Biomedical subjects

M W Collins

Publications and source records attributed to M W Collins.

At least 19 recordsLinked to original sources

PubMed2006

[The undetected brain lesion in sports. Minor traumatic brain injury and its sequelae].

The minor traumatic brain injury (mTBI) in sports is often looked at as a bagatelle. The treating physician underestimates the severity of the injury suspecting that a mTBI is a nonstructural lesion with an overall excellent prognosis in the majority of the cases. This paper shows that the minor traumatic brain injury may be a structural brain lesion with potentially life-threatening dangers. The therapy should follow exactly defined guidelines, e.g., stepwise protocol of the Concussion in Sports (CIS-) Group. Return to sports activities should happen only when all physical but also cognitive symptoms have subsided. All mTBIs that have been sustained prior to the actual injury have to be recorded properly because repeated mTBIs may cause chronic degenerative brain damage. Neuropsychological testing will aid in the correct diagnosis of a mTBI and is a useful parameter in the course of the injury. In the future biochemical markers may serve as indicators of the severity of the brain injury and may also aid in predicting the outcome after TBI. Today biochemical markers do not serve as a substitute for neuroimaging.

Adolescent↗

PubMed2006

No cumulative effects for one or two previous concussions.

BACKGROUND: Sports medicine clinicians and the general public are interested in the possible cumulative effects of concussion. OBJECTIVE: To examine whether athletes with a history of one or two previous concussions differed in their preseason neuropsychological test performances or symptom reporting. METHOD: Participants were 867 male high school and university amateur athletes who completed preseason testing with ImPACT version 2.0. They were sorted into three groups on the basis of number of previous concussions. There were 664 athletes with no previous concussions, 149 with one previous concussion, and 54 with two previous concussions. Multivariate analysis of variance was conducted using the verbal memory, visual memory, reaction time, processing speed, and postconcussion symptom composite scores as dependent variables and group membership as the independent variable. RESULTS: There was no significant multivariate effect, nor were there any significant main effects for individual scores. There was no measurable effect of one or two previous concussions on athletes' preseason neuropsychological test performance or symptom reporting. CONCLUSION: If there is a cumulative effect of one or two previous concussions, it is very small and undetectable using this methodology.

Adolescent↗

PubMed2002

Effects of stents under asymmetric inflow conditions.

Patient-to-patient variations in artery geometry may determine their susceptibility to stenosis formation. These geometrical variations can be linked to variations in flow characteristics such as wall shear stress through stents, which increases the risk of restenosis. This paper considers computer models of stents in non-symmetric flows and their effects on flow characteristics at the wall. This is a fresh approach from the point of view of identifying a stent design whose performance is insensitive to asymmetric flow. Measures of dissipated energy and power are introduced in order to discriminate between competing designs of stents.

Arteriosclerosis↗

PubMed2001

The assessment of sport-related concussion: the evidence behind neuropsychological testing and management.

Because of the lack of valid evidence to support the current recommendations for the management of mild traumatic brain injury (concussion), many physicians, athletic trainers, coaches, and athletes have called into question the way concussions are treated in athletics. This review article discusses the current evidence for the management of concussion in high school, college, and professional sports. A complete review of the epidemiologic and neuropsychological studies to date is presented and critically reviewed, as are other assessment and management tools in concussion. The appropriate use of neuropsychological testing, grading scales, and return-to-play recommendations are discussed in depth based on the current evidence. Additionally, areas requiring further research are identified and future trends are briefly discussed.

Athletic Injuries↗

PubMed1999

Relationship between concussion and neuropsychological performance in college football players.

CONTEXT: Despite the high prevalence and potentially serious outcomes associated with concussion in athletes, there is little systematic research examining risk factors and short- and long-term outcomes. OBJECTIVES: To assess the relationship between concussion history and learning disability (LD) and the association of these variables with neuropsychological performance and to evaluate postconcussion recovery in a sample of college football players. DESIGN, SETTING, AND PARTICIPANTS: A total of 393 athletes from 4 university football programs across the United States received preseason baseline evaluations between May 1997 and February 1999. Subjects who had subsequent football-related acute concussions (n = 16) underwent neuropsychological comparison with matched control athletes from within the sample (n = 10). MAIN OUTCOME MEASURES: Clinical interview, 8 neuropsychological measures, and concussion symptom scale ratings at baseline and after concussion. RESULTS: Of the 393 players, 129 (34%) had experienced 1 previous concussion and 79 (20%) had experienced 2 or more concussions. Multivariate analysis of variance yielded significant main effects for both LD (P<.001) and concussion history (P=.009), resulting in lowered baseline neuropsychological performance. A significant interaction was found between LD and history of multiple concussions and LD on 2 neuropsychological measures (Trail-Making Test, Form B [P=.007] and Symbol Digit Modalities Test [P=.009]), indicating poorer performance for the group with LD and multiple concussions compared with other groups. A discriminant function analysis using neuropsychological testing of athletes 24 hours after acute in-season concussion compared with controls resulted in an overall 89.5% correct classification rate. CONCLUSIONS: Our study suggests that neuropsychological assessment is a useful indicator of cognitive functioning in athletes and that both history of multiple concussions and LD are associated with reduced cognitive performance. These variables may be detrimentally synergistic and should receive further study.

Adolescent↗

PubMed1999

Flow in carotid bifurcations: effect of the superior thyroid artery.

The superior thyroid artery was ignored in previous fluid dynamics studies of carotid bifurcations. However, it is not clear to what extent the flow patterns within the carotid might be influenced by the presence of this outflow tract in reality. In this study, quantitative effects of the superior thyroid artery upon the flow patterns and wall shear stress in the carotid bifurcation were investigated in detail by a numerical simulation method. Comparisons of the maximum reversed flow velocities, flow patterns and wall shear stress were made between models with and without the superior thyroid artery. Results demonstrate that this small artery has only a marginal effect on the overall flow characteristics within the carotid sinus. However, it does have significant effects on flow patterns in the common-external side branch. An alternative approach is proposed to compensate for the absence of this small artery in numerical calculations.

Adult↗

PubMed1999

Does loss of consciousness predict neuropsychological decrements after concussion?

OBJECTIVE: To investigate the importance of loss of consciousness (LOC) in predicting neuropsychological test performance in a large sample of patients with head injury. DESIGN: Retrospective comparison of neuropsychological test results for patients who suffered traumatic LOC, no LOC, or uncertain LOC. SETTING: Allegheny General Hospital, Pittsburgh, Pennsylvania. PATIENTS: The total number of patients included in this study was 383. MAIN OUTCOME MEASURES: Neuropsychological test measures, including the visual reproduction, digit span, and logical memory subtests of the Wechsler memory scale (revised), the Trail Making test, Wisconsin Card Sorting test, Hopkins Verbal Learning test, Controlled Oral Word Association, and the Galveston Orientation and Amnesia test (GOAT). RESULTS: No significant differences were found between the LOC, no LOC, or uncertain LOC groups for any of the neuropsychological measures used. Patients who had experienced traumatic LOC did not perform more poorly on neuropsychological testing than those with no LOC or uncertain LOC. All three groups demonstrated mildly decreased performance on formal tests of speed of information processing, attentional process, and memory. CONCLUSION: The results of this study cast doubt on the importance of LOC as a predictor of neuropsychological test performance during the acute phase of recovery from mild traumatic brain injury. Neuropsychological testing procedures have been shown to be sensitive in measuring cognitive sequelae of mild traumatic brain injury (concussion) in athletes. The failure of this study to find any relationship between LOC and neuropsychological functioning in a large sample of patients with mild head trauma calls into question the assignment of primary importance to LOC in grading severity of concussion. This study also does not provide support for the use of guidelines that rely heavily on LOC in making return-to-play decisions. Continued research is necessary to determine the relative importance of markers of concussion in athletes.

Adult↗

PubMed1999

Reconstruction of blood flow patterns in human arteries.

Local haemodynamic factors in large arteries are associated with the pathophysiology of cardiovascular diseases such as atherosclerosis and strokes. In search of these factors and their correlation with atheroma formation, quantitative haemodynamic data in realistic arterial geometry become crucial. At present no in vivo non-invasive technique is available that can provide accurate measurement of three-dimensional blood velocities and shear stresses in curved and branching sites of vessels where atherosclerotic plaques are found frequently. This paper presents a computer modelling technique which combines state-of-the-art computational fluid dynamics (CFD) with new noninvasive magnetic resonance imaging techniques to provide the complete haemodynamic data in 'real' arterial geometries. Using magnetic resonance angiographic and velocity images acquired from the aortic bifurcation of a healthy human subject, CFD simulations have been carried out and the predicted flow patterns demonstrate the non-planar-type flow characteristics found in experimental studies.

Aorta, Abdominal↗

PubMed1998

Magnetic resonance image processing and structured grid generation of a human abdominal bifurcation.

Magnetic resonance angiography (MRA) offers a non-invasive approach to the acquisition of anatomically accurate human arterial structure. Combining the latest computational fluid dynamics (CFD) techniques with clinical data from MRA, the detailed haemodynamics information in the human circulation system can be obtained. In this paper, a novel computer method is presented, which generates automatically a computational grid for a human abdominal bifurcation from a set of conventional MRA images. The method covers the complete sequence from MR image segmentation, 3-D model construction, grid generation, to grid quality evaluation. Results demonstrate that the computer program developed is capable of generating a good quality grid for human arterial bifurcations from MRA images with minimum user input. The resultant grid can be used directly for further computer simulation of the flow.

Abdomen↗

PubMed1998

Neuropsychological assessment of the college football player.

The application of neuropsychological assessment procedures to the evaluation of athletes has recently become an area of intense interest and debate and has led to the development of research initiatives at both the amateur and the professional level. However, to date, only a handful of research studies have been completed that have addressed the special issues that accompany the use of neuropsychological assessment instruments with athletes. This article reviews the past use of psychological testing in sports and presents a model of neuropsychological assessment that is currently being utilized in the National Football League. In addition, the extension of this approach to major college football is discussed and test-retest data from a sample presented to provide the basis for comparison of athletes who have suffered a concussion. Recommendations of a national panel of neuropsychologists who are involved in the evaluation of athletes are presented in hopes of encouraging new research initiatives in this area.

Adolescent↗

PubMed1998

The numerical analysis of fluid-solid interactions for blood flow in arterial structures. Part 1: A review of models for arterial wall behaviour.

The structural response of a large artery is characteristically complex and includes the highly non-linear, history-dependent response of a nonhomogeneous anisotropic structure undergoing finite deformations. The mechanics of the arterial wall has been studied for nearly two centuries. The goals of such research range from the desire to have a basic knowledge and understanding of the mechanics and physiology of this complex structure to the need for data and methods for the design of arterial prostheses. In this paper, the models for arterial wall behaviour are critically reviewed. Firstly, the structure and general characteristics of the arterial wall are discussed. This is followed by a comprehensive review of the constitutive laws. Finally, structural analyses of the arterial wall by mathematical and numerical methods are discussed. Predictions using the authors' preferred models give focus to important issues, and in Part 2 the review and predictions are extended to the fluid solid coupled situation.

Anisotropy↗

PubMed1998

The numerical analysis of fluid-solid interactions for blood flow in arterial structures. Part 2: Development of coupled fluid-solid algorithms.

In this paper, the authors extend their study of wall mechanics given in Part 1 to the overall problem of fluid-solid interactions in arterial flows. Fluid-solid coupling has become a specific topic in computational methods and applied mechanics. In this review, firstly, the effects of elasticity of blood vessels on wave propagation and local flow patterns in large arteries are discussed. Then, numerical techniques are reviewed together with the alternative coupled methods available in fluid--wall models. Finally, a novel numerical alogorithm combining two commercial codes for coupled solid/fluid problems is presented. As a consequence of the present studies, wall effects are now able to be included in predictions of haemodynamics in a clinical context.

Algorithms↗

PubMed1998

The combination of magnetic resonance angiography and computational fluid dynamics: a critical review.

Computational Fluid Dynamics (CFD) has proven to be a valuable technique in the study of blood flow in arteries because of its capability of obtaining quantitatively velocities and wall shear stress. However, the "bottleneck" problem limiting the application of CFD is the difficulty of constructing anatomically realistic arterial geometries. In this survey, an overview is presented of the progress over the last decade in the development of magnetic resonance angiography (MRA) techniques, medical image processing and CFD, as well as the combination of these techniques in hemodynamics research. It is demonstrated that with modern angiographic techniques such as MRA, noninvasive measurement of human angiograms becomes possible and practical. Together with digital medical image processing and analysis techniques, computational models can be constructed for the "real" human arteries without making any geometric assumptions. When allied with state-of-the-art CFD codes, velocity and wall shear stress distributions, as well as particle trajectories, can be determined in the arteries.

Animals↗

PubMed1997

Isolation and structure elucidation of the major degradation products of cefaclor formed under aqueous acidic conditions.

The aqueous acidic degradation of the oral cephalosporin cefaclor was investigated. A number of degradation products were isolated and characterized. The degradation products can be loosely classified into three categories: thiazole derivatives, pyrazine derivatives, and simple hydrolysis or rearrangement products. Degradation pathways are proposed that involve (1) hydrolysis of the beta-lactam carbonyl with subsequent rearrangement, (2) ring contraction of the six-membered cephem nucleus to five-membered thiazole derivatives through an episulfonium ion intermediate, and (3) attack of the primary amine of the phenylglycyl side chain on the "masked aldehyde" at carbon-6 to form fluorescent substituted pyrazines.

Cefaclor↗

PubMed1997

Isolation and structure elucidation of the major degradation products of cefaclor in the solid state.

Cefaclor is a beta-lactam antibiotic that degrades slowly under normal storage conditions to several minor products. To obtain samples large enough to permit structure elucidation, cefaclor was allowed to degrade at 40 degrees C (75% relative humidity) and at 85 degrees C. The profile of degradation products formed under these conditions is qualitatively similar to the profile of degradation products observed in samples of cefaclor aged for 14 years at room temperature, although some products found in the sample degraded at 85 degrees C are not formed at the lower temperatures. Using preparative reversed-phase high-performance liquid chromatography (rp-HPLC) and a combination of spectroscopic methods, we have isolated and characterized 17 of these degradation products. Some of these products were also isolated from studies of aqueous degradations. The major products appear to have arisen from five distinct pathways: (1) isomerization of the double bond in the dihydrothiazine ring; (2) decarboxylation; (3) ring contraction of the cephem nucleus to thiazole structures; (4) oxidative attack at carbon 4 of the dihydrothiazine ring; and (5) intramolecular attack of the primary amine of the side chain on either the beta-lactam carbonyl to form 3-phenyl-2,5-diketopiperazines or the "masked aldehyde" at carbon 6 to form 2-hydroxy-3-phenylpyrazine derivatives. The pathway involving oxidation at carbon 4 is particularly important at ambient temperatures and is unique to the solid-state degradation.

Cefaclor↗

PubMed1997

Flow in a simple model skeletal muscle ventricle: comparison between numerical and physical simulations.

Flow patterns generated during ventricular filling have been investigated for three different combinations of flow rate and injection volume. The numerical solutions from a commercially available computational fluid dynamics package were compared with observations made under identical flow conditions in a physical model for the purpose of code validation. Particle pathlines were generated from the numerical velocity data and compared with corresponding flow-visualization pictures. A vortex formed at the inlet to the ventricle in both cases: During the filling phase, the vortex expanded and traveled toward the apex of the ventricle until, at the end of filling, the vortex occupied the full radial extent of the ventricle; the vortex continued to travel once the filling process had ended. The vortices in vitro were more circular in shape and occupied a smaller volume than those generated by the numerical model. Nevertheless, comparison of the trajectories of the vortex centres showed that there was good agreement for the three conditions studied. Postprocessing of velocity data from the numerical solution yielded wall shear-stress measurements and particle pathlines that clearly illustrate the mass-transport qualities of the traveling vortex structure. For the cases considered here, the vortex transit produced a time-dependent shear stress distribution that had a peak value of 20 dynes cm-2, with substantially lower levels of shear stress in those regions not reached by the traveling vortex. We suggest that vortex formation and travel could reduce the residence time of fluid within a skeletal muscle ventricle, provided that the vortex travels the complete length of the ventricle before fluid is ejected at the start of the next cycle.

Blood Flow Velocity↗

PubMed1996

Formation and travel of vortices in model ventricles: application to the design of skeletal muscle ventricles.

Vortex-ring production was studied in axisymmetric elastomeric ventricles designed to stimulate flow in a cardiovascular assist device. A flow visualization technique was used to investigate the effects of reducing the inlet diameter and predilating the ventricle on vortex travel in two ventricles of different shape and size. In most cases, vortex rings formed during the filling phase. They were bounded by the incoming jet of fluid and the ventricular wall. The velocity of their centres during the filling period was proportional to the inflow velocity. During filling, vortex velocity was substantially independent of the shape and diameter of the two ventricles studied. It was dependent mainly on orifice diameter: a narrower inlet led to greater inflow velocities and proportionately greater vortex velocities. At the end of the filling phase, each vortex increased in size to occupy the full radial extent of the ventricle. This process was associated with a decrease in the axial velocity and strength of the vortex. At low flow rates, these losses resulted in the arrest of the vortex at end filling. Vortex motion in ventricles is particularly important in the design of a cardiovascular device such as the skeletal muscle ventricle (SMV), where small ejection fractions may leave blood at the apex of the ventricle relatively undisturbed. It is suggested that inlet diameter could be selected to favour the formation and travel of vortices, with a resultant reduction in apical residence time and hence a reduced risk of thrombus formation.

Coronary Circulation↗

PubMed1996

Modelling nanoscale fluid dynamics and transport in physiological flows.

The concept of nanotechnology is discussed, and its connection with biomedical engineering is elucidated. For the specific field of nanoscale flow and transport problems of physiological relevance, some typical examples are presented, and their interaction is discussed for some classic biomechanical problems like the flow in arteries with blood-wall coupling. Then, existing computational models are presented and classified according to the length scale of interest, with emphasis on particle-fluid problems. Final remarks address the essential unity of biomedical and engineering behaviour and the possible relevance to small-scale industrial research.

Biological Transport, Active↗