the compustim 10b programming interface

THE COMPUSTIM 10B PROGRAMMING INTERFACE Ewins DJ*, Wright PA, Burridge JH, Mann GE, Swain ID, Taylor PN and Wood DE *Address for correspondence: Biomedical Engineering Group, School of Mechanical and Materials Engineering, University of Surrey, Guildford, Surrey GU2 5XH, UK Department of Medical Physics and Biomedical Engineering, Salisbury District Hospital, Salisbury, Wiltshire SP2 8BJ, UK ABSTRACT The Compustim 10B stimulator is a portable, 2 channel, microcontroller based device, designed to facilitate the development of control algorithms for use in hemiplegic gait assistance. To maximise the ease with which the bioengineer and therapist can set up the stimulator in the clinical setting, a computer based interface has been developed using the National Instruments LabVIEW programming environment. Feedback from the clinical team has been a vital part of this development. In the paper the LabVIEW based software is described and areas of future work outlined. Keywords: electrical stimulation, hemiplegia, gait, therapy. INTRODUCTION A common problem in hemiplegic gait is foot drop - the inability to dorsiflex and evert the foot. This results in an impaired gait pattern, with the patient often moving his leg in a cyclical manner (circumduction of leg), in order to attain adequate foot clearance during the swing phase of gait. It was demonstrated by Liberson in 1961 [1], and by many other groups since then, that foot drop can be successfully corrected by electrical stimulation of the common peroneal nerve. However, some patients still experience problems through weakness or inadequate control of further muscle groups in the leg, requiring additional channels of stimulation. In the clinical setting, the benefits of multi-channel stimulation have to be weighed against key concerns such as cosmetic appearance, time to donn/doff, and the difficulties in selecting and maintaining appropriate stimulation algorithms. In this work, the approach has been to use a maximum of two stimulation channels and to develop a clinically acceptable programming environment for algorithm development. METHOD A dual channel, microcontroller based stimulator has been developed for use in the clinical setting [2]. Sensors (currently force sensitive resistors placed in the shoe) are used to enable the stimulator to identify specific stages of the gait cycle. A suite of software in the National Instruments LabVIEW 'G' language has been written to handle interactive control of the Compustim 10B stimulator (through an RS232 port), and off-line display and processing of data. The software is divided into three core modules- PROGRAMME, MONITOR and REVIEW. PROGRAMME enables the bioengineer/therapist to control a range of possible stimulating options. These include the stimulation parameters of pulsewidth, frequency and amplitude, the stimulation parameter to be controlled by the

stimulator's front panel control (e.g. stimulation intensity or pulsewidth), the timing and composition of stimulation waveforms and the initiate/terminate conditions from a maximum of 4 sensors (e.g. foot switches). Once set, the parameters can be downloaded to the stimulator, on-line if required. MONITOR has been developed so that the changes in stimulation and sensor output can be observed graphically whilst the subject moves and can be used, for example, to assist in adjusting the sensitivity and positioning of the foot-switches. This module also allows the data displayed to be recorded for later analysis in REVIEW. Detailed, on-line help, for all the software functions has also been built into the software, together with tools to overcome common difficulties in establishing a serial link between the stimulator and the wide range of computers available in clinics. DISCUSSION Feedback from the clinical team, who have used the programming interface in the correction of hemiplegic gait, has been important in the software development, and the present release has been well received. The software is currently being used in a clinical trial [3] from which further development in the software will result, e.g. on-line database of algorithms for single and dual channel stimulation gait assist and 'intelligent' support for algorithm development based on data from gait analysis. Further details of the software will be provided at the conference. REFERENCES 1. Liberson WT, Holmquest HJ, Scot D, Dow M. Functional Electrotherapy: Stimulation of the Peroneal Nerve Synchronised with the Swing Phase of the Gait of Hemiplegic Patients. Arch Phys Med Rehabil, 42, pp. 101-105, 1961. 2. Michael P. Developments in Surface Electrical Orthoses for the Re-education of Hemiplegic Gait. PhD Thesis, University of Surrey, 1996. 3. Wright PA, Burridge JH, Ewins DJ, Mann GE, McLellan DL, Swain ID, Taylor PN and Wood DE. The Compustim 10B in Stroke: Control Algorithms and Patient Selection Criteria. Proceedings of IFESS '99, Sendai, Japan, 1999. ACKNOWLEDGMENTS This project is funded by the University of Surrey and Action Research.