Search

Surface recorded somatosensory evoked potentials (SEPs) are neural signals elicited by an external stimulus. In the case of electrically induced SEPs, the artifact generated by the stimulation process can severely distort the signal. The artifact is characterized by a large impulse followed by a slowly decaying tail. In some cases, the artifact tail often lasts well into the initiation of the SEP making the determination of absolute latency very difficult. While the literature often states that the recording instrumentation plays a part in the generation of this artifact tail, no firm evidence has ever been presented. In this work, comparisons are made between three instrumentation systems (BJT, JFET and CMOS) with differing input impedances in an attempt to quantify the effects on the artifact tail. The conclusions from this investigation show that there is no significant interaction between the input impedance of the recording instrumentation and the duration of the artifact tail. Each amplifier type produced results with no significant statistical differences. It was also found that while stimulation amplitude has a weak effect on the artifact tail, the greatest contribution to variation has an inter-subject origin. Consequently, it is concluded that the time constant of the artifact tail must originate from other sources that are subject dependent.

Modifications were made to the Series III-311 Omnikinetic Hydra-Gym apparatus (Hydra-Fitness Industries Inc., Belton, TX) in an effort to provide relatively inexpensive yet clinically useful isokinetic strength measurements. Signal transmission and processing functions were installed to calculate relevant strength characteristics for knee extension/flexion motions. Results from the modified Hydra-Gym were compared with matched procedures on the Kin-Com (model 500-10, Chattecx Corporation, Chattanooga, TN). Subjects (N = 10) performed three maximal concentric right knee extension/flexion cycles at different resistance settings (2, 4, and 6) on the Hydra-Gym and the corresponding angular velocities on the Kin-Com (190, 125, and 40 degrees/sec, respectively). Each subject completed eight testing sessions, four on each dynamometer. A five-way analysis of variance on the peak torque data revealed no significant difference between dynamometers; however, there was a significant interaction between dynamometer and extension/flexion measurements. The variance in angle of peak torque data was significantly different between dynamometers, with Hydra-Gym showing superior reproducibility (p < 0.005). Mechanical differences between dynamometers produced slightly different, though comparable and consistent, measurement values. Care must be taken when evaluating hamstring/quadriceps ratios from the Hydra-Gym because the interaction noticed between dynamometer and extension/flexion may exaggerate muscle imbalances. In summary, modifications to the Hydra-Gym appear to provide clinicians with a reliable and clinically useful strength testing alternative.

In this paper, a microcomputer-based system is described which facilitates the evaluation of different myoelectric control strategies. The system is based on an IBM-PC/AT microcomputer which generates and develops tracking targets, processes and displays the operator's response, and computes tracking performance. The dynamics of the prosthetic elbow, hand, and forearm are simulated in software which drives a stick figure in response to the operator's input. Performance is measured in terms of integral absolute error in target-response match. Control strategies to simulate different systems are easily modified through software and are evaluated under identical conditions. As a test of this evaluation system and to obtain some comparative data on control strategies, four strategies which are either in use or proposed for use are evaluated. The test procedure is divided into a control training session and a control evaluation session. Data collected from groups of three normally-limbed subjects per strategy over a period of five control evaluation sessions are presented. The results of this evaluation are discussed and improvements in the evaluation system suggested.