Blood Pump Design Variations and Their Influence on Hydraulic Performance and Indicators of Hemocompatibility.

Patients with ventricular assist devices still suffer from high rates of adverse events. Since many of these complications are linked to the flow field within the pump, optimization of the device geometry is essential. To investigate design aspects that influence the flow field, we developed a centrifugal blood pump using industrial guidelines. We then systematically varied selected design parameters and investigated their effects on hemodynamics and hydraulic performance using computational fluid dynamics. We analysed the flow fields based on Eulerian and Lagrangian features, shear stress histograms and six indicators of hemocompatibility. Within the investigated range of clearance gaps (50-500 µm), number of impeller blades (4-7), and semi-open versus closed shroud design, we found association of potentially damaging shear stress conditions with larger gap size and more blades. The extent of stagnation and recirculation zones was reduced with lower numbers of blades and a semi-open impeller, but it was increased with smaller clearance. The Lagrangian hemolysis index, a metric commonly applied to estimate blood damage, showed a negative correlation with hydraulic efficiency and no correlation with the Eulerian threshold-based metric.

[Lacrimal duct treatment with ring intubation in injuries of the upper and lower eyelids]. / Tränenwegsversorgung mittels Ringintubation bei Verletzungen des Ober- und Unterlids.

BACKGROUND: Treating injuries of the lacrimal system with a silicon intubation is an approved method to prevent post-traumatic epiphora. MATERIALS AND METHODS: Between 1990 and 1999, operations were carried out on 44 patients with injuries of the canaliculi with silicon ring intubations. Interesting for us were the age distribution, causes of injuries, localisation and mid- to long-term postoperative complications. RESULTS: The age of the patients was between 1.75 and 74 years, 48% of the injuries were caused by household accidents, 23% by violence, 20% by traffic accidents and 9% by job-related accidents. The canaliculus inferior was injured in 68% of all patients. We found 10 postoperative complications, e.g. ectropia, a too long silicon ring or granuloma. We found a positive anatomical readapted lacrimal system in 88% and 12% of our patients complained of distinct to severe epiphora. CONCLUSIONS: The treatment of lacrimal laceration with a silicon intubation is an excellent method but special care should be taken with correct positioning of the lid margin.