Influence of orientation of bi-leaflet valve prostheses on coronary perfusion pressure in humans

Orientation of a bi-leaflet prosthesis (BLP) might influence coronary perfusion. The aim of this study was to investigate the influence of the orientation on coronary perfusion pressure during hyperemia and adrenergic stimulation. During hyperemia perfusion pressure determines coronary blood flow. Fourteen patients with normal coronary angiogram underwent aortic valve replacement (AVR) by a BLP, and seven received a bio-prosthesis. Patients receiving a BLP were randomized to either orientation A (hinge mechanism perpendicular to a line drawn between the coronary ostia) or B (hinge mechanism parallel to the line between the ostia). Six months after surgery all patients underwent cardiac catheterization. Pressures were measured during resting conditions, during maximum hyperemia, and during maximum adrenergic stimulation with a guiding catheter in the aortic arch (Pao), simultaneously with a sensor tipped guide wire in the coronary artery (Pcor) and in the aortic root (Proot). Pao-Proot described a flow-induced pressure drop in the aortic root (Venturi effect) and the gradient Proot-Pcor described coronary ostium abnormalities. Only small non-significant differences in myocardial perfusion pressure were found between different orientations of a bi-leaflet prosthesis or between bi-leaflet prostheses and bio-prostheses in Pao-Proot and Proot-Pcor

Validation of a patient-specific hemodynamic computational model for surgical planning of vascular access in hemodialysis patients

Vascular access dysfunction is one of the main causes of morbidity and hospitalization in hemodialysis patients. This major clinical problem points out the need for prediction of hemodynamic changes induced by vascular access surgery. Here we reviewed the potential of a patient-specific computational vascular network model that includes vessel wall remodeling to predict blood flow change within 6 weeks after surgery for different arteriovenous fistula configurations. For model validation, we performed a multicenter, prospective clinical study to collect longitudinal data on arm vasculature before and after surgery. Sixty-three patients with newly created arteriovenous fistula were included in the validation data set and divided into four groups based on fistula configuration. Predicted brachial artery blood flow volumes 40 days after surgery had a significantly high correlation with measured values. Deviation of predicted from measured brachial artery blood flow averaged 3% with a root mean squared error of 19.5%, showing that the computational tool reliably predicted patient-specific blood flow increase resulting from vascular access surgery and subsequent vascular adaptation. This innovative approach may help the surgeon to plan the most appropriate fistula configuration to optimize access blood flow for hemodialysis, potentially reducing the incidence of vascular access dysfunctions and the need of patient hospitalization

Geometric representations for minimalist grammars

We reformulate minimalist grammars as partial functions on term algebras for strings and trees. Using filler/role bindings and tensor product representations, we construct homomorphisms for these data structures into geometric vector spaces. We prove that the structure-building functions as well as simple processors for minimalist languages can be realized by piecewise linear operators in representation space. We also propose harmony, i.e. the distance of an intermediate processing step from the final well-formed state in representation space, as a measure of processing complexity. Finally, we illustrate our findings by means of two particular arithmetic and fractal representations.Comment: 43 pages, 4 figure