Thomas Sinkjær
Center for Sensory-Motor Interaction,
Fredrik Bajers Vej 7D-3,
DK-9220 Aalborg, Denmark, ts@smi.auc.dk
ABSTRACT
In this presentation, I will review our experience as to how signals
recorded from cutaneous and muscle nerves can be applied to restore foot, hand,
and bladder control in subjects with central nervous lesions.
Electric stimulation of the peroneal nerve used for
correction of gait is used to enhance dorsiflexion in the swing phase of
walking in lower extremities of hemiplegic patients. Instead of an artificial
external heel switch, we have tested the use of a nerve cuff electrode picking
up information from the sural nerve and calcaneal nerve and feeding this into a
one channel
In natural hand control, cutaneous receptors from the
fingers play an important role in controlling the muscle activation level. We
have implemented an algorithm that makes an
For restoration of bladder function in SCI patients,
the sacral root stimulator by Brindley is useful in controlling the emptying of
the bladder. At present we are carrying out experiments on animals using cuff
electrodes on sacral roots and the pelvic nerve to detect hyperreflexia and to
give "warning signals" when the bladder gets full (Jezernik et al.,
1999) This information can potentially be used to inhibit unwanted bladder
contractions and to trigger the FES system and thereby bladder emptying.
KEYWORDS
Natural sensors,
feedback , Neural Prosthesis devices, hand, foot, bladder
INTRODUCTION
New developments in electrode design
(Kallesøe et al., 1996; Struijk et al., 1995), implantable amplifiers (Zhou et
al., 1998) and signal processing (Jezernik and Sinkjær, 1999) to do long-term
and reliable recordings from peripheral nerves emphasise the use of the body´s
own sensors in Neural Prosthesis devices (Sinkjær et al., 1999). The body’s own
sensors have been installed and optimised through natural evolution during
million of years. Reliable recorded information from these natural sensors can
be applied as signals, e.g.:
i)
to
control electrical stimulation (ES) that produces a movement
ii)
to
detect unwanted (spastic) muscle contractions which can then be inhibit by,
e.g. ES
iii)
to
communicate with the brain through, e.g. electrocutaneous cognitive feedback
systems (Riso, 1999; Matjacic et al., 1999)
in users who have impaired motor and sensory functions
because of central nervous lesions.
NATURAL SENSORY INFORMATION USED IN DROP FOOT PROSTHESIS
Electrical stimulation of the peroneal nerve used for
correction of gait has proven to be a potentially useful mean for enhancing
dorsiflexion in the swing phase of walking in lower extremities of hemiplegic
patients. The stimulation is applied during the swing phase of the affected leg
and prevents drop foot. This makes the patient walk faster and more securely.
The stimulator is often located distally to the knee on the lateral part of the
tibia. The stimulator can be either external or partly implantable. In most
commercial systems today the stimulator is triggered by an external heel-switch
linked to the stimulator through a wire running from the switch under the heel
up to the stimulator, but new implantable devices are being developed (Childs
et al., this meeting).
The rationale for implanting
a cuff electrode on a cutaneous nerve innervating the foot is to remove the
external heel switch used in existing systems for foot drop correction and
thereby making it possible to use such systems without footwear and preparing
it to be a totally implantable system. During walking,
the nerve signal modulates strongly and gives a response at foot contact and a
silent period when the foot was in the air through the swing phase of the
walking cycle. Reliable
detection of afferent nerve signals is essential if such signals are to be of
use in artificial sensory-based Functional Electrical Stimulation neural
prosthetics. By feeding the processed neural signals to an Adaptive Logic
Network (ALN) (Kostov et al., 1996) the ALNs can discriminate precise timing of
heel contact as well as heel lift during FES assisted walking, having a
detection rate of nearly 100 %.
NATURAL SENSORY INFORMATION USED IN HAND PROSTHESIS
Healthy subjects are able to control the grip force
when holding a given object, independent of the weight and surface texture of
the object. This is possible because the cutaneous receptors give information
about small slips and skin deformation. We have implemented an algorithm that
makes an FES system able to mimic this function based on the compound
information from the cutaneous receptors in the index finger as recorded by a
nerve cuff electrode. The algorithm was initially developed in an animal
preparation, and later we have implemented it in two spinal cord injured
subjects (Haugland et al., 1999).
Results from a 27-year-old tetraplegic male with a
complete C5 spinal cord injury (two years post injury) are presented here. The
patient had no voluntary elbow extension, no wrist function, and no finger
function. He used a splint for keeping the wrist stiff. He had partial
sensation in the thumb, but no sensation in 2nd-5th finger.
The processed signals from the receptors in the index
finger are used to control the “Freehand” system (NeuroControl Inc. Ohio, USA)
and it is today developed to an extent where the subject can use it during
functional tasks (Inmann et al., this meeting). During an eating session, where
the subject has a fork in his instrumented hand (grasped between the thumb and
index finger), the control system is designed to decrease the stimulation of
the finger muscles until the feedback signal from the skin sensors detects a
slip between the index finger and the fork. When a slip is detected, the
stimulation to the thumb increases automatically proportional to the strength
of the sensory feedback, and if no further slips are detected, the controller
again start to decrease the stimulation. A typical eating session will last
20-30 min. A large fraction of this time is dedicated to “non-eating” activities.
During such times, the stimulation is at a minimum (keeping the fork in the
hand with a loose grasp) and thereby preventing the hand muscles to be
fatigued. When the feedback is taken away, the subject will typically leave the
stimulation on at a high stimulation intensity for the full eating session.
This will fatigue the stimulated muscles, and the subject will try to eat his
dinner faster, or he will rest his muscles at intervals by manually decreasing
the stimulation. An effort that requires more attention from the subject than
the automatic adjustment of the stimulation intensity.
NATURAL SENSORY INFORMATION USED IN
CONTROL OF NEUROGENIC BLADDER
In the case of neurogenic bladder,
the elevated intravesicular pressure can force urine to travel back up to the
kidneys and produce upper urinary tract infection. Equally common are
infections of the lower urinary tract caused by insufficient voiding which
leaves a persistent high volume of residual urine. In addition to these
problems, overfilling of the bladder can lead to a condition of autonomic
dysreflexia, which can also be life threatening.
These
problems could be reduced if it would be possible to provide spinal injured
individuals with information about the state of fullness of the bladder. This
requires that there will be some sensors which can monitor the bladder volume
and bladder pressure.
Recently, it has been demonstrated that a nerve cuff
applied around the sacral roots or the pelvic nerve innervating the bladder in
anaesthetised pigs can record activity that correlates with the status of
fullness of the bladder (Jezernik et al., 1999). Further more, in an
anaesthetised “hyperreflexive bladder” cat model rhythmic contractions can be
reliably detected by the cuff electrode recordings and the bladder contraction
inhibited by e.g. electrical stimulation of the sacral roots (Jezernik et al.,
this meeting). This demonstrate that patients with a hyperreflexive bladder
(SCI, some incontinence patients) could, when needed, get a closed loop controlled
FES implant that uses this recorded sensory input. Present solutions for such
patients are suppression of reflex contractions by drugs and bladder emptying
by catheterisation. In some cases, drugs do not work - then surgical
intervention is needed, where the detrusor is deafferented by cutting the
dorsal sacral roots to prevent reflex contractions, and the bladder can be
emptied by use of a sacral root stimulator that has electrodes on the sacral
ventral roots. Dorsal rhizotomy increases the bladder capacity, but reflex
erection in male patients is lost. To prevent cutting dorsal sacral roots, one
could detect fast pressure rises and detrusor activation with nerve cuff
recordings from bladder nerves, and the controller could then take appropriate
actions as, e.g. inhibit detrusor contractions by stimulating pudendal or
penile nerves, or block efferent or afferent pelvic nerve transmission to
prevent reflex detrusor contractions (Jezernik et al., 1999; Rijkhoff et al.,
1998). In this way continence could be re-established, low pressure voiding
achieved, bladder functional capacity increased, and beside medical status
improvement, patients would become more independent as well and could socialise
more easily.
The use of cuff electrodes to record the activity of
cutaneous and bladder afferents in peripheral nerves was described with
emphasis on making functional use of natural sensors in FES systems. An
important area not being dealt with in this paper is the multitude of different
electrode designs which have been used and are being developed for recording
(and stimulation) of peripheral nerves (Naples et al., 1988; Struijk et al.,
1995). Future developments of cuff electrodes will probably focus on
fabrication methods, such as the use of thin film electrodes, addition of
electronics on the cuff, improvement of signal to noise ratio, cuffs for
fascicle selective recordings (Struijk et al., 1997; 1999), and signal
processing (Upshaw and Sinkjær, 1998; Sinkjær et al., 1998, Jezernik et al.
this meeting). In this respect, it is important to evaluate the long-term
implant of such electrodes (Slot et al., 1997; Larsen et al., 1998).
Application of the cuff in FES can also be used for sensing of proprioceptive
information from, for example, muscle afferents (Jensen et al.; Micera et al –
this meeting) to control joint positions and in cognitive feedback systems
(Riso, 1999). Cuff electrodes may thus be a valuable part to provide sensory
feedback information in fully implantable FES systems. For a detailed description
on applying cuff electrodes for long-term implants in humans, see Sinkjær et
al. (1999).
The Danish National Research Foundation,
The Danish Research Councils, The European Research programmes BIOMED-II and
TMR, Villum Kann Rasmussens Foundation, and The Obel Family Foundation are
kindly acknowledged for financial support.
Childs C et al., this meeting.
Haugland M.K., Lickel A., Haase J., Sinkjær T. Hand
neuroprosthesis controlled by natural sensors. IEEE Trans. Rehab. Eng., In
press, (1999).
Haugland M.K., Sinkjær T. Cutaneous whole nerve
recordings used for correction of footdrop in hemiplegic man. IEEE Trans.
Rehab. Eng., 3 (1995), pp. 307-317.
Inmann, A. et al., this meeting.
Jensen, W. et al, this meeting.
Jezernik S., Wen J.G., Rijkhoff N.J.M., Djurhuus J.C., Sinkjær T.
Analysis of nerve cuff electrode recordings from preganglionic pelvic nerve and
sacral roots in pigs. J. Urology, Submitted, (1999).
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recordings. IEEE BME Journal, Accepted (1999).
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