strength duration curves procedure

PROCEDURE MANUAL –ELECTROTHERAPY 1

Procedure 10 ELECTRODIAGNOSIS

SD CURVE

Aim : To plot SD curve for various major nerves in the body .

Apparatus : Electrical stimulator with Diagnostic interupted Galvonic current facility

1. Skin resistance tray consisting of

a) bowl of tap water

b) soap

c) macintosh

d) kidney tray /plastic bowl

e) towels & tissue paper

2. Treatment tray consisting of

a) Leads

b) electrodes

c) Lint

d) 1% saline warm water in plastic bowl .

e) Supporting pads,pillows

f) Cotton

g) Talcum powder

h) Vaseline

i) Towels

j) Velcrow straps /adhesive plaster

GOWRISHANKAR


Procedure :

1. Greet the patient 2. Introduce yourself to the patient.3. Take preliminery introduction and brief history from the patient.

Method of application :

Preparation of the apparatus :

First an electric stimulator with Diagnostic interupted Galvonic current facility is selected.

Make sure that all the wires from mains to plug box and to the machine are intact and properly insulated

Check the leads for any breaks in the insulation

Test the machine by attaching leads and electrodes to the terminals and feel the current by switching ‘on’ the machine and increasing the intensity

Make sure that before ‘on’ or ‘off’ an apparatus ,all the knobs of intensity are at ‘zero’

Select the appropriate and suitable electrode

The electrodes should be properly linted.

The inactive electrode is applied to some convinient area usually on the mid line of the body ,or over the origin of the muscle.

The active electrode is usually a pen electrode.

To assess a nerve, we choose a proximal muscle and a distal muscle supplied by that nerve in its course.

The active pen electrode is placed over the motor point of the muscle to be tested

The longest pulse duration is choosen first and the intensity of the current is increased until the minimum observable contraction is obtained.

Note the intensity of current and reduce the intensity to zero

Now shift the duration to secong longest duration and repeat the procedure.

GOWRISHANKAR


Note the intensity of current required to get the similar and equal contraction for various durations as described below.

Duration (millisec) Intensity (milli amp)

300

100

30

10

3

1

0.3

0.1

0.03

0.01

Now plot on a graph paper by taking duration on X-axis and intensity in Y-axis

SD curve is drawn by connecting the plotted points.

Inference:

By plotting the curve ,we can know whether a nerve is :

a) Completely innervated

b) Completely denervated

c) Partially innervated and partially denervated

Then, find the rheobase and chronaxie.

Rheobase: the rheobase is the smallest current that will produce a muscle contraction.

Chronaxie : it is the duration of the shortest impulse that will produce a response with a current of double rheobase.

GOWRISHANKAR


Winding off:

Remove the electrodes and clean the area with a tissue or cotton.

Check the area for any adverse eefects, if found any document it and report to the HOD or your supervisor.

ADVANTAGES :

Can determine the extent of degeneration in the nerve.

To identify and estimate prognosis

To plan the therapy.

GOWRISHANKAR