strength duration curves procedure

PROCEDURE MANUAL –ELECTROTHERAPY 1 Procedure 10

ELECTRODIAGNOSIS ELECTRODIAGNOSIS SD CURVE

Aim : To : To plot SD curve for various major nerves in the body . Apparatus : Electrical stimulator stimulator with Diagnostic Diagnostic interupted Galvonic Galvonic current facility 1. Skin resistan resistance ce tray tray consi consistin sting g of  a) bowl bowl of tap tap wat water er b) soap c) macin acinto tos sh d) kidney kidney tray tray /pla /plast stic ic bowl bowl e) towels towels & tiss tissue ue pape paperr 2. Treatm Treatment ent tray tray cons consist isting ing of  of  a) Leads b) elec electr trod odes es c) Lint d) 1% saline saline warm water in plasti plastic c bowl bowl . e) Suppor Supportin ting g pads,pi pads,pillo llows ws f) Cotton g) Talc Talcum um powd powder er h) Vas Vaselin eline e i) Towels  j) Velcr Velcrow ow straps straps /adhes /adhesive ive plaste plasterr

GOWRISHANKAR

PROCEDURE MANUAL –ELECTROTHERAPY 1 Procedure : 1. Gree Greett the the pati patien entt 2. Introduc Introduce e yours yourself elf to the patient. patient. 3. Take prelimin preliminery ery introduc introduction tion and brief brief history history from the the patient. 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’ ‘off’ an apparatus ,all the 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

PROCEDURE MANUAL –ELECTROTHERAPY 1 •

Note the intensity of current required to get the similar and equal contraction for various durations as described below. Durati ration on (mil (milli lis sec) ec)

Inte Intens nsit ity y (mi (milli lli 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) Comple Completel tely y inne innerva rvated ted b) Comple Completel tely y dener denervat vated ed c) Partially Partially inner innervated vated and and partiall partially y denervated denervated

•

•

•

 Then, find the rheobase and chronaxie. Rheobase: 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

PROCEDURE MANUAL –ELECTROTHERAPY 1 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