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Biomedical subjects

J P Seguin

Publications and source records attributed to J P Seguin.

7 recordsLinked to original sources
PubMed1996

Water activity by 1H nuclear magnetic resonance spectroscopy: application to the study of water exchange in biphasic media.

The water activity (alpha w) of the liquid phase is investigated by means of 1H NMR for both monophasic and biphasic systems. The chemical shift or the area of the signal of the hydroxylic hydrogens is compared to calibration curves obtained from mixtures equilibrated at different water activities, thus allowing determination of the alpha w of the system. The chemical shift varies linearly as a function of the alpha w of the system. Through simple calculation the hydroxylic hydrogen concentration obtained from the area gives the water concentration in the medium; the sorption curve is thus obtained through NMR. The application of this method to a biphasic system composed of a liquid phase (an equimolar mixture of acid-alcohol) and a solid phase (a lipase), equilibrated separately at two different water activities, gives information on the water exchange between both phases during the lag phase of the esterification reaction. Light and slow water exchanges are observed from the solid phase at high alpha w toward the liquid phase at low alpha w. The lag phase of the esterification reaction is too short for the water activity equilibrium to be reached before the reaction starts.

Absorption↗
PubMed1995

Loads on spinal tissues during simultaneous lifting and ventilatory challenge.

Muscles of the torso have been implicated to play a role in stabilization of the low back, and to assist in ventilation. This motivated an investigation to combine a load challenge to the low back with a breathing challenge, similar to that which a worker might experience when shovelling snow. Perhaps modulation of muscle activity needed to facilitate breathing may compromise the margin of safety of tissues that depend on constant muscle activity for support. Eight young healthy males dynamically lifted, and isometrically held, large loads (73-95 kg) and breathed a 10% CO2 gas mixture to elevate breathing (both with and without hand-held loads). Individual tissue forces were calculated using an anatomically detailed, dynamic model of the torso that was sensitive to individual variation by utilizing myoelectric signals, intra-abdominal pressure, ventilation rate and spine kinematics, obtained from each subject, as input. For large loads in the hands, most subjects appeared to stabilize the trunk with large muscle forces relegating the responsibility of creating lung air flow to the diaphragm. When reasonably small low-back demands were coupled with a breathing challenge and higher ventilation rates two out of eight subjects demonstrated entrainment of abdominal activity to breathing that resulted in additional cyclic low-back compressive loading of the order of 1000 N. Ergonomists should consider the additional tissue loading from physiologically demanding tasks and the related ventilation challenge, together with the tissue loads required to support external objects and maintain body posture.

Adult↗
PubMed1994

Physicochemical properties of extracellular (1-->4)-beta-D-glucuronan produced by the Rhizobium meliloti M5N1CS strain during fermentation: evidence of degradation by an exoenzyme activated by Mg2+.

The mutant Rhizobium meliloti M5N1CS (NCIMB 40472) produced a partially acetylated (1-->4)-beta-D-glucuronan during fermentation. The polysaccharide (EPS) extracted from broth during fermentation by microfiltration and ultrafiltration (using a 100 kDa cut-off membrane) was characterized by size exclusion chromatography. The weight-average molecular weight (Mw) of the EPS decreased from 7.5 x 10(5) to 5 x 10(5) between 27 and 75 h of fermentation. When MgSO4.7H2O (0.8 gl-1 per day) was present in the medium during the same period, the Mw of the EPS decreased to 1.5 x 10(5). Since EPS degradation was detected after microfiltration of the fermentation medium supplemented with magnesium, the Mw decrease of the EPS extracted during fermentation may be explained by enzymic degradation of the polymer activated by Mg2+ ions.

Bacterial Proteins↗