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Biomedical subjects

M Hugon

Publications and source records attributed to M Hugon.

At least 19 recordsLinked to original sources
PubMed2005

[Long-term effects of iterative diving on visual field, color vision and contrast sensitivity in professional divers].

PURPOSE: To assess long-term functional effects of iterative diving, we studied visual field, color vision, and contrast sensitivity in 21 French Navy professional divers and 21 controls. PATIENTS AND METHODS: This retrospective study investigated a population of 21 divers and 21 controls. All subjects were male. The inclusion criterion for divers was a total number of dives greater or equal to 1,000. Exclusion criteria for the two groups were glaucoma, ocular hypertension, smoking, and vasospastic risks. Additional exclusion criteria for controls were any history of diving practice and of hyperbaric oxygen therapy. The visual field was examined with a Humphrey Central 30-2 threshold test. Moreover, we explored spatial contrast sensitivity using Metrovision Moniteur Ophtalmologique "STAT" program and color vision with desaturated 15 hue test. RESULTS: None of the divers had any loss of spatial contrast sensitivity. There was a high frequency of yellow-blue axis color vision defects (45.2%) in the diver group. Regarding visual field, corrected pattern standard deviation was significantly higher in divers (p<0.01). CONCLUSION: These findings suggest that iterative diving may cause subclinical functional effects on vision. Further studies will be needed to determine the exact setting of this repercussion upon macula and/or the optic nerve.

Adult↗
PubMed2004

[Improvement in postural orientation and stability after stereotactic gamma irradiation of acoustic neurinomas].

Non-surgical stereotactic gamma ionizing irradiation was developed in order to produce a lethal effect on unilateral acoustic neurinomas (vestibular schvannomas). We present a study of postural vestibular dependent performances in 218 patients before and after curative irradiation. Subjects were asked to stand at ease on a static dynamometric foot-plate, gazing at a fixed point in front of them (EO condition) or to stand eyes closed (EC condition). Statokinesigrams were registered during two consecutive sessions of 51.2 sec, under EO and EC conditions. These sessions were first managed the days before (d-1), and after (d+1) irradiation; others were performed later (d+1 to 5 Years; n=37). Center of pressure (CofP) mediolateral (X) and sagittal (Y) positions were quantified every 100 msec. Mean Xm session value (with SD) was taken as a personal parameter for left or right body inclination. Area S for 90% of the XY successive placements of the CofP observed during a session was taken as an index for 2D postural way. Before irradiation the overall average of the 218 personal Xm mean values demonstrated a statistically significant body inclination toward the affected side, however under EC condition only. The day after irradiation, a significant reduction of the overall mean value of body inclination was observed. Paired Xm statistics of confirmed this trend toward usual symmetry. The day after stereo-irradiation, averaging areas S of ellipses indicated a shift of instability toward normality. For the two parameters, the pseudo-Romberg ratios (performance EC/performance EO) indicated that a special visual contribution to balance control is present in patients with a neurinoma tumor (here I and II grades). The relative importance of this visual support declined shortly after ionizing treatment. Because the radiation is neither noxious nor excitatory we think such a rapid recovery is due to some recovery of vestibular nerve afferent conduction, and a rapid neural reprogramming of the balance control. These attractive results call for deeper investigations of both vestibular and auditory functions.

Cohort Studies↗
PubMed2001

The hydroxyanilide fenhexamid, a new sterol biosynthesis inhibitor fungicide efficient against the plant pathogenic fungus Botryotinia fuckeliana (Botrytis cinerea).

Fenhexamid, a recently developed botryticide, is shown here to inhibit sterol biosynthesis. When the fungus Botryotinia fuckeliana was grown in the presence of fenhexamid, the ergosterol content was reduced, and three 3-keto compounds, 4 alpha-methylfecosterone, fecosterone and episterone, accumulated, suggesting an inhibition of the 3-keto reductase involved in C-4 demethylation. Thus, fenhexamid belongs to a new, promising class of sterol biosynthesis inhibitors not previously used in agriculture or in medicine.

Amides↗
PubMed1997

[Proprioceptive and cutaneous evoked somatosensory potentials in the baboon: cycles of GABAergic excitability and inhibition].

Double stimulations induce deep and long-lasting inhibition (0-300 ms) of the P16-N30 components of somatosensory potentials (SEP) evoked by sciatic or sural nerve stimulation. This inhibition is evidenced on both S1 and M1 cortical areas, demonstrating similar course and duration, whatever the source (right or left limb) and/or the modality (extero- or proprioceptive) of conditioning and testing afferences. The depth of this inhibition depends on the relative amplitude of the conditioning to testing SEP. After muscle injection of a subconvulsive dose of bicuculline, tSEPs are facilitated when individually elicited. When double stimulations are used, the inhibition of the SEP test is sharply reduced (with a 30-ms interstimulus delay). However, disinhibition of the conditioned SEP does not depend on separate individual SEP facilitations. Cortical GABAergic type a circuits are likely to be involved in inhibition of the conditioned SEP. This inhibition would be a non-invasive image of inhibitions that preserve the specificities of sensory messages in primary areas.

Animals↗
PubMed1996

[Somatosensory evoked potentials: interference and perceptual masking of cutaneous afferents in man].

Somatosensory evoked potentials (SEP) are attenuated following double electrical stimulation of the fingers (II + III). This effect is observed at cervical (N13), parietal (N20-P27) and frontal (P22-N30) levels. We simultaneously observed in the same subjects that cutaneous perception of the test-shock is completely suppressed with interstimulus intervals (ISI) within a 0-10 msec range. With 25-30 msec ISI, the perceptive function totally recovers, but SEP inhibition remains at 50 % of the control. The SEP reduction does not result in a perception deficit as long as the cortical-test response exceeds 50% of control. These results suggest that: SEP inhibition could be a local but durable phenomenon occurring at both cervical and cortical levels. Cutaneous perception does not necessitate a maximal SEP development. The perceptive process involves other associative areas (5,7...) and is activated when the primary cortical activation exceeds a certain threshold which was found at 50% of the unconditioned response voltage.

Adult↗
PubMed1996

[Evoked somatosensory potentials in the baboon: intracortical localization and nature studies using pharmacology and analysis of sources of current].

SEPs were elicited by stimulation of the sciatic (proprioceptive) or sural (exteroceptive) nerves. SEPs were recorded through epidural chronic electrodes implanted in the related S1 cortical surface. They were studied after systemic or local cortical administration of subconvulsive doses of bicuculline (a specific GABAa antagonist). A powerful increase in the amplitude of the P16 component, along with an inhibition of the N30 component were observed. From a cortical Current Source Densities analysis, the P16 facilitation was shown to result from blockade of the GABAa inhibitory synapses on the somas of pyramidal cells that are responsible for the P16 wave. Reduction of the N30 wave was attributed to a bicuculline-induced reduction of an axo-dendritic depolarisation of the apical dendrites belonging to pyramidal cells. A neurophysiological model of the SEP primary waves elicited by the thalamocortical proprioceptive or cutaneous inputs is suggested.

Animals↗
PubMed1996

[Somatosensory evoked potentials: morphology and interareal S1-M1 relationships in the baboon (Papio papio)].

Primary somatosensory potentials (SEPs) were elicited by electrical stimulation of the medial sciatic (proprioceptive) or sural (cutaneous) nerves. They were detected by contacts on SI and MI dura on both cortical sides against a cephalic reference. SEPs were averaged (n = 20). Primary SI SEP consisted of positive, then negative, PI6/N30 waves. N30 was absent from MI records. Local electrocoagulation of the SI cortex on one side has entailed some reduction, but not suppression of together the homolateral MI and contralateral SI and MI SEP. The residual SEPs have increased in latencies by a few milliseconds. Additional coagulation of the MI area on the same side has resulted in loss of the SI and MI SEP on the opposite hemisphere when evoked by a stimulation ipsilateral to this intact cortex. Normal SEPs were elicited from the intact cortex by any of the used stimulation. No evoked signal could be evidence from the lesioned areas. It was concluded that negligible passive electrical diffusion from any SEP area was present onto any of the other SEP reception sites. From close comparison between the different records, we came to the following propositions: each of the SI and MI areas harbours a neural mass generator for SEPs elicited by contralateral nerve stimulation. SI and MI SEPs cannot be directly elicited by ipsilateral stimulus. SI and MI SEP ipsilateral to the nerve stimulation are due to some cortico-cortical trans-sagittal excitatory message arising from the contralateral SI/MI areas. Data stand for exteroceptive or proprioceptive stimulation as well. The absence of ipsilateral direct spino-cortical projection for SEP evidenced under barbiturate does also exist in the baboon after total recovery of surgery. A scheme is given which summarizes these active relationships between somesthetic areas.

Animals↗
PubMed1994

The limits of equilibrium in young and elderly normal subjects and in parkinsonians.

Body sway was studied at various body inclinations, voluntarily maintained for about 1 min, in young and elderly normals and in idiopathic parkinsonians. They stood on a dynamometric platform, whose output gave the instantaneous centre of foot pressure (CFP), its mean value and body sway area, with eyes open (EO) or closed (EC). Subjects held the normal upright stance, or the maximum possible inclined posture (body straight, rotated at the ankle joints) in forward or backward direction, or intermediate postures. EMG was recorded from tibialis anterior (TA), soleus (Sol), extensor digitorum brevis (EDB) and flexor digitorum brevis (FDB). The cross-correlation function between the profile of the EMG envelope and the profile of the shift of CFP along the sagittal plane was calculated. In young subjects standing with EO, the maximum extent of antero-posterior (A-P) displacement of CFP was about 60% of foot length. EC reduced this value to about 50%. In the elderly normals, the maximum A-P displacement was about 40% (EO) and 30% (EC). In both groups, sway area was minimal during normal stance with EO and increased progressively when the subjects leant forward or backward. With EC, sway area further increased during normal stance and the rate of increase in relation to inclination augmented markedly. Sol was tonically active during normal stance. Forward leaning increased Sol EMG and induced activity in FDB. TA and EDB were active during backward leaning. The peak of the cross-correlation function between Sol EMG and instantaneous CFP was higher during normal stance than forward inclination, while the reverse was true for FDB. This suggests a role of FDB in the fine-tuning of postural adjustment during forward leaning, and a weight-supporting role of Sol. During backward inclination, TA but not EDB was cross-correlated with CFP. In the parkinsonians, maximum A-P displacement of CFP was just about 30% of foot length (EO; about 20% with EC); its extent was inversely correlated with the severity of the disease. The relationship between sway area and A-P displacement was similar to the elderly, both with EO and EC, within the common range of inclination. In the patients affected by the long-term syndrome, A-P displacement was further reduced while sway area increase at the critical postures was often absent. In all patients, the relationship between muscle activity and body inclination was comparable to normal.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1993

[Conservation of tap water in metallo-plastic bags: observed modifications and possible health risks].

Conservation of tap water kept in soft plastic bags and stocked at different temperatures (20, 37 and 55 degrees C) and its health incidences were studied over one year by samples taken at regular intervals. Pollutants generated were studied by investigating the consequences of the choice of the plastic and of the aseptic agent used at different temperatures versus the length of the period of contact. Microbiological, chemical, and physico-chemical characteristics reported here showed the existence of an exchange between the contents and the container. The presence of two toxic substances indicates that one should be careful when using inadequate material. This is a matter to think about without further speculation.

Environmental Health↗
PubMed1990

Modulation of cutaneous flexor responses induced in man by vibration-elicited proprioceptive or exteroceptive inputs.

The effects of muscle tendon or skin vibration on the early and late components of polyphasic cutaneous responses elicited in the flexor carpi radialis by electrical stimulation of the radial nerve at the wrist were studied in the human, with all muscles at rest. Both early and late flexor responses were enhanced by flexor vibration and depressed by extensor vibration; facilitation was accompanied by a reduction of latency. Furthermore, when an "antagonist vibration response" was present, inhibition of the flexor reflexes was replaced by a facilitation. Palm skin vibration depressed both components of the flexor reflex, while dorsal or "back-hand" skin vibration induced either a facilitation or an inhibition. In addition, back-hand vibration modified the location of the sensations evoked by electrical stimulation of the nerve. In all cases, vibratory stimulus attenuated the perceived intensity of the electrical stimulus. These observations indicate that proprioceptive or exteroceptive information can modulate the gain of the cutaneous reflex loops in a flexible way, under supraspinal control. These data also suggest a possible impairment of the protective withdrawal reflex under vibratory environmental conditions at rest and eventually in active muscles.

Adaptation, Physiological↗
PubMed1990

Excitatory and inhibitory amino-acidergic determinants of the pressure-induced neuronal hyperexcitability in rat hippocampal slices.

In a previous study we found that the intrinsic excitability of the hippocampal CA1 pyramidal cells increased under helium pressure (80 bar). We presently show that drugs inhibiting gamma-aminobutyric acid (GABA) uptake or facilitating GABA binding partially reversed the pressure-induced hyperexcitability of the CA1 pyramidal cells. When these drugs were simultaneously applied with 2-D,L-aminophosphonovaleric acid, a specific antagonist of N-methyl-D-aspartate (NMDA) receptors, the effect of pressure on the neuronal excitability was nearly abolished. These results suggested that the observed pressure-induced hyperexcitability of pyramidal cells resulted from reduced efficiency of GABA transmission and facilitated excitation mediated by NMDA receptors.

Animals↗
PubMed1989

Acquisition of co-ordination between posture and movement in a bimanual task.

The acquisition of co-ordination between posture and movement was investigated in human subjects performing a load lifting task. Sitting subjects held their left (postural) forearm in a horizontal position while supporting a 1 kg load via an electromagnet. Perturbation of the postural forearm position consisted of the load release triggered either by the experimenter (control) or by the subject voluntarily moving the other arm. In the latter case, the movement involved the elbow joint (load lifting (A), isometric force change at the wrist level (B), elbow rotation (C) and pressing a button with the wrist (D] or the fingers (grip isometric force change). We recorded the maximal amplitude and maximal velocity of the rotation of the postural forearm, the EMG of the forearm flexors on both sides and the force exerted either by the load on the postural arm or by the isometric contraction of the moving arm. The maximal forearm angular velocity after unloading was known to be related to the level of muscle contraction before unloading. 1. In the control situation, repetition of the imposed unloading test resulted in a progressive reduction in the maximal forearm rotation without any decrease in the maximal velocity. The amplitude and duration of the unloading reflex were found to increase in parallel. These results suggest that an adaptive mechanism took place which increased the gain of the unloading reflex loop and reduced the mechanical effect of the perturbation. This mechanism was found to come into play not only in the control situation but also in other paradigms where the perturbation was expected by the subjects. 2. A decrease in both maximal amplitude and velocity of forearm rotation together with a weak "anticipatory" deactivation of the forearm postural flexors was observed when the unloading was caused by an elbow movement (situations A, B, C) which indicates that a feedforward postural control took place. An interlimb coordination was built up and stabilized after 40-60 trials. Pressing a button with the wrist (weak force and displacement) was a less effective means of inducing an anticipatory control of the flexors of the postural forearm, which indicates that the intensity of the central control plays a role in the building up of the coordination. 3. A distal grip action exerting either weak (100 g) or a high (1 kg) force was able to reduce the maximal amplitude of the forearm rotation, but not the maximal velocity, which indicates that an improved reflex action takes place, but not a feedforward anticipatory postural control.(ABSTRACT TRUNCATED AT 400 WORDS)

Elbow Joint↗
PubMed1989

[Spinal reflexes and somatosensory evoked potentials studied in the baboon in the presence of anti-arrhythmic drugs].

Intragastric administration of the anti-arrhythmic drugs CM 7857 (Sanofi) or disopyramide, as expected, significantly reduced the heart rate in normal baboons at rest. At the same time, the variability in the heart rate increased. In vitro studies by Sanofi have previously shown the anti-arrhythmic effects of these drugs, i.e., a slowing of the transmembrane currents evidenced in several categories of heart cells especially when activated. Similar ion currents are known to be involved in extracardiac sensory-motor activities. However the H-reflex in soleus underwent no systematic changes in latency or amplitude with the drugs; the non-nociceptive early and nociceptive late polysynaptic responses elicited in the tibialis anterior muscle by sural nerve stimulation demonstrated a barely perceptible increase in integrated EMG value. No change could be seen in latency or amplitude of the cortical potentials evoked by sciatic or sural stimulation which was also used for reflex responses. Overall there was no definitive evidence of change in the extra-cardiac sensory-motor responses in the normal awake monkey, after administration of relatively high doses of the cardio-active compounds.

Animals↗
PubMed1989

[The thorax of patients in diving accidents. Radiologic study].

On the basis of a series including 185 files on diving accidents gathered between 1981 and 1988, the authors carry out a radiological study of the thoracic signs observed after drowning and lung overpressure. The typical radiological form and the various clinical forms of drowning and lung overpressure are described in this article. Emergency plain thoracic radiography in bed in the method of choice. However, the existence of many false-negative findings leads to proposing a study with computed tomography (CT) after initial treatment in order to better assess the lesions and to characterize the accident. The utility of radiology is also demonstrated for the follow-up of evolution. Lastly, the authors lay stress on the necessity to prevent such accidents, to which radiologists can contribute by detecting thoracic lesions (dystrophy and other evolutive lesions) for which diving is contraindicated.

Decompression Sickness↗
PubMed1988

Decrease of recurrent and feed-forward inhibitions under high pressure of helium in rat hippocampal slices.

The effect of high helium pressure on inhibitory synaptic transmission was studied in rat hippocampal slices with extracellular recordings. Both feed-forward and recurrent GABAergic inhibition were tested in the CA1 region with paired-pulse stimulation paradigms. The efficiency of both types of inhibition decreased under high pressure (80 atm). However, the depression of synaptic and antidromic field potentials induced by perfusion of GABA or muscimol were not significantly affected by pressure. High pressure induced hyperexcitability of CA1 pyramidal cells. This effect was reduced by the application of 2-aminophosphonovalerate or GABA. The present results suggest that: (1) high pressure reduces the efficiency of the GABAergic inhibitory transmission but does not affect the sensitivity of GABAA receptors; (2) two different processes (reduction of GABAergic inhibition and facilitation of N-methyl-D-aspartate-mediated excitation) might be a direct consequence of the change in the voltage-sensitive ion channels under high pressure and might be involved in the development of the pressure-induced hyperexcitability of CA1 pyramidal cells.

2-Amino-5-phosphonovalerate↗
PubMed1988

The influence of helium pressure on the reduction induced in field potentials by various amino acids and on the GABA-mediated inhibition in the CA1 region of hippocampal slices in the rat.

In a previous study, it was shown that helium pressure depressed excitatory synaptic transmission mediated by the Schaffer-commissural afferents and increased the intrinsic excitability of pyramidal cells, in the CA1 region of hippocampal slices in the rat. In the present study, the neurochemical bases of these changes was investigated. Various excitatory amino acids were studied under normal and up to 80 atm of helium. At normal pressure, the amino acids tested induced a decrease in the field excitatory postsynaptic potential (EPSP) and antidromic field potential of CA1 pyramidal cells. These changes probably resulted from the well known depolarizing effect of the compounds. Quisqualate is supposed to activate the synaptic receptors of the pathway tested. Since the effect of this amino acid and other agonists were not significantly affected by helium pressure, it is suggested that the depressed hippocampal synaptic potentials under pressure did not result from reduced sensitivity of synaptic receptors. On the other hand, helium pressure enhanced the action of N-methyl-D-aspartate (NMDA) and depressed the GABA-mediated inhibition of CA1 pyramidal cells. Given that the excitability of these neurones is modulated by NMDA-related events and GABA inhibition, these results indicate that both neurochemical systems were probably involved in the helium pressure-induced hyperexcitability of the cells studied.

Action Potentials↗
PubMed1987

Helium pressure potentiates the N-methyl-D-aspartate- and D,L-homocysteate-induced decreases of field potentials in the rat hippocampal slice preparation.

We examined the influence of helium pressure on the depression induced by various excitatory amino acids in CA1 hippocampal field potentials. The effects of quisqualate, L-glutamate, L-aspartate and kainate were not significantly affected by helium pressure, while those of N-methyl-D-aspartate and D,L-homocysteate were enhanced. These findings suggest that helium pressure specifically increased the sensitivity of the N-methyl-D-aspartate receptor type in the hippocampus. Other hypotheses are discussed.

Action Potentials↗