Computational flow modeling in hollow-fiber dialyzers

A three-dimensional finite volume model of the blood-dialysate interface over the complete length of the dialyzer was developed. Different equations govern dialyzer flow and pressure distribution (Navier-Stokes) and radial transport (Darcy). Blood was modeled as a non-Newtonian fluid with a viscosity varying in radial and axial direction determined by the local hematocrit, the diameter of the capillaries, and the local shear rate. The dialysate flow was assumed to be an incompressible, isothermal laminar Newtonian flow with a constant viscosity. The permeability characteristics of the membrane were calculated from laboratory tests for forward and backfiltration. The oncotic pressure induced by the plasma proteins was implemented as well as the reduction of the overall permeability caused by the adhesion of proteins to the membrane. From the calculated pressure distribution, the impact of flow, hematocrit, and capillary dimensions on the presence and localization of backfiltration can be investigated.     

Colorectal hemangioma: radiologic findings

The authors correlated radiographs with the clinical and histologic data of 12 patients with colorectal hemangioma. All patients presented with rectal bleeding, which was chronic in seven. Phleboliths were also visible in seven cases, which correlated with chronic bleeding in five. On barium studies, three masses were soft and three produced rigid narrowing. The atypical features of rigid luminal narrowing, which might mimic a carcinoma, and hypovascularity correlated with chronic bleeding or visible phleboliths, which suggest the correct diagnosis of colorectal hemangioma.     

Dialysate partitioning in the Genius batch hemodialysis system: effect of temperature and solute concentration

BACKGROUND: The Genius batch system contains a 75-L closed reservoir from which fresh dialysate is extracted at the top, and to which spent dialysate is returned at the bottom. In vivo studies have demonstrated that almost the entire amount of dialysate can be used before contamination of fresh with spent dialysate occurs. The question is raised whether density differences cause this separation, and what the relative contributions of temperature and solute content are. METHODS: As patient substitute, a container filled with dialysate was loaded with various amounts of urea. Temperature differences between spent and fresh dialysate were imposed by not heating the dialysate at the outlet line from the dialyzer (A), heating the outlet to obtain continuously equal temperatures at inlet and outlet (B), or to temperatures as in vivo (C). With a dialysate flow set at 300 mL/min, urea is not expected at the inlet before 250 minutes. RESULTS: With a urea concentration of 33 mg/dL, urea contamination at the dialysate inlet line occurred after 185 +/- 20 (A), 122 +/- 11 (B), and 175 +/- 12 minutes (C) of dialysis, whereas with 67 mg/dL, this happened at 219 +/- 5 (A), 162 +/- 11 (B), and 202 +/- 8 minutes (C). With 100 and 150 mg/dL, urea contamination appeared at 224 +/- 2 (A) and 204 +/- 14 minutes (B), and 227 +/- 5 (A) and 232 +/- 3 minutes (B), respectively. CONCLUSION: Both temperature differences between spent and fresh dialysate and solute content of spent dialysate contribute to dialysate partitioning in the Genius dialysis system.     

Discovery of pyrimidyl-5-hydroxamic acids as new potent histone deacetylase inhibitors

A series of pyrimidyl-5-hydroxamic acids was prepared for evaluation as inhibitors of histone deacetylase (HDAC). Amino-2-pyrimidinyl can be used as a linker to provide HDAC inhibitors of good enzymatic potency.