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Biomedical subjects

D Laurent

Publications and source records attributed to D Laurent.

At least 73 records · Page 4Linked to original sources
PubMed1992

Behavioural and cognitive characteristics of conduct disordered-hyperactive boys from age 6 to 11: a multiple informant perspective.

Three subgroups of kindergarten boys (stable conduct disordered-hyperactive (SCDH), stable conduct disordered (SCD), stable non-deviant control (SC)) were defined and followed up three, four and five years later in primary school. Using assessments from multiple informants (teachers, mothers, peers, self), the results showed that SCDH boys were more hyperactive (i.e. overactive/inattentive) and displayed a greater diversity of conduct problems in school and home at follow-up compared to the other groups. These results and the fact that during early adolescence SCDH boys tend to develop a worse prognosis than SCD boys suggest that they should be distinguished.

Antisocial Personality Disorder↗
PubMed1992

Effect of prior exercise in Pi/PC ratio and intracellular pH during a standardized exercise. A study on human muscle using [31P]NMR.

Seven subjects underwent a standard localized exercise of calf muscles in order to investigate whether the metabolic exercise-induced steady-state, as revealed by the evaluation of inorganic phosphate/phosphocreatine ratio, depends on the conditioning of the muscle just prior to the exercise. The experimental protocols consisted of two separate experiments using first [31P]nuclear magnetic resonance spectroscopy and second (on 3 subjects) infrared oxyphotometry to respectively follow variation of energy metabolism and tissular deoxygenation. The exercise consisted of 240 successive plantar flexions (0.5 Hz frequency) against a high load equivalent to 80% of the maximal voluntary contraction. This exercise was accomplished before cold exercise and after warm exercise, a warming-up period bringing to approximately 50% of VO2max. The results showed that: (1) steady-state level of phosphate/phosphocreatine and intracellular acidosis was significantly lowered by warming-up; (2) cold and warm exercise steady-state of calculated adenosine diphosphate values were not significantly different; (3) cold exercise rapidly induced a high tissular deoxygenation that is not observed during warm exercise; and (4) time-constant of phosphocreatine resynthesis is lowered after warm exercise but the initial slope of time-evolution is not modified. Parallel experiments also showed that phosphate/phosphocreatine steady-state was not modified in comparison with warm exercise when the same power of exercise was reached by stepwise incrementation of the charge. From these results we postulate that a better tissue oxygenation due to a global or localized warming-up allows to reach the same mechanical performance with a lower decrease of PCr content, owing to a faster adjustment of oxidative metabolism during the transitional period.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1991

Impairment of muscular metabolism in chronic respiratory failure. A human 31P MRS study.

The calf muscle metabolism of 7 patients with stable chronic respiratory failure (PaO2 below 65 Torr) was studied using 31P NMR spectroscopy. NMR spectra were acquired at rest, during the course of 360 pedal movements at 20, 35 and 50% of the maximal voluntary contraction (MVC) and during recovery. Eight normal aged-matched subjects served as a control group. In resting muscle, no significant differences were observed between both groups as regards intracellular pH, inorganic phosphate/phosphocreatine (Pi/PCr) and beta-ATP/PCr + Pi + phosphomonoester (PME) ratios. Although effective power outputs were similar for both groups at each work level, patients exhibited a higher Pi/PCr ratio than healthy controls (3.19 +/- 1.01 vs 0.49 +/- 0.05 at 50% MVC; p less than 0.01) and a lower pHi (6.65 +/- 0.11 vs 7.06 +/- 0.02 at 50% MVC; p less than 0.01). Moreover, PCr resynthesis during recovery was slower in patients than in control subjects (t1/2 PCr = 1.26 +/- 0.30 vs 0.47 +/- 0.05 min; p = 0.01). These results suggest impairment of aerobic capacity in a non-ventilatory working muscle, probably due to hypoxemia in patients with chronic respiratory failure.

Adenosine Triphosphate↗
PubMed1991

Fumonisin, a toxin from the fungus Fusarium moniliforme sheld, blocks both the calcium current and the mechanical activity in frog atrial muscle.

The effects of fumonisin, a toxin isolated from the fungus Fusarium moniliforme sheld were studied on transmembrane potentials and currents of the frog heart muscle using the double sucrose gap technique. Fumonisin (280 microM) shortened the plateau duration of the action potential. Under voltage clamp conditions, fumonisin inhibited the Ca current. The block occurred without alteration of either the kinetic parameters or the apparent reversal potential of the current suggesting that the toxin blocked the maximal Ca conductance. Fumonisin reduced mainly the phasic component of the peak tension. The time to peak tension was unchanged whereas its relaxation phase was accelerated at positive membrane potentials suggesting that Na-Ca exchange was accelerated by fumonisin. Dose-response curves for the Ca current and the peak tension indicated half inhibition at about 100 microM fumonisin and a stoichiometric parameter of 1.7, suggesting that more than one toxin molecule interacted with the Ca channel. The data suggested that the effect of fumonisin on the Ca current and the tension might account for cardiac failure reported in animal intoxication by Fusarium moniliforme.

Action Potentials↗
PubMed1991

Functional and metabolic effects of uridine and UTP on the skeletal muscle of the rat submitted to exercise.

Twenty millimolar and 2 mM uridine triphosphate and 2 mM uridine were injected intra-arterially into rat leg muscles during a 20 min period of intense exercise and during the recovery phase (20 min). Administration of 20 mM uridine triphosphate during exercise, provoked a complete depression of muscle contractility. On the contrary, supply of 2 mM uridine triphosphate or 20 mM uridine induced a reduction in the decrease of muscular developed tension during the exercise period of time and favoured functional recovery. This positive effect of pyrimidine compounds on muscular functional parameters did not seem to be correlated with metabolic effects. Indeed, 2 mM uridine supply did not modify the evolution of intramuscular glycogen and lactate concentrations and made worsened the adenine nucleotide degradation induced by exercise.

Animals↗
PubMed1988

Bistramide A, a new toxin from the urochordata Lissoclinum bistratum Sluiter: isolation and preliminary characterization.

Two cases of human intoxication caused by the lyophilized powder of Lissoclinum bistratum Sluiter, a New Caledonian ascidian, are reported. The symptoms observed were caused by a substance designated bistramide A (C40H68N2O8) of hitherto unknown chemical structure. Preliminary toxicological investigations indicate that bistramide A may effect the central nervous system, leading to paresthesia and loss of muscle tone. A progressive decrease in cardiac rhythm was also observed in animals. Bistramide A (1.4 x 10(-6) M) did not alter the resting potential of frog heart and skeletal muscle but reduced the amplitude and duration of cardiac action potential and prolonged the interval between action potentials. Bistramide A also has a marked cytotoxic effect on cancer cells KB (IC50 = 4.5 x 10(-8) M) and P 388 (IC50 = 2.0 x 10(-8) M) and on normal endothelial cells (IC50 = 2.2 x 10(-8) M). However, it has not been possible to relate the cytotoxic property to the symptoms of intoxication. Bistramide A may originate from the urochordate itself or from symbiotic algae.

Acetamides↗
PubMed1986

Scanning spectrophotometry for the dynamic study of tissue respiration in intact organs.

For use with intact perfused organs a spectrophotometer system has been developed, both for dual-wavelength absorption measurements and for spectral scanning. A monochromator is used for illumination and scanning in the visible and near infrared. Optic fibres conduct light to the specimen under examination and from the specimen to a detecting photomultiplier. System control is exercised by a microcomputer, which also processes the collected data. The performance of the system on isolated perfused rat heart is demonstrated, in the spectral scanning mode and in the dual-wavelength mode, by studying simultaneously the kinetics of cytochrome aa3, and myoglobin oxidation-reduction.

Animals↗
PubMed1985

[Arterial disobliteration by the laser].

In order to determine the optimal conditions for disobliteration of occluded arteries without damaging the arterial wall, the effects of a Nd-YAG laser connected to a 0.2 mm diameter fibre optic system were studied on post-mortem coronary arteries and popliteal and tibial arteries of amputated limbs. Vaporisation of atheromatous plaques was consistently obtained with energies of 300 to 600 joules associated with perfusion of the vessel with dilated blood (3 g/100 ml of haemoglobin) at a flow rate of 20 ml/min. Protection of the arterial wall was ensured by introducing the fibre aortic system through a balloon catheter and by cooling with the perfusion liquid. The reproducibity of these results in the absence of major arterial wall damage, and the facility of manipulation of the fibre optic system due to its flexibility and narrow diameter, encouraged us to use this method clinically. The first three applications on peripheral arteries (femoral and popliteal arteries) confirmed that this method of arterial disobliteration can be used with a certain degree of efficacy with only a slight risk of arterial perforation. Further studies are essential to improve the degree of laser penetration of the arterial obstruction and to increase the diameter of the tunnel of recanalisation.

Arterial Occlusive Diseases↗
PubMed1985

Theophylline: a haemoperfusion modelisation.

A dynamic study of the kinetics of theophylline adsorption in aqueous medium by two adsorbent resins is proposed. The adsorption process involves Van der Walls pattern physical bonds. An in vitro haemoperfusion apparatus was schematized and data describing the adsorption-desorption process was obtained. A mathematical treatment led to the conclusion that first-order adsorption and desorption rates are involved, results which led to the consideration of a model of in vivo haemoperfusion in the case of first-order adsorption and desorption, with first-order corporeal elimination. The results indicate that one of the resins used, Amberlite XAD4, already known as a haemocompatible resin, is useful in eliminating theophylline.

Adsorption↗
PubMed1985

Theoretical study of haemoperfusion: drugs obeying a one-compartment pharmacokinetics model.

A general theory of haemoperfusion for drugs obeying the one-compartment pharmacokinetics model is proposed. The following theoretical cases are investigated: First case Adsorption and desorption are first-order reactions without biotransformation, and elimination rate is first-order. Two particular cases are examined: no desorption and alpha = beta. Second case: Adsorption and desorption rates are first-order, without biotransformation, and elimination rate is zero-order. Third case: Adsorption rate is first-order and desorption rate is zero-order, without biotransformation, and elimination is either first-order or zero-order. Fourth case Adsorption rate is zero-order and desorption rate is first-order, without biotransformation, and elimination is either first-order or zero-order. Fifth case: Adsorption and desorption rates are first-order, with biotransformation. In all these pharmacokinetics models for haemoperfusion, theoretical computations lead to the values of adsorbed amount and plasma level, in relation to time. Clearances are also computed. In most cases, haemoperfusion must be performed quickly because of the desorption phenomenon. Parameters modulating the adsorption process are: surface area, blood flow, drug concentration in blood, adsorbent nature and adsorbent quantity.

Adsorption↗
PubMed1984

Imaging mammalian tissues and organs using laser collimated transillumination.

Images of mammalian organs were built up using a Laser collimated transillumination device equipped with a bidirectional scanning setup. A microcomputer was used to run the scanning process, acquisition of detected signals and images restitution. The images featured a satisfactory resolution of optical discontinuities on both sample surfaces. Light scattering within biological tissues restricted the spatial discrimination encountered with geometrical selection approach. By combining space and time resolution at various wavelengths, the production of an efficient tomospectroscopy could be envisaged.

Animals↗
PubMed1984

Recanalization of human arteries using Nd-YAG laser carried by optical fibre.

Nd-NAG laser carried by optical fibres 0.2 mm diameter was used in experimental studies to recanalize obstructed human cadaver arteries. Successful perforation of atheromatous plaques was obtained in all cases with a power of 12 W and a duration of exposure of 30-50 s provided that blood and not saline was used. The arterial wall was protected from injury by coaxial position of the optical fibre that was inserted into an inflated balloon catheter, and by circulating blood that cooled the system. The feasibility of guiding these devices in man was demonstrated in femoral and coronary arteries.

Arterial Occlusive Diseases↗