of the blood. This result constrains to a decoupled approach of the entire system organism-extracorporeal circulation, when the interpretation of values measured in the arterial part of this system and the judgment of the haemodialysis system following from this are concerned.

Acetates↗
PubMed1985

[Behavior of the hypothalamo-hypophyseal unit to stimulation with arginine, GnRH and TRH in patients with chronic uremia].

In 11 women aged from 20 to 47 years (average age 33,1 years) with chronic uremia, treated by hemodialysis, a sequential stimulation test (SST) with 0.5 g arginine hydrochloride per kg body weight, 25 micrograms GnRH and 200 micrograms TRH was performed to examine the responsibility of the hypothalamo-pituitary unit. For evaluation of basal and stimulated secretion of PRL, LH, FSH, TSH, and HGH the corresponding serum levels were determined by RIA. 10 of the 11 women showed a galactorrhoea. No correlation between levels of PRL and creatinine could be found. Menstrual disorders in women with chronic uremia are discussed in the context of basal LH serum levels nearly always unphysiologically increased. In a few cases disturbances of basal secretion of TSH and HGH, respectively, could be observed.

Adult↗