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Biomedical subjects

W K Durfee

Publications and source records attributed to W K Durfee.

6 recordsLinked to original sources
PubMed1991

Open-loop position control of the knee joint using electrical stimulation of the quadriceps and hamstrings.

The clinical acceptability of functional electrical stimulation (FES) as an aid for restoration of paraplegic gait is limited by the inability to accurately and repeatedly position the lower extremity. To gain insight into the causes of and possible solutions to this problem, the responses of the quadriceps and hamstrings to FES were studied in able-bodied subjects. Isometric torque was dependent on knee angle and changed unpredictably with time. An open-loop feedforward knee-joint position controller was also tested. The results demonstrated that it is beneficial to account for the dependence of torque on position, that modifications to this open-loop controller might improve accuracy and that closed-loop control may be essential for functional restoration of gait.

Adolescent↗
PubMed1991

Simulator for evaluating shoulder motion as a command source for FES grasp restoration systems.

A simulator has been developed to evaluate the command channels through which a quadriplegic patient controls an upper limb neural prosthesis. The simulator consists of an animated grasping task implemented on a video screen. The patient controls the motion of an animated hand on the screen by moving his or her own hand while the animated hand opens and closes under control of the tested command channel. Experiments were performed using both able-bodied and quadriplegic subjects to evaluate shoulder motion as a command-channel source. The results demonstrated that optimal combinations of shoulder command-channel parameters are subject specific, which suggests using the simulator in the prescription of upper limb neural prostheses and in training quadriplegic persons who use them. Additionally, the experimental results quantified the reduction in performance that came from using ipsilateral vs contralateral shoulder control and the enhancement in performance realized when using substitute sensory force-feedback displays.

Computers↗
PubMed1990

Regulating knee joint position by combining electrical stimulation with a controllable friction brake.

Hybrid FES gait restoration systems which combine stimulation with controllable mechanical damping elements at the joints show promise for providing good control of limb motion despite variations in muscle properties. In this paper we compared three controllers for position tracking of the free swinging shank in able-bodied subjects. The controllers were open-loop (OL), proportional-derivative closed-loop (PD), and bang-bang plus controlled-brake control (CB). Both OL and PD controllers contained a forward path element, which inverted a model of the electrically stimulated muscle and limb system. The CB control was achieved by maximally activating the appropriate muscle group and controlling the brake to be a "moving-wall" against which the limb pushed. The CB control resulted in superior tracking performance for a wide range of position tracking tasks and muscle fatigue states but required no calibration or knowledge of muscle properties. The disadvantages of CB control include excess mechanical power dissipation in the brake and impact forces applied to the skeletal system.

Biomechanical Phenomena↗
PubMed1989

Task-based methods for evaluating electrically stimulated antagonist muscle controllers.

Single-joint motor neural prosthesis control algorithms were tested in a novel animal model. The model consisted of a human subject who provided joystick inputs to a controller. The controller output determined the stimulus activation levels of two antagonist muscles which manipulated the ankle joint of an intact, anesthetized cat. Using visual feedback, the subject manipulated the system to perform positioning tasks which simulated normal activity of an intact limb. Three controllers were evaluated, open-loop reciprocal control, P-D closed-loop reciprocal control, and open-loop cocontraction control. The results demonstrated that in the presence of visual feedback, open-loop cocontraction control compared favorably in performance to a P-D closed loop controller. This has a practical value for the implementation of clinical neural prostheses since it suggests that in some cases, feedback transducers may not be required for fine control.

Animals↗
PubMed1989

Methods for estimating isometric recruitment curves of electrically stimulated muscle.

Four methods for estimating the recruitment curve of isometric, electrically stimulated muscle are described. Three of the methods were tested experimentally in isolated tibialis anterior and medial gastrocnemius muscles of cats. The three methods are steady-state step response, peak impulse response, and deconvolved ramp response. The fourth method, described but not tested, is a stochastic iteration technique. The results demonstrate that estimations of recruitment curves depend on the method used and that all methods are sensitive to short-term and long-term time-variations in muscle properties. While the step response technique is the traditional method for estimating recruitment curves, the ramp deconvolution method appears to offer acceptable accuracy with much shorter testing times.

Animals↗