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Biomedical subjects

F C Bakker

Publications and source records attributed to F C Bakker.

At least 19 recordsLinked to original sources
PubMed1999

Shedding some light on catching in the dark: perceptual mechanisms for catching fly balls.

To catch a lofted ball, a catcher must pick up information that guides locomotion to where the ball will land. The acceleration of tangent of the elevation angle of the ball (AT) has received empirical support as a possible source of this information. Little, however, has been said about how the information is detected. Do catchers fixate on a stationary point, or do they track the ball with their gaze? Experiment 1 revealed that catchers use eye and head movements to track the ball. This means that if AT is picked up retinally, it must be done by means of background motion. Alternatively, AT could be picked up by extraretinal mechanisms, such as the vestibular and proprioceptive systems. In Experiment 2, catchers reliably ran to intercept luminous fly balls in the dark, that is, in absence of a visual background, under both binocular and monocular viewing conditions. This indicates that the optical information is not detected by a retinal mechanism alone.

Adult↗
PubMed1998

[Bone transplantation and bone replacement materials].

There is a growing need for immediately available material with appropriate qualities for reconstruction of large bone defects. Autologous spongy bone grafts are optimal as to biocompatibility, but are in short supply. Allogenic and xenogenic bone grafts evoke an immunological reaction after implantation and are not biocompatible. In the last thirty years ceramic implants and composites have been developed for bone substitution. New calcium phosphate bone substitutes undergo processes of resorption and precipitation of carbonate apatite that play a part in formation of new bone. These materials are easy to use because of their pastelike consistence. Resorption properties are influenced by particle size, crystallinity and composition. So far, no serious adverse reactions were reported. More clinical experience is necessary especially with composites and combinations with antibiotics, bone growth factors and collagen, to specify the place of these modern calcium phosphates in bone replacement and bone substitution.

Apatites↗
PubMed1998

[Resorbable rods and screws for fixation of ankle fractures. A randomized clinical prospective study].

A prospective randomized clinical trial was performed to evaluate the use of self-reinforced absorbable composites (Biofix) in the fixation of ankle fractures. The aim of this study was to demonstrate that fixation with Biofix rods and screws is as good as the standard A.O. fixation. The benefits of Biofix rods and screws are: a reduction in costs since no secondary operation is needed, prevention of stress-shielding and thereby diminishing the risk of bone porosity. Patients aged between 16 and 75 years old with closed, non-comminuted fractures of the lateral and/or medial malleolus and dislocation of the fracture fragments greater than 2 mm were included in the study. 22 patients were treated with Biofix rods and screws and the control group of 19 patients with a standard technique. After 3, 6 and 12 months, rontgenograms were taken. At the same time functional results were evaluated following the criteria of Olerud and Molander. Two patients were withdrawn from the trial for non-medical reasons. 22 patients (12 from the Biofix group, 10 from the AO group) operated two or more years ago were contacted to see if any complications had occurred since they were last seen. In 4 cases a Biofix screw broke down just beneath the head during insertion. This did not result in an insufficient fixation of the fracture. There were no early post-operative complications. The functional and rontgenological results in both groups were equal. In three cases a sterile sinus developed at the site of screw insertion. Biofix rods and screws, made of polylactic acid, are a good alternative for the fixation of fractures of the ankle. The use of resorbable fracture fixation material has the advantage that a second operation to remove osteosynthesis material is not necessary. The long term results are good. There is, however, a possibility of development of tissue reaction to the resorbable material.

Adolescent↗
PubMed1998

Quantification of fracture healing with three-dimensional computed tomography.

Quantitative methods are necessary for an objective evaluation of fracture healing. Three-dimensional computed tomography (CT) for the measurement of callus volume and density could be such a method and was investigated in an animal model. In 23 goats a closed tibial fracture was created and stabilized with a cast. The animals were killed at 2, 4 and 6 weeks for radiographical, CT and biomechanical analysis. From the CT scans a three-dimensional reconstruction of the callus was made to measure its volume and mean density. At 2 weeks the callus volume had already reached its maximum. In contrast, callus density, torsional strength and torsional stiffness increased over time (P < 0.0001, analysis of variance, ANOVA). Multiple regression analysis showed that the callus volume was not related to the torsional properties. However, callus density was a significant explanatory variable for both torsional strength (R2 = 0.72, P < 0.0001) and torsional stiffness (R2 = 0.82, P < 0.0001). Therefore, callus density as measured by three-dimensional CT is a predictor of the extent of fracture consolidation. CT with three-dimensional reconstruction of the callus seems a valid technique for the quantification of fracture healing.

Analysis of Variance↗
PubMed1997

[The body-packer syndrome].

In four patients, a woman of 35 and men of 27, 38, and 22 years old, body-packer syndrome was diagnosed. Body-packer syndrome is seen in people concealing drugs in special containers within the body; this may lead to rupture with acute intoxication or to ileus. The clinical presentation can be very deceptive. An abdominal X-ray often reveals the packages. If there are no symptoms treatment is with mild laxatives, acute intoxication requires immediate laparotomy. One of the four patients died, the others recovered. Legally (Dutch law), the physician best delivers the drug to the police as a lost object, without revealing the patient's identity.

Adult↗
PubMed1997

The effects of baseball experience on movement initiation in catching fly balls.

Previous research has shown that skilled athletes are able to respond faster than novices to skill-specific information. The aim of this study was to ascertain whether expert outfielders are faster than non-experts in acting on information about the flight of a fly ball. It was hypothesized that expert outfielders are better attuned to this information; as a result, faster and more accurate responses were expected. This hypothesis was tested by having non-expert and expert outfielders judge, as quickly as possible, where a ball would land in the front-behind dimension (perceptual condition) and, in another condition, to attempt to catch such balls (catching condition). The results of the perceptual condition do not support the hypothesis that expert outfielders are more sensitive to ball flight information than non-experts, but the results of the catching condition reveal that experts are more likely to initiate locomotion in the correct direction.

Adaptation, Physiological↗
PubMed1996

The relevance of action in perceiving affordances: perception of catchableness of fly balls.

The catchableness of a fly ball depends on whether the catcher can get to the ball in time; accurate judgments of catchableness must reflect both spatial and temporal aspects. Two experiments examined the perception of catchableness under conditions of restricted information pickup. Experiment 1 compared perceptual judgments with actual catching and revealed that stationary observers are poor perceivers of catchableness, as would be expected by the lack of information about running capabilities. In Experiment 2, participants saw the 1st part of ball trajectories before their vision was occluded. In 1 condition, they started to run (as if to catch the ball) before occlusion; in another, they remained stationary. Moving judgments were better than stationary judgments. This supports the idea that perceiving affordances that depend on kinematic, rather than merely geometric, body characteristics may require the relevant action to be performed.

Adult↗
PubMed1996

Performance-influencing factors in homogeneous groups of top athletes: a cross-sectional study.

Sport scientists have identified many factors as prerequisites for a good athletic performance in various sports. It is not clear whether these factors also influence the best performers in the homogeneous groups of top athletes selected for national teams. In this study, this issue is addressed with members of the Dutch National Junior Speed Skating Team. A total of 237 different technical, physiological, anthropometrical, and psychological parameters were collected, including many that correlated with performance in previous studies. High speed film analyses during the National Championships provided the technique parameters. A 30-s sprint test and a 150-s supramaximal test on a cycle ergometer underlie the physiological data, and questionnaires were used to measure personality traits and emotional feelings. Only trunk position and the direction of push-off (push-off angle phi) correlated consistently with skating performance in this group (r = 0.61-0.73 and r = -0.65 to -0.70, respectively). The small number of meaningful correlations means that sport scientists will have to develop more reliable methods, models, and theories to contribute significantly to knowledge useful to top athletes and their coaches.

Adolescent↗
PubMed1995

Surgical treatment of liver injury with an absorbable mesh: an experimental study.

Uncontrollable bleeding remains a life-threatening problem in severe liver injury. The application of an absorbable mesh has been reported in a small number of patients. To evaluate an absorbable mesh wrap in standardized conditions, we performed an experimental study in 14 female pigs. A standard liver laceration imitating a blunt injury grade IV (Liver Injury Scale of the American Association for the Surgery of Trauma) was made in all animals. Heparin was administered to mimic coagulopathy. After randomization, seven animals received a polyglycolic acid (Vicryl) mesh wrap to control bleeding. Seven animals served as controls. Six of seven animals with a mesh wrap survived. Six of seven animals in the control group died (p = 0.02, Fisher's exact test). Intrahepatic pressures in the treated group varied from 3 to 55 mm Hg. Liver function tests in surviving animals were temporarily elevated. Necropsy at 2 weeks demonstrated adhesions to the wrapped lobe, but no hematoma, free bile, or abscess. Histologic examination showed a foreign-body reaction to the mesh and necrotic parts in the liver. It is concluded that an absorbable mesh wrap can effectively control bleeding from severe liver injury and improve survival in an animal model, although it may cause some damage to liver tissue.

Animals↗
PubMed1994

Catching balls: how to get the hand to the right place at the right time.

Information specifying the future passing distance of an approaching object is available (in units of object size) in the ratio of optical displacement velocity and optical expansion velocity. Despite empirical support for the assumption that object size can serve as a metric in the perception of passing distance, the present series of experiments reveals that in catching a ball subjects do not rely on such "point-predictive" information. The angle at which (real and simulated) balls approached the subject systematically affected verbal and manual estimates of future passing distance, as well as the kinematic characteristics of catching movements. To catch a ball, the actor uses momentary action-related information instead of spatiotemporal estimates. The hand velocity is geared to information specifying the currently required velocity. This secures ending up at the right place in the right time, regardless of where this may be.

Adult↗
PubMed1994

Longitudinal development of young talented speed skaters: physiological and anthropometric aspects.

A longitudinal analysis of a group of speed skaters was done to identify the performance-determining factors for a successful speed skating career. This paper presents both the physiological and anthropometric results of this longitudinal study. Twenty-four athletes from the Dutch National Junior Speed Skating Team were followed from age 16-17 yr to age 20-21 yr. During the development from junior to senior speed skater, a number of anthropometric and physiological variables changed. There were no differences between successful and unsuccessful speed skaters from an anthropometric perspective; consequently, it was not possible to distinguish successful from unsuccessful athletes on anthropometric grounds. The longitudinal data showed that at a younger age the successful speed skaters had similar oxygen consumption, mechanical efficiency, and power output values compared with the unsuccessful speed skaters. Later in the study, successful speed skaters distinguished themselves by the ability to produce higher power output values. There were no anthropometric or physiological relationships found in this study on which performance at the age of 20-21 yr could be predicted with measurements at a junior age.

Adolescent↗
PubMed1992

Supramaximal cycle tests do not detect seasonal progression in performance in groups of elite speed skaters.

Seven female and eight male elite junior skaters performed cycle ergometer tests at four different times during the 1987/1988 season. The tests consisted of a Wingate-type 30-s sprint test and a 2.5-min supramaximal test. The subjects were tested in February, May and September 1987 and in January 1988. Maximal oxygen consumption was measured during the 2.5-min test. With the exception of the maximal oxygen consumption of the women in May which was about 6% lower than in the other three tests, no seasonal changes in the test results could be observed--this, in spite of a distinct increase in training volume (from 10 to more than 20 h.week-1) and training intensity in the course of the season. When the test data were compared to those of elite senior skaters, it appeared that the junior skaters showed the same values for mean power output during the sprint test [14.2 (SD 0.4) W.kg-1 for the men and 12.6 (SD 0.5) W.kg-1 for the women] and maximal oxygen consumption [63.1 (SD 2.8) ml.kg-1.min-1 for the men and 55.3 (SD 3.5) ml.kg-1.min-1 for the women, respectively] as found for senior skaters. It seemed, therefore, that the effects of training in these skaters had already levelled off in the period before they participated in this investigation. In contrast to previous studies, no relationship could be shown between the test results and skating performance. This was most likely due to the homogenous character of the groups (mean standard deviations in power and oxygen consumption were only 5%).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Criteria for reliable selection of the lowest level of amputation in peripheral vascular disease.

To improve the chances for the amputee to become ambulatory the most distal level of amputation should be selected in patients with end-stage peripheral vascular disease. Physical examination alone provides insufficient information when amputation levels are closely related to areas with signs and symptoms of ischemia. In the present series of 85 lower extremity amputations the predictive values of clinical parameters and skin perfusion pressure measurements are assessed. The role of clinical judgment is clarified: the most distal level of amputation is to be selected by physical examination, but further information is required to assess the healing potential at the selected level. The presence of palpable pulses immediately above the selected level correlates well with primary wound healing (p less than 0.001, negative predictive value 100%). The absence of palpable pulses and angiographic patency scores are of no clinical value in amputation level selection. Skin perfusion pressure measurements were of excellent predictive value (p less than 0.001, positive predictive value 89%, negative predictive value 99%). According to these data a strategy is proposed for routine determination of the lowest level of amputation, where primary wound healing can be expected.

Adult↗
PubMed1991

Antibiotic concentrations in the groin wound after vascular prosthetic implantation.

The kinetics of systemically and locally administered cefuroxime or ceftazidime in wound fluid were investigated in the period after vascular prosthetic implantation. Cefuroxime or ceftazidime was administered intravenously in patients. Simultaneously 250 mg ceftazidime or cefuroxime was added to preclotted blood. Locally administered antibiotics could not be detected in our samples. In groin fluid samples 24-48 h after the operation the average concentration of cefuroxime was 8.3 and of ceftazidime 5.0 mg/l. The decline of the concentration of cefuroxime or ceftazidime in groin fluid seems to be much slower than one would expect from the half-lives of the antibiotics. We conclude that cefuroxime and to a lesser extent ceftazidime are suitable as prophylactic agents in arterial reconstruction.

Aged↗
PubMed1991

Individual differences in reactivity to and coping with the stress of lecturing.

The aim of this study was to evaluate the moderating effect of several psychologically and biologically defined characteristics for both psychological and physiological indices of reactivity to and coping with lecturing stress. Student teachers were measured in two standardized lecturing situations: once at the start of a three-month practice period and once at the end of this period. Reactivity was operationalized as an increase in heart rate, cortisol excretion and subjective anxiety responses in anticipation of and at the start of the lecture. Coping was operationalized as the attunement of these responses during, or recovery after lecturing (short term coping), and as the adaptation of these responses across the three-month practice period (long term coping). It was found that reactivity to and (particularly long term) coping with the lecturing stressor could well be predicted by moderators such as physical fitness, extraversion, neuroticism, social anxiety and several coping styles. Specificity of predictor sets for sex and response parameters is discussed.

Adaptation, Psychological↗