THE COMPUSTIM 10B PROGRAMMING INTERFACE
Ewins
DJ*, Wright PA, Burridge JH, Mann GE, Swain ID,
Taylor PN and
*Address for correspondence: Biomedical
Engineering Group,
Department
of Medical Physics and Biomedical Engineering,
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,
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,
ACKNOWLEDGMENTS
This project
is funded by the