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Biomedical subjects

J Payan

Publications and source records attributed to J Payan.

At least 19 recordsLinked to original sources
PubMed1992

Neuropathy in chronic obstructive pulmonary disease: a multicentre electrophysiological and clinical study.

The incidence and type of neuropathy in patients with chronic obstructive pulmonary disease (COPD) were assessed. In a selected group of 89 patients, abnormal nerve conduction studies were found in 44%. Electrophysiological signs of a generalized peripheral neuropathy were found in 5-18%, depending on diagnostic criteria. Lesions which were thought to be due to compression or other forms of trauma were present in a further 24%. In the patients with peripheral neuropathy, the changes were distally predominant, affected mainly sensory fibres, and were consistent with an axonal type of neuropathy. There was a significant correlation between age and the incidence of peripheral neuropathy. Electrophysiological evidence of neuropathy was three times as common as clinical evidence. Much of the variation in the reported incidence of neuropathy in COPD is probably due to imprecise diagnostic criteria.

Adult↗
PubMed1991

Acute onset spinal muscular atrophy in siblings.

We describe two sisters who each presented in infancy with acute, severe, generalised weakness and are-flexia in association with an intercurrent infection. The clinical picture resembled acute polyneuritis, but EMG findings and the later clinical features were consistent with a diagnosis of spinal muscular atrophy. Although symptoms in SMA may be exacerbated by infection, immunisation or trauma, this unusual presentation of the condition in siblings suggests that this may constitute a genetically distinct subgroup of the disorder.

Acute Disease↗
PubMed1990

Peripheral neuropathy in Leigh's disease.

Sural nerves were examined in 3 childhood cases of Leigh's disease (from 2 families), each with electrophysiological documentation of peripheral neuropathy. Postmortem confirmation of Leigh's disease was made in 2 cases; the third had characteristic CT scan appearances. Myelinated fibre densities were within normal limits, with no evidence of degeneration or regeneration. The myelin sheaths, however, appeared thin and this was confirmed quantitatively. In teased fibres there was no demyelination in 2 cases but some in 1 case. The findings suggest that there is hypomyelination of peripheral nerves leading eventually to demyelination.

Brain↗
PubMed1989

[Intraocular pressure during vitrectomy in the diabetic patient].

23 eyes underwent vitrectomy for diabetic proliferative retinopathy complications: vitreous hemorrhage with or without tractional retinal detachment. After 6 months of follow-up, 64% of eyes had final visual acuities of 1/40 or better. Preoperative iris neovascularization and preoperative detachment of the macula have a worse prognosis. Decrease of peroperative complications is allowed by checking of intraocular pressure during vitrectomy.

Adolescent↗
PubMed1989

[Intraocular pressure during vitrectomy in diabetic patients].

23 eyes underwent vitrectomy for diabetic proliferative retinopathy complications: vitreous hemorrhage with or without tractional retinal detachment. After 6 months of follow-up, 64% of eyes had final visual acuities of 1/40 or better. Preoperative iris neovascularization and preoperative detachment of the macula have a worse prognosis. Decrease of peroperative complications is allowed by checking of intraocular pressure during vitrectomy.

Adolescent↗
PubMed1989

[Photographic study of retinal nerve fibers in glaucoma and ocular hypertension].

Photographic study of retinal nerve fiber (RNF) in glaucoma and ocular hypertension. Photographic study of retinal nerve fiber layer try to show defects in case of glaucoma or ocular hypertension. After describing the method used and the different aspects met, we present the results of confrontation between the exam and campimetry for 49 eyes, with control of the evolution for 30 eyes during an average time of thirty months.

Atrophy↗
PubMed1989

[Deficits of the layer of retinal nerve fibers and glaucoma. Comparison with campimetry and control of the course].

Photographic study of retinal nerve fiber layer try to show early defects in case of glaucoma or ocular hypertension. Among the recent techniques trying to indicate the first marks of glaucoma, this method appears easy, reproducible, objective, and uses a very common equipment. We describe the equipment and the technic used, and present the main physiological and pathological aspects. Our series includes 49 eyes (30 patients) and, for 30 among them (17 patients), a control of the evolution has been done within an average period of thirty months. In each case, visual field was studied, principally with the programs of early detection of glaucomatous damage available on the Octopus 2000 R (prog. No 31, 33 and G1). We explore and comment upon the results obtained by the confrontation between these exams.

Adolescent↗
PubMed1987

Experimental observation of silver and gold penetration into dental ceramic by means of a radiotracer technique.

A radiotracer technique was used to study silver and gold diffusion into dental porcelain under experimental conditions close to the real conditions in prosthetic laboratories for porcelain bakes. It was clearly shown that these non-oxidizable elements were able to diffuse into the ceramic as well as oxidizable ones. The penetration depth varied widely according to the element. The ratio DAg/DAu was about 10(3) around 850 degrees C. In contrast to gold, the silver diffusion rate was high enough to allow silver, from the metallic alloy, to be present at the external ceramic surface after diffusion into the ceramic. Hence, the greening of dental porcelains baked on silver-rich alloys could be explained mainly by a solid-state diffusion mechanism.

Chemical Phenomena↗
PubMed1986

Changes in physical and chemical properties of a dental palladium-silver alloy during metal-porcelain bonding.

The hardening ability of a dental palladium-silver (Pd-Ag-Sn-In) bonding alloy has been investigated, and the distribution of the elements along the metal-ceramic interface have been studied by microprobe analysis. The alloy was found to be highly heterogeneous in its 'as-cast' condition, but homogenized alloy was obtained after heating the alloy at 1000 degrees C for 2 h. Hardening occurred after annealing at 650 degrees C for 1 h. A longer thermal treatment caused the hardness to decrease (over-ageing). The change in hardness could be attributed to an internal oxidation phenomenon. The additional elements tin and indium segregated towards the ceramic-metal interface, with a diffusion of indium only into the porcelain. Diffusion of silver in the ceramics, supposed to be the cause of the 'greening' of dental porcelains baked on silver-rich alloys, has not been detected by the microprobe across the interface.

Chemical Phenomena↗
PubMed1979

Evaluation of alternative alloys to precious ceramic alloys. 1. Mechanical properties.

In the first part of this study, the microstructures and the mechanical properties of precious, semi-precious, and nonprecious dental casting alloys for the porcelain-baked-to-metal technique have been determined. The semi-precious alloys contained only 50% gold, and palladium, silver, and some base metals. The nonprecious alloys were of the nickel-chromium type. Discs and miniaturized tensile bars have been cast and tested either in the as cast condition, or after a simulation of the various porcelain bakes. Proof stress, ultimate tensile strength, elongation, and plastic stiffness have been measured and results compared by use of analyses of variance. The microstructure examination shows that the simulation of the porcelain bakes improves the homogeneity of the precious and semi-precious alloys. Simultaneously, the mechanical properties of the same alloys are also improved. One semi-precious alloy, still under development at the time of these tests, has its mechanical characteristics markedly downgraded by the thermal treatments. The nickel-chromium alloys exhibit the best range of mechanical properties for the porcelain-baked-to-metal technique, when considering the three most relevant properties: proof stress, plastic stiffness, and modulus of elasticity.

Chemical Phenomena↗
PubMed1977

[Comparative testing of various resins for model dies].

The value of resins for model dies is controversial. This objective study indicates that epoxy- and epimine resins may be successfully used as die materials, if certain measures are taken as a precaution. The resin should be centrifuged and a slight contraction of the material must be calculated into the chain of manufacture. The material should not be poured into hydrocolloid impressions, as the humidity of this impression material may interfere with the proper polymerization of the resin. A major inconvenience are the frequent formation of air bubbles on the angles of the preparation, and this in spite of the use of the vibrator.

Acrylic Resins↗
PubMed1975

[Attempt at a statistical analysis of the values of the free-way space measured on a sample of 54 patients].

The measurements of the free-way space (= distance between physiologic rest position and centric occlusion) vary according to the method used. In order to get a more distinct reference point, the authors suggest tattooing the Menton (lowest chin point) rather than the Pogonion (most anterior chin point). The free-way space measured in this study ranged from 0.5 to 8 mm. 75% of all cases examined revealed a free-way space between 1 and 2 mm and only 5% showed extreme values such as 0.5 and 8 mm. In contrast to Thompson, who believes that the vertical dimension of occlusion equals the vertical dimension in rest position minus 2 mm the results of this study are in agreement with the findings of those authors, who observed an individually great variation of the free-way space.

Cephalometry↗