Article published on juin 2008Functional rehabilitation:
The patient regains control
Standing up by means of a gesture-triggered electrical stimulation of the leg muscles: this is the prospect opened to paraplegic patients by a motion recognition module developed by CEA/LETI researchers. Soon to be tested in a rehabilitation centre in Montpellier, it could eventually lead to the development of an industrial product.
A paraplegic patient who, by merely
tilting the head forwards, triggers an electrical
stimulation of the leg muscles and
stands upright: this striking image could
become a reality someday thanks to the
work carried out by CEA/LETI researchers in
collaboration with a rehabilitation centre*
and a public laboratory** in Montpellier.
CEA/LETI researchers have a developed a 3D
attitude determination unit***. Rodolphe
Héliot, doctoral researcher at CEA/LETI
and INRIA Rhône-Alpes, has developed a
very refined signal processing technique
capable of identifying the intention to
stand up (see figures below): 'whether able
or disabled, we anticipate the change from
the sitting to the upright position by tilting
the head forwards. The current version of
our system recognises this gesture with
97% accuracy and discards 76% of head
tilting movements associated with other
purposes, e.g. picking up a glass in front
of oneself'. These results are to be improved
to allow a paraplegic person to voluntarily
trigger an electrical stimulation of the lower
limbs.
'Living at the same level as able
persons no longer means living
in a wheelchair'.
This stimulation technique is still at the
experimental stage and is being investigated
by the Propara rehabilitation centre
in collaboration with the LIRMM laboratory
in Montpellier. 'The objective is to identify
the muscular
activation sequence
that best combines
efficiency, stability
and safety, both for
performing the standing-up movement
and maintaining the upright position',
explains Dr. Charles Fattal, Senior physician
at Propara. 'Subsequently, we also intend
to study the factors causing muscular
fatigue, to allow the upright position to be
maintained as long as possible'.
As compared to a 100% external stimulation
(i.e. without the patient's participation), the
system developed by CEA/LETI researchers has the advantage of focusing on the
patient's will and making the movement
as natural as possible:'The key has been the
development of a real-time control process
perfectly synchronised with the natural
sequence of gestures', explains Rodolphe
Héliot. 'To achieve this, we have developed
algorithms that reduce the computation
time to 1 to 2 ms, despite the complexity
of the signal to be
processed.'
Beyond rehabilitation
in a specialised
centre, paraplegic
persons could also gain increased
autonomy in their daily lives: reaching for
a book on a shelf, standing upright at a
public service booth or when speaking to
other guests in a social gathering, etc.
If the clinical tests are conclusive, CEA/LETI
intends to integrate the attitude determination
unit and computation algorithm into
a marketed electrical stimulation device,
with the support of an industrial partner familiar with the medical area and associated
technical standards.
At the same time, a laboratory team has
been using a bipedal robot to test the
system for the purpose of hemiplegic
patient rehabilitation. The attitude
determination unit is attached to the valid
lower limb, records the step frequency
and amplitude, and triggers an equivalent
electrical stimulation of the deficient lower
limb to maintain balanced walking. In this
case as well, the overall movement is triggered
by the patient's voluntary gesture
and not by an external device.
* Propara neurological centre (Montpellier)
** Demar team at the LIRMM laboratory (CNRS - INRIA
- University of Montpellier)
*** Subject to a technology transfer and license
agreement with Movea, a start-up company created
this year
