PubMed Health⌕ Search

Biomedical subjects

K Häusler

Publications and source records attributed to K Häusler.

7 recordsLinked to original sources
PubMed2006

Oscillating viscometer--evaluation of a new bedside test.

A viscometer for bedside blood measurements was developed, consisting of an oscillating resonator probe mounted directly into a disposable vacutainer tube for blood withdrawal. It was tested in vitro on blood samples with variable hematocrits (20-60%), increasing fibrinogen concentrations (0-20 g/l), increasing concentrations of an admixed radiographic contrast medium and erythrocyte suspensions in dextran 40 and dextran 70. Results were compared with those obtained with a conventional Couette viscometer. Oscillating viscometry yielded generally higher values than Couette viscometry, and had a good sensitivity for changes in hematocrit with a good correlation between the two methods (r=0.96, p<0.0001). Oscillating viscosity depended on the resonator frequency, it was higher at 3900 Hz than at 215 Hz, suggesting a viscoelastic behavior of blood. Erythrocyte aggregation, induced by increasing fibrinogen concentrations or dextran 70, affected oscillating viscometry. At a high frequency, i.e. a smaller penetration depth of the shear wave, oscillating viscosity tended to decrease, which suggests a depletion of the boundary layer from erythrocytes when they aggregate. At low frequency with a deeper shear wave penetration (about 50 microm), erythrocyte aggregation increased oscillating viscosity. Bedside tests in 17 patients with coronary heart disease and 10 controls confirmed the easy practicability of the test and showed lower oscillating viscosity in these patients despite higher fibrinogen concentrations presumably due to increased erythrocyte aggregation. We conclude that oscillating viscometry is an interesting bedside test, which is capable of providing new information on the biorheology of the erythrocyte-poor boundary layer near the vessel wall.

Blood Circulation↗
PubMed1998

Rheological properties of blood as assessed with a newly designed oscillating viscometer.

A newly designed type of oscillating viscometer was tested for blood viscosity measurements. The viscometer consists of a probe (either a tube or a rod) oscillating at a resonance frequency with amplitudes in the micro- and nanometer range. The torsional oscillations are dampened by fluids flowing through the tube or surrounding the rod. The degree of damping depends on the viscosity of the fluid, which allows to measure viscosity. Data obtained with these instruments were compared with those obtained with a conventional Couette viscometer. An increase of erythrocyte aggregation by the addition of dextran 70 in vitro led to the expected increase of viscosity in the Couette viscometer; in the oscillating tube viscometer, however, it remained unchanged, which may be explained by a decreased erythrocyte concentration near the tube wall due to increased aggregation and flow of erythrocytes in the tube center. In ex vivo experiments on blood flowing without anticoagulant directly through the tube viscometer an inverse correlation between viscosity and fibrinogen concentration was found. This is in contrast to actual knowledge and may indicate that high fibrinogen levels have a beneficial rheological effect at the tube or vessel wall. Our data suggest that the new oscillating tube viscometer is an interesting tool, which may contribute to a more comprehensive understanding of blood flow.

Adult↗
PubMed1992

[Increasing the adhesion of glass ionomer cements in bracket bonding].

For attaching orthodontic brackets glass ionomer cements are being discussed as an alternative material to synthetic glues since they are less aggressive toward the tooth enamel. A serious disadvantage consists in a lower degree of adhesion to enamel. The adhesion can, however, be increased to some extent by enamel preparation. In order to investigate further improvement in this area, 250 freshly extracted bovine teeth were treated with 22 chemicals and their enamel-conditioning properties were tested. For the attachment of the brackets the glass ionomer cements AqaCem and Ketac-cem are used. Tensile shear tests were carried out with a Wolpert universal testing machine. Best results were obtained with the aromatic carbonacids benzoic acid and salicylic acid in acetonic solution. The mean adhesive power was 9.8 MPa. This means an increase of 38% as compared to other pre-conditioning materials such as polyacrylic acid. It can be assumed, that aromatic carbonacids as small, very reactive molecules can establish a closer contact to the phosphate groups of enamel than can the macromolecular polyacrylic acid. Thus, a further step on the way to using glass ionomer cements as a bracket bonding material seems to have been taken.

Adhesiveness↗
PubMed1991

[Fluorine distribution in the enamel in the use of glass ionomer cements as bonding materials].

The rise in the fluorine content of dental enamel after bonding orthodontic attachments with glass ionomer cement (GIC) was analysed in an in vitro study. Twenty-four freshly extracted caries-free premolars from adolescent patients were available for investigation. The teeth were cleaved longitudinally in the oro-vestibular direction to obtain a test specimen and reference sample. The GIC Aquacem was used as bonding material. The fluorine was measured with an electron beam microprobe (Camebax SX 50) 10, 20, 40 and 80 days after bonding. A rise of fluorine in dental enamel of more than 120% was observed after the bonding procedure. This rise was especially rapid in the first ten days, and a saturation value was reached after 40 days. The depth of penetration into the dental enamel was 20 microns, and the surface spreading was at least 3 mm. An equilibrium state is attained between the 40th and 80th day. A preventive action on caries in the vicinity of attachments bonded with glass ionomer cement is to be expected owing to the accumulation of fluorine in the dental enamel.

Adolescent↗
PubMed1989

[Material related aspects of surface structured endoprostheses].

In this article technical problems of surface-structured endoprostheses for cementless implantation are discussed. On the basis of four prostheses (two hip and two knee endoprostheses) various different porous coating technologies are compared. One sintered sphere layer, a cast sphere layer, a cast layer with "spongy-bone" structure and a plasma sprayed coating were compared. The quality of the bonding between the prosthesis and the porous surface layer was examined metallographically using polished specimens, with additional investigation of fraction surfaces of special tension test specimens. Additional information is given on the notch effect of the different coatings, in terms of a reduction in fatigue strength. The notch sensitivity differs for each material, and the reduction in fatigue strength is discussed for different implant alloys and different technologies for surface structuring. The investigation shows that the present quality of surface-structured endoprostheses is not satisfactory. We would like to thank the Dr. Johannes Heidenhain Foundation for financial support of this research.

Biomechanical Phenomena↗
PubMedDate not supplied

A newly designed oscillating viscometer for blood viscosity measurements.

A newly designed type of oscillating viscometer is described. The viscometer consists of either a tube or a rod oscillating at a resonance frequency with amplitudes in the micro- and nanometer range. A fluid flowing through the tube or surrounding the rod damps the torsional oscillations. The increase in the damping depends on the viscosity of the fluid and is used to determine viscosity. It was found that viscosity measurements are feasible during blood flow. This new type of viscometer may be useful to the study of biophysical properties of blood at the wall surface during flow and give new insights into blood flow. The device allows direct viscosity measurement on blood directly as it is drawn from the vein through the tube without any anticoagulant.

Blood Viscosity↗