The routine diagnosis of osteoporosis is based on radiological measurements of bone mineral content. An osteoporotic failure is influenced both by a loss of mineralized bone and internal bone structure. The structure cannot be estimated by bone reconstruction based on standard radiological equipment. To investigate the influence of structure on cancellous bone stiffness, a new finite element model of cancellous bone is developed. The model describes a cancellous bone unit as an open-celled structure. Trabecular length, trabecular thickness, diameter of trabecular connections, relative lattice disorder and relative bone loss determine the real architecture. Using this model, the loss of stiffness as a result of trabecular thinning and loss of trabecular connections is estimated. The volume fraction as a scalar value for a volume can not be a marker for orthotropic stiffness changes. A formula in the form Y = e(a *1 n(X) + b) can describe the correlation between cancellous bone stiffness and volume fraction. These formulas are appropriate for those cases, when the loss of bone mineral (decrease in trabecular thickness) is closely connected to a loss of structure (increasingly perforated trabecular network).

Bone Density↗

PubMed1996

Colour term knowledge in two-year-olds: evidence for early competence.

It is commonly believed that colour terms are acquired unusually slowly. However, several recent studies suggest that preschoolers have more colour term knowledge than previously believed. In two studies, we investigated the colour term knowledge of 49 two-year-olds and the influence of schooling on their colour term acquisition. Both studies revealed considerable knowledge in such young children. A longitudinal comparison of children with and without school experience in Study 2 indicated that the higher performance of the school group could not be accounted for by differences predating that group's experience. In reviewing the evidence from the children's performance, we conclude that contemporary children's early and frequent experience with colour terms may account for this cohort's improved performance over previous generations of children.

Child Language↗

PubMed1996

Quality Determining Parameters of Balloon Angioplasty Catheters.

The investigations carried out on balloon angioplasty catheters using a parameter test unit allow an objective comparison and a qualitative assessment of catheter brands with respect to their stenosis passability. The design of the test unit allows the measure of other parameters important for clinical practice, such as pushability and trackability. Altogether 8 over-the-wire and 10 monorail-catheters from 7 different manufacturers were investigated by our study. Between modern over-the-wire and monorail systems there exists no fundamental difference in passage capability. In some brands of catheter the stenosis model shows no increase in the amount of thrust required, even after repeated inflation; this is accountable to the good folding properties of the balloon. Angioplasty balloons made of less overstretchable or thinner material yielded the best results. The fact that changes in balloon quality may result from pre-inflation should carry weight in discussions concerning the reuse of catheters. The measurement results are useful for the correct selection of a catheter appropriate to the therapy task at hand.

Journal Article↗

PubMed1995

[Imprints of coronary plaque particles in the PTCA balloon surface during the dilatation processing].

UNLABELLED: Seventy-six PTCA-balloons after coronary angioplasty were studied for superficial changes using scanning electron microscopy (SEM) after fixing in glutardialdehyde. Coronary plaque particles were identified on the balloon surface in 52 cases (68%). Twelve new and unused balloons were subjected to the same chemical treatment and SEM showed no imprints. The average length of the longest imprinted plaques was 128 +/- 201 microns and the average number of plaque particles per balloon was 4.9 +/- 2.7. The maximal dilatation pressure and the number of dilatations showed no influence on the impregnation of plaque particles. However, longer plaque imprints tended to occur under low dilatation pressure. Imprints of plaque particles were significantly higher in patients with low cholesterol (p = 0.0001) and low triglycerides (p = 0.0016). No correlation was seen between imprint length and lipid levels. Similarly, the different balloon materials (polyethylene, polyolefincopolymer) showed no significant differences with regard to plaque occurrence. The PTCA-balloons, plaque particles and six coronary plaques obtained after endatherectomy were subjected to energy dispersive x-ray analysis (EDX) under SEM as EDX reveals qualitative and quantitative information about the structural elements. Highly significant differences in calcium, sodium, phosphorus and silicon contents (p = 0.0000) between plaque particles and balloon surface were observed, owing to the absence of these in balloon material. Thus EDX offers additional advantages over SEM in that it clearly differentiates deformed balloon surface, plaque particle, and retained contrast medium. CONCLUSION: Plaque particles can be recovered from balloon surfaces after PTCA. Depending upon their size, they could lead to coronary spasm or microembolic phenomenon.

Adult↗

PubMed1991

[A measuring procedure for experimental determination of tensile strength of catheters and flexible probes].

In order to obtain a more objective description of the properties usually subsumed under such terms as the "handling" of catheters, it is necessary to measure the significant parameter bending stiffness. A contact-free method of recording the oscillations of rod-shaped elements is presented. The stiffness EI can be calculated from the measured characteristic frequency. The logarithmic decrement can be derived from the damped natural oscillation and the damping properties of the catheter thus characterised. In addition, a consideration of imposed oscillations can be employed to calculate resonance frequency. A computer-driven measuring set-up employing a CCD line camera for the non-contact recording of oscillations of rodshaped elements, together with the software required is presented. The measuring principle and possible errors are discussed and a measurement described by way of an example.

Biomechanical Phenomena↗

PubMed1990

[Testing materials for clinical use].

Explore the source record for details and available documents.

Animals↗

PubMed1988

[Hemocompatibility testing in the rat model by noninvasive blood flow measurement using an arteriovenous shunt].

The flowing periods of blood through biomaterial shunts were measured by means of a noninvasive sensor with sufficient reliability. Falsifications of the measuring results by foreign influences as roller pumps, punctures, changes of the cross section, or the coupling of different materials were avoided extensively. The accomplishment of the test is possible routinely without a great display of apparatus.

Animals↗

PubMed1987

[Catheter problems in the use of ventricular cardiovascular assist systems].

The prerequisite for efficient assist-ventricles and impulses in the pulsatile pumping function are sufficiently dimensioned afflux and flowing off connections. In systematic investigations on the hydraulic circulation model the cannulas from an internal parameter of 12 mm with a total length of the connection distance to the inflow and outflow valve, respectively, at the bypass ventricle of 30 cm proved sufficient for performing a volume of output of 5-6 l/min in clinic-relevant filling pressures in a hypodynamic circulatory situation. Connection cannulas for the heart-lung machine used in routine work are not sufficient in periodic filling and ejection processes in the pulsatile pumping function for an effective decompression and effective increase of the cardiac output. In case of an ECG-triggered mode of action of the ventricular assist-system an increase of frequency up to 130/min in after that incomplete filling of the assist-ventricle does not remarkably restrict the effectiveness of the assist-system.

Assisted Circulation↗