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Biomedical subjects

D Geiger

Publications and source records attributed to D Geiger.

64 records · Page 4Linked to original sources
PubMed1983

[Replacement of the anterior cruciate ligament by carbon fibers. An experimental study].

The authors have excised the anterior cruciate ligament in 14 sheep and replaced it by carbon fibres. The animals were sacrificed after 12 to 18 months. Eight had a satisfactory new ligament without any evidence of arthrosis and with stability of the knee. In 2 cases, there was moderate instability and arthrosis associated with a lax ligament and in 3 cases the new ligament had ruptured with severe instability and arthrosis. Microscopic examination shows a satisfactory acceptance of the carbon filament both inside the bone as well as in the joint. There was no difference between cases repaired immediately or 6 months after excision of the ligament. A study of aortic lymph nodes showed the presence of carbon particles. The rupturing strength of the new ligaments and of normal ligaments were similar. The visco-elasticity of the new ligaments was also studied and was found to be satisfactory. It was considered that the use of carbon fibre may be valuable but more studies should be done to improve the elasticity and to decrease the migration of carbon material.

Animals↗
PubMed1976

[Wall rheology and arterial hydrodynamics: theoretical and hydromechanical models (author's transl)].

Recent results in research on transport of macromolecules between blood and the arterial wall have shown that endothelial cells are very sensitive to mechanical events localised in the flow boundary layer. Cardiac pressure waves of finite amplitude are characterized by non linear propagation phenomena in which the fluid-wall interaction plays an important role through the wall rheology. Different models of the mechanical behavior of arterial wall have been studied and their influence on blood flow field have been analysed.

Animals↗
PubMed1976

[Piezo-electric activity of dental tissues].

The appearance of electrical charges on dental samples submitted to 10 daN compression strains was confirmed. In a first series of experiments a correlation was determined between the charges measured and the importance of the organic element at the studied locations. In a second series of measurements carried out on dental specimens after extraction of their organic content there was an almost complete disappearance of the piezoelectric phenomenon. Thus the piezoelectric phenomenon appears essentially in the organic stroma and perhaps also in certain non centro-symmetrical crystals the existence of which has to be demonstrated.

Electrophysiology↗
PubMedDate not supplied

Concrete use of the joint coordinate system for the quantification of articular rotations in the digital joints of the horse.

A method is detailed allowing the computation of three-dimensional (3D) joint angles. Each joint of the equine digit is modelled as a sequence of three single axis rotary joints. The Joint Coordinate System was used; it involves a specific sequence of cardanic angles. The decomposition of the angles was chosen so that the three elementary angles coincide with the flexion/extension, passive abduction/adduction and lateral/medial rotations. The algorithms and kinematic procedures were described for the equine front digital joints. This method was tested in vitro on four forelimbs. For each limb, angle values were measured while the member was loaded by a press (from 500 to 6000 N). These tests were repeated while a wedge raised one part of the hoof (toe, heel, lateral and medial sides) in order to induce modifications of the angular patterns of the joints. This method allowed a precise quantitative determination of 3D joint movements. The modifications occurring with the wedges are clearly identified and confirm some previously published semi-quantitative observations. Moreover, this method provides a way to collect objective data on the functional anatomy of joints and could be used to study connective shoeing thoroughly. It may be directly applied to other species and may be used by researchers interested in discreet articular movements, especially occurring in other planes than the sagittal one.

Anatomy, Veterinary↗
PubMedDate not supplied

Automatic selection of loop breakers for genetic linkage analysis.

Pedigree loops pose a difficult computational challenge in genetic linkage analysis. The most popular linkage analysis package, LINKAGE, uses an algorithm that converts a looped pedigree into a loopless pedigree, which is traversed many times. The conversion is controlled by user selection of individuals to act as loop breakers. The selection of loop breakers has significant impact on the running time of the subsequent linkage analysis. We have automated the process of selecting loop breakers, implemented a hybrid algorithm for it in the FASTLINK version of LINKAGE, and tested it on many real pedigrees with excellent performance. We point out that there is no need to break each loop by a distinct individual because, with minor modification to the algorithms in LINKAGE/FASTLINK, a single individual that participates in multiple marriages can serve as a loop breaker for several loops. Our algorithm for finding loop breakers, called LOOPBREAKER, is a combination of: (1) a new algorithm that is guaranteed to be optimal in the special case of pedigrees with no multiple marriages and (2) an adaptation of a known algorithm for breaking loops in general graphs. The contribution of this work is the adaptation of abstract methods from computer science to a challenging problem in genetics.

Algorithms↗
PubMedDate not supplied

Gastrointestinal translocation as a possible source of candidemia in an AIDS patient.

Apart from cryptococcosis and histoplasmosis, which are mycoses contained by T cell-mediated mechanisms of host defense, fungemia is rarely found in AIDS patients. The frequency of fungemia due to Candida spp. has been reported to be as low as 1%. We report a non-neutropenic AIDS patient who presented a candidemia which probably arose from her gastrointestinal tract.

AIDS-Related Opportunistic Infections↗
PubMedDate not supplied

Kinematic symmetry index: a method for quantifying the horse locomotion symmetry using kinematic data.

This study was conducted to evaluate a method for quantifying locomotion symmetry at trot in sound and lame horses. Using a 3D kinematic analysis system, the kinematics of the limb joints of sound and lame horses were recorded. The differences in motion between the left and right homologous joints were then quantified using a symmetry index based on an inter-correlation method. This method was used to calculate the symmetry indices of the vertical displacements and angle-time diagrams of the joints of each horse. In order to evaluate the sensitivity of this method of quantifying the locomotion symmetry, the symmetry indices of horses suffering from the three main types of lameness (forelimb, hind limb and bilateral lamenesses) were compared with those calculated for a reference group of clinically sound horses. The symmetry indices calculated using this method were sensitive enough to distinguish different degrees of lameness. Except for symmetrical bilateral lameness, the indices obtained also allowed us to determine which of the fore or hind limbs were lame. The results of this study make it possible to consider potential applications of this method in research and clinical fields.

Animals↗
PubMedDate not supplied

Kinematics of the equine back: a method to study the thoracolumbar flexion-extension movements at the trot.

This study was conducted to evaluate a method for quantifying the flexion-extension movements of the back of horses trotting on a track in the conditions of the clinical lameness examination. Using a 3-D kinematic analysis system, the successive positions of four markers placed at regular intervals between the withers and the tuber sacrale were recorded. To isolate the flexion-extension movements of the back, the positions of these four markers were recomputed in a trunk-related co-ordinate system of the horse. Then, for each frame, the equation of the third-order polynomial that best fitted the position of the four markers was determined. Using these equations, it was then possible to interpolate the vertical displacement of any point situated between the withers and the tuber sacrale. The accuracy of this method was evaluated using three additional markers placed between the four previous ones. The vertical displacements of these three markers were recorded and compared to the interpolated displacements provided by this method. The results showed that the experimental and interpolated values did not present any statistical difference except in the lumbar region. In this region, the general shape of the vertical displacement curve was conserved but magnified by 17%. This study showed that despite the weakness of the range of the flexion-extension movements of the equine back at trot, these movements can be quantified with reliability. This method was then used on a lame horse. The results obtained demonstrated the usefulness of this method to study the flexion-extension movements of horses suffering from various locomotor disorders.

Animals↗