Relation between cervical and thoracic spinal canal stenosis and the development of spinal cord decompression sickness in recreational scuba divers.

STUDY DESIGN: Retrospective case-control study. OBJECTIVES: The intent of this study was to investigate the relationships between vertebral degenerative changes resulting in spinal canal stenosis, spinal cord lesions and the development of spinal cord decompression sickness (DCS) in scuba divers. SETTING: Referral hyperbaric facility, Toulon, France. METHODS: We examined 33 injured divers less than 50 years old by cervical and thoracic MRI and compared them with 34 matched control divers. The number of intervertebral disk abnormalities and the degree of canal compression were analyzed on T2-weighted sagittal images using a validated grading system developed recently. The presence and the distribution of hyperintense cord lesions in relation with the accident and the recovery status at 6 months were also assessed. RESULTS: Canal spinal narrowing was more common in injured divers than in controls (79% vs. 50%, OR=3.7 [95% CI, 1.3-10.8], P=0.021). We found a significant linear association between the extent of canal stenosis, multisegmental findings and the development of spinal cord decompression sickness. MRI intramedullary lesions were significantly more frequent in divers with incomplete recovery (OR=16 [95% CI, 2.6-99], P=0.0014), but statistical analysis failed to demonstrate a significant relationship between canal compression, signal cord abnormalities and a negative clinical outcome. CONCLUSIONS: These results suggest that divers with cervical and thoracic spinal canal stenosis, mainly due to disk degeneration, are at increased risk for the occurrence of spinal cord decompression sickness.

Risks factors for recurrent neurological decompression sickness in recreational divers: a case-control study.

AIM: Individual or environmental factors that predispose to the recurrence of neurological decompression sickness (DCS) in scuba divers are not known and preventive measures designed to mitigate the risk of a subsequent episode remain empirical. The aim of this controlled study was to examine some potential risk factors predictive of recurrent DCS event that may lead to practical recommendations for divers who wish to continue diving after an initial episode. METHODS: Age, gender, diving experience, presence of a large right-to-left shunt (RLS) and diving practice following post-DCS resumption were evaluated as potential predictors of a further DCS in recreational divers admitted in our hyperbaric facility over a period of 12 years. RESULTS: Twenty-four recurrent cases and 50 divers treated for a single DCS episode which continued diving were recruited after review of medical forms and follow-up interview by telephone. After controlling for potential confounding variables between groups, multivariate analysis revealed that experienced divers (OR, 3.8; 95%CI, 1.1-14; P=0.03), the presence of large RLS (OR, 5.4; 95%CI, 1.5-19.7; P=0.006) and the lack of changes in the way of diving after prior DCS (OR, 8.4; 95%CI, 2.3-31.1; P=0.001) were independently associated with a repeated episode. CONCLUSION: The findings highlight the importance for divers to adopt conservative dives profiles or to use preferentially oxygen-enriched breathing mixtures after an initial DCS. Closure of a documented RLS through a large patent foramen ovale as a secondary preventive procedure for individuals that cannot adapt their diving practice remains debatable.

Prognostic factors of spinal cord decompression sickness in recreational diving: retrospective and multicentric analysis of 279 cases.

BACKGROUND: This study aims to determine the potential risk factors associated with the development of severe diving-related spinal cord decompression sickness (DCS). METHODS: Two hundred and seventy nine injured recreational divers (42 ± 12 years; 53 women) presenting symptoms of spinal cord DCS were retrospectively included from seven hyperbaric centers in France and Belgium. Diving information, symptom latency after surfacing, time interval between symptom onset and hyperbaric treatment were studied. The initial severity of spinal cord DCS was rated with the Boussuges severity score, and the presence of sequelae was evaluated at 1 month. Initial recompression treatment at 2.8 ATA with 100% oxygen breathing or deeper recompression up to 4 or 6 ATA with nitrogen or helium-oxygen breathing mixture were also recorded. RESULTS: Twenty six percent of DCS had incomplete resolution after 1 month. Multivariate analysis revealed several independent factors associated with a bad recovery: age ≥ 42 [OR 1.04 (1-1.07)], depth ≥ 39 m [OR 1.04 (1-1.07)], bladder dysfunction [OR 3.8 (1.3-11.15)], persistence or worsening of clinical symptoms before recompression [OR 2.07 (1.23-3.48)], and a Boussuges severity score >7 [OR 1.16 (1.03-1.31)]. However, the time to recompression and the choice of initial hyperbaric procedure did not significantly influence recovery after statistical adjustment. CONCLUSIONS: Clinical symptoms of spinal cord DCS and their initial course before admission to the hyperbaric center should be considered as major prognostic factors in recovery. A new severity score is proposed to optimize the initial clinical evaluation for spinal cord DCS.

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.

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.

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.

[Spinal reflexes and somatosensory evoked potentials studied in the baboon in the presence of anti-arrhythmic drugs]. / Réflexes spinaux et potentiels évoqués somesthésiques étudiés chez le babouin en présence de drogues anti-arythmiques.

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.

[Evoked somatosensory potentials in the baboon: intracortical localization and nature studies using pharmacology and analysis of sources of current]. / Potentiels évoqués somesthésiques chez le babouin: localisation intracorticale et nature étudiées par pharmacologie et analyse des puits et sources de courants.

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.

[Somatosensory evoked potentials: morphology and interareal S1-M1 relationships in the baboon (Papio papio)]. / Potentiels évoqués somesthésiques: morphologie et relations interaréales SI-MI chez le singe (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.

[Proprioceptive and cutaneous evoked somatosensory potentials in the baboon: cycles of GABAergic excitability and inhibition]. / Potentiels évoqués somesthésiques proprioceptifs et cutanés chez le babouin: cycles d'excitabilité et inhibitions GABAergiques.

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.

[Somatosensory evoked potentials: interference and perceptual masking of cutaneous afferents in man]. / Potentiels évoqués somesthésiques: interférences et masquage perceptif des afférences cutanées chez l'homme.

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.

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.

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.

[Animal modeling and experimental pharmacology of human spasticity]. / Modélisation animale et pharmacologie expérimentale de la spasticité humaine.

The first part of the paper exposes the basic characteristics of the human spasticity which should be modeled: No hypertonia at rest; velocity-dependent myotatic responses, and fatigability. To model a syndrome including these signs is a related but different problem. Results and limits of the clinical neurophysiology concerning the spasticity are briefly quoted. Animal models would better assist the human neurophysiology when having their neuroanatomy closer to the human one. The second part confirms that a local unilateral excision of the ad hoc sensorimotor cerebral cortice of the Baboon induces a permanent palsy of the contralateral foot and leg, and after delay signs of spasticity in the Sol. Neither clasp-knife phenomenon nor fatigability is observed. There is no sign of motoneuron hyper-excitability. A GABA-related pharmacology suggests a significant defect in the presynaptic inhibition of the reflexogenic IA in-put, and possibly a defect in a post-synaptique gabaergic inhibition. Finally the monkey is considered as a valuable support for modeling the human spasticity, symptom and possibly syndrome.

[The thorax of patients in diving accidents. Radiologic study]. / Le thorax de l'accidenté de plongée. Etude radiologique.

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.

[Improvement in postural orientation and stability after stereotactic gamma irradiation of acoustic neurinomas]. / Effets posturaux du traitement par gamma knife des neurinomes de l'acoustique (schwannomes vestibulaires).

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.

[Conservation of tap water in metallo-plastic bags: observed modifications and possible health risks]. / Conservation d'eau du réseau en sachets métalloplastiques: modifications observées et risques sanitaires éventuels.

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.

[Proprioceptive proximo-distal relationships between the quadriceps and soleus muscles in man]. / Liaisons proprioceptives proximodistales entre muscles quadriceps et soléaire chez l'homme.

Electrical stimulation of femoral nerve modulates voluntary tonic activity o of ipsilateral soleus muscle. Stimulus time-locked inhibitory and facilitatory phases can be distinguished. EMG temporal analysis suggests that early perturbations are correlated with spinal effects of centripetal electrical activity. The inhibitory effects which momentarily abolish voluntary soleus activity are thought to result from quadriceps Ib fibres recruitment. While no heteronymous activity is induced at rest, femoral nerve Ia fibres activation can produce soleus muscle reflex when soleus motor nucleus excitability is increased by voluntary command. Recurrent discharge resulting from soleus reflex response enhances inhibition initially due to quadriceps Ib volley. Secondary effects of isometric quadriceps contraction (and soleus contraction when the femoral stimulus elicits a reflex in this muscle) have their own effects later. These findings suggest that proprioceptive relationships of the two muscular groups are efficient during tonic isometric voluntary command.