Search PubMed⌕ Search

Biomedical subjects

B Merz

Publications and source records attributed to B Merz.

At least 19 recordsLinked to original sources
PubMed2003

Differentiation of parkinsonian syndromes according to differences in executive functions.

Groups of patients with Parkinson's disease (PD), striatonigral degeneration-type multiple system atrophy (MSA) or progressive supranuclear palsy (PSP) with motor disability stages II and III according to Hoehn and Yahr, and a healthy control group were compared using neuropsychological tests of executive functions. The results indicate that all three patient groups were impaired in the tests of executive functions. In comparison with healthy subjects, the three patient groups showed impaired performance regarding verbal fluency, problem solving and verbal and figural working memory. Patients with PD differed significantly from healthy subjects in a test of verbal recency, while patients with MSA or PSP were unimpaired. The comparison of patient groups revealed no differences between PD and MSA patients. However, patients with PSP showed greater impairment in both phonemic and semantic fluency than patients with PD or MSA. Using discriminant function analysis, it was found that variables derived from four verbal fluency tasks (simple and alternate semantic and phonemic fluency) discriminated among the three patient groups at a level significantly exceeding chance. Over 90% of patients with PSP were correctly classified. Patients with PD and MSA were correctly classified in over 70% of cases. These results suggest that verbal fluency tasks may be sensitive measures in the differential diagnosis of PD, MSA and PSP.

Aged↗
PubMed2003

Botulism type B presenting as pure autonomic dysfunction.

Botulism nowadays is a rare mostly food-borne disease caused by the toxin of Clostridium botulinum. On the other hand, botulinum toxin blocking cholinergic transmission has become a most powerful treatment option for many focal movement disorders and is increasingly used to treat autonomic disorders [2, 7, 8]. Although muscle weakness is the hallmark of botulism, autonomic dysfunction may be the leading clinical symptom in rare cases and should be included in the differential diagnosis of pure dysautonomia. Here, we describe a patient with autonomic dysfunction as the leading symptom of botulism type B.

Adult↗
PubMed2001

Time and knowledge barriers to recognizing occupational disease.

Traditionally, inadequate training has been considered the major barrier to recognition of occupational disease. A survey of 136 practitioners was conducted to determine which barriers were actually considered most relevant. The sample included three subgroups: primary care, occupational medicine-oriented, and Mexican. Four aggregate indices were derived: Knowledge, Time, Unpleasant aspects, and Importance. Inadequate Time was as important as inadequate Knowledge, whereas perceived lack of Importance and Unpleasant aspects were less relevant. Patterns among the subgroups were generally comparable. This study implies that training more occupational medicine specialists in increasing recognition is not sufficient unless specific strategies to overcome time constraints are also implemented. For example, emphasizing a "complete occupational history" may be counterproductive. Limiting histories to selected patients; use of focused, brief histories; and, perhaps, computer-based methods are needed.

Attitude of Health Personnel↗
PubMed2001

Frequency of occupational health concerns in general clinics.

Studies have suggested that occupational disease and injury are under-recognized by clinicians. To estimate the frequency of occupational factors in disease and injury, 108 patients in a general (not occupational) health care facility were interviewed about the frequency and types of workplace-health interactions. Thirty-nine percent reported possible causation by work, and 66% reported a possible increase in symptoms by work, even if not caused by work. Twenty-seven percent reported changing jobs and/or tasks because of work-health interactions. The majority of men and women reported that worksite changes could improve their functional ability at work. This study therefore indicates that (1) occupational health concerns are common in primary care clinics, even if not addressed by clinicians; (2) the definition of occupational health concerns should be broadened to include disease caused by work, disease symptoms worsened by work, and the need for occupational accommodation even if the disease itself is not caused by work; and (3) inquiring about patient concerns about workplace-health interactions can provide clinicians with significant opportunities for primary, secondary, and tertiary prevention.

Accidents, Occupational↗
PubMed2000

Intelligent database generated occupational questionnaire system.

Obtaining an adequate occupational history requires special expertise to "ask the right questions" that are relevant to a particular patient's specific health conditions and potential exposures. This article describes a way to systematically accomplish this by means of a computer system that can overcome limited availability of necessary clinical occupational health expertise. The Intelligent Questionnaire system is a computer-based system for generating case-specific questionnaires about the influence of work on respiratory disease. Intelligent Questionnaire includes three databases: Questions, Responses, and Calls (clues to identify questions). The Questionnaire also arranges questions in a logical manner and provides a customized data entry screen for each subject. This approach provides primary practitioners with expertise on a case-by-case basis. It also facilitates occupational health surveillance because it allows acquiring detailed case-specific information in a systematic fashion. A computer-based system can facilitate obtaining occupational histories with high specificity and consistency without depending on general availability of a human occupational health clinical expertise.

Artificial Intelligence↗
PubMed2000

[Testing dental implants with an in vivo finite element model].

The finite element method (FEM) makes it possible to simulate biomechanical situations on a computer. In the present study the so-called voxel method [9, 14, 17, 18, 19] was used for the construction of the mandible model. For this, the relationship between the biological tissue (e.g. bone) and the corresponding attenuation coefficient of CT data (Hounsfield units = HU) were utilized. The CT data were obtained from an edentulous patient provided with a prosthesis borne on two titanium implants. In a parallel study, the bite forces of the same individual were measured. These were recorded digitally in three dimensions (cranio-caudal, anterior-posterior and left-right) The forces determined by a special program were then transferred to the FEM model implants. We were able to show that a bar joining the implants had a far greater effect on maximum equivalent stress than was expected from the measuring data alone. The highest stress at maximum occlusive force was lowered by 704% on using the connecting bar. On chewing, a stress reduction of 59.9% was observed. The reduction in stress achieved by the bar could, we believe, prolong the life of the implant.

Biomechanical Phenomena↗
PubMed1999

Tension and bending, but not compression alone determine the functional adaptation of subchondral bone in incongruous joints.

In the present study, we tested the hypothesis that tension and bending, rather than compression alone, determine the functional adaptation of subchondral bone in incongruous joints. We investigated whether tensile stresses in the subchondral bone of the humero-ulnar articulation are affected by the direction of muscle and joint forces, and whether the tensile stresses are large enough to cause microstructural adaptation, specifically a preferential alignment of the trabeculae and the subchondral collagen fibres. Using a previously validated finite element model of the human humero-ulnar joint, we calculated the contact pressure, the principal compressive and tensile stresses, and the strain energy density in the subchondral bone for various flexion angles. A bicentric (ventro-dorsal) pressure distribution was found in the joint at 30 degrees to 120 degrees of flexion, with contact pressures of up to between 2.5 and 3 MPa in the ventral and dorsal aspects of the ulnar joint surface, but less than 0.5 MPa in the centre. The principal tensile stress in the subchondral bone of the trochlear notch quantitatively exceeded the principal compressive stress at low flexion angles (maximum 8.2 MPa), and the distribution of subchondral strain energy density differed substantially from that of the contact stress (r=-0.72 at 30 degrees and r=+0.58 at 90 degrees of flexion). No important tensile stress was computed in the trochlea humeri. On contact radiography, we found sagittally orientated subarticular trabeculae in the notch, running tangential to the surface. Furthermore, we observed sagittally orientated split lines in the subchondral bone of the notch of 20 cadaver joints, suggesting a ventro-dorsal orientation of the collagen fibres. The trochlea humeri, on the other hand, did not show a preferential direction of the subchondral split lines, these findings confirming the predictions of tensile stresses in the model. We conclude that, due to the important contribution of tension to subchondral bone stress, the distribution of subchondral density cannot be directly employed for assessing the long term distribution of joint pressure at the cartilage surface. The magnitude of the tensional stress varies considerably with the direction of the muscle and joint forces, and it appears large enough to cause functional adaptation of the subchondral bone on a microstructural level.

Adaptation, Physiological↗
PubMed1999

Decision model for optimizing respirator protection.

Respirators are widely used for protection against inhaled toxins. The emphasis of research and implementation effort has evolved through several stages: the respirator device itself, use situation, respirator program factors under employer control, individual worker factors not under employer control, and occupational health systems. For this study, a computer-simulation decision assistance model was developed to assess the impact of various factors on the number of workers receiving adequate protection. Factors include the respirator protection factor, identification of sites needing respirator protection, selection of proper device, availability when needed, frequency of ever use, regularity of use among users, and variability in personal susceptibility or other factors. This analysis demonstrates that for both moderate-risk and high-risk (i.e., IDLH, immediately dangerous to life and health) exposures under current circumstances, the actual protection afforded depends upon the optimization of program factors and detection of atypical outlier persons and worksites. Therefore, programs and research must focus on these areas. Occupational medicine specialists should help optimize these areas and, in addition, use each case of respiratory protection failure as an index case to improve the overall programs.

Computer Simulation↗
PubMed1997

Mechanical implications of humero-ulnar incongruity--finite element analysis and experiment.

Previous studies show that the humero-ulnar joint is physiologically incongruous [Eckstein et al. (1995a) Anat. Rec. 243, 318-326] and exhibits a bicentric (ventro-dorsal) distribution of subchondral mineralization [Eckstein et al. (1995b) J. Orthop. Res. 13, 286-278]. We therefore asked: (1) Does humero-ulnar incongruity bring about a bicentric distribution of contact pressure? (2) Do tensile stresses occur in the subchondral bone of the trochlear notch that are in the same order of magnitude as the compressive stresses? (3) Do ventral and dorsal maxima of subchondral bone density correlate with a bicentric distribution of strain energy density? To that end, a two-dimensional finite element model was designed. The shape and material properties of the bones were based on CT and the boundary conditions selected to agree with resisted elbow extension at 90 degrees of flexion. The incongruity and contact areas were determined experimentally from casts, and the pressure distribution with Fuji Prescale film. In the model and the experiment contact stresses above 2 MPa were recorded in the ventral and dorsal parts of the joint, and values below 0.5 MPa in the depth of the notch. In the model, tensile stresses of 2.9 MPa were observed in the subchondral bone of the ulna, but not in the humerus. The subchondral strain energy density yielded a bicentric pattern in a model with homogeneous subchondral bone properties. It is shown that humero-ulnar incongruity brings about a bicentric distribution of contact pressure, a tensile stress in the notch that is in the same order of magnitude as the compressive stress, and a distribution of strain energy density that correlates with subchondral density patterns.

Adult↗
PubMed1996

Sensitivity of femoral strain pattern analyses to resultant and muscle forces at the hip joint.

An automated geometrical preprocessor was developed with the aim of creating three-dimensional finite element models (FEM) of the human femur. On the basis of postprocessed computed tomography data, this preprocessor makes possible rapid, flexible and regular meshing with 'brick' elements. Three different material properties were modelled at the present stage of development. Sensitivity analyses demonstrated that the strain energy density (SED) patterns of the different femoral parts were most sensitive to the implementation of an iliotibial tract force. The variation of the resultant hip force and abductor force direction within the sagittal plane demonstrated a SED minimum at an anterior inclination of 13 degrees; the variation of the resultant force direction within the frontal plane demonstrated a minimum SED at a medial inclination of 21 degrees relative to the mechanical axis of the lower limb. The orientation of the connecting line between the surface-SED-peaks in the horizontal view was found to be most sensitive to the variation of the resultant force within the sagittal plane.

Biomechanical Phenomena↗
PubMed1996

Automated finite element analysis of excised human femora based on precision -QCT.

The creation of 3-D finite element (FE) models of bone and implant-bone systems is a labor-intensive task due to the need to model different cases and variations, to perform patch tests and to account for the nonhomogeneous material properties with an acceptable amount of work. In this study, we developed an interface between a precision QCT and a FE system and applied it to a specimen bone. With the new method, the time necessary for model generation was reduced substantially. Furthermore, the elastic properties for each element were automatically derived from the corresponding CT-values. In order to demonstrate the importance of taking into account inhomogeneity, a comparison between the nonhomogeneous model and a homogeneous, "averaged" model was performed.

Biomechanical Phenomena↗
PubMed1995

Morphomechanics of the humero-ulnar joint: II. Concave incongruity determines the distribution of load and subchondral mineralization.

BACKGROUND: A deeper joint socket (concave incongruity) is found at most angles of flexion of the humero-ulnar joint and maintained over a wide range of physiological loading. It is, however, unclear how far this incongruity affects the distribution of load and subchondral mineralization of this joint as compared with a congruous configuration. METHODS: Two nonlinear, axisymmetrical finite element models with two cartilage layers were constructed, one congruous and one incongruous, with a joint space of realistic magnitude. The distribution of subchondral mineralization was determined by computed tomography osteoabsorptiometry in the same six specimens that were investigated in the first part of the study, and compared with the biomechanical data obtained there and the predictions of the models. RESULTS: In the congruous case, the center of the socket is highly loaded, whereas the periphery does not experience mechanical stimulation. A central bone density maximum is predicted. With concave incongruity the position of the contact areas shifts from the joint margin towards the center as the load increases, and the peak stresses are considerably lower. A bicentric ventro-dorsal distribution pattern of subchondral mineralization is predicted, and this is actually found in the six specimens. CONCLUSIONS: Concave incongruity is shown to determine load transmission and subchondral mineralization of the humero-ulnar joint. It is suggested that this shape leads to a more even distribution of stress, provides intermittent stimulation of the cartilaginous tissue, and has beneficial effects on the metabolism, nutrition, and lubrication of the articular cartilage during cyclic loading.

Absorptiometry, Photon↗
PubMed1994

Acetylcholine receptors of the Drosophila brain: a 900 bp promoter fragment contains the essential information for specific expression of the ard gene in vivo.

The ard gene encodes a beta-subunit of Drosophila nicotinic acetylcholine receptors specifically expressed in a subset of neurons. To identify the cis-regulatory region responsible for this cell-specific expression, various 5' fragments of the ard gene were fused to a lacZ reporter gene and introduced into the Drosophila genome. A DNA fragment spanning approximately 760 bp upstream and approximately 140 bp downstream of a cluster of putative transcription start sites produced a pattern of beta-galactosidase activity that resembles the distribution of ARD transcripts. Both in embryos and adults the levels of lacZ RNA were similar to those of endogenous ARD transcripts, suggesting that the 900 bp fragment harbors all essential elements for proper expression of the ard gene.

Animals↗
PubMed1994

The influence of geometry on the stress distribution in joints--a finite element analysis.

The incongruity of human joints is a phenomenon which has long been recognized, and recent CT-osteoabsorptiometric findings suggest that this incongruity influences the distribution of stress in joints during their normal physiological use. The finite element method (FEM) was therefore applied to five different geometric configurations consistent with the anatomy of articular surfaces, and a program with variable contact areas (Marc) was used to calculate the stress distribution for loads of 100 to 6,900 N. The assumption of congruity between head and socket results in a "bell-shaped" distribution of stress with a maximum value of 61.5 N/mm2 in the depths of the socket, decreasing towards zero at its edges. In the model with a flatter socket the von Mises stresses are higher (max. 101.3 N/mm2); with a deeper socket, lower (max. 53.0 N/mm2). If the diameter of the head is greater, the stresses build up from the periphery of the socket and move towards its depths as the load increases. The combination of an oversized head and a deeper socket results in the most satisfactory stress distribution (max. 43.2 N/mm2). These results extend previous photoelastic findings with incongruous joint surfaces. The calculated mechanical conditions show a relationship to the location of osteoarthritic changes, and are reflected by the distribution pattern of subchondral bone density. A more satisfactory stress distribution is found with functionally advantageous, incongruous joint surfaces (oversized head and deepened socket) than in the congruous joint, and a better nutritive situation for the articular cartilage seems likely.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorptiometry, Photon↗
PubMed1994

[Automatic generation of 3-D finite element codes of the human femur].

The extremely irregular geometry of bones makes it very difficult to develop and preprocess three-dimensional finite element models (FEM). In the field of biomechanics, the finite element simulation method is a research tool of increasing importance for the prediction of stresses and the stress-compatibility testing of endoprostheses. With this in mind, a FEM preprocessor was developed with the aim of creating three dimensional models of human femurs. On the basis of postprocessed computed tomography data, this preprocessor makes possible rapid, flexible and regular cross-linking. "Brick" elements are used, which are of advantage in terms of computing time, accuracy and computer storage requirements. The software simplifies the generation of models and facilitates the investigation of individual variations, thus providing the basis for utilizing the method in the clinical setting.

Biomechanical Phenomena↗
PubMed1990

Structure and developmental expression of the D alpha 2 gene encoding a novel nicotinic acetylcholine receptor protein of Drosophila melanogaster.

Nicotinic acetylcholine receptors (nAChRs) represent a heterogeneous group of excitatory neurotransmitter receptors in the insect brain. We have characterized the D alpha 2 gene of Drosophila melanogaster, a new member of the nAChR gene family. The protein coding region is interrupted by six introns. The positions of three of these introns are shared with all other nAChR genes. The deduced D alpha 2 protein shows the structural features of ligand-binding nAChR alpha-subunits. Cytogenetically, the D alpha 2 gene maps at position 96A of the 3rd chromosome, close to the ALS gene which also encodes an alpha-like nAChR subunit. D alpha 2 transcripts are predominantly expressed in late embryos and in fly heads.

Animals↗