Henry S. Ho

Simulated tissue loads for testing of transcutaneous electrical stimulators

Sensory and motor threshold excitation from a human study with a constant voltage source were used to develop ideal simulated loads for monophasic, biphasic and amplitude modulated waveforms to test transcutaneous electrical stimulators. A comparison with resistive loads or the AAMI standard load was made, indicating that the ideal forearm loads can more accurately represent the human loading condition.<<ETX>>

Effects of electrode size on basic excitatory responses and selected electric stimulator parameters

This electrical stimulation study investigates the effects of electrode size on the basic excitatory responses of four healthy Subjects. Four different sizes of self-adhesive surface electrodes from (2.25 cm2) to (40.3 cm2) were applied over the medial and lateral gastrocnemius muscles. The excitatory levels considered were sensory threshold (ST), motor threshold (MT), pain threshold (PT) and maximally tolerated painful (MP) stimulation. The stimulus was a symmetric biphasic waveform with 200 µSec phase duration and a repetition rate of 50 Hz. The amplitude of the stimulus was increased until the appropriate excitatory response was achieved, at which time the computerized system recorded the peak voltage and peak current and computed the associated phase charge. The data showed that for all dependent variables tested the largest electrode (40.3 cm2) required about 40 percent lower peak voltage and 400 percent higher peak current compared to the smallest electrode (2.25 cm2). The ratio of the peak voltage to the peak current decreased non-linearly as electrode size increased. The data also showed that phase charge increased 700 percent and phase charge density (phase charge divided by electrode surface) decreased 60 percent as electrode size increased. The peak currents and phase charges that elicit a painful response were much lower as the electrode size became smaller. We concluded that electrode size effects are non-linearly related to the stimulus parameters required for inducing common excitatory responses. This information could be very useful in the development of a load simulating the electrode-tissue interface for different types of electrodes.

Charges associated with threshold excitation of peripheral nerves using various waveforms

The dependence of sensory and motor nerve excitation on phase charge and total pulse charge of five waveforms was investigated. A neuromuscular stimulation system provided a monophasic waveform, a symmetric biphasic and multiphasic waveform of 10 pulses per burst or 25 pulses per burst, and an amplitude-modulated waveform. These waveforms were delivered through surface electrodes to the right forearm or leg of four healthy human subjects. The results indicate that for threshold excitation of the sensory and motor nerves the phase charge for the five waveforms do not differ markedly while the corresponding total pulse charge increases substantially with multiphasic and amplitude-modulated waveforms.<<ETX>>

Threshold excitations of sensory and motor nerves using different biphasic pulse bursts

The dependence of peripheral nerve excitation on a peak voltage and current amplitudes with different number of pulses in a biphasic pulse burst was investigated. The stimulation, consisting of a symmetrical biphasic pulse and a 10- or 25-biphasic pulse burst, was applied to the forearm and the leg of a human subject. The results indicate that the charge associated with the peak threshold current increases substantially with an increase in the number of pulses per burst while corresponding voltage and current peak amplitudes decrease slightly.<<ETX>>

Intra And Inter Electrode Charge Distributions And Their Effects On Threshold Excitation Of Human Peripheral Motor Nerves

The effect of three types of surface electrodes on phase charge, peak current and peak voltage during threshold of motor nerve excitation was tested. In order to assure the selection of electrodes that are different in electrical characteristics, the uniformity of the conductive properties across the surface of three electrodes was studied. The data were analyzed statistically using ANOVA. No significant differences were found between trials, areas or days. Significant differences between the three electrodes were found in the averaged phase charge. Despite the varied conductive properties of the electrodes, forearm and leg motor threshold excitation of three healthy subjects occurred at about the same value of phase charge, but not same peak voltage and current.