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Conformity with the following standards:
EN 60 601-1; 14971:2000; EN 60601-1-1; EN 60601-2-10; EN 60601-1-4
EN 60601-1-2; 13485:2003/ AC2007; 9001:2000; UL 60601; MPG; HWG, Directive 93-42-EC
2.4 Constant voltage or constant current
According to Ohm‘s law U
⫽
R
⫻
I, it is possible to use both, the voltage and the current intensity as the
quantity to be measured to determine the intensity (amplitude) of the electrical stimulus. The devices
are respectively referred to as voltage-constant or current-constant.
The electrical resistance (impedance) in the electrical circuit of a stimulation, which represents the
sum of skin-, tissue-, cannula-, electrode cable-resistance etc., will vary within wide ranges. It may vary
between < 1 k
⍀
and infi nite. The factors skin humidity, conductivity of the skin and of the tissue and
the potential resistance of the adhesive electrode can hardly be infl uenced.
If the voltage (V) is selected as the measure for the intensity of the stimulus impulse, then currents may
appear during an application, which – in accordance with Ohm‘s law and depending on the resistance
– will differ by a manifold.
It is therefore better to use a nerve stimulator which permits the exact adjustment of the current inten-
sity (mA) between the two electrodes, the adhesive electrode (anode) and stimulation cannula (cath-
ode).
The stimulator with constant current setting must, however, be provided with a very high output
impedance – ideally infi nite – so that the resistances which may perhaps occur in the external electri-
cal circuit will be negligible, and so that the actually fl owing current will be indicated exactly on the
display.
Current-constant devices which permit the selection of the current intensity (mA) for the stimulus
impulse have gained acceptance within the last few years.
For the MultiStim SWITCH, the external load resistance can amount to as much as 12 k
⍀
. If this load
resistance is exceeded, then the actually fl owing patient current (the actual stimulation current) can be
lower than the adjusted nominal stimulation current. In this case, the nominal stimulation current and
the actual stimulation current are indicated separately and visual and acoustic warning indications are
emitted. And the relevant impedance is continuously calculated and indicated on the LCD-display in
addition.
The MultiStim SWITCH is a precision instrument for the localization of nerve tracts in the human
organism. It was developed to stimulate nerve fi bers in the living organism using cannulae and special
catheters for invasive stimulation which normally show a very high contact impedance, to be able to
determine the spatial position of these nerve fi bers in relation to the tip of the electrode. The stimula-
tion cannulae are designed so that a local anesthetic can be injected in the proximity of the nerve fi ber,
which will cause a reversible interruption of the conductive system.
2.5 Accessories
The MultiStim SWITCH can (unlike the model SENSOR) be exclusively connected with a patient cable
for cannula and catheter:
Yellow connection: CATHETER
White connection: CANNULA
Clamp for adhesive electrode
In addition patient main cable for cannula stimulation only is available:
White connection: CANNULA
Clamp for adhesive electrode
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XS190174B MultiStim SWITCH GB.indd 28
XS190174B MultiStim SWITCH GB.indd 28
12.03.10 13:53
12.03.10 13:53
