H. Kern*, C. Hofer*,
M. Mödlin, C. Forstner, D. Raschka-Högler, W. Mayr**, H. Stöhr***
*Ludwig Boltzmann Institute of Electrostimulation and Physical
Rehabilitation,
Department of Physical Medicine,
**Department of
Biomedical Engineering and Physics,
***Department of
Biomedical Research,
SUMMARY
Prior clinical work showed that electrical stimulation
therapy with exponential current is able to slow down atrophy and maintaining
the muscle during non permanent flaccid paralysis. But exponential currents are
not sufficient for long-term therapy of denervated
degenerated muscles (DDM).
We initiated a European research project investigating
the rehabilitation strategies in human but also studying the underlying basic
scientific knowledge of muscle regeneration from satellite cells or myoblast activity in animal experiments.
The necessary stimulation parameters used in the prior
studies that are sufficient for long-term treatment of DDM are forbidden by
current EU regulations. In spite of this fact we were able to show that
stimulation training of denervated degenerated
muscles is possible. At beginning of training only single muscle twitches can
be elicited by biphasic pulses with durations of 120 – 150ms. Later with an
improved structural and metabolic muscle state the tetanic
contraction of the muscle with special stimulation parameters (pulse duration
of 30 – 50ms, stimulation frequency of 16 – 25Hz,
pulse amplitudes of up to 250mA) can be achieved /14/. Since there are no nerve
endings for conduction of stimuli large size anatomically shaped electrodes are
used for stimulation. The electrodes made of soft conducting rubber are applied
with a wet sponge cloth or gel directly to the skin. This ensures an evenly
contraction of the whole muscle.
PRIOR RESEARCH
In the last 15 years we examined the possibility of
training denervated human muscles by means of
functional electrical stimulation (
In patients with complete conus
cauda lesion (Frankel A) was examined if by using
appropriate electrical stimulation muscular degeneration could be prevented and
and already degenerated muscles could be improved to
an extent that tetanic contractions and functional
movements could be triggered using FES. These patients started training with
electrical stimulation within the first 2 years after the lesion. Tetanic muscle contractions with knee extension moments of
about 20Nm could be obtained after one and a half year.
Muscle training was begun in the sitting position with
single twitches (biphasic rectangular pulse, average pulse width 120 ms). Later
on training with tetanic contraction cycles (on: 2
seconds, off: 2-4 seconds) was performed. Initially without weight until nearly
complete knee extension was achieved and later with weight cuffs 0,5 – 1 kg on the ankle (8 – 12 repetitions, 4 - 6 series,
once a day).
Improvement in muscle force (+60%) and muscle
cross-section area (about 35%) within 1 year of tetanic
muscle training was documented by means of torque measurement and computer tomography respectively.
As knee
stabilization in the standing position requires relatively low muscle force and
standing up is supported by the upper body, standing training can be started
early on. In our patients
CLINICAL PROBLEMS
OF
The prior study showed that denervated
muscle can be treated with electrical stimulation, but at the same time
highlighted problems that remain unsolved:
1.
Maximum time span between injury and onset of
stimulation training where successful restoration of DDM is still achievable
2.
Slow increasing contraction force
3.
Daily time expenditure for training is very high
4.
High variation in developed contraction force (knee
extension torque varies 20-25%) due missing warning signal in case of overstraining
the muscle like pain or co-contraction that are reducing the knee extension
torque
5.
Muscle endurance is very low despite daily training of
up to 2 x 30min.
Maximum time span elapsed after denervation
Stimulation therapy for denervated
musculature should start within 5 years after denervation.
After 5 years degeneration of muscle with connective tissue and fat is
progressed so far that restoration of muscle tissue is hardly achievable. But
to date 2 patients with a complete conus
cauda lesion started stimulation after about 25 years
and 1 patient with a plexus lesion started stimulation after 12 years are
participating in our program.
The underlying mechanism of regeneration of denervated degenerated muscle and the factors triggering this mechanisms are at present unknown. Especially if there
is a spontaneous regeneration of myoblasts
(autonomous regeneration) or an electrically induced activity of satellite
cells is to be answered still.
Long time span for hyperplasia
and hypertrophy
If training with
This explains the slow increasing muscle force and
combined with it the slow functional improvement of the muscle.
Intramuscular structural
changes are much bigger than measurable gain of muscle force because of
connective tissue and fat as well as broken sarcomeres
have to be transformed and rebuilt.
Daily training time expenditure
Due to the fact of missing nerves and thus no
distribution of the stimulation pulses each muscle or muscle group respectively
has to be trained individually. Treatment of multiple muscles is impossible
because of technical limitations regarding the maximum stimulation current.
Connective tissue and fat acting as an electrical shunt are reducing the
difference of electrical potential that is needed to excite the muscle cell
membrane. The decreased membrane resting potential and the reduced metabolism
of the muscle fiber seem to be the reason for the long pulse duration and the
slow twitch character and fatigue of the muscle.
High variations in developed knee extension torque
In spite of continuous
Different co-activation of the hamstrings by the
electrical field distributed over the whole thigh could be one of the effects
causing this variations. Another reason for this
effect could be a local overstrain of the muscle that is not prevented because
of missing warning signals like pain. An accompanying monitoring of CPK acting
as an indicator for muscle overstrain would be
desirable in the future. We did not perform in our outpatients this monitoring
of CPK because of its short half-life period and the necessary frequent
measurements.
Endurance of muscle is very low
In the experimental work already done the
concentration of aerobe muscle enzymes recovered up to the normal range.
Nevertheless muscle endurance during standing exercises with switching
stimulation alternating left and right (simulation of gait) was not very high.
With this intermitting stimulation (1s on- 1s off-time) sufficient blood
circulation was ensured, but the stimulated musculature fatigued very fast.
This behavior might be caused by the long diffusion
distance between the capillaries and the muscle fibers because of the intrafibrillary located mitochondria in electrically
trained muscles. Contrary to voluntary trained muscle where the mitochondria
are subsarcolemmal located. These observations and
the hypothesis regarding the long diffusion distance are to be proved in the
proposed European project. Additionally should be examined if the site of
mitochondria formation could be influenced by
/1/
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/2/
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/3/
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/4/
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/6/
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/12/
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/13/
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/15/
/16/
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Univ. Doz. Dr.
Dr.
Helmut
Kern
Ludwig Boltzmann Institute of
Electrostimulation and Physical Rehabilitation,
Department of Physical Medicine and Rehabilitation,
Wilhelminenspital
Wien
Montleartstrasse
37
A-1171 Wien helmut.kern@phys.wil.magwien.gv.at