Biomedical subjects

G Lacroix

Publications and source records attributed to G Lacroix.

At least 19 recordsLinked to original sources

PubMed2002

Decrease in ovalbumin-induced pulmonary allergic response by benzaldehyde but not acetaldehyde exposure in a Guinea pig model.

The pulmonary effects of two environmentally relevant aldehydes were investigated in nonsensitized or ovalbumin (OA)-sensitized guineapigs (GPs). Four-week-old male Hartley GPs, weighing about 400 g, were intraperitoneally injected with 1 ml of an NaCl solution containing 100 microg OA and 100 mg Al(OH)(3). They were then exposed to either acetaldehyde (200 ppb) or benzaldehyde (500 ppb) for 4 wk (6 h/d, 5 d/wk). At the end of exposure, GPs were challenged with an OA aerosol (0.1% in NaCl) and pulmonary functions were measured. The day after, guinea pigs were anesthetized and several endpoints related to inflammatory and allergic responses were assessed in blood, whole-lung histology, and bronchoalveolar lavage (BAL). Sensitized nonexposed GPs showed bronchial hyperresponsiveness to OA and an increased number of eosinophils in blood and BAL, together with a rise in total protein and leukotrienes (LTB(4) and LTC(4)/D(4)/E(4)) in BAL. In nonsensitized GPs, exposure to acetaldehyde or benzaldehyde did not induce any change in the tested parameters, with the exception of irritation of the respiratory tract as detected by histology and an increased number of alveolar macrophages in animals exposed to acetaldehyde. In sensitized GPs, exposure to acetaldehyde induced a moderate irritation of the respiratory tract but no change in biological parameters linked to the inflammatory and allergic responses. In contrast, exposure to benzaldehyde induced a decrease both in OA-induced bronchoconstriction and in eosinophil and neutrophil numbers in BAL, an increase in the bronchodilatator mediator prostaglandin E(2) (PGE(2)), and a decrease in the bronchoconstrictor mediators LTC(4)/D(4)/E(4). Further investigations are needed to determine if the attenuated response observed in sensitized GPs exposed to benzaldehyde is due to an alteration of the mechanism of sensitization or to a more direct effect on various mechanisms of the allergic response.

Acetaldehyde↗

PubMed2000

Functional diversity governs ecosystem response to nutrient enrichment.

The relationship between species diversity and ecosystem functioning is a central topic in ecology today. Classical approaches to studying ecosystem responses to nutrient enrichment have considered linear food chains. To what extent ecosystem structure, that is, the network of species interactions, affects such responses is currently unknown. This severely limits our ability to predict which species or functional groups will benefit or suffer from nutrient enrichment and to understand the underlying mechanisms. Here our approach takes ecosystem complexity into account by considering functional diversity at each trophic level. We conducted a mesocosm experiment to test the effects of nutrient enrichment in a lake ecosystem. We developed a model of intermediate complexity, which separates trophic levels into functional groups according to size and diet. This model successfully predicted the experimental results, whereas linear food-chain models did not. Our model shows the importance of functional diversity and indirect interactions in the response of ecosystems to perturbations, and indicates that new approaches are needed for the management of freshwater ecosystems subject to eutrophication.

Animals↗

PubMed2000

Analysis of volatile contaminants in vegetable oils by headspace solid-phase microextraction with carboxen-based fibres.

The headspace solid-phase microextraction (HS-SPME) efficiencies from vegetable oil of the recently available Carboxen-poly(dimethylsiloxane) (PDMS) and divinylbenzene-Carboxen-PDMS fibres were found to be much greater than those of the PDMS fibre for a number of volatile contaminants. Using these Carboxen-based fibres, the commonly used HS-SPME equilibration times for aqueous matrices of 30-45 min at room temperature for a number of halogenated and aromatic analytes with volatilities ranging from 1,1-dichloroethylene to hexachlorobenzene were found to be insufficient for the effective extraction of the less volatile analytes from vegetable oil. HS-SPME at 100 degrees C for 45 min, followed by rapid cooling to 0 degrees C with a 10 min continuing extraction, however, significantly increased the SPME efficiencies for the less volatile analytes. Spiking solutions were prepared in vegetable oil instead of methanol as the latter was found to displace analytes from the Carboxen material. Using either of the Carboxen-based fibres and SPME at 100 degrees C, all the target analytes could be determined at low or sub-microg kg(-1) with repeatability < or =10%, even though an equilibrium SPME of the less volatile analytes was not achieved.

Chromatography, Liquid↗

PubMed1999

Reasoning about apparent contradictions: resolution strategies and positive-negative asymmetries.

Apparent contradictions, e.g. Did Susan like her supper?--Yes and no, involve asserting and denying the same proposition. They therefore violate the classical law of non-contradiction, suggesting the use of non-classical interpretive structures in natural language and reasoning. Experiment 1 explores the range of such interpretive structures available to adults (n = 24) in their reasoning about an apparent contradiction. Experiment 2 uses a similar task to study the emergence of these interpretive structures in young children's reasoning (3;6 to 8;4, n = 48). Results suggest an early facility with resolution strategies relating to object structure (as in, Maybe Susan liked one part of supper but didn't like another part) and an initial tendency to focus on the negative by referring to it first (as in, Maybe Susan didn't like one part of supper but did like another part). We discuss the results in terms of the natural logic of objects and their properties, and the logical resources available to young children.

Adult↗

PubMed1998

[Ozone and the immune system].

This review focuses on the effect on health of changes in the immune system secondary to ozone exposure and on various mechanistic hypotheses put forward. Beyond the problems related to the variability of study criteria (e.g. age, sex, concentration and duration of different types of exposure, the slightly volatile nature of ozone and the complexity of the immune system), ozone may induce immunostimulation as shown by intensified allergic phenomena or immunosuppression expressed by increased sensitivity to bacterial infections. Different functions of the immune response (for example macrophage and polynuclear phagocytic and bactericidal activity, NK activity, cytokine and antibody production ...) are affected. In terms of risk, the consequences of these changes depend on their intensity, their perennial nature and their association with particular genetic characteristics or other forms of external aggression, for example infection. The effect of exposure to a mixture of pollutants with unknown interactions should also be taken into consideration. Finally, the problem of normal but possibly exaggerated immune response to a compound whose allergenicity may have been modified by ozone must also be taken into account.

Antibody Formation↗

PubMed1996

Treatment of postoperative nausea and vomiting: comparison of propofol, droperidol and metoclopramide.

PURPOSE: To compare the efficacy of propofol in a subhypnotic dose (10 mg iv), droperidol (1.25 mg iv), or metoclopramide (10 mg iv) in the treatment of PONV in the post anaesthesia care unit (PACU). METHODS: In a prospective, randomized, double-blind protocol, over four months, all eligible inpatients and outpatients were asked to give their consent to be included in the study should they suffer PONV in the PACU. They received a standardized general anaesthetic without any prophylactic antiemetic drug. In the recovery room, patients complaining of persistent nausea (lasting more than ten minutes) and/or experiencing at least two episodes of retching or vomiting were given one of the three study drugs. Recurrence of retching or vomiting was recorded for 60 min after administration of the study drug and nausea severity was assessed on a visual analog scale. Patients still complaining of PONV 30 min after administration of the study drug received a rescue medication (dimenhydrinate). RESULTS: Seventy-eight patients received one of the study drugs. The recurrence of retching or vomiting was higher with propofol (58%) than with droperidol (4%) or metoclopramide (24%) (P < 0.001). More patients who received propofol needed the rescue medication (54%) than those who received droperidol (15%) or metoclopramide (28%) (P < 0.02). No difference was observed in nausea severity. CONCLUSION: A subhypnotic dose of propofol (10 mg iv) is less effective than the conventional antiemetic drugs droperidol and metoclopramide for the treatment of PONV in the PACU.

Adult↗

PubMed1996

The choice of medical providers in rural Bénin: a comparison of discrete choice models.

In this paper we estimate three different discrete choice models of provider choice using data from the rural District of Ouidah in Bénin. These three model are: Multinomial Logit (ML); (2) Independent Multinomial Probit (IMP); (3) Multinomial Probit (MP). A comparison of IMP and MP allows us to reject the independence assumption between providers. Furthermore, the cross-price elasticities computed from the restrictive specifications (ML and IMP) are dramatically different from those computed from the more general one (MP). These results cast some doubt on the validity of the previous findings and policy recommendations that are typically based on the ML specification.

Benin↗

PubMed1993

Application of solid-phase microextraction to the headspace gas chromatographic analysis of halogenated volatiles in selected foods.

Solid-phase microextraction (SPME), with the poly(dimethylsiloxane)-coated silica fiber suspended and equilibrated in the headspace, has been applied to the capillary gas chromatographic (GC) analysis of 33 halogenated volatile contaminants in model aqueous solutions and in foods. With electrolytic conductivity detection, the limits of detection in water ranged from 1.5 micrograms/kg for vinyl chloride to < or = 0.005 microgram/kg for the tri- to hexachlorobenzenes. Headspace SPME-GC shows a much greater response for the less volatile analytes than those of greater volatility, a procedure complementing headspace GC with gas sampling. In model systems or foods, increasing lipid material decreased the headspace extraction. With 50 mg of lipid, the headspace extraction decreased about 50% for analytes with LODs about 0.1 microgram/kg and by > or = 99.5% for the above chlorobenzenes. Standard addition was used to analyze a variety of beverages and dry foods and to determine the analyte partitions.

Beverages↗

PubMed1993