1 2 . e l e c t r O t H e r a P y t H e O ry
94
EN
WIRELESS PROFESSIONAL
12.1 introduction
In recent years, significant progress has been made in field of electrotherapy of which many users are
still largely unaware. Changes and improvements in electrotherapy are so numerous that this discipline
appears to be a new concept that can only be applied correctly and effectively using sophisticated, high-
tech equipment.
The aim of these articles is to develop this new concept for potential users and provide anyone already
working with this equipment with explanations and data that will allow them, based on current
knowledge and scientific work carried out, to optimise the use of their stimulators.
12.1.1 the fundamental law of electrostimulation
Electrostimulation is a technique which involves producing action potentials in the excitable cells (nerve
and muscle) using an electric current.
Nerve cell membranes have a resting potential with an average value of -70mV, as the internal face of the
membrane has negative polarity compared to the external face.
To excite the membrane of the nervous fibre, i.e. causing an action potential to appear at its surface, the
resting potential simply has to be reduced to a certain threshold value, which is -50 mV on average (Fig. 1).
Once this threshold value has been reached the membrane changes from a state of rest to a state of
activity. An action potential appears which then moves along the nerve fibre. The nerve impulse either
goes towards the muscles to instruct them to contract or returns from the surrounding areas towards the
brain to relay information regarding the senses.
Electrostimulating the nerve fibre essentially involves reducing the membrane’s resting potential to the
threshold value by applying an electric current to the skin.
The first question is, of course, which stimulating current to choose.
Which type of current will we use?
A single current must obviously be used, one which can reduce the resting potential to the threshold value
but keep the patient as comfortable as possible. In other words, the electrical parameters of this current
must be kept to a minimum, and its stimulation energy and duration must be as low as possible.
0
+40
+30
+20
+10
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
Action potential
Threshold
Rest potential
Fig. 1