Biomedical subjects

Frank Rattay

Publications and source records attributed to Frank Rattay.

6 recordsLinked to original sources

PubMed2007

Posterior root-muscle reflexes elicited by transcutaneous stimulation of the human lumbosacral cord.

Continuous epidural stimulation of lumbar posterior root afferents can modify the activity of lumbar cord networks and motoneurons, resulting in suppression of spasticity or elicitation of locomotor-like movements in spinal cord-injured people. The aim of the present study was to demonstrate that posterior root afferents can also be depolarized by transcutaneous stimulation with moderate stimulus intensities. In healthy subjects, single stimuli applied through surface electrodes placed over the T11-T12 vertebrae with a mean intensity of 28.6 V elicited simultaneous, bilateral monosynaptic reflexes in quadriceps, hamstrings, tibialis anterior, and triceps surae by depolarization of lumbosacral posterior root fibers. The nature of these posterior root-muscle reflexes was demonstrated by the duration of the refractory period, and by modifying the responses with vibration and active and passive movements. Stimulation over the L4-L5 vertebrae selectively depolarized posterior root fibers or additionally activated anterior root fibers within the cauda equina depending on stimulus intensity. Transcutaneous posterior root stimulation with single pulses allows neurophysiological studies of state- and task-dependent modulations of monosynaptic reflexes at multiple segmental levels. Continuous transcutaneous posterior root stimulation represents a novel, non-invasive, neuromodulative approach for individuals with different neurological disorders.

Adult↗

PubMed2006

Conjugate eye movements and gamma power modulation of the EEG in persistent vegetative state.

BACKGROUND: Power in the gamma band EEG increases during saccades in normal subjects. OBJECTIVE: To develop a potential method to quantify signs of cortical responsiveness in persistent vegetative state (PVS) we quantified gamma range EEG in association with conjugate slow ballistic eye movements (SBEM). METHODS: The EEG and the simultaneous electro-oculogram were recorded in 14 (8F/6M) PVS patients. Clinical scoring was based on the Glasgow Coma Scale (GCS) and Coma Rating Scale (CRS). The Wavelet Transform, followed by Hilbert transform was applied to the EEG and gamma power distribution was quantified relative to the timing of an eye movement. We correlated the clinical and the neurophysiological measures. RESULTS: Gamma activity was present in all PVS patients. Its power was modulated in association with eye movements only in less severely affected patients, with minimum power prior to, and maximum power during the eye movement. In severely affected patients there was no evidence of a temporal relationship between gamma power and the phase of the eye movement. CONCLUSIONS: Detecting changes in the time course of gamma power in relation to conjugate ballistic eye movements provides a quantitative neurophysiological method for prospective longitudinal studies to explore if the preservation of this CNS function relates to the potential for recovery in PVS patients.

Adult↗

PubMed2005

Analysis of calculated electrical activation of denervated muscle fibers in the human thigh.

Finite difference models of the human thigh are used to analyze the excitation process in the fibers of denervated skeletal muscles in conjunction with functional electrical stimulation (FES) via surface electrodes. The Matlab tool "FES-Analyze" was developed to simulate and analyze the super-threshold regions in a human thigh. Action potential is simulated with a muscle fiber model of the Hodgkin Huxley type and with a generalized form of the activating function. With FES-Analyze it is possible to compare the stimulation at the end of the muscle fiber and the stimulation at the central part of the muscle fiber, both in cross- and longitudinal-section, as well as to observe the effect of different impulse intensities and lengths during FES. Simulating with "Standard Values" of the pulse duration (20 ms) and the amplitude (80 V) one discovers that the main part of the activation takes place at the end of the muscle fiber. To obtain activation at the central part of the muscle fiber, higher amplitudes and longer pulse durations are needed.

Electric Stimulation↗

PubMed2004

Frequency-dependent selection of alternative spinal pathways with common periodic sensory input.

Electrical stimulation of the lumbar cord at distinct frequency ranges has been shown to evoke either rhythmical, step-like movements (25-50 Hz) or a sustained extension (5-15 Hz) of the paralysed lower limbs in complete spinal cord injured subjects. Frequency-dependent activation of previously "silent" spinal pathways was suggested to contribute to the differential responsiveness to distinct neuronal "codes" and the modifications in the electromyographic recordings during the actual implementation of the evoked motor tasks. In the present study we examine this suggestion by means of a simplified biology-based neuronal network. Involving two basic mechanisms, temporal summation of synaptic input and presynaptic inhibition, the model exhibits several patterns of mono- and/or oligo-synaptic motor output in response to different interstimulus intervals. It thus reproduces fundamental input-output features of the lumbar cord isolated from the brain. The results confirm frequency-dependent spinal pathway selection as a simple mechanism which enables the cord to respond to distinct neuronal codes with different motor behaviours and to control the actual performance of the latter.

Action Potentials↗

PubMed2004

Effective electrode configuration for selective stimulation with inner eye prostheses.

The quality of visual perception with retinal prostheses strongly depends on the local selectivity. Electrode arrays at the surface of the retina should excite exclusively cells within a local area but they are expected to co-stimulate bypassing axons originating from ganglion cells of the outer regions. Long electrodes parallel to these axons are shown to be good candidates for avoiding the co-stimulation phenomenon. Efficiency of focal excitation depends on the length and resistance of the electrodes.

Action Potentials↗

PubMed2002

Simulation of the three-dimensional electrical field in the course of functional electrical stimulation.

Optimization of stimulation parameters as well as shape and positioning of electrodes are important questions in functional electrical stimulation (FES) of paraplegic patients. For that reason a MATLAB tool, called FES-FIELD, modeling the three-dimensional electric field in the human body, has been developed to calculate the electric field in a region of interest. The simulation tool provides a graphic user interface. In case of denervation of the lower extremities, an important target muscle is the m. quadriceps femoris. The electrical potential distribution along its fibers is representative for its functional activation. For this special application, the human thigh stimulated by skin electrodes was modeled. The simulation process was done in 5 steps: reading the geometric information of the thigh from 50 computed tomographic slices, segmentation in tissue types by pixel value and definition of each conductivity, selection of electrode geometry and positioning, calculating the electric field iteratively by solving the system of linear equations, and visualization of the solution by equipotential lines in either cross or length sections of the thigh.

Computer Simulation↗