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Biomedical subjects

J F Vincent

Publications and source records attributed to J F Vincent.

At least 19 recordsLinked to original sources
PubMed2001

Affine versus non-affine deformation in soft biological tissues, measured by the reorientation and stretching of collagen fibres through the thickness of compressed porcine skin.

Skin is a complex three-dimensional structure of cells, collagen fibres and other proteins. However most mechanical analyses treat skin as a two-dimensional membrane, neglecting the through thickness structure. In this paper we investigate through thickness reorientation of collagen fibres. The mode of deformation of skin is also considered. For modelling purposes deformation is usually assumed to be affine. This assumption was tested by constructing a simple geometrical, affine deformation model to predict the through thickness reorientation of collagen fibres, from their initial through thickness angle and the measured deformations of skin samples during compression. The measured reorientation of collagen fibres was found to be very variable, however the average reorientations were consistent with the predictions of the model, with the inclusion of a systematic error. The variation in the reorientation of individual fibres can be explained by the variations in the structure at a micrometre scale. The systematic deviation of reorientations from the model predictions can be explained by a non-affine relationship between the collagen fibres and ground substance at a micrometre scale. However, non-affine deformations at a micrometre scale caused by irregularities of structure are likely to average out at a millimetre scale, because at this level material is evenly distributed.

Animals↗
PubMed2000

Maximizing therapeutic effects in treating sexual offenders in an Australian correctional system.

In Australia, the community response to sexual offenders is marked by uncertainty as to whether offenders should be incarcerated as punishment or provided treatment in order to reduce the likelihood of re-offense. The incarceration of sexual offenders results in particular management, ethical, and political issues. Nevertheless incarceration can provide leverage to encourage the offender to participate in treatment while delivering punishment for wrongdoing and acting to protect the community. In the state of Victoria the CORE Sex Offender Programs have developed a statewide strategy in the public correctional system in order to assess, manage, and treat male sexual offenders. However, such offenders are notoriously reluctant to engage in treatment to address offending behaviors. A critical element of the strategy has been the Victorian Adult Parole Board, an entity that can determine that an offender needs to engage in treatment before he is considered for parole. Using the therapeutic jurisprudence framework as outlined by Wexler (1990), strategies to minimize the anti-therapeutic effects of the Victorian Adult Parole Board and maximize the therapeutic effects of the CORE Sex Offender Programs are highlighted.

Adult↗
PubMed1999

From cellulose to cell.

The cell wall is often pictured as a more-or-less random feltwork of cellulose microfibrils in association with other polysaccharide and protein complexes. There is evidence from morphology, morphogenesis and mechanics that the structures in the cell wall are far more regular and that their interactions are driven by their chemical and morphological properties. In particular, a model based on liquid crystal structures has more than morphological implications.

Biomechanical Phenomena↗
PubMed1996

Young's moduli and shear moduli in cortical bone.

Young's modulus and shear modulus are determined for cortical bone from mammals and birds and for antler bone, using three-point bending at a range of span-to-depth ratios between 25 and 10. Young's modulus is obtained by extrapolating the values for the flexural modulus Eapp to infinite span-to-depth ratios. The shear modulus is obtained from the dependance of Eapp on this ratio. The main determinant for the mechanical properties is the mineral content. For mammalian bone the frequency of Haversian systems correlates negatively with stiffness and resistance to shear. However, because Haversian systems have a lower mineral content than laminar bone (the main component), material and structural determinants can not be separated at present. The ratio of Young's modulus to shear modulus is of the order of 20:1. This high value is discussed in terms of the Cook-Gordon theory of controlled crack propagation as well as in its significance for protecting hollow bones from failing upon local impact.

Animals↗
PubMed1996

Pulmonary toxoplasmosis after allogeneic bone marrow transplantation: case report and review.

We report an isolated case of toxoplasma pneumonitis in a 27-year-old man. This acute infection occurred after induction chemotherapy for AMLo relapsing 3 years post-allogeneic BMT. The detection of Toxoplasma gondii in the bronchoalvolar lavage (BAL), by culture in fibroblast cell line MRC5 enabled us to make the diagnosis. Pyrimethamine and sulfadiazine were effective.

Acute Disease↗
PubMed1995

Adrenocortical function during septic shock.

OBJECTIVE: To investigate, in patients with severe septic shock, the adrenocortical function assessed by daily plasma cortisol determinations during the first 72 h and by the short synthetic ACTH stimulation test performed within 24 h of the onset of shock. DESIGN: Prospective clinical investigation. SETTING: Medical intensive care unit in a university teaching hospital. PATIENTS: 40 consecutive patients with documented septic shock requiring at least hemodynamic resuscitation and respiratory support. INTERVENTIONS: There were no interventions. MEASUREMENTS AND RESULTS: Basal cortisol concentrations were increased with a mean value of 36.8 micrograms/dl (range 7.9-113). Of the overall cortisol determinations 92% were above 15 micrograms/dl. No statistically significant differences in basal cortisol concentrations were found when survival, type of infection, and positive blood cultures were considered. Patients with hepatic disease had significantly higher cortisol (50.1 (+/- 6.2) micrograms/dl versus 35.9(+/- 3.3) micrograms/dl, p = 0.035) levels compared to other patients. No correlations were found between basal plasma cortisol concentrations and factors such as SAPS, OSF, hemodynamic measurements, duration of shock, and amount of vasopressor and/or inotropic agents. Cortisol concentrations had significant but weak correlation with ACTH levels in survivors (r = 0.4; p = 0.03; n = 28) but not in non-survivors (r = 0.03; p = 0.85; n = 52). Cortisol levels in non-survivors increased significantly from enrollment time to the 72nd hour of the survey (day 1: 38.9(+/- 3.8) micrograms/dl versus day 3: 66.7(+/- 17.1) micrograms/dl; p = 0.046) and were significantly higher than those recorded in survivors. Responses to the short ACTH stimulation test were not significantly different between survivors and non-survivors. According to the different criteria used to interpret the response to the ACTH stimulation test, incidence of adrenocortical insufficiency was highly variable ranging from 6.25-75% in patients with septic shock. Only one patient had absolute adrenocortical insufficiency (basal cortisol level below 10 micrograms/dl; response to the ACTH stimulation test below 18 micrograms/dl). CONCLUSION: Our data suggest that in a selected population of patients with severe septic shock single plasma cortisol determination has no predictive value. The short ACTH stimulation test performed within the first 24 h of onset shock can neither predict outcome nor estimate impairment in adrenocortical function in patients with high basal cortisol level. Adrenal insufficiency is rare in septic shock and should be suspected when cortisol level is below 15 micrograms/dl and then confirmed by a peak cortisol level lower than 18 micrograms/dl during the short ACTH stimulation test.

Adrenal Cortex↗
PubMed1995

[Detection of left cardiopathy using echocardiography during acute respiratory failure in chronic respiratory insufficiency].

Echocardiography was performed in a systematic fashion in 58 patients suffering from on-chronic respiratory failure (IRC) who were admitted to the intensive care unit. The prevalence of left ventricular disease in patients with IRC who were admitted to the intensive care unit was 31%, there were 18 cases of cardiac disease: nine had hypertrophic cardiac disease (two with intraventricular gradients), three had dilated cardiomyopathies, and there were six cases of ischaemic cardiac disease. Among these cases, six had not previously been diagnosed as having cardiac disease (10%). In cases with poor echogenicity by the transthoracic root, oesophageal echocardiography was performed and this improved the feasibility of a good examination with only a five per cent failure rate. Left ventricular disease was implicated in the clinical assessment eleven times (19%), either on admission (nine times) or during the course of the in-patient treatment (twice). In directing the initial assessment and the aetiological treatment, echocardiography directly contributed to better management in six cases (10%). As regards the number of cases of cardiac disease which were detected, the study confirms the value of this technique at the bedside of the patient. The use of the transoesophageal route improves the diagnostic value including those patients who were intubated and ventilated.

Acute Disease↗
PubMed1991

Poisson's ratio in skin.

Poisson's ratio of cow teat skin was measured uni- and biaxially and shown to be anisotropic and dependent on aspect ratio. At strains below 0.1 (where Cauchy and Hencky strain are indistinguishable) the Poisson's ratio of cow teat skin measured biaxially is very much greater than 1.0, whereas the Poisson's ratio of distending artery is between 0.5 and 0.3. Knitted fabric behaves similarly to cow teat skin in that it can give a negative Poisson's ratio at low strains. Skin is therefore probably to be considered mechanically as an open feltwork of fibres rather than some sort of continuum.

Animals↗
PubMed1990

Measuring the forces acting during microtomy by the use of load cells.

The forces acting upon the cutting blade during microtomy can be accurately measured by using a load cell. From the information obtained, the optimal knife angles (rake, clearance and slant) can be determined. In addition, the speed of cutting and thickness of sections can also be optimized. The information obtained from the load cell additionally reveals variations in tissue composition which affect the cutting forces. This paper is a preliminary communication to illustrate the possible roles for a modified microtome in (a) the study of microtomy and (b) comparative studies of tissue density.

Brain↗
PubMed1981

Morphology and design of the extensible intersegmental membrane of the female migratory locust.

The morphology of the extensible intersegmental membrane (i.s.m.) of the female Locusta migratoria migratorioides is dictated by three main requirements: (a) high extensibility (1500%), (b) low stiffness (5 X 10(3) Pa), (c) low Poisson ratio in the plane of the cuticle (0.01 or less). These requirements can be met only orientating the chitin orthogonally to the direction of extension and having the protein phase uncross-linked and of very low modulus. The Poisson ratio requirement also implies that for the material to be extended at constant volume extreme thinning must occur during extension, giving rise to high shear strains in the direction of extension. The ultrastructure and morphological elements are modified from 'normal' cuticle such as to provide for high extensibility (due to unfolding) of the epicuticle and epidermal cells and a complex system of intracuticular fibres which are probably necessary to retain the topology of the components during high shear straining. No new morphological elements are adduced in this study but the extreme adaptability of those established for other cuticles is illustrated.

Animals↗