Biomedical subjects

P Guihéneuc

Publications and source records attributed to P Guihéneuc.

10 recordsLinked to original sources

PubMed2004

[Mechanisms which control the peripheral nerve excitability].

Peripheral nerve excitability is currently tested via the strength/duration curves, and by measuring the minimal intensity level (rheobase) of an efficient stimulation, and the minimal duration (chronaxy) for a stimulus equal to two times the minimal threshold. New "threshold tracking techniques" were recently described (Bostock et al., 1991), which afford an automatic evaluation of nerve excitabilty. These methods investigate the mechanisms responsible for the membrane potential: passive ionic currents, activity of ionic pumps like the Na-K-ATPase; and the dynamic behaviour of large conductance sodium, potassium, and calcium channels, responsible for the generation and conduction of action potentials. Results obtained must however be evaluated taking into account the following items: stimulation is delivered through the skin and subcutaneous tissue; a nerve trunk is explored, and not a single fiber; most often the response is recorded over a muscle, hence through neuromuscular synapses.

Axons↗

PubMed1999

The effects of desflurane on the nervous system: from spinal cord to muscles.

UNLABELLED: Monitoring of motor pathways via muscle contraction recording is sensitive to anesthetics, particularly volatile anesthetics. However, the specific action sites of these anesthetics on the spinal cord and the peripheral nervous system are not well known in humans. Therefore, we studied proximal and distal motor and sensory nerve conduction, neuromuscular junction transmission, and spinal cord excitability (H/M amplitude ratio and F-wave amplitude and persistency) using standard neurophysiological techniques in 10 patients who underwent orthopedic surgery. Muscle potentials evoked by spinal cord stimulation were recorded in five additional patients. Desflurane was introduced to achieve end-tidal concentration of 3.7% and 7.4%, in 50% O2/N2O and in 100% O2. Measurements were obtained before desflurane administration and 20 min after obtaining a stable level of each concentration. Peripheral nerve conduction and neuromuscular function were not significantly affected by desflurane. However, spinal cord excitability was significantly decreased by desflurane administration (H/M ratio 37% +/- 9%, 12% +/- 5%, 7% +/- 4% at desflurane concentration 0.0%, 3.7%, and 7.4% in 100% O2, respectively). Muscle potentials evoked by spinal cord stimulation were abolished by desflurane. These data rule out the possibility that desflurane specifically alters peripheral nerve conduction or synapse transmission at the neuromuscular junction. They demonstrate that desflurane acts preferentially at the level of the spinal motoneuron. IMPLICATIONS: We used neurophysiological techniques to assess the effects of desflurane on spinal cord conduction and excitability, motor and sensory peripheral nerve conduction, and neuromuscular transmission. Our data demonstrate that desflurane acts preferentially at the level of the spinal motoneuron, providing useful information for neurophysiological monitoring and immobilization during surgery and for minimum alveolar anesthetic concentration definition.

Action Potentials↗

PubMed1998

Usefulness of neurogenic motor evoked potentials for spinal cord monitoring: findings in 112 consecutive patients undergoing surgery for spinal deformity.

Neurogenic motor evoked potential (NMEP) monitoring, which basically represents a monitoring of both motor and somatosensory tracts, has been proposed as a warning system in preventing neural damage during spinal surgery. The aim of this study was to report our clinical experience in 112 consecutive patients undergoing surgery for spinal deformity, and to emphasize the interest of NMEP monitoring. NMEPs were elicited in each patient by electrical stimulation of the spinal cord via needle electrodes placed by the surgeon in the rostral part of the surgical field, and recorded from the right and left sciatic nerves. Concomitantly, somatosensory evoked potentials (SSEPs) were obtained using a standard method. No false-negative cases of intra-operative spinal cord damage were reported. In 3 patients, both NMEPs and SSEPs suddenly disappeared during specific surgical manipulations of the vertebral implants. In these patients, the level of the lesion was easily recognized by moving the stimulating electrodes of NMEPs along the spinal cord, allowing the surgeon to perform laminectomy at the appropriate vertebral level. Spinal cord decompression was a success in two patients, the last unfortunately being paraplegic. Two additional patients exhibited transient reduction in NMEP amplitude at the insertion of a rod while SSEPs did not change significantly. In these two cases, the surgeon modified his procedure according to the NMEP changes, possibly avoiding a neurological complication. Each time evoked potentials were significantly altered, significant information was more rapidly acquired with NMEPs than with SSEPs. These results suggest that NMEPs can be used as primary choice for detecting impeding lesion of the spinal cord during critical steps of spinal surgery.

Adolescent↗

PubMed1997

[Peripheral neuropathies of chronic renal insufficiency. Review].

Described at the end of the 19th century, investigated from the development of dialysis since 1960, peripheral neuropathy occurs almost constantly in patients with a pre-dialytic renal failure. Clinical signs are mainly sensory ones Severe nerve deficiencies are rarely found. Electrophysiological techniques are performed to quantify the demyelinating and axonal lesions, to verify the long term adequacy of dialysis, and to observe improvement after kidney transplantation. Diabetes and vascular lesions can induce important axonal damage. Nerve entrapments (Median nerve in the carpal tunnel) are frequent and may worsen in a few months. Factors involved in the development of peripheral neuropathy in uremic patients remain partly unknown.

Electrophysiology↗

PubMed1996

Effects of isoflurane and desflurane on neurogenic motor- and somatosensory-evoked potential monitoring for scoliosis surgery.

BACKGROUND: Most techniques used to monitor spinal cord tracts are sensitive to the effects of anesthesia, particularly to volatile anesthetic agents. The aim of this prospective study was to show that evoked potentials recorded from the peripheral nerves after spinal cord stimulation, so-called neurogenic motor evoked potentials, are resistant to clinical concentrations of isoflurane or desflurane, compared with somatosensory-evoked potentials. METHODS: Twenty-three patients were studied during surgery to correct scoliosis. The background anesthetic consisted of a continuous infusion of propofol. Isoflurane (n = 12) or desflurane (n = 11) were then introduced to achieve 0.5 and 1.0 end-tidal minimum alveolar concentrations (MAC), both in 50% oxygen-nitrous oxide and in 100% oxygen. Somatosensory-evoked potentials were elicited and recorded using a standard method, defining cortical P40 and subcortical P29. Neurogenic motor-evoked potentials were elicited by electric stimulation of the spinal cord via needle electrodes placed by the surgeon in the rostral part of the surgical field. Responses were recorded from needle electrodes inserted in the right and left popliteal spaces close to the sciatic nerve. Stimulus intensity was adjusted to produce a supramaximal response; that is, an unchanged response in amplitude with subsequent increases in stimulus intensity. Measurements were obtained before introducing volatile agents and 20 min after obtaining a stable level of each concentration. RESULTS: Isoflurane and desflurane in both 50% oxygen-nitrous oxide and 100% oxygen were associated with a significant decrease in the amplitude and an increase in the latency of the cortical P40, whereas subcortical P29 latency did not vary significantly. Typical neurogenic motor-evoked potentials were obtained in all patients without volatile anesthetic agents, consisting of a biphasic wave, occurring 15 to 18 ms after stimulation, with an amplitude ranging from 1.3 to 4.1 microV. Latency or peak-to-peak amplitude of this wave was not significantly altered with isoflurane and desflurane, either in the presence or in the absence of nitrous oxide. CONCLUSIONS: Compared with cortical somatosensory-evoked potentials, neurogenic motor-evoked potential signals are well preserved in patients undergoing surgery to correct scoliosis under general anesthesia supplemented with isoflurane or desflurane in concentrations as great as 1 MAC.

Adolescent↗

PubMed1995

Facilitation of motor evoked potentials: timing of Jendrassik maneuver effects.

Remote voluntary contraction, such as the classical Jendrassik maneuver (JM), is a procedure routinely used to increase the amplitude of tendon reflexes in the lower limb. In 8 healthy subjects we studied the effects of JM on the motor evoked potentials (MEP) recorded from tibialis anterior muscle, produced by transcranial magnetic stimulation (stimulus output of 5-10% over motor threshold). In this study, JM consisted here of a bilateral violent handgrip, preceding magnetic stimulation from 100 to 50 ms (steps of 100 ms). Compared to the control test, latencies remained unchanged. MEP amplitudes were greatly enhanced with a JM test interval from 200 to 400 ms (170% of control amplitude at 300 ms). We also studied 6 patients with severe alterations of MEPs from tibialis anterior muscle. In each case, JM preceding magnetic stimulation (stimulus output 100%) from 300 ms induced reappearance of response or marked enhancement of amplitude, allowing calculation of central conduction time. Such a technique, which is easy to perform, may be useful in clinical practice to calculate central motor conduction time, where it would otherwise be difficult or impossible.

Adult↗

PubMed1995

Late facilitations of motor evoked potentials by contralateral mixed nerve stimulation.

The effect on motor evoked potentials (MEPs) of a peripheral afferent volley (a single square pulse delivered to the contralateral median nerve at the wrist) was studied in abductor digiti minimi muscle of 9 normal patients following magnetic stimulation of the motor cortex. Long intervals were used (200-700 msec) between the electrical conditioning stimulus and magnetic test stimulation. An MEP amplitude increase, with no change in latency, was observed when the C-T interval was about 500 msec, and the motor threshold was decreased by the conditioning stimulation. The observed long latency and duration of the facilitation effect would seem consistent with activation of suprasegmental areas.

Action Potentials↗

PubMed1995

Prognostic significance of electrophysiological investigations in stroke patients: somatosensory and motor evoked potentials and sympathetic skin response.

A prospective 3-month follow-up examination was carried out in 12 patients with supratentorial stroke. Motor evoked potentials (MEP), somatosensory evoked potentials (SEP) and sympathetic skin responses (SSR) were performed 1-7 days, 30 days and 3 months after stroke. The functional outcome measured by a daily activity index (Barthel index) was assessed 3 months after the stroke. There was a significant correlation between SEP and MEP results obtained for the first week and recovery of sensation and motility 3 months later. When initially normal, motor potentials evoked by transcranial magnetic stimulation had a significant predictive value for long-term functional outcome, whereas SEP and SSR did not. SSR present at the initial stage was correlated with the state of consciousness.

Adult↗

PubMed1994

Central nervous system involvement in multifocal demyelinating neuropathy with persistent conduction block.

We report the case of a 27-year-old man treated for bilateral optic neuritis 5 and 3 years before who within a few months developed sensorimotor disorders of the arms and legs characterized by asymmetric distribution and distal prominence. In addition to sensorimotor defects, which were particularly marked in the left arm and right leg, clinical examination showed nearly generalized areflexia. Electrophysiological studies revealed a multifocal neuropathy with persistent distal and proximal conduction blocks associated with a considerable slowing of motor nerve conduction, as well as central nervous system involvement indicated by motor-, somatosensory-, and visual-evoked potentials. CSF analysis showed a mildly elevated protein level; anti-GM1 activity was negative. Sural nerve biopsy revealed onion-bulb-like formations, and cerebral MRI showed a small, isolated, and aspecific high signal for white matter. First described by Lewis and Sumner in 1982, multifocal neuropathy with persistent conduction blocks may be associated with central demyelination. Our case is compared with 3 similar ones in the literature, and the favorable effects of steroid therapy are emphasized.

Adult↗

PubMed1993

Electrophysiological study of a case of diffuse loss of sweating with segmental hyperhidrosis associated with areflexia.

Electrophysiological investigations were carried out on a 43 year-old man with segmental hyperhidrosis in three radicular territories, generalized anhidrosis elsewhere and areflexia. A recurrent labial herpetic rash and a history of sweating disorders in his grandfather were the only associated clinical data. Sympathetic skin response was found to be absent in anhidrotic territories, including the hands and feet, although it was present in hyperhidrotic territories. Peripheral adrenergic sympathetic fibers evaluated by photoplethysmography were normally responsive, as were visceral vegetative regulations involved in cardiovascular control during postural changes or exercise. The present case is compared to the previously described Ross Syndrome, associating segmental hypohidrosis, areflexia and tonic pupils. Our results and observations in the literature are consistent with the occurrence of lesions affecting postganglionic cholinergic fibres of the sympathetic system.

Adult↗