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Biomedical subjects

H Gauthier

Publications and source records attributed to H Gauthier.

At least 19 recordsLinked to original sources
PubMed2007

Influence of the intercalated cations on the surface energy of montmorillonites: consequences for the morphology and gas barrier properties of polyethylene/montmorillonites nanocomposites.

Organically modified montmorillonites obtained by cation exchange from the same natural layered silicate were studied. The surface properties of the pristine and a series of organically modified clays were determined by inverse gas chromatography and the water adsorption mechanisms were studied by a gravimetric technique coupled with a microcalorimeter. A significant increase of the specific surface area, a decrease of the water adsorption, and a decrease of the dispersive component of the surface energy were observed when the sodium cations of the natural montmorillonite were exchanged for a quaternary ammonium. Slighter differences in surface properties were observed, on the other hand, between the different types of organically modified montmorillonites. Indeed, similar dispersive components of the surface energy were determined on the organoclays. Nevertheless, the specific surface area increased in the range 48-80 m(2)/g with increasing d-spacing values and the presence of specific groups attached to the quaternary ammonium, such as phenyl rings or hydroxyl groups, led to some specific behaviors, i.e., a more pronounced base character and a higher water adsorption at high activity, respectively. Differences in interlayer cation chain organization, denoted as crystallinity, were also observed as a function of the nature of the chains borne by the quaternary ammonium. In a later step, polyethylene-based nanocomposites were prepared with those organically modified montmorillonites. The clay dispersion and the barrier properties of the nanocomposites were discussed as a function of the montmorillonite characteristics and of the matrix/montmorillonite interactions expected from surface energy characterization.

Journal Article↗
PubMed2005

[Soft sarcoma tissue of extremities: medical imagery in post-therapeutic follow-up].

After treatment of primary soft tissue sarcoma, a third of patients will develop local or distant (lung in 90% of cases) recurrence. For an individual patient, the issue of cancer recurrence is a binary event. However, when developing surveillance strategies for large groups of patients, knowledge of the risks (tumor biology, natural history of the disease), the benefits (potential efficacy of salvage therapy) and diagnosis test performances is necessary to formulate a rationale and resource effective follow-up algorithm.

Diagnostic Imaging↗
PubMed2005

[Soft tissue sarcoma: role of imaging for initial diagnosis and treatment].

Soft tissue sarcomas are uncommon heterogeneous group of tumour derived from mesenchym. The most common location is the lower extremity, but they can occur in the upper extremity, and abdominal and chest walls. The first radiological evaluation may include plain films and ultrasonography in viewing to assess the probability of soft tissue sarcomas. MRI with contrast is the main modality to evaluate these lesions and choose which part of tumour must be biopsied. Computer tomography (CT) is secondary used to perform core needle biopsy and detect lung metastases. The role of PET begins to be more clear in case of need global assessment before radical surgery. A multidisciplinary approach is essential to perform rational treatment planning and avoid partial surgery.

Diagnostic Imaging↗
PubMed2004

[Ultra-late metastasis of ocular melanoma: about two cases].

INTRODUCTION: Ocular melanoma is associated with extended risk of metastases, mainly liver metastases. Nevertheless, the late and ultra-late recurrence (respectively 10 and 15 years after initial treatment) are exceptional events. EXEGESIS: We describe hereafter two cases. In the first case, the treatment is palliative chemotherapy with death 12 months after metastasis diagnosis. In the second case, the patient underwent two resections of metastases (lung and liver). This patient had excellent quality of live, and survived 11 months later after palliative surgery. DISCUSSION: Follow-up of ocular melanoma patients should include liver enzymes and ultrasonography of liver in the long run.

Aged↗
PubMed2001

Prognostic value of radionuclide angiography in patients with right ventricular arrhythmias.

BACKGROUND: The prognosis of patients with right ventricular (RV) arrhythmias remains uncertain. This study prospectively evaluated the prognostic value of RV and left ventricular (LV) involvement assessed by radionuclide angiography (RNA) as predictors for sudden death. METHODS AND RESULTS: Patients (n=188) with severe arrhythmias originating from the RV were followed up for a mean of 45+/-34 months. Data on clinical presentation, resting and stress ECG, signal-averaged ECG, 24-hour Holter monitoring, and programmed stimulation were collected along with RNA. Patients were classified as group I (n=82) with normal RNA or group II (n=106) with an abnormal RV suggestive of arrhythmogenic RV cardiomyopathy, classified as diffuse or localized disease, with or without associated LV abnormalities. During follow-up, 14 patients died suddenly, all in group II. None of the clinical and electrical data were predictive of death. An abnormal RNA study was a highly predictive factor for death (P<0.005), as well as the presence of LV abnormalities (P<0.01). CONCLUSIONS: The present study confirms that arrhythmogenic RV cardiomyopathy is a severe disease with a high risk for cardiac death. Evidence of RV abnormalities in patients presenting with RV arrhythmias is highly predictive for sudden death, as is its association with LV involvement.

Adolescent↗
PubMed2001

Socio-economic disparities in preterm birth: causal pathways and mechanisms.

Preterm birth is the leading cause of infant mortality in industrialised societies. Its incidence is greatly increased among the socially disadvantaged, but the reasons for this excess are unclear and have been relatively unexplored. We hypothesise two distinct sets of causal pathways and mechanisms that may explain social disparities in preterm birth. The first set involves chronic and acute psychosocial stressors, psychological distress caused by those stressors, increased secretion of placental corticotropin releasing hormone (CRH), changes in sexual behaviours or enhanced susceptibility to bacterial vaginosis and chorioamnionitis, cigarette smoking or cocaine use, and decidual vasculopathy. The second hypothesised pathway is a gene-environment interaction based on a highly prevalent mutation in the gene for methylenetetrahydrofolate reductase (MTHFR), combined with low folate intake from the diet and from prenatal vitamin supplements, consequent hyperhomocysteinemia, and decidual vasculopathy. We propose to test these hypothesised pathways and mechanisms in a nested case-control study within a prospectively recruited and followed cohort of pregnant women with singleton pregnancies who deliver at one of four Montreal hospitals that serve an ethnically and socio-economically diverse population. Following recruitment during the late first or early second trimester, participating women are seen at 24-26 weeks, when a research nurse obtains a detailed medical and obstetric history; administers several scales to assess chronic and acute stressors and psychological function; obtains blood samples for CRH, red blood cell and plasma folate, homocysteine, and DNA for the MTHFR mutation; and performs a digital and speculum examination to measure cervical length and vaginal pH and to obtain swabs for bacterial vaginosis and fetal fibronectin. After delivery, each case (delivery at < 37 completed weeks following spontaneous onset of labour or prelabour rupture of membranes) and two controls are selected for placental pathological examination, hair analysis of cotinine, cocaine, and benzoylecgonine, and analysis of stored blood and vaginal specimens. Statistical analysis will be based on multiple logistic regression and structural equation modelling, with sequential construction of models of potential aetiological determinants and covariates to test the hypothesised causal pathways and mechanisms. The research we propose should improve understanding of the factors and processes that mediate social disparities in preterm birth. This improved understanding should help not only in developing strategies to reduce the disparities but also in suggesting preventive interventions applicable across the entire socio-economic spectrum.

Adult↗
PubMed2000

Systematic lung scans reveal a high frequency of silent pulmonary embolism in patients with proximal deep venous thrombosis.

BACKGROUND: A high frequency of asymptomatic pulmonary embolism (PE) has been reported in patients with deep venous thrombosis (DVT) in studies of a limited number of patients using varying criteria for lung scan assessment. OBJECTIVES: To estimate the frequency of PE using systematic lung scans in a large group of outpatients with DVT and to compare the results using varying lung scan assessment criteria. METHODS: An international multicenter study comparing 2 different regimens of low-molecular-weight heparin nadroparin in DVT: perfusion lung scans were performed in 622 outpatients with no clinical indication of PE and with proximal DVT confirmed by venography. Three hundred seventy-nine of these patients underwent ventilation lung scans. High-probability (HP) scans for PE were assessed separately using either ventilation scans or chest radiographs to define mismatched perfusion defects. RESULTS: Perfusion scans showed abnormalities in 82% of the patients; 59% had segmental defects and 30% had normal scans or scans with a very low probability of PE. Depending on the criteria used, 32% to 45% had HP scans for PE; these percentages were higher in young patients. No relationship was found between extent of thrombosis and HP scans. The estimated frequency of silent PE was 39.5% to 49.5%. During a 3-month follow-up period during which the patients received therapy, the rate of PE recurrence was low (1.3%) and did not differ between patients with baseline HP scans and those with normal scans. CONCLUSIONS: Regardless of what interpretative criteria are used for assessing lung scans in PE, the frequency of silent PE is 40% to 50% in patients with DVT. A baseline lung scan may easily detect PE in these patients but is not useful for predicting early thromboembolic recurrences that may occur during therapy.

Adolescent↗
PubMed1995

[Demographic variables and social dependency: annual and intergenerational comparisons].

"Drawing on a profile of age-specific expenditures for selected [Canadian] Government programmes (services and transfers), we examine the effect of demographic changes and labour force participation on social expenditures in the upcoming decades. In terms of cross-sectional analysis, increased activity rates and particularly a postponed retirement age would exercise a major impact.... Using a different approach, it is possible to distinguish for each generation the social benefits received and corresponding contributions. Whereas the amount of benefits received by a specific cohort essentially depends on its size, contributions vary according to annual social expenditures. The demographic structures are such that the generations born before 1991 will profit from an excess in benefits...while for the following generations the situation will be reversed.... For all scenarios with negative population growth, future generations may expect to incur a deficit in terms of social expenses." (SUMMARY IN ENG AND SPA)

Age Factors↗
PubMed1991

[Consequences of population aging on social expenditures].

The impact of demographic aging on social expenditures is examined, with particular reference to Canada. "The merits of four of the mechanisms or means that are proposed to alleviate the additional cost of aging are reviewed: economic growth, increase in the labour force participation rate, economies of scale and [restructuring] of social expenditures. We bring up many uncertainties regarding the mechanisms or means proposed. Therefore we should not take for granted that the effect of aging will be easily absorbed." (SUMMARY IN ENG)

Americas↗
PubMed1990

[Changes in the age structure of the labor force by occupation in Quebec, 1981-1986].

The author examines trends in the age structure and size of the labor force in Quebec, Canada, for the period 1981-1986. "Using simulations, the author shows that the occupational structure of workers as a whole is less influenced by the decrease in the number of young workers...than by occupational changes observed among young workers." (SUMMARY IN ENG AND SPA)

Age Distribution↗
PubMed1986

[Three projections of population decline for Quebec: characteristics and implications for the working population].

"After a brief review of various projections of population decline for Quebec, the author analyses some previous examples of depopulation, and emphasizes that public opinion will have to change much if immigration is to be used as a tool for avoiding population decline. He then investigates four implications of the projected decline: the size of the working population, its age and sex structure, the labor force participation ratio, and the economic dependency ratio." (SUMMARY IN ENG AND SPA)

Age Factors↗