PubMed Health⌕ Search

Biomedical subjects

V A Pollak

Publications and source records attributed to V A Pollak.

8 recordsLinked to original sources
PubMed1993

Simulation of the conduction velocity properties of nerve fibres by an electrical model.

The paper presents a simple electrical circuit model from which the relationship between the diameter of the axon and its conduction velocity can be derived. The model is primarily intended for the larger myelinated fibres in peripheral nerves. However, a simplified model is also shown for nonmyelinated fibres, where the relationship is quite different. In the conclusion some qualitative considerations are presented for thin myelinated fibres with a slow velocity of conduction. The conduction velocity/diameter relationship of these fibres gradually approaches that for nonmyelinated fibres with decreasing diameter.

Axons↗
PubMed1993

Analysis of stability of human upright posture based upon the measurement of the head sway.

The paper is dealing with the description of a simple and inexpensive technique for recording and measuring of the head sway during upright stance. In particular the recording system and the evaluation of the body sway data are highlighted. The objectives of the head sway signal analysis are the determination of sway components in the side-to-side (lateral) direction and forward-backward (anteroposterior) direction. It is anticipated that it will be possible to extract from the digitized data some information about the transfer characteristic and stability margin of the neuromuscular control system concerned with the maintenance of equilibrium. Additional information of potential clinical significance could be obtained by correlating the measured sway data with electromyographically determined changes in the activity of the main postural muscles. The information obtained is comparable to that gathered by more sophisticated, and more expensive conventional devices. A special feature is the easy portability of the system which permits collection of stabilometric data even in remote locations, while the analysis on which the diagnostic assessment is based can be performed at a later date in a central facility equipped with the necessary instrumentation.

Head↗
PubMed1983

A simple and inexpensive technique for the measurement of head sway.

The paper presents a relatively simple and economic system for measuring human head sway. The recording device is a downward looking 35-mm still camera which photographs a flashing infrared light emitting diode (LED) that is mounted on the top of the head. The pictures so obtained are then digitized and fed into a computer for stabilometric analysis. If desired the film can be advanced continuously at an adjustable speed to obtain a deconvoluted recording.

Head↗
PubMed1980

The risk of retina damage from high intensity light sources.

The risk of thermal damage to the retina of the eye by exposure to excessive light intensities from continuous and pulsed man-made sources is discussed. The probability of injury increases, the larger the radiant power absorbed by the retina and the smaller the size of the retinal image of the source. A mehtod of estimating the temperature increase of the immediately affected area of the retina is presented. The time constants involved are also briefly considered. Using numerical values from literature for the relevant parameters of the eye, threshold values for a variety of conditions can be established. Below these values little risk of retina damage should exist. The degree of hazard when these values are exceeded depends upon the circumstances. A case study of a welding accident showed good agreement between the conclusions of the theoretical analysis and clinical findings.

Hot Temperature↗
PubMedDate not supplied

A fast communication aid for non-verbal subjects with severe motor handicaps.

A computer-based communication system for non-verbal persons with severely deficient coordination of the upper extremities is described. The device doubles as an environmental control unit. Modular design is chosen throughout. Commercially available subunits are used to reduce cost. Input is by a 3 x 3 keyboard, when the user has some command over his hands. Otherwise a binary 'autoscan' access mode is used, which is controlled by repeated closures of a single binary switch. Output is in written form on a display or acoustical by synthesized speech. Hard-copy output can also be provided. Remote communication is possible by modem or by synthesized speech. Speed of message generation is increased by establishing a vocabulary, which contains, in addition to signs and letters of the alphabet, whole words and stereotyped phrases. The data blocks of the latter are accessed by a single input cycle similar to that used for the selection of isolated letters, symbols, etc.

Communication Devices for People with Disabilities↗
PubMedDate not supplied

Non-invasive determination of the distribution of the conduction velocity of the large-diameter fibers in peripheral nerves. Estimate based upon a single recording of the stimulus response of the nerve.

The paper describes a method for the estimation of the frequency of occurrence of fibers with a given conduction velocity among the stronger myelinated fibers of superficial nerves. The method is primarily suited for the examination of sensory nerves. To mixed nerves it can be applied only if interference by excited myopotentials is sufficiently weak. A single averaged recording of the compound action potential of the nerve evoked by a supra-maximal electrical stimulus serves as input. It is shown that integration of that curve with respect to time yields an amplitude weighted graph of the density of fibers with given travel times between the stimulus site and the recording electrode. Unweighting that curve yields the distribution characteristic of the travel delays which can easily be converted to a graph of the conduction velocity density of the fibers in the excited ensemble.

Action Potentials↗