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Biomedical subjects

P Bessou

Publications and source records attributed to P Bessou.

At least 19 recordsLinked to original sources
PubMed1999

Specificity of the monocular crescents of the visual field in postural control.

Postural reactions elicited by monocular visual stimulation in the temporal crescent of the visual field were studied in adult subjects in dynamic balance on a rocking platform. Circular translation of a visual scene was induced in the temporal crescent by the rotation of membrane prisms placed laterally to the stimulated eye. In anteroposterior balance, postural reactions are identical whichever eyes is stimulated: ventral extension of the body when the visual scene moves upwards and dorsal extension when it moves downwards. In lateral balance, postural reactions vary with the stimulated eye: extension of the right side of the body when the right eye is stimulated by an upward displacement of the visual scene, extension of the left side when the left eye is stimulated. This difference, which contrasts with the similarity of reactions elicited by the stimulation of either para-foveal fields, suggests that the most peripheral part of the nasal retina has a specific role in head and body stabilisation.

Adult↗
PubMed1999

A persistent pharyngohyostapedial artery: embryologic implications.

A 3-year-old child was examined because of otorrhagia. CT scans showed an unusual vessel, confirmed by angiography, related to a persistent pharyngohyostapedial artery. This embryonic persistent artery associated with the normal internal carotid artery would explain the "duplication" aspect of the internal carotid artery.

Angiography, Digital Subtraction↗
PubMed1998

Anteroposterior dynamic balance reactions to circular movement of the visual field without ocular pursuit.

It has been hypothesised that during natural vision, retinal image motion and eye motion information exert antagonistic effects on balance that cancel each other out. In a previous study, we found that pursuit movements of the eye unaccompanied by background slip on the retina induced strong, stereotyped anteroposterior sway in dynamic balance. In the present work, we investigated the influence of background retinal image slip alone on anteroposterior dynamic balance. We expected that retinal slip without ocular pursuit would induce large anteroposterior sway. Circular slip without rotation of the whole visual field image on the retina was obtained using a rotating prism. In this study, carried out on monocular vision, eye movement was prevented by fixating a stationary target seen through a small aperture in the prism. Anteroposterior dynamic balance conditions were elicited by a rocking platform. Strong, stereotyped anteroposterior sway accompanied by a visual illusion of target motion was observed. The induced sway was synchronised to the stimulus and led to a significant disturbance of balance. The similarity in magnitude of the effects of both retinal image motion studied here and eye motion information obtained previously, and their opposing phases, strongly support the initial hypothesis that the antagonistic effects of the two sources of information provided by normal ocular pursuit could interact in an additive algebraic mode.

Electrooculography↗
PubMed1998

Lateral dynamic balance reactions to circular translation of the visual field.

Lateral sway of subjects in spontaneous dynamic balance conditions on a seesaw platform was measured during a visual stimulation monocularly produced by a rotating glass covered with a prism membrane. Prism rotation induced the perception of a circular translation of the whole visual field and an ocular pursuit movement. Therefore, the retinal slip that occurs in normal pursuit was cancelled. Strong stereotyped postural reactions were observed in a direction that depended upon both the vertical visual field deviation and the eye stimulated: upper position of the right visual field induced a leftward sway resulting from an extension of the right hemibody; symmetrical reactions occurred for the left stimulation. The results suggest that the postural reactions recorded depend on the isolated oculomotor activity and, in addition, on retinal afferences corresponding to the temporal crescent of the stimulated side, which orientates the postural reaction on the homolateral lower limb muscles.

Eye Movements↗
PubMed1998

[Benign vertebral osteoblastoma. Report of 6 cases].

We present six cases of benign spinal osteoblastoma. This localization of this uncommon benign bone tumor occurring in young subjects is rare. The patients were explored with radiotomography, computed tomography, myelography and medullo-spinal angiography. These benign tumors may appear radiographically as pure bone lysis mimicking malignancy. The size of these tumors often leads to widening search for extension, particularly in recurrent, aggressive, multifocal forms which require wide resection, and sometimes total vertebrectomy. Medullo-spinal angiography can confirm the vascular involvement of the tumor nidus and is require to identify arteries supplying the spinal canal which would modify operative strategy.

Adolescent↗
PubMed1997

Unusual vestibular and visual input in human dynamic balance as a motion sickness susceptibility test.

BACKGROUND: Motion sickness (MS) is commonly thought to arise from a sensory conflict. However, few quantitative methods based on this theory are available to detect MS susceptibility. HYPOTHESIS: It was asked whether the standardized unusual stimulation of a single sensory channel under quantified dynamic balance conditions in man could elicit a sensory conflict and therefore trigger motion sickness (MS) METHODS: Vestibular and visual channels were stimulated by galvanic current and rotating prismatic glasses, respectively. The moving platform used to create the requirements for dynamic balance conditions was chosen not only to worsen the malaise but also to obtain an objective measurement of the balance consequences of the stimulations. RESULTS: Both vestibular and visual stimulation, applied separately, elicited MS-like symptoms (in 56% and 73% of subjects, respectively) and stereotyped balance reactions. A relationship was found between subjective MS-like symptoms and objective measurements of dynamic balance performance. Subjects sensitive to unusual vestibular messages differed from the others by a greater increase in the parameters indicating a difficulty of balance whereas subjects sensitive to unusual visual messages were recognized by the strategy they used to balance themselves. CONCLUSIONS: These results demonstrated that a sensory conflict can trigger MS-like symptoms. We conclude that the measured parameters of a global somatomotor activity, such as the dynamic balance task proposed here, could be useful for objectively detecting subjects predisposed to MS, for training them and testing the efficiency of anti-MS drugs.

Adult↗
PubMed1996

Anteroposterior dynamic balance reactions induced by circular translation of the visual field.

The anteroposterior sway of subjects under conditions of spontaneous dynamic balance on a wobbly platform was measured during visual stimulation by a visual target executing a circular trajectory in the frontal plane. The target was either a component of the whole moving visual scene or moving on a stationary background. With the former stimulation, obtained through the use of rotating prismatic glasses, every point of the visual field appeared to describe a circular trajectory around its real position so that the whole visual field appeared to be circularly translated, undistorted, inducing a binocular pursuit movement. Under these conditions, stereotyped anteroposterior dynamic balance reactions synchronous with the position of the stimulus were elicited. The latter stimulation consisted of pursuing a luminous target describing a trajectory similar to that of the fixation point seen through the rotating prisms on the same, this time stable, visual background. Although pursuit eye movements were comparable, as demonstrated by electro-oculographic recordings, no stereotyped equilibration reaction was induced. It is concluded that the translatory motion of the background image on the retina in the latter experiments contributed to the body's stability as well as to the perception of a stable environment.

Adult↗
PubMed1995

[Role of hormonal exploration in avoiding of the failures of anterior pituitary gland surgery in Cushing disease].

Patients with Cushing's disease are not cured by transsphenoidal microsurgery in about 30% of the cases. Beside the problem of invasive macroadenomas, these failures are due either to diagnostic errors, or to very small microadenomas that could no be found. Positive diagnosis of hypercortisolism is quite straightforward and the problem is sensitivity rather than specificity. Primary adrenocortical hypercortisolism should not be mistaken. Depression-related hypercortisolism can be difficult to distinguish from Cushing disease: most cases are recognized after clinical story and CRF stimulation test. Ectopic ACTH secretion by a carcinoid tumor represents at least 8% of ACTH-dependant hypercortisolism. It cannot be reliably distinguished from corticotroph microadenoma by either classical dynamic tests or anterior pituitary imaging. However measurements of ACTH in the inferior petrosal sinus under basal condition and CRF stimulation allow the diagnosis of central or peripheral ACTH secretion with a quasi 100% sensitivity and specificity. In contrast this technique is of poor help for the diagnosis of lateralization of corticotroph microadenomas, for which it gives erroneous results in 25 to 50% of the cases. Rapid intraoperative measurement of ACTH in peripituitary blood seems a more reliable approach. In our series it gave correct results in 11 out of 12 cases. In 1995 hormonal exploration of Cushing disease should limit the failures of anterior pituitary surgery to the cases of invasive macroadenomas that cannot be completely removed.

Adrenocorticotropic Hormone↗
PubMed1994

Step-length biofeedback device for walk rehabilitation.

A biofeedback gait training system for step length is proposed, adapted to the correction of spatial walking asymmetries by means of a simple, quick and reliable method for daily clinical use. The system is composed of a walkway and a gait analysis device (locometer) measuring the main temporal and distance factors of gait. The step length is imposed on the subject by lighted targets appearing on the walkway, alternately on the right and left side; the subject is asked to place a swinging foot on the lighted target. Feedback to the subject is supplied by direct visual information (the subject looking at the movement and the position of the foot with respect to the lighted target) and an acoustic signal delivered in real time when the length step error is greater than an allowed value. The method is validated on a population of hemiparetic patients who have suffered from a stroke and who have been reeducated with traditional rehabilitation methods. The patients were divided into two groups; one group following a gait training with biofeedback (BFB group) and one group following a gait training without biofeedback (reference group). Preliminary results are presented, showing a significant beneficial effect of the biofeedback method in increasing the step length of paretic limbs and in correcting step-length asymmetry.

Aged↗
PubMed1994

Unusual visual stimulation in dynamic balance conditions: proposal for a space motion sickness test.

We previously demonstrated the efficiency of normal vision/unusual vestibular cues conflict to induce motion sickness. In the present study, we investigate whether, inversely, unusual visual information/normal vestibular function conflict also elicited motion sickness. The experiments were again carried out in dynamic balance conditions to increase proprioceptive input. Circular translation of the visual field with diplopia were produced by rotating Fresnel prismatic glasses. The stimulation triggered SMS-like symptoms and dynamic balance disturbance. A positive relationship was found between discomfort and balance disturbance. Unusual visual information should therefore be included in Space Motion Sickness susceptibility testing.

Adult↗
PubMed1994

[Intracranial dural fistula with spinal cord venous drainage. Apropos of 2 cases].

The authors report 2 new cases of intracranial dural fistula draining into spinal veins. Comparisons with 19 other published cases showed that dural fistulae of the spine share common features with intracranial fistulae. The first case concerned a 78-year old woman presenting with a thoraco-lumbar myelopathy which proceeded by increasingly severe bouts and ended within 6 months in a flaccid sensorimotor paraplegia with urinary incontinence. Paraclinical examinations consisted of MRI, myelography and spinal as well as cerebral arteriography. MRI and thoraco-lumbar myelography displayed marks of dilated retrospinal vessels. Spinal arteriography showed no arteriovenous malformation, but the venous return of Adamkiewicz artery was not visible. Diagnosis was made by cerebral arteriography which demonstrated an intracranial arteriovenous fistula in the occipital region, draining into the posterior spinal vein. Treatment was endovascular and consisted of embolization by micro-coils, but clinical improvement was mediocre. Six months later, as the clinical picture was getting worse a second arteriography was performed. It showed recanalization of the fistula which was embolized again, using both coils and particles. No improvement in spinal cord deficit was observed. The second case was that of a 42-year old man presenting with paraparesis, tetrapyramidal syndrome, sensory deficit at T9, peribuccal dysaesthesias and genito-urinary sphincteral disorders, all gradually getting worse. The paraclinical exploration was the same as in the first case. MRI and myelography showed retrospinal vascular impressions. Spinal arteriography was normal, except for the lack of venous return of Adamkiewicz artery. Cerebral arteriography detected an intracranial dural arteriovenous fistula in the occipital region, draining into the anterior and posterior spinal veins. Treatment was surgical, consisting of exclusion of the arteriovenous fistula. Partial clinical improvement was noted. These two cases, compared with those of the literature, shared a number of features with spinal dural arteriovenous fistulae: they occur in middle-aged and predominantly male patients, and the clinical signs of ascending myelopathy are caused by the same physiopathological mechanism of spinal vein hyperpressure. Lesions of the medulla oblongata or the cervical spinal cord are found only in intracranial arteriovenous fistulae draining into spinal veins. Diagnosis is based on data provided by myelography (impressions of dilated and sinous vessels) and MRI (low-intensity perispinal signals, widening of the conus medullaris with high-intensity centrospinal signal); spinal cord angiography only shows a lack of venous return of Adamkiewicz artery without any other abnormality, whereas cerebral arteriography confirmed the diagnosis of intracranial dural arteriovenous fistula draining into spinal veins.

Adult↗
PubMed1994

[Computed tomographic aspects of secondary cholesteatomas of the middle ear and petrous bone].

The authors present their experience of secondary cholesteatomas of the middle ear explored by computerized tomography (CT). Following a brief anatomicopathological description of secondary petrous bone cholesteatomas, and of the CT technique used for their exploration, they describe and illustrate the classical "bag-shaped" internal or external attical forms usually extended to the antrum and the mastoid process, and the less common locations often due to relapse or postoperative recurrences (anterior hypotympanic or posterior mastoidal). The holotympanic forms, usually due to "lamellar" cholesteatomas, create diagnostic problems with other opacities in the cavity, as also do certain forms that are evacuated spontaneously or by aspiration. One of the qualities of CT lies in the preoperative extension assessment. The lesion may extend towards the internal wall of the cavity (lateral semicircular canal, second portion of the facial nerve), towards the labyrinth to the petrosal apex and/or the geniculate ganglion, and above all towards the inferior labyrinth which might bring the cholesteatoma into contact with large vessels (e.g. jugular vein bulb for postero-inferior extensions, carotid canal for antero-inferior extensions). Extension into anfractuosities of the cavity walls (sinus tympani, subratubal fossette) must be systematically looked for in order to avoid postoperative recurrences.

Bone Diseases↗
PubMed1993

Effects of unilateral selective hypergravity stimulation on gait.

The purpose of this work is to analyse the neural mechanisms of human motor perturbations induced by dynamic changes in gravity. A unilateral selective hypergravity stimulation (USHS) was produced by stretching an elastic band between the right shoulder and foot. The consequences of the extensor muscle tone change due to the positioning (increased muscular loading) and to its removal (decreased muscular loading) by the elastic band were observed on motor gait skill. Gait spatio-temporal parameters (horizontal displacement of both feet) and lower limb functional length variations (efficiency of flexion and extension movements of the lower limbs) were measured. The latter measure was performed using a device specially designed for that purpose. The main results were: (1) during and after USHS, gait perturbations appeared on the left--the body side not directly stimulated, (2) just after the end of USHS, perturbations were present on the right (homolateral) side evidencing a post treatment effect which caused a decrease in functional shortening of the lower limb during extension and an increase of functional shortening of the lower limb during stance (opposite in sense to the modification observed during swing). Such results afford evidence that, in addition to vestibular receptors, the mechanoreceptors of extensor muscles are involved in determining the changes in motor skills observed at the beginning and at the end of space flights.

Adaptation, Physiological↗
PubMed1990

Evidence of the co-activation of alpha-motoneurones and static gamma-motoneurones of the sartorius medialis muscle during locomotion in the thalamic cat.

The activity in alpha and gamma efferent axon populations and in group I and group II afferent fibre populations innervating a flexor muscle, the sartorius medialis, was observed during spontaneous locomotor movements in the thalamic cat. Multi-unit discharges of each kind of fibre were obtained by electronic sorting of the action potentials from the overall activity of a thin, intact branch of the sartorius medialis nerve. The following results were obtained: (1) The gamma-motoneurones have a phasic behaviour characterized by a single discharge period during the hip flexion (swing phase of the step-cycle). (2) The gamma-motoneurones are co-activated with the homonymous alpha-motoneurones. (3) Between rhythmic alpha and gamma discharges, i.e. during the hip extension (stance phase of the step cycle), both alpha- and gamma-motoneurones were normally silent. However, in 5 out of 17 experiments, a few units of the gamma population fired at very low frequency. (4) Two observations indicate that the gamma-motoneurones that are co-activated with the alpha-motoneurones by central locomotor commands are predominantly of the static type. In actual locomotion, the rhythmic fusimotor discharges over-compensate the depressor effect on the firing rate of the group II afferents of the unloading of muscle spindles by the active shortening of the parent muscle. In fictive locomotion, when the transmission of the excitation is blocked by selective curarization in alpha skeleto-motor junctions alone, the rhythmic fusimotor discharges elicit in-phase modulations not only of the group I but also of the group II fibres.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗