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Biomedical subjects

P Gervais

Publications and source records attributed to P Gervais.

At least 37 records · Page 2Linked to original sources
PubMed1999

Slow heat rate increases yeast thermotolerance by maintaining plasma membrane integrity.

Thermal resistance of Saccharomyces cerevisiae was found to be drastically dependent on the kinetics of heat perturbation. Yeasts were found to be more resistant to a plateau of 1 h at 50 degrees C after a slope of temperature increase (slow and linear temperature increments) than after a shock (sudden temperature change). Thermotolerance was mainly acquired between 40-50 degrees C during a heat slope, i.e., above the maximal temperature of growth. The death of the yeasts subjected to a heat shock might be related to the loss of membrane integrity: intracellular contents extrusion, i.e., membrane permeabilization, was found to precede cell death. However, the permeabilization did not precede cell death during a heat slope and, therefore, membrane permeabilization was a consequence rather than a cause of cell death. During a slow temperature increase, yeasts which remain viable may have time to adapt their plasma membrane and thus maintain membrane integrity.

Cations↗
PubMed1999

Saccharomyces cerevisiae viability is strongly dependant on rehydration kinetics and the temperature of dried cells.

The effects of rehydration kinetics and temperature on the viability of Saccharomyces cerevisiae dehydrated by drying were studied. During rehydration, a water activity range of 0.117-0.455 must be crossed slowly in order to maintain cell viability. If this range is crossed rapidly, cell viability can be preserved if rehydration takes place at 50 degrees C. Several hypotheses have been proposed to explain previous results. One hypothesis, which relates cell mortality after rapid rehydration to water flow through the membrane in phase transition, is the more plausible and requires further investigation.

Colony Count, Microbial↗
PubMed1999

Yeast cell mortality related to a high-pressure shift: occurrence of cell membrane permeabilization.

The shrinkage of yeast cells caused by high-pressure treatment (250 MPa, 15 min) was investigated using direct microscopic observation. A viable staining method after treatment allowed the volume variation of two populations to be distinguished: an irreversible volume decrease (about 35% of the initial volume) of pressure-inactivated cells during pressure holding time, and viable cells, which were less affected. A mass transfer was then induced during high-pressure treatment. Causes of this transfer seem to be related to a pressure-induced membrane permeabilization, allowing a subsequent leakage of internal solutes, where three ions (Na+, K+ and Ca2+), plus endogenous glycerol, were verified. This glycerol leakage was found to occur after yeast pressurization in a medium having low water activity, although the yeast was not inactivated. All these observations lead to the hypothesis that pressure-induced cell permeabilization could be the cause of yeast inactivation under pressure.

Calcium↗
PubMed1998

Influence of the shape of phospholipid vesicles on the measurement of their size by photon correlation spectroscopy.

The influence of shape transformation of large unilamellar vesicles (LUV) on their size measurement by photon correlation spectroscopy (PCS) has been investigated. The experimental size of vesicles after hyperosmotic contractions of increasing intensities have been compared to the theoretical volume decrease determined by applying Boyle Van't Hoff's law. The main observation is that PCS size measurement gives overestimated values when LUV have been subjected to a volume decrease of more than 20% of their initial volume. The PCS size overestimation is related to the influence of the shape transformation of the vesicles on their diffusion coefficient (D) as shown by modelling the evolution of D of a sphere which is transformed into an ellipsoid by internal volume reduction under constant area.

Absorptiometry, Photon↗
PubMed1998

Escherichia coli and Lactobacillus plantarum responses to osmotic stress.

Escherichia coli and Lactobacillus plantarum were subjected to final water potentials of -5.6 MPa and -11.5 MPa with three solutes: glycerol, sorbitol and NaCl. The water potential decrease was realized either rapidly (osmotic shock) or slowly (20 min) and a difference in cell viability between these conditions was only observed when the solute was NaCl. The cell mortality during osmotic shocks induced by NaCl cannot be explained by a critical volume decrease or by the intensity of the water flow across the cell membrane. When the osmotic stress is realized with NaCl as the solute, in a medium in which osmoregulation cannot take place, the application of a slow decrease in water potential resulted in the significant maintenance of cell viability (about 70-90%) with regard to the corresponding viability observed after a sudden step change to same final water potential (14-40%). This viability difference can be explained by the existence of a critical internal free Na+ concentration.

Cell Size↗
PubMed1997

Shape modification of phospholipid vesicles induced by high pressure: influence of bilayer compressibility.

Giant vesicles composed of pure egg yolk phosphatidylcholine (EYPC) or containing cholesterol (28 mol%) have been studied during a high hydrostatic pressure treatment to 285 MPa by microscopic observation. During pressure loading the vesicles remain spherical. A shape transition consisting of budding only occurs on the cholesterol-free vesicles during pressure release. The decrease in the volume delimited by the pure EYPC bilayer between 0.1 and 285 MPa was found to be 16% of its initial volume, whereas the bulk compression of water in this pressure range is only 10%. So the compression at 285 MPa induced a water exit from the pure EYPC vesicle. The shape transition of the EYPC vesicle during pressure release is attributed to an increase in its area-to-volume ratio caused by the loss of its water content during compression. Because bulk compression of the cholesterol-containing vesicle is close to that of water, no water transfer would be induced across the bilayer and the vesicle remains spherical during the pressure release.

Cholesterol↗
PubMed1997

Onset of action and efficacy of terfenadine, astemizole, cetirizine, and loratadine for the relief of symptoms of allergic rhinitis.

BACKGROUND: Terfenadine, astemizole, cetirizine, and loratadine are compared in their abilities to produce relief of symptoms of allergic rhinitis. OBJECTIVE: The aim of this study was to compare the onset of action and efficacy of the study medications. METHODS: 111 ragweed-sensitive subjects were primed with pollen in the Environmental Exposure Unit. Study entry required adequate symptoms over a 3 hour exposure to 5000 +/- 300 grains/m3 of ragweed pollen. On the test day, subjects were given a single dose of either terfenadine 60 mg (22), astemizole 10 mg (22), cetirizine 10 mg (23), loratadine 10 mg (22), or placebo (22) when sufficiently symptomatic after a 60-minute exposure. Allergen levels were maintained and symptoms recorded every 30 minutes. RESULTS: Proportions of subjects with clinically important relief were cetirizine, 69.6%; terfenadine, 54.5%; loratadine, 50.0%; astemizole, 40.9%; and placebo, 31.8% but differences weren't significant between treatment groups (P = .119). Survival curves for times to onset of clinically important relief for the four treatment groups were not different (P = .119). Subjects realizing definitive relief were cetirizine, 65.2%; terfenadine, 45.5%; loratadine, 31.8%; placebo, 27.3%; and astemizole, 22.7% (P = .023). Survival analysis of onset time for definitive relief found significant differences (P = .010). The ranking was cetirizine --> terfenadine --> loratadine --> astemizole (quickest to slowest). Global evaluation based on subject willingness to take the medication again yielded percentages: cetirizine, 82.6%; terfenadine, 66.7%; astemizole, 63.6%; loratadine, 40.9%; and placebo, 36.4% (P = .036). CONCLUSION: Cetirizine and terfenadine continuously ranked higher in terms of onset of action and efficacy, while loratadine and astemizole ranked lower. Significance was detected in definitive relief and relative efficacy.

Adolescent↗
PubMed1997

Effects of the kinetics of water potential variation on bacteria viability.

The effect of the kinetics of water potential variation (psi) on the viability of bacteria subjected to hyperosmotic stresses in water-glycerol solution was studied. The three bacteria used were Lactobacillus plantarum L-73, Leuconostoc mesenteroides LM057 and Escherichia coli TG1. These strains were submitted to a final water potential of -107.2 MPa, -170.9 MPa and/or -244.7 MPa. In any case the kinetics of water potential variation was found to have a great effect on the cell viability. The application of slow water potential decreases could maintain an important cell viability (about 80-100%) with regard to the corresponding viability observed after a sudden step change for the same final water potential (15-57%). For each strain tested, an optimal dehydration kinetics was determined which depended on the final water potential. The existence of this optimum could be explained thanks to the opposition of two actions affecting cell viability: a positive action relative to the slowness of the water potential variation and a negative action relative to the residence time of cells in a critical range of water potential.

Escherichia coli↗
PubMed1996

Passive response of Saccharomyces cerevisiae to osmotic shifts: cell volume variations depending on the physiological state.

The passive osmoregulation phase of S. cerevisiae has been characterized for different physiological states. The relative cell volume decrease of exponential cells was found to be greater than the volume decrease of stationary ones during the hyperosmotic shock. The application of a slow and linear increase in osmotic pressure has allowed the distinguishing of two phases in the passive osmoregulatory response of cells and to calculate the turgor pressure of S. cerevisiae. Cells in the exponential phase have a weak turgor pressure (0.05 MPa) compared to the turgor pressure of stationary phase cells (0.2 MPa). Nevertheless, the turgor pressure and the relative decrease in volume were found to be independent of the size of cells for the same physiological state.

Culture Media↗
PubMed1995

A new design intended to relate high pressure treatment to yeast cell mass transfer.

A new optical device has been developed to allow the observation of microorganisms during a high pressure treatment up to 700 MPa. To measure cell volume variation during the high pressure application, an image analysis system was connected with the light microscope. With this device, growth of Saccharomyces cerevisiae was studied at moderate pressure (10 MPa) through the observation of individual cell budding. Cell volume variations were also measured on the yeast Saccharomycopsis fibuligera on fixed cells as well on a population sample and a shrinkage in average cell volume was observed consequently to a pressure increase of 250 MPa. The observed compression rate (25%) under pressure and the partial irreversibility of cell compression (10%) after return to atmospheric pressure lead to the conclusion that a mass transfer between cell and cultivation medium occurred. The causes of this transfer could be explained by a modification of membrane properties, i.e., disruption or increase in permeability.

Hydrostatic Pressure↗
PubMed1995

Effect of the kinetics of temperature variation on Saccharomyces cerevisiae viability and permeability.

The variation rate of the temperature increase was found to have a great effect on the viability of Saccharomyces cerevisiae subjected to heat perturbations between 25 degrees C and 50 degrees C. A low intensity of the increase rate of temperature could maintain an important viability of the cells (about 34% of the initial population) with regard to the corresponding viability (about 1%) observed after a sudden step change for the same final temperature level of 50 degrees C. A cell volume reduction more important (22% of the initial volume) has been observed in cells submitted to a heat shock than for the cells which have been submitted to a slow kinetic of temperature increase (9%). Such an observation allowed to propose a relation between the membrane permeability and the kinetics of temperature variation.

Cell Membrane Permeability↗
PubMed1995

[Internal breast prostheses of silicone: accidents and medico-legal consequences].

The authors gathered the principal information obtained from medical and medicolegal data relating to silicone breast implants. The publications collected and the opinions of various administrative, judiciary and private authorities do not permit at present to determine a complete coherent point of view. The internal silicone breast implants could provoke some inflammatory phenomenons and local sclerosis. The durability and life span of these prostheses is still matter of concern. Though not proved by epidemiological studies the risk of group connective-tissue diseases cannot be definitely dismissed 10 years after the prosthesis implantation, the risk is probably low. Finally the practitioners, especially cancerologists, should continue to use these prostheses. It is to hope that experimental epidemiological research and the progress of manufacturing control allow the use of silicones for medical and chirurgical purposes.

Biocompatible Materials↗
PubMed1994

A prediction of an optimal performance of the handspring 1 1/2 front salto longhorse vault.

The handspring 1 1/2 front salto vault in the tucked position is deemed to be an important high-level vault. It was the compulsory vault of the 1988 Olympics and is a building block for more advanced skills in the handspring family. The purpose of this study was to predict an individual's optimal performance of a handspring 1 1/2 front salto vault. An assessment of the athlete's present performance ability was determined using cinematographical analysis of three trials. These trials were judged as being typical high-level performances of the vault. Secondly, an objective function was identified based on the performance result of points awarded. The objective function was composed of those performance variables that, if maximized, would result in minimal deductions. Postflight height and distance were identified as those variables. Angular momentum was included in a penalty function form to ensure that sufficient angular momentum was present for successful completion of the skill. A Lagrangian approach was used to derive the equations of motion and a Rayleigh-Ritz procedure, using fifth-degree polynomials, was used to represent and discretize the state variables. The predicted optimal performance of the skill displayed greater virtuosity in postflight height, distance and angular momentum when compared to the individual's best trial performance. The results of this study generally fall within the limits observed for elite vaulters.

Biomechanical Phenomena↗
PubMed1994

Persistent asthma after inhalation of a mixture of sodium hypochlorite and hydrochloric acid.

Chlorine gas inhalation can lead to temporary mucous membrane irritation, pulmonary edema, and transient bronchospasm. Existence of respiratory sequelae is debated. We report a case of asthma, persisting 2 years after the inhalation of a mixture of sodium hypochlorite and hydrochloric acid. Bronchial histologic findings and transmission electron microscopy examinations showed uncommon abnormalities supporting irritation for cause of this nonimmunologic asthma.

Accidents, Home↗