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Biomedical subjects

J van Hoof

Publications and source records attributed to J van Hoof.

15 recordsLinked to original sources
PubMed2004

Aspects of seat modelling for seating comfort analysis.

The development of more comfortable seats is an important issue in the automotive industry. However, the development of new car seats is very time consuming and costly since it is typically based on experimental evaluation using prototypes. Computer models of the human-seat interaction could accelerate this process. The objective of this paper is to establish a protocol for the development of seat models using numerically efficient simulation techniques. The methodology is based on multi-body techniques: arbitrary surfaces, providing an accurate surface description, are attached to rigid bodies. The bodies are connected by kinematic joints, representing the seat back recliner and head restraint joint. Properties of the seat foam and frame have been lumped together. Further, experiments have been defined to characterise the mechanical properties required for the seat model for comfort applications. The protocol has been exemplified using a standard car seat. The seat model has been validated based on experiments with rigid loading devices with human-like shapes in terms of force-deflection characteristics. The response of the seat model agrees well with the experimental results. Therefore the presented method can be a useful tool in the seat development process, especially in early stages of the design process.

Automobiles↗
PubMed2004

A finite element model of the human buttocks for prediction of seat pressure distributions.

Seating comfort is becoming increasingly important for the automotive industry. Car manufacturers use seating comfort to distinguish their products from those of competitors. However, the development and design of a new, more comfortable seat is time consuming and costly. The introduction of computer models of human and seat will accelerate this process. The contact interaction between human and seat is an important factor in the comfort sensation of subjects. This paper presents a finite element (FE) model of the human buttocks, able to predict the pressure distribution between human and seating surface by its detailed and realistic geometric description. A validation study based on volunteer experiments shows reasonable correlation in pressure distributions between the buttocks model and the volunteers. Both for simulations on a rigid and a soft cushion, the model predicts realistic seat pressure distributions. A parameter study shows that a pressure distribution at the interface between human and seat strongly depends on variations in human flesh and seat cushion properties.

Adult↗
PubMed2003

Estimation of spinal loading in vertical vibrations by numerical simulation.

OBJECTIVE: This paper describes the prediction of spinal forces in car occupants during vertical vibrations using a numerical multi-body occupant model. BACKGROUND: An increasing part of the population is exposed to whole body vibrations in vehicles. In literature, vertical vibrations and low back pain are often related to each other. The cause of these low back pains is not well understood. A numerical human model, predicting intervertebral forces, can help to understand the mechanics of the human spine during vertical vibrations. METHODS: Numerical human and seat models have been used. Human model responses have been validated for vertical vibrations (rigid and standard car seat condition): simulated and experimental seat-to-human frequency response functions have been compared. The spinal shear and compressive forces have been investigated with the model. RESULTS: The human model seat-to-pelvis and seat-to-T1 frequency response functions in the rigid seat condition and all seat-to-human frequency response functions in the standard car seat condition approach the experimental results reasonably. The lumbar and the lower thoracic spine are subjected to the largest shear and compressive forces. CONCLUSIONS: The human model responses correlate reasonable with the volunteer responses. The predicted spinal forces could be used as a basis for derivation of hypothetical mechanisms and better understanding of low back pain disorders. RELEVANCE: In order to solve the problem of whole body vibration related injuries, knowledge about the interaction between human spinal vertebrae in vertical vibrations is required. This interaction cannot be measured in volunteer experiments. This paper describes the application of a numerical human model for prediction of spinal forces, that could be used as a basis for derivation of hypotheses regarding low back pain disorders.

Adult↗
PubMed2003

The development, validation and application of a finite element upper extremity model subjected to air bag loading.

Both frontal and side air bags can inflict injuries to the upper extremities in cases where the limb is close to the air bag module at the time of impact. Current dummy limbs show qualitatively correct kinematics under air bag loading, but they lack biofidelity in long bone bending and fracture. Thus, an effective research tool is needed to investigate the injury mechanisms involved in air bag loading and to judge the improvements of new air bag designs. The objective of this study is to create an efficient numerical model that exhibits both correct global kinematics as well as localized tissue deformation and initiation of fracture under various impact conditions. The development of the model includes the creation of a sufficiently accurate finite element mesh, the adaptation of material properties from literature into constitutive models and the definition of kinematic constraints at articular joint locations. In order to make the model applicable for full-scale simulations, it was coupled with a computationally efficient human model. The model was validated against available cadaver experiments, including static and dynamic three-point-bending tests to the arm and forearm, as well as frontal air bag to forearm impact tests. The sensitivity of the model to changes in air bag properties and upper limb orientation are demonstrated by performing parametric studies. It is shown that the risk of forearm fracture increases substantially with proximity to the deploying frontal air bag and air bag aggressiveness, which corresponds to experimental findings. However, it is shown that increasing the forearm supination angle is protective for the occurrence of forearm fracture. In conclusion, the developed model proves to be a useful research tool to investigate trends in injury severity as a result of a changing frontal air bag to upper extremity loading environment.

Journal Article↗
PubMed1999

Retardation in depression: assessment by means of simple motor tasks.

BACKGROUND: Psychomotor retardation in depression has mostly been assessed with tasks requiring both cognitive and motor processes. This study tested whether retardation could be measured if the cognitive demands of the task were minimal. METHODS: 30 inpatients with a major depressive episode were compared one week after the start of antidepressant treatment, to 30 healthy control persons, matched for age, sex and educational level. Tests consisted of ten simple drawing tasks. The kinematics of drawing movements were recorded using a specially designed pen, a graphics tablet and a personal computer. RESULTS: Patients showed marked motor slowing on all the tasks: longer movement durations, longer pauses and lower velocities. CONCLUSIONS: Psychomotor retardation in depressed patients treated with antidepressants occurs during drawing tasks, in which the cognitive demands are minimal and less than those required in the figure copying tasks used in our previous studies. LIMITATIONS: The use of co-medication can have influenced the results, although no correlations were found between the use of medication and the kinematic variables. CLINICAL RELEVANCE: Detailed registration and analysis of drawing movements enable a more precise diagnosis of psychomotor disturbances in depressed patients.

Adolescent↗
PubMed1997

Depressive retardation and treatment with fluoxetine: assessment of the motor component.

Changes in motor slowing between the start and end of treatment were studied in 22 inpatients with a Major Depressive Episode and 22 normal, healthy control persons. The degree and pattern of motor slowing were measured and analysed using computer-aided simple drawing tasks that did not require any higher order cognitive processing. The patients were treated with fluoxetine 20 mg/day for 6 weeks. Tests took place after 1 week (T0) and 6 weeks (T1). At T0 patients showed marked slowing, apparent in longer movement times and lower velocities than their controls. The differences between groups increased as the size of the movement increased or the accuracy demands increased. In all the trials, patients showed clear initiation difficulties. At T1 the motor slowing of the depressed patients had improved, but not disappeared. Significant differences remained between the two groups.

Adolescent↗
PubMed1996

Changes in fine motor retardation in depressed patients treated with fluoxetine.

Changes in psychomotor slowing were studied in 21 inpatients with a Major Depressive Episode. Fine motor retardation was measured and analysed using computer-aided drawing and figure-copying tasks at T0 (the start of 6 weeks treatment with fluoxetine 20 mg/day) and 5 weeks later (T1). The differences in reaction time between the patients and a group of healthy, matched controls at T0 had disappeared at T1. The initial motor deficit, expressed in longer movement times, had not improved at T1. These findings combined with the effect of manipulation of cognitive and motor demands, suggested that only cognitive processes had accelerated.

Adolescent↗
PubMed1986

On the presence of proteolytic activity in glycosaminoglycan-degrading enzyme preparations.

A solid-phase protease assay has been used to screen different commercial preparations of glycosaminoglycan-degrading enzymes for the presence of proteolytic activity. Proteases cannot be detected in preparations of testicular hyaluronidase and of chondroitinase at the concentration used for histochemical purposes. Commercial Streptomyces hyaluronidase contains proteolytic contaminants detectable at the concentration used for histochemistry. At higher concentrations, all preparations appear to be contaminated with proteases. The results obtained using this assay suggest that addition of a mixture of proteinase inhibitors containing N-ethylmaleimide, EDTA, pepstatin, and phenylmethanesulfonylfluoride or soybean trypsin inhibitor has little effect on the proteolytic activity of the glycosaminoglycan-degrading enzyme preparations, irrespective of the pH used. Moreover, the use of EDTA in this mixture is questionable. This study also describes two testicular hyaluronidase preparations that may be particularly useful in functional studies of the living organism, as they are only slightly contaminated.

Animals↗
PubMed1984

Occurrence of Salmonella in a chemical wastewater treatment plant.

In a chemical wastewater treatment plant located in a pig slaughterhouse, quantitative examinations for Salmonellae were carried out on samples collected from the balancing tank and the proper treatment system. The wastewater coming from the slaughterhouse (influent balancing tank) was highly contaminated: 0.95 log to 2.46 log Salmonellae per ml. During the storage of the wastewater in the balancing tank, the number of Salmonellae increased which resulted in a statistically higher contamination of the effluent. Two sources were detected, namely the sludge and the water from the balancing tank. From the sludge containing high numbers of Salmonellae, wastewater can be contaminated. On the other hand it was shown that at 18-20 degrees C (temperature of the wastewater in the balancing tank) a fast increase of Salmonella is possible in the wastewater. The reduction of Salmonella by chemical treatment process depended on the working-pH. By a pH from 2.3 to 2.5, the mean minimal reduction was at least 4.84 log per ml. When the pH increased somewhat, the removal efficiency decreased to an average of 3.20 log per ml.

Abattoirs↗
PubMed1981

Removal of indicator organisms by chemical treatment of wastewater.

Recently a new chemical wastewater treatment process based upon precipitation of proteins by sodium lignosulphonate under acid conditions is used to purify the wastewater from slaughterhouses and poultry processing plants. In order to determine the reduction of indicator organisms due to this treatment process, influent and effluent samples from two of such plants (plant A in a pig slaughterhouse and plant B in a poultry processing plant) were examined. The results demonstrated that the pH used in the process, has a considerable influence on the reduction of the indicator organisms. On the first sampling day in plant A the initial working-pH was 4 and the corresponding reduction of the different microorganisms varied from 0.7 to 1.5 log. According to the decrease of the pH to 2.3, the reduction increased to a minimum of at least 1.9 and a maximum of at least 4.5 log. In the other samples from this plant (working-pH 2.4) the elimination ranged from 1.8 to 4.0 log. In plant B, the removal of the indicator organisms brought about by a working-pH of 3.0 ranged from 2.1 to 3.1 log. The results showed that in comparison with the biological treatment processes this chemical wastewater treatment process realized a significant greater removal of indicator organisms.

Abattoirs↗
PubMed1980

Bacteriological contamination in wastewaters from slaughterhouses.

Eighty samples of wastewater from 4 slaugherhouses (A and B pig and cattle, C pig and D cattle slaughterhouse), were examined to determine the bacteriological contamination. At the same time, attention was given to the influence of the types of slaughterhouses and the presence of a guttery on the composition of the bacterial flora in the wastewater. The total viable bacteria at 37 degrees C and 22 degrees C varied from 10(6) to 10(8)/ml. The coliforms and E. coli in the samples of the same slaughterhouse varied widely. The slaughtering of pigs did increase the contamination of wastewater with Salmonella compared with that of the slaughtering of cattle. The cleaning and scraping of the gut increased considerably the number of coliforms, E. coli and Salmonellae. All samples examined were contaminated with Coagulase and/or DNase positive staphylococci of which the maximum number was 1.5 x 1.0(4)/ml. Strains coming from slaughterhouse C belonged to the species Staph, aureus and Staph. hyicus subsp. hyicus and those of slaughterhouse D only to the species Staph. hyicus subsp. hyicus.

Abattoirs↗
PubMed1979

Influence of ante- and peri-mortem factors on biochemical and physical characteristics of turkey breast muscle.

The course of post-mortem breakdown of glycogen and ATP in turkey pectoralis major muscle was markedly influenced by several ante- and peri-mortem variables. Application of a proper stunning procedure was highly effective in preventing peri- and post-mortem muscle stress reactions. The physiological level of glycogen and ATP was not significantly affected by road transportation covering 260 km. Birds which rested for 24 hrs following transportation had lower glycogen and ATP levels at the moment of slaughter than non-rested birds. According to the changes in the rate and extent of post-mortem biochemical reactions, several meat characteristics such as water-holding capacity, colour, and tenderness were significantly changed. Furthermore, the results also indicate that turkey breast muscle is susceptible to a PSE-like condition as described in pork.

Adenosine Triphosphate↗
PubMedDate not supplied

A one-plate microbiological screening test for antibiotic residue testing in kidney tissue and meat: an alternative to the EEC four-plate method?

A one-plate screening method is described for the microbiological detection of antibiotic residues by growth inhibition of Bacillus subtilis in agar medium, at pH 7, which contains trimethoprim for better detection of sulphonamides. beta-Glucuronidase is added to the samples to enable the detection of chloramphenicol residues. The sensitivity was determined for 16 antimicrobial substances frequently used in animal husbandry. A comparison was made with the sensitivity of the EEC four-plate test and existing maximum residue levels. The method has been used in Belgium for 5 years for the monitoring of antimicrobial residues in kidney tissue and meat of slaughter animals.

Anti-Bacterial Agents↗
PubMedDate not supplied

Evaluation of the European four-plate test as a tool for screening antibiotic residues in meat samples from retail outlets.

A modified 4-plate test was used to screen 4795 meat samples from retail outlets in the European Community (EC). This microbial inhibition test uses 3 media seeded with Bacillus subtilis at different pH values (6, 7.2, or 8) and a fourth medium seeded with Micrococcus luteus. Positive samples were confirmed by a receptor test for macrolides, a thin-layer chromatographic method for sulfonamides, or an enzyme-linked immunosorbent assay test for tetracyclines. Inhibition on M. luteus plates, often by beef and veal samples, could not be confirmed. Circumstantial evidence indicated these test results had to be considered presumptively false positives. Of the samples, 95 inhibited at least one plate seeded with B. subtilis. Usually, samples were positive on more than one plate: 70 samples were positive on all 3 plates, and only 6 samples did not inhibit the plate at pH 6. The majority of positive results on plates seeded with B. subtilis, 77 of 89 samples tested, contained tetracycline antibiotics. One sample also contained sulfadimidine. Two other samples contained high levels of enrofloxacine and ciprofloxacine. The 4-plate test is not sensitive enough to detect sulfonamides and quinolones at the EC maximum residue limits, but higher levels may cause inhibition. The 4-plate test can be used to detect meat samples containing tetracycline residues, but the method is too complicated when used only for that purpose.

Animals↗