Simulation of intrafascicular and extraneural nerve stimulation

A model of nerve stimulation for control of muscle contraction and ensuing isometrical muscle force has been developed and implemented in a simulation algorithm. A description of nerve fiber excitation was obtained using probability distributions of a number of excitation parameters. The volume conduction model of the stimulated nerve incorporates both inhomogeneities and anisotropy within the nerve. The nerve geometry was assumed to be cylindrically symmetric. The model of the nerve fiber excitation mechanism was based on that of D.R. McNeal (1976), using the Frankenhaeuser-Huxley equations. Simulations showed that the diameter dependence of nerve fiber recruitment is influenced by the electrode geometr

Absence of Buckling in Nerve Fiber

In this study we give a geometrical model which employs the smoothness of nerve fibers as differentiable curves. We show that a nerve fiber may encounter large curvature due to the possible helicial bending and hence it could cause the fiber to buckle. However, its membrane structure provides a mechanism, entirely geometrical to avoid it. To overcome the challenge of emerging helix we project it into a plane.Comment: 7 pages no figure. Final version presented at The 10th International Physics Conference of the Balkan Physical Union (BPU10), 26-30 August 2018. To be published in AIP Conference Proceeding

Retinal nerve fiber layer photography as an indicator of nerve fiber integrity in ocular hypertensive subjects

To evaluate the usefulness of retinal nerve fiber layer (RNFL) photography in the estimation of nerve fiber layer integrity in ocular hypertensive subjects; we examined 89 eyes of normal (59 eyes, 48 subjects), ocular hypertensive (26 eyes, 14 subjects), and glaucomatous (4 eyes, 2 subjects) patients. Preliminary studies included verification of the Statpac program for the Humphrey field analyzer, and establishing the method of nerve fiber layer photography sensitive enough to detect nerve fiber layer loss. The main study matched 14 ocular hypertensive subjects with 14 normal subjects. The subjects were matched by age(+/- 5 years), sex, and race. It was found that 2 of the 59 total normal eyes (3.4%) [ 2 of the 48 normal subjects (4.2%)]; 2 of the 15 matched normal eyes (13.3%) [2 of 14 matched normal subjects (14.3%)]; and 2 of 24 assessable ocular hypertensive eyes (8.3%) [2 of 13 subjects (15.4%)] showed suspected focal nerve fiber layer defects. None of our normal or ocular hypertensive subjects showed diffuse nerve fiber layer loss. We feel that retinal nerve fiber layer photography is a valuable indicator of nerve fiber layer integrity

Abnormal LDIflare but Normal Quantitative Sensory Testing and Dermal Nerve Fiber Density in Patients with Painful Diabetic Neuropathy

OBJECTIVE—Abnormal small nerve fiber function may be an early feature of diabetic neuropathy and may also underlie painful symptoms. Methods for assessing small-fiber damage include quantitative sensory testing (QST) and determining intraepidermal nerve fiber density. We recently described a reproducible physiological technique, the LDIflare, which assesses small-fiber function and thus may reflect early dysfunction before structural damage. The value of this technique in painful neuropathy was assessed by comparing it with QST and dermal nerve fiber density (NFD)

Evaluation of progressive visual dysfunction and retinal degeneration in patients with parkinson’s disease

PURPOSE. To quantify changes in visual function parameters and in the retinal nerve fiber layer and macular thickness over a 5-year period in patients with Parkinson’s disease (PD). METHODS. Thirty patients with PD and 30 healthy subjects underwent a complete ophthalmic evaluation, including assessment of visual acuity, contrast sensitivity vision, color vision, and retinal evaluation with spectral-domain optical coherence tomography (SD-OCT). All subjects were reevaluated after 5 years to quantify changes in visual function parameters, the retinal nerve fiber layer, and macular thickness. Association between progressive ophthalmologic changes and disease progression was analyzed. RESULTS. Changes were detected in visual function parameters and retinal nerve fiber layer thickness in patients compared with controls. Greater changes were found during the follow-up in the PD group than healthy subjects in visual acuity, contrast sensitivity, Lanthony color test (P < 0.016), in superotemporal and temporal retinal nerve fiber layer sectors (P < 0.001), and in macular thickness (all sectors except inner superior and inner inferior sectors, P < 0.001). Progressive changes in the retinal nerve fiber layer were associated with disease progression (r = 0.389, P = 0.028). CONCLUSIONS. Progressive visual dysfunction, macular thinning, and axonal loss can be detected in PD. Analysis of the macular thickness and the retinal nerve fiber layer by SD-OCT can be useful for evaluating Parkinson’s disease progression

A mathematical description of nerve fiber bundle trajectories and their variability in the human retina

AbstractWe developed a mathematical model wherein retinal nerve fiber trajectories can be described and the corresponding inter-subject variability analyzed. The model was based on traced nerve fiber bundle trajectories extracted from 55 fundus photographs of 55 human subjects. The model resembled the typical retinal nerve fiber layer course within 20° eccentricity. Depending on the location of the visual field test point, the standard deviation of the calculated corresponding angular location at the optic nerve head circumference ranged from less than 1° to 18°, with an average of 8.8°

Clinical Studies in Scanning Laser Polarimetry

Glaucoma is the second leading cause of irreversible blindness worldwide. When left untreated, glaucoma results in visual field loss and eventually in blindness. In considering the diagnosis of glaucoma, the physician will evaluate the intraocular pressure, the optic nerve head and the visual field. This seems to be a straightforward diagnostic process, but, surprisingly, there is still no consensus on the criteria for the signs on which the diagnosis is based. Glaucoma is a progressive optic neuropathy characterized by death of retinal ganglion cells. The course of events that eventually leads to death of these cells is not exactly known, but the retinal nerve fiber layer, which is made up of the axons of the retinal ganglion cells, thins. Scanning laser polarimetry is an imaging technique that can detect glaucoma by assessing the thickness of the retinal nerve fiber layer. Scanning laser polarimetry came onto the market in 1993. The working principle is based on the fact that in the nerve fiber layer a phase shift occurs in polarized laser light that is sent through the nerve fiber layer. This so called retardation is thought to be linearly correlated with nerve fiber layer thickness. In the past, scanning laser polarimetry has shown to discriminate well between normal and glaucomatous eyes. The goal of this thesis was to investigate the clinical performance of the GDx (a revised version of the first scanning laser polarimeter, the Nerve Fiber Analyzer). In summary, the GDx provides fast, objective and quantitative data on nerve fiber layer thickness. The applicability and reproducibility of measurements are high and the image acquisition is user and patient friendly. The GDx yields useful sensitivity and specificity values for the detection of glaucoma, whereas its role in follow-up remains to be investigated. As it stands, the GDx holds insufficient validity to serve as a single test for glaucoma. It does, however, provide a very useful addition to the existing tests we run in patients to make the correct diagnosis

The Association between serum cytokines and damage to large and small nerve fibers in diabetic peripheral neuropathy.

Diabetic peripheral neuropathy (DPN) is a frequent complication of type 2 diabetes mellitus (DM) and may involve small and large peripheral nerve fibers. Recent evidence suggests a role of cytokines in DPN. The paper is aimed at exploring whether the serum concentration of cytokines is associated with small and large nerve fiber function and with neuropathic pain (NP). We recruited a group of 32 type 2 DM patients who underwent serum cytokines (TNF-α, IL-2, IL-4, IL-6, and IL-10) dosage as well as electrodiagnostic and quantitative sensory testing (QST) assessment to explore damage to large and small nerve fibers. Raised serum levels of IL-6 and IL-10 correlated with markers of large nerve fiber sensory and motor axonal damage. Raised IL-10 serum level was associated with signs of motor nerve demyelination. No differences were found in pain characteristics and electrodiagnostic and QST markers of small nerve fiber function in relation to cytokines serum levels. IL-6 and IL-10 serum levels were associated with large nerve fiber damage but not to small fibers function or NP. IL-6 and IL-10 cytokines might play a role in the pathogenesis of nerve fiber damage or represent a compensatory or neuroprotective mechanism