Document Reference: ENG-UMAN-000731
Revision: 5.00
Page 38 of 61
8.14.3
Chronaxie and Rheobase Test
This program can be used to automatically obtain measures of the Chronaxie and Rheobase
of the stimulated neurons.
Rheobase: The minimum current required to elicit neural activation in the spinal
cord at infinite pulse width.
Chronaxie: The minimum stimulation pulse width required to elicit neural activation
when the amplitude of stimulation current is equal to twice the rheobase current.
The Chronaxie and Rheobase test 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 test:
1.
Ensure the electrode configuration and filter settings have been optimized for ECAP
measurement.
2.
Touch ‘Chronaxie and Rheobase’
from the neurophysiological measurement
menu.
3.
Use the sliding scale to input the
maximum charge factor (default is 0.8)
and touch ‘Continue’.
4.
Use the sliding scale to input the Current
ramp speed (default 20 steps) and touch
“Continue”.
5.
Touch ‘Yes’ if you wish to set the program parameters to the Chronaxie and
Rheobase test defaults.
6.
Touch ‘No’ if you wish to use the existing program parameters.
a.
The pulse width must be greater than 240µs to start the test.
7.
Start stimulation in open-loop mode and then touch ‘Continue.
8.
With the patient ready to begin, increase the current until the patient reports that it
is very strong (maximum).
9.
Touch ‘continue’ to begin test.
Note: Begin the test immediately after increasing the stimulation current to maximum
(Step 8) in order to minimise patient discomfort.
10.
Ask the patient to remain still for the duration of the test and that the stimulation
current and pulse width will be automatically changed by the CPA. Ask the patient
to inform you if the stimulation becomes too strong.
11.
Touch the ‘Pause’
button to stop the current changing. This may be required
if the stimulation becomes too strong. The current will then remain constant until
you press one of the following buttons:
