|
THE |
|
M.
Bijak W. Mayr, M. Rakos**, C. Hofer*, H. Lanmüller, D. Rafolt, M. Reichel, S.
Sauermann, |
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Department of Biomedical Engineering and
Physics, *Department of Physical Medicine and
Rehabilitation, Wilhelminenspital, **Otto Bock, Austria |
SUMMARY |
An eight-channel stimulation system,
currently intended for stimulation of lower extremities was developed and is
introduced. Major development goals were easy handling, modularity to make the
system easy adaptable for other
For paraplegic stepping the system worn by the patient consists of two four channel stimulation modules, a central unit holding the battery and circuitry for power management and communication control, a wireless remote control unit and a palmtop computer as main control and input device.
A software package for MS-Windows supports the design and optimisation of stimulation sequences in the rehabilitation centre.
First tests with patients used to
STATE OF THE ART
Stimulation of leg muscles in
spastic paraplegia to restore standing up from the wheelchair, stepping and
sitting down into the wheelchair is a well-known
Surface stimulation needs careful
system setup before usage, has a limit in the amount
of useful channels and a worse muscle selectivity in comparison to implanted
systems but does not require any surgical intervention.
MATERIAL AND METHODS
The introduced stimulation
system (Fig. 1) consists of two four-channel stimulators (one for each leg), a
control device (Central unit) and a Windows CE based palmtop computer. An
additional battery powered Command Unit can be mounted on a crutch or a walker
for manual wireless stimulator control by pressing push buttons.
A special software package, installed on a standard PC or Laptop computer supports stimulation pattern design and interactive testing.
Stimulation
module:
The stimulation
module houses four independent stimulation stages (channels). Each channel is
controlled by its own microprocessor (PIC 16F876, Microchip,
The micro controller drives the impulse
generating output stage. 
For safety reasons and to keep the electrodes potential free an output
transformer is used.
Electrode impedance measurement and m-wave
acquisition are implemented even though the m-wave is currently not evaluated.
All channels are linked together and are
controlled via Inter-Integrated Circuit bus (I2C bus).
The chosen microprocessor is flashable and
allows in circuit firmware update.
Central unit:
The central unit holds the batteries, power supply and battery charging
circuitry, bus management circuitry, the RS232 / I2C translation unit and the
433 MHz receiver (RX2-433, Radiometrix Ltd,
Two RS232 ports are available to connect a
Palmtop Computer and a PC. During the initialisation phase the Bus Manger can
be programmed to connect the PC to the RS232 / I2C Interface or palmtop
computer to the RS232 / I2C Interface giving them access to the stimulation
devices or to connect PC and palmtop for direct data transfer via RS232.
Beside this the Bus Manager is also responsible
for the decoding of the control signals sent by the command unit (standard
RS232 protocol, 9600 baud). The state of the Command Unit can be polled either
from the Palmtop or the PC. Further more the Bus Manger can be configured (via
I2C) to trigger autonomously the stimulation devices on Command Units request.
Therefore multimaster management had to be implemented in both, I2C interface
and Bus Manger.
Command Unit
The Command Unit is based on a commercially
available 433MHz FM transmitter (TX2-433, Radiometrix Ltd,
The described data transmission procedure
results in a sample rate of the pushbuttons of 250/s, in 250/s for one analog
channel and 62.5/s each for four analog channels.
After an idle time of 10 minutes the command
unit enters sleep mode to reduce power consumption. Wakeup is performed when
any button is pressed.
The radio link can be bypassed by a cable
connection in the case when more Command Units are operating in a close
distance and interfere with each other.
Palmtop Computer
A MS-Windows CE based device with touch screen (Ipaq 3130, Compaq,
As development environment MS Embedded Visual
C++ is used. ADOCE, also a MS product, supports data exchange with MS Access
databases while ActiveSync provides all drivers for automatic database
synchronisation.
The graphical user interface is designed as
simple as possible. The often used buttons are sized to be easily activated
with the fingertip. After turning on the device, the patient can choose a
stimulation sequence from the database for standing up, walking and sitting
down. In the next step each single channel can be tested with the possibility
to adapt the stimulation amplitude within a 20% range. Finally the stimulation
is activated and the Palmtop can be stowed away. Then the control is handed
over to the Command Unit.
When the stimulation is running the screen
shown in Fig. 4 offers the opportunity to adjust the stimulation amplitude of
all channels at once, again in a 20% range.
Changes of the device’s state like switching
from standing up to walking are confirmed by either playing a wav-file or
activating the beeper. Obviously the sound volume can be adjusted or switched
off.
A wireless LAN connection to the PC, also
supported by the operating system and ActiveSync, can be used for data exchange
but requires additional hardware (a PCMCIA wireless LAN card and a PC card
jacket) to be mounted on the Palmtop Computer.
PC Software Package
The software package for Laptop Computer or PC
is designed to devise and optimise stimulation sequences.
Different visual and non-visual software
components were created with
In this particular case the described
components are used to build a comfortable Graphical User Interface (GUI) to
ease the patient individual stimulation parameter optimisation. During the
testing phase the PC controls the stimulators via cable connection directly or
with the wireless LAN connection via the Palmtop Computer.
After the stimulation pattern works satisfying
the patient related data is extracted from the underlying MS-Access database
and transferred to the Palmtop Computer for patients
personal use.
RESULTS
The strictly kept modular concept (in hardware
as well as in software design) allowed to break down the whole functionality to
specific tasks and to distribute them to eleven microprocessors that cooperate
among each other and with one PC and one Palmtop Computer reliably.
First tests showed that the whole system is easy to use although some software improvements are still ongoing.
The previous version had nearly the same
features like the described system, but was more bulky and was not intended to
be used outside the clinic or rehabilitation centre. Two T6 patients, familiar
with
The prototype was also successfully adapted for
a project where paraplegic patients rode a newly constructed tricycle by means
of
DISCUSSION
The
introduced eight-channel stimulation system for lower extremities is now
subject to an industrial transfer project with Otto Bock
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ACKNOWLEDGEMENTS
This
project is supported by Otto Bock