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Biomedical subjects

R H Nathan

Publications and source records attributed to R H Nathan.

9 recordsLinked to original sources
PubMed1995

Three-dimensional current density distribution under surface stimulation electrodes.

Overflow to non-target tissue during FNS can be reduced by controlling current density distribution under surface stimulating electrodes. A method is introduced for the acquisition of 3-D current density distributions under complex surface stimulating FNS electrode geometries. The method makes use of a phantom model in which a conventional homogeneous model has been improved by adding a layer to simulate skin impedance properties, based on specific FNS parameters. Signal acquisition and processing circuits have been developed to simulate the process by which excitable tissue responds to external stimulation. In addition, a data analysis method has been introduced to allow for the characterisation of stimulation current intensity, electrode geometry and pulse waveform required to achieve target muscle activation, with minimal overflow and to avoid pain or burning. Measurements of integrated differential voltage corresponding to current density distribution acquired under electrodes of various geometries are presented in terms of 3-D attenuation coefficient maps as examples of the applicability of the method.

Computer Simulation↗
PubMed1993

Control strategies in FNS systems for the upper extremities.

The condition of the paralyzed patient is described, regarding both the primary paralysis and the secondary physiological changes in the upper limb resulting in abilities and disabilities in upper limb function. Although the review relates mainly to spinal cord injuries at the C4, C5, and C6 levels, other conditions are noted such as hemiplegia. Activation of muscle by functional neuromuscular stimulation (FNS) is discussed. The biomechanics of the FNS-activated paralyzed upper limb is analyzed for activation by both implanted and by surface electrodes, and a review is presented of open-loop strategies for systems in clinical use. Closed-loop strategies applied to the upper extremity are reviewed for analog and digital systems, and regimes developed for specific functional activities are outlined. Finally, adaptive control strategies are surveyed.

Arm↗
PubMed1992

The isometric action of the forearm muscles.

The isometric forces and moments generated at the hand segment by thirteen of the forearm muscles were measured on three test subjects. Small bipolar surface electrodes were used to activate each muscle separately. The direction of the force vector generated at the fingertips and the percentage torque generated about the longitudinal axis of the hand segment were measured and were modeled for one subject as a parabolic function of the position of the wrist and radioulnar joints in their ranges of motion. The results exhibited a high standard deviation. It is proposed that a significant component of this standard deviation is inherent in the biomechanics of the musculo-skeletal system. Variations in the test protocol were used to test this hypothesis. The standard deviation was found to be significantly larger in the flexor muscles than the extensors. It was concluded that the stability and elasticity of the soft tissue structures in the region of the wrist joint may significantly influence the direction of the generated joint moment vector.

Elasticity↗
PubMed1990

Upper limb functions regained in quadriplegia: a hybrid computerized neuromuscular stimulation system.

A new, computerized neuromuscular stimulation system was applied to the upper limbs of two patients with complete quadriplegia below the C4 level. The stimulation-generated movements were integrated and augmented by residual, voluntary shoulder girdle movements and mechanical splinting. Up to 12 muscles were stimulated individually with high-resolution surface electrodes; coordination and control of the stimulation was effected by microcomputer. Simple vocal commands to the computer triggered preprogrammed hand prehensions, arm motion, and other functions, giving the patient complete control over the system. In pilot clinical trials of six weeks, writing, eating, and drinking, including picking up and replacing the pen or cup, were achieved.

Adult↗
PubMed1987

A third world wheelchair.

A wheelchair was designed specifically for manufacture, maintenance, and use in Third World countries. An experimental prototype was constructed and tested, and subsequently, a production model was manufactured after modifications to the original design were made.

Developing Countries↗
PubMed1979

A dynamometer for biomechanical use.

A dynamometer has been designed for measuring isometric forces in human body limb segments. The dynamometer constrains the chosen segment, and measures two orthogonal components of the force reaction between the segment and the dynamometer in a plane perpendicular to the long axis of the segment, plus the torque reaction parallel to the long axis of the segment. The testing and operating characteristics of the dynamometer are described, and it is concluded that in view of its versatility and accuracy, the dynamometer may be suitable both for research and for clinical use.

Biomechanical Phenomena↗