Living donor kidney transplantation from the elderly donor.

PURPOSE: The organ shortage has led to increasing acceptance of living donation in all transplant centers. Although the risk of impaired long-term outcome seems to be greater using elderly donors, these organs are not generally refused for transplantation. We report our experience with 25 living donor kidney transplantations from donors older than 60 years. METHODS: Between 1995 and 2004, 124 living donor procedures were performed in our center from 83 related and 41 unrelated donors. Twenty-five donors (19 female, 6 male) were 60 years or older (mean, 65.3 +/- 3.9 years). The recipient included (10 females and 15 males) showed a higher degree of variance in age (46.1 +/- 14.6 years). The immunosuppressive protocol was cyclosporine (CyA)-based regimen in related cases and tacrolimus-based in unrelated cases. RESULTS: We transplanted 16 left and 9 right kidneys from older donors. The mean cold ischemia time was 171 +/- 64 minutes with a second warm ischemia time of 24 +/- 6 minutes. Severe arteriosclerosis made vascular reconstruction by graft interposition necessary in two recipients. The acute rejection rate was 20%. Two patients (8%) required dialysis in the early postoperative course, whereas initial function was excellent in 22 patients (88%). The mean serum creatinine concentration after 12 months was 1.6 +/- 0.3 mg/dL (n = 24) and 2.0 +/- 0.7 mg/dL (n = 16) at 4 years. In comparison, the mean creatinine concentration after 4 years in donors under 60 years was 1.6 +/- 0.9 mg/dL. Our analysis showed no significant difference in long-term graft function comparing young versus old donors in the setting of living donor transplants. CONCLUSION: Using living donors older than 60 years for transplantation is a feasible and safe option. The difference in long-term creatinine between young and old donors was not significant.

Modelling gradient elution of bioactive multicomponent systems in non-linear ion-exchange chromatography.

A theoretical framework for the ion-exchange behaviour of bioactive substances in non-linear ion-exchange chromatogaphy is described. The aim of the study was the creation of a model basis to support a process design for production-scale ion-exchange chromatography. The theory can be applied to a whole variety of biological substances, such as amino acids, polysaccharides, peptides and proteins and either isocratic or gradient elution can be carried out. The influence of the eluent concentration on the ion-exchange as well as on the characteristic charge was considered. Experimental measurements showed a strong non-linear ion-exchange equilibrium with a transition from a Langmuir-type to a sigmoidal isotherm at higher eluent concentrations. Hereby, the compound binds to the surface though it is not ionic. Therefore, the model considered the possibility of ion-exchange as well as adsorption. A simplified distribution of the counter-ions based on the Gouy-Chapman theory with a discrete distribution of the counter-ions was used. The theory was extended by a selectivity in the double layer to allow specific adsorption. Calculations of adsorption-elution cycles showed, in agreement with the experimental observations, the development of non-linear elution profiles with a desorption fronting. As a result, the column loading and the eluent concentration were varied. The effect of contaminants, in this case sodium ions, was investigated and included in the model. Finally, the model was extended to multicomponent systems to investigate the effect of side components on the retention behaviour. The development of the characteristic elution profiles and the effect of the column loading on the separation are discussed. Calculated concentration profiles along the column at discrete time steps were used to reveal the influence of side components and the underlying separation mechanism. The simulations provided a new insight into the phenomena involved in biochromatography and make convenient design concepts at least doubtful as the separation is in this case mainly determined by the loading step and not by the choice of the elution gradient.

Desorption of a fixed-bed adsorber by ultrasound.

Adsorption processes offer the possibility to remove trace impurities of liquid process streams. An important step in adsorption processes is the regeneration of the adsorbent as it does not only affect the adsorption-desorption cycle but also the expenses of the following process steps. In this study, various desorption experiments of a loaded polymeric resin have been conducted. They were performed with cold and hot water as well as with ultrasound at different frequencies and intensities. The results indicate, that an important factor of ultrasound enhanced desorption is the temperature rise due to ultrasonication. But as regeneration is more effective at higher frequencies even though temperatures inside the column are lower, another ultrasonic effect occurs during ultrasonic desorption.

Effect of the homogeneity of the column set on the performance of a simulated moving bed unit. I. Theory.

Although it is impossible to manufacture identical columns for use in a simulated moving bed (SMB) process, theoretical studies assume that all the columns in an SMB unit have identical characteristics. In practice, calculations in modeling and optimization studies are made with the average values of each column parameter set. In this report, the effects on SMB process performance caused by column-to-column fluctuations of the parameters are discussed. As a first step, we show how the differences in porosity of the columns may be taken into account with a revised set of separation conditions. Reductions in the purity of the extract and the raffinate streams are quantitatively related to the column-to-column fluctuations of the retention times of the two components arising from these porosity differences. For the sake of simplicity, the discussion first addresses the case of a four-column SMB operating under linear conditions. Then, the scope is extended to the cases of SMB units incorporating several columns in each section and to SMB units operating under nonlinear conditions.