neuroConn DC-Stimulator, User Manual

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Chapter 2 - Safety
15
Histological limit for the duration of DC current applications
To avoid permanent injury of tissue, duration of DC current applications should be
temporary. The charge per surface area should not exceed a value of 216 C/cm
² .
E.g.: Using electrodes with a surface area of 35 cm ² with a current of 1 mA over a
period of 15 min applies a charge of 0.025 C/cm ² .
To calculate the charge per surface area for intermittent DC current, the current density
must be included as well as the number of pulses and its duration.
Safe stop mode
At high currents, aborting the stimulation causes an unpleasant, sometimes even painful
“current leap” for the patient. The “safe stop mode” can prevent this by reducing the current
slowly and continuously (1 mA per second) down to 0
µ A.
The “safe stop mode” is active in any stimulation mode and works during either manual and
automatic abortion since it exceeds thresholds of impedance, current or voltage, as well as
during the turning on and off the device.
The output current is continuously monitored by the microcontroller program, but
it needs a finite time to discover high impedances and start the “safe stop mode”
procedure. If there is a very short lasting interruption of the current path that lasts
in the order of 200-500 ms or less the stimulator will not detect it. Short
interruption of the current path has to be avoided during direct current stimulation.
Do not disconnect the electrodes if current is flowing for this will cause a strong
stimulus to be delivered.