Evoke
®
SCS System Clinical Manual
CLIN-UMAN-005175
Revision: 9.00
Page 53 of 101
7.8.2
Chronaxie and rheobase measurement
Collect data to estimate the chronaxie and rheobase of the stimulated neurons
.
The chronaxie
and cheobase measurement involves automatically increasing then decreasing current at
different pulse widths. Stimulation may be stopped at any time with the Stop button
.
To perform a chronaxie and rheobase measurement:
1.
Ensure the electrode configuration has been optimized for ECAP measurement.
2.
Touch
Chronaxie & Rheobase
from the neurophysiological measurement menu.
3.
Use the sliding scale to input the
maximum charge factor (default is 0.8,
see
Section 20.4 for definition) and touch
Continue
.
4.
Use the sliding scale to input the current
ramp
speed (default is 20 steps) and touch
Continue
.
5.
Touch
Yes
if you wish to set the program parameters to the chronaxie and rheobase
measurement defaults.
6.
Touch
No
if you wish to use the existing program parameters.
Note:
The pulse width must be greater than 240µs.
7.
Start stimulation with closed-loop disabled and then touch
Continue
.
8.
Ask the patient to remain still for the duration of the test and to inform you if the
stimulation becomes too strong. Inform the patient that the stimulation current and
pulse width will be automatically adjusted by the CPA during the measurement.
9.
With the patient ready to begin, increase the current until the patient reports that it is
at the maximum level (can tolerate for approximately 1 minute).
10.
Touch
Continue
to begin data collection.
Note:
Begin the test immediately after increasing the stimulation current to maximum
(Step 9) in order to minimize patient discomfort.
11.
Touch the
Pause
button, at any time, to stop the current changing. This may be
required if the patient does not want the stimulation to increase any further. The
current will then remain constant until you press one of the following buttons:
a.
Touch
Resume
to continue changing current in the same direction.
