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Biomedical subjects

R Mathieu

Publications and source records attributed to R Mathieu.

15 recordsLinked to original sources
PubMed2006

Physiological differences of elite and professional road cyclists related to competition level and rider specialization.

AIM: The aim of this investigation was to study the physiological response to laboratory tests in elite and professional cyclists, and to relate it to the level at which riders compete and their specialization. METHODS: A total of 71 cyclists were divided into two groups, elite and professional, and were assessed for physical measurements, a maximal graded test and a 30 s all-out test, both performed on a cycle ergometer. The sample included 24 uphill riders (UR), 32 flat terrain riders (FTR), 11 all terrain riders (ATR) and 4 sprinters (SP). RESULTS: Professional riders showed significantly higher gross mechanical efficiency (GME) than their elite counterparts (25.6+/-2.6 vs 24.4+/-2%), but otherwise no other physiological differences emerged from the comparison between these two groups. However, many differences exist as a function of rider specialization, especially between UR and FTR. Compared with FTR, UR showed a higher VO2max (78.2+/-5.5 vs 72.6+/-6.5 mL x min(-1) x kg(-1)) and a lower maximal aerobic power (438.5+/-40.8 vs 465.3+/-36.2 W). From the 30 s all-out test, SP presents the highest maximal power (P < 0.05) and maximal velocity (P < 0.05) compared with all the other groups. CONCLUSIONS: The results for GME indicate a better efficiency for professional riders and suggest the importance of technical aspects related to movement pattern in cycling. The sensitivity of the maximal graded test and the 30 s all-out test did not allowed other differentiations between elite and professional cyclists.

Adult↗
PubMed2005

Calculations of dose distributions using a neural network model.

The main goal of external beam radiotherapy is the treatment of tumours, while sparing, as much as possible, surrounding healthy tissues. In order to master and optimize the dose distribution within the patient, dosimetric planning has to be carried out. Thus, for determining the most accurate dose distribution during treatment planning, a compromise must be found between the precision and the speed of calculation. Current techniques, using analytic methods, models and databases, are rapid but lack precision. Enhanced precision can be achieved by using calculation codes based, for example, on Monte Carlo methods. However, in spite of all efforts to optimize speed (methods and computer improvements), Monte Carlo based methods remain painfully slow. A newer way to handle all of these problems is to use a new approach in dosimetric calculation by employing neural networks. Neural networks (Wu and Zhu 2000 Phys. Med. Biol. 45 913-22) provide the advantages of those various approaches while avoiding their main inconveniences, i.e., time-consumption calculations. This permits us to obtain quick and accurate results during clinical treatment planning. Currently, results obtained for a single depth-dose calculation using a Monte Carlo based code (such as BEAM (Rogers et al 2003 NRCC Report PIRS-0509(A) rev G)) require hours of computing. By contrast, the practical use of neural networks (Mathieu et al 2003 Proceedings Journees Scientifiques Francophones, SFRP) provides almost instant results and quite low errors (less than 2%) for a two-dimensional dosimetric map.

Algorithms↗
PubMed2004

Colossal magnetoresistance without phase separation: disorder-induced spin glass state and nanometer scale orbital-charge correlation in half doped manganites.

The magnetic and electrical properties of high-quality single crystals of A-site disordered (solid solution) Ln0.5Ba0.5MnO3 are investigated near the phase boundary between the spin-glass insulator and colossal-magnetoresistive ferromagnetic metal, locating near Ln=Sm. The temperature dependence of the ac susceptibility and the x-ray diffuse scattering of Eu0.5Ba0.5MnO3 are analyzed in detail. The uniformity of the random potential perturbation in Ln0.5Ba0.5MnO3 crystals with a small bandwidth yields, rather than the phase separation, an homogeneous short ranged charge or orbital order which gives rise to a nearly atomic spin-glass state. Remarkably, this microscopically disordered "charge-exchange-glass" state alone is able to bring forth the colossal magnetoresistance.

Journal Article↗
PubMed2004

A prospective study of pregnant patients with rheumatoid arthritis and ankylosing spondylitis using validated clinical instruments.

OBJECTIVE: : To analyse the disease course of patients with rheumatoid arthritis (RA) and ankylosing spondylitis (AS) during and after pregnancy by validated clinical instruments for measurement of disease activity, and assess their usefulness in pregnant patients. METHODS: Included were 10 patients with RA and 9 with AS (10 pregnancies). Clinical examination and blood/urine sampling was performed before conception, at each trimester, and weeks 6, 12, and 24 post partum. Assessment of RA was by the RA Disease Activity Index (RADAI), the 44 joint count, and the Health Assessment Questionnaire; assessment of AS by the Bath Ankylosing Spondylitis Activity Index (BASDAI), the Dougados Functional and Articular Index, and a night pain index. Common for all patients were the patient's and physician's global assessment. RESULTS: : Most patients with RA showed sustained or increased improvement of disease activity during pregnancy. Higher disease activity scores were found in the patients with AS with a frequent increase of disease activity in the second trimester and mitigation of symptoms in the third trimester. Analysis specifically for the patient's assessment of pain showed continuously higher pain scores in the patients with AS than in those with RA. Rank correlation showed good to moderate correlation between most clinical measurements and RADAI or BASDAI, respectively. Functional indices were confounded by physiological changes of late pregnancy. CONCLUSION: RA can be monitored during and after pregnancy by the swollen joint count and RADAI without interference from pregnancy related symptoms, whereas usual measures of disease activity are not always applicable in pregnant patients with AS.

Adult↗
PubMed2002

Defect-induced magnetic structure in (Ga(1)-(x)Mn(x))As.

We show that magnetic structures involving partial disorder of local magnetic moments on the Mn atoms in (Ga(1)-(x)Mn(x))As lower the total energy, compared to the case of perfect ferromagnetic ordering, when As defects on the Ga sublattice are present. Such magnetic structures are found to be stable for a range of concentrations of As antisites, and this result accounts for the observed magnetic moments and critical temperatures in (Ga(1)-(x)Mn(x))As. We propose an explanation for the stabilization of the partially disordered magnetic structures and conclude that the magnetization and critical temperatures should increase substantially by reducing the number of As antisite defects.

Journal Article↗
PubMed1992

[Systemic Nocardia infection in an AIDS patient].

We report the case of a patient with Aids, Kaposi's sarcoma and a systemic nocardial infection. After surgical drainage and adequate antibiotic treatment the infection was cured. Under secondary antimicrobial prophylaxis no relapse has occurred to date. Generalized N. asteroides infections have been rarely described in patients with Aids and the possible reasons for this are discussed.

Acquired Immunodeficiency Syndrome↗
PubMed1991

Caffeine and sport: role of physical exercise upon elimination.

Urinary excretion of caffeine in two populations (men and women) of cyclotourists was measured, at rest and during exercise, after oral administration of 350 mg of caffeine in aqueous solution. The so-called "total metabolites", as measured by the EMIT test, were also determined, as well as urinary creatinine. At rest, elimination in relation to body weight was identical in men and women. During exercise a fivefold decrease in the female and twofold decrease in the male populations were observed. After exercise, caffeine elimination was greater than during the physical trial but remained lower for women than for men. "Total metabolites" excretion showed evidence for a slowing of caffeine catabolism during exercise and a restart of it after exercise. The caffeine content of beverages varies considerably from one country to another, depending on local customs, so that caffeine intake may be highly variable. Our results lead us to query the validity of the upper authorized official limit for urinary caffeine (12 micrograms.ml-1) in doping controls. The nature of the sporting event, sex, weight, and sampling delay after exercise are all factors that argue against the utilization of a unique standard.

Adult↗
PubMed1989

Reduction of sternal infection by application of topical vancomycin.

Sternal or mediastinal infection after heart operations occurs infrequently but carries a high cost in money, morbidity, and mortality. At our hospital, Staphylococcus nonaureus causes most of these infections and is uniformly sensitive to vancomycin. In a prospective study of 416 patients having cardiac operations, randomized by hospital record number, topical vancomycin was applied to the cut sternal edges in 223 patients (group V) and was omitted in the control group (C) of 193 patients. The vancomycin was applied in a hemostatic paste of topical thrombin and powdered absorbable gelatin; in the control group only the hemostatic paste was applied. All patients received prophylactic systemic antibiotics for 2 days. Sternal infection occurred in one patient in group V (0.45%) and in seven patients in group C (3.6%) (p = 0.02). Infection also correlated with longer operative times (p = 0.027). By multivariate testing, vancomycin (p = 0.013) and shorter operative times (p = 0.014) independently predicted reduced infection rates. In the one patient with an infection in group V, Staphylococcus aureus was cultured; this organism was also cultured in two patients in group C, with Staphylococcus nonaureus being the culprit in the other five patients with sternal infections in group C. Topical vancomycin applied to the cut sternal edges reduces the risk of postoperative sternal infection.

Administration, Topical↗
PubMed1976

Mineralocorticoid activity of 16beta-hydroxydehydroepiandrosterone and related steroids.

16beta-Hydroxydehydroepiandrosterone (16beta-OH-DHEA) and related C19-steroids have recently been reported to be etiologic in low-renin essential hypertension. The mineralocorticoid potency of 16beta-OH-DHEA and several C19-steroids (16-oxo-A-diol, 16-oxo-testosterone, 16beta-OH-epiandrosterone, 5-androstene-3beta, 16beta,17beta-triol, 19beta-OH-testosterone, 18-OH-DHEA, and 16alpha-OH-DHEA) were investigated in two different rat bioassay systems under a variety of experimental conditions. In all but one instance, only negligible mineralocorticoid activity was observed, usually less than 0.1 per cent that of aldosterone. Since 16beta-OH-DHEA has negligible mineralocorticoid activity in the rat bioassay and the toad bladder assay (as reported by others), does not cause hypertension when injected chronically into the rat, and does not displace aldosterone from its renal receptors, it appears unlikely to be etiologic in low-renin essential hypertension. On the other hand, when 16-oxo-testosterone was injected intraperitoneally instead of subcutaneously, it demonstrated a slight increase in mineralocorticoid activity (from less than 0.1 per cent to 0.2 per cent) which equaled that of 18-hydroxydeoxycorticosterone (18-OH-DOC) injected subcutaneously. Thus, the possibility remains that 16-oxo-testosterone or a closely related metabolite may have sufficient mineralocorticoid activity to be involved in certain forms of hypertension in man.

Animals↗