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Biomedical subjects

H Reul

Publications and source records attributed to H Reul.

138 records · Page 8Linked to original sources
PubMedDate not supplied

Collected nondimensional performance of rotary dynamic blood pumps.

"Nonpulsatile" or "continuous flow" blood pumps are a relatively new application of the rotary dynamic blood pumping principle. They fall outside the normal envelop of pumps, considering their small size, viscosity of the fluid pumped, need for particularly good internal flow patterns, and desire for high efficiency. This article establishes the state of the art in the field of blood pump performance. Trends in efficiency, shut off pressure coefficient, and nondimensional power behavior as a function of nondimensional flow are identified. Blood pumps show agreement with the published effects of low Reynolds numbers in conventional pumps.

Biomedical Engineering↗
PubMedDate not supplied

[Thermal knot fixation].

Knots represent the weakest point in suture material. As a result of bending and tension, forces develop within the knot that exceed the strength of the suture material and lead to rupture. Furthermore, because of their relatively large surface area, the most pronounced reactions occur in the vicinity of knots. The results of in vitro experiments conducted with the aim of improving the strength of knots are reported. The knot holding capacity of polypropylene filaments (EP 5/USP 2) was determined at room temperature (22 degrees C) after exposure to temperatures of 63, 98 and 150 degrees C. Knots that were exposed to a temperature of 98 degrees C for 10 seconds had a 50% higher holding capacity than untreated knots. With a higher knot holding capacity, secure fixation can be achieved with fewer knots. Since fewer knots have a smaller surface area, a reduction in tissue reaction may be expected.

Heating↗
PubMedDate not supplied

[Suture surface and suture strength of polypropylene monofilaments].

Knots form the weakest sections in suture materials. The addition of forces in the knot caused by bend and tension exceed the strength of the suture material and lead to rupture in the knot. Furthermore the most pronounced tissue reactions occur in the surrounding of knots because of their relatively large surface as compared to the linear filament. With a higher knot holding capacity a secure fixation can be achieved with less knots. As a reduced number of knots leads to a smaller surface a reduced tissue reaction can be expected. Because of high rigidity and a low coefficient of friction synthetic monofilaments achieve only a low knot holding capacity. To improve the knot holding capacity a usually large number of knots is being used. With increasing surface of exogenous materials the extent of foreign-body reactions increases, e.g. formation of granuloma. Results of in-vitro experiments are reported that were conducted to identify the smallest secure knot in polypropylene filaments of various diameters.

Humans↗
PubMedDate not supplied

A synthetic three-leaflet valve.

To increase durability and decrease calcification tendencies, the reduction of mechanical leaflet stress is of prime importance. In order to achieve this for a three-leaflet valve, the leaflets of a new design of prosthesis (the J-3) are manufactured in a medium open, almost flat shaped position, whereby the stent posts are expanded by a cone-shaped mold. Owing to this design, the leaflets have stable closed and open positions, the transition succeeds with low opening pressure. Valves are manufactured by dip-coating in polyurethane. Hydrodynamic evaluation of this polyurethane valve shows minimum pressure drop and very low energy losses compared with other commercially available valves. Very low shear stresses in the flow field downstream of the valve are observed by laser-Doppler-anemometry. In durability tests, prototypes have reached lifetimes equivalent to 17 years. For comparative testing of durability and biocompatibility, six bioprostheses and seven J-3 valves were implanted in mitral position of growing Jersey calves. While animal tests are encouraging, they also reveal necessary manufacturing improvements.

Animals↗
PubMedDate not supplied

Advances in design principle and fluid dynamics of a flexible polymeric heart valve.

The three leaflet J-3 valve is manufactured in a medium open position with almost flat leaflets, whereby the stent is expanded by a cone shaped mold. After manufacturing, the dipcoated leaflets have stable closed and open positions. The transition succeeds with very low membrane stresses. Due to this design, the J-3 polymer valve showed superior hydrodynamic performance compared with commercial valves. In durability tests, prototypes have reached lifetimes up to 17 years. While animal tests are encouraging, they also reveal needed manufacturing improvements.

Animals↗
PubMedDate not supplied

A tricuspid polyurethane heart valve as an alternative to mechanical prostheses or bioprostheses.

The main disadvantages of today's heart valve prostheses are the need for lifelong anticoagulation for mechanical valves and problems with biodegradation for tissue valves. Therefore, a new valve type devoid of these problems would be a major step forward. In order to evaluate a new valve design made by dipmolding with different PU materials, an animal test series was carried out in which two valves from each material were implanted into the mitral position of growing Jersey calves. The surgical procedure and postoperative catheterization data are presented. The survival times ranged between 127 and 291 days. Organs and explanted valves were examined post mortem according to general pathology standards. Specifically, the valves were histologically examined for calcium deposits and investigated by light microscopy, REM and EDAX. All explanted valves showed calcification and immobilization, but the results suggest that at least two PU materials attain survival times which are far beyond the lifetime of bioprostheses under the same implant conditions, justifying further in vivo studies in adult animals.

Animals↗
PubMedDate not supplied

A novel implantable electromechanical ventricular assist device. First acute animal testing.

A novel ventricular assist device (HIA-EMLVAD-AT1, Helmholtz Institute Aachen-Electromechanical Left Ventricular Assist Device-Animal Test Version 1), driven by a uniformly and unidirectionally rotating actuator and a patented hypocycloidic pusherplate displacement gear unit, was developed and tested in an acute animal experiment. The excellent free filling behavior of the pump chamber with a stroke volume of 65 ml is obtained by a 2:3 ejection-filling time relationship. The uniform motor rotation facilitates simple sensorless pre and afterload detection by motor current analysis. In contrast to common apical cannulation, the inlet cannula was placed via the left atrium through the mitral valve into the left ventricle. This connection mode is preferable for left ventricular recovery and preservation. Left atrial, left ventricular, and aortic pressure curves, as well as pulmonary artery flow data, were obtained. The data show very effective unloading of the natural ventricle and demonstrate the feasibility of this novel assist device. Directions for further improvement of technical features were also identified.

Animals↗