Repetitive Nerve Stimulation

Centre for converging technologies

UOR, Jaipur

Name: Mohit kumar pate

IX sem

PLAN OF THE TALK

Physiology of Neuromuscular junction

Procedure, technical aspects

Interpretation

Application in various conditions

RNS-TECHNIQUE

RNS study is one of the most useful electro

diagnostic test for diagnosing pre- and postsynaptic

neuromuscular transmissions.

DEFINITIONS

Quantum. A quantum is the amount of Ach packaged in a single vesicle.

Each quantum (vesicle) 1 mV change of postsynaptic membrane potential.

Rest, MEPP

The number of quanta released after a nerve action potential depends on the number of quanta in the immediately available (primary) store and calcium stores

Normally 50-300(60) vesicles

DEFINITIONS

End plate potential -EPP is the potential generated at the postsynaptic membrane following a nerve action potential and neuromuscular transmission.

60 mV change in the amplitude of the membrane potential.

Safety factor. The safety factor of neuromuscular transmission is simply defined as the difference between the EPP and the threshold potential for initiating an action potential.

MFAP

CMAP

CALCIUM AND QUANTA DYNAMICS

calcium :diffuses slowly out of the presynaptic terminal in

100–200 msec.

Ach stores: immediately available (primary) store and

secondary (or mobilization) store

Inter stimulus interval

rapid RNS (more than every 100 msec, or stimulation

rate >10 Hz), calcium influx is greatly enhanced and the

probability of release of Ach quanta increases.

RNS-TECHNIQUE

RNS is performed on selected motor nerves with

recording by surface electrodes.

G1-motor point,G2-tendon

Supramaximal stimulus

Initial sharp negative deflection

MUSCLE SELECTION

Clinically weak muscles should be selected.

Usually facial and proximal limb muscles shows greater

abnormality than distal muscles.

Cholinesterase inhibitors should be stopped 12-24 hrs

before.

MACHINE SETUP FOR RNS

Sensitivity (mV/div) 2-5

Sweep time (ms/div) 2

Low filter (Hz) 2-5

High filter (KHz) 2-3

Stimulus duration (msec) 0.1

Stimulus rate -low <5

Stimulus rate -high 30-50

IMPORTANT POINTS:

Immobilization and isometric electrode position.

Supramaximal stimulus

Temperature must be controlled

AchI withheld 4 hrs prior to study.

Proximal site better than distal site

Distal easy; proximal difficult.

STIMULUS TECHNIQUE

Best at 3-5 hz

Decrement increases with stimulus rates up to

10hz.

Higher rates cause movement artifacts and painful

Pseudo facilitation

LOW RATE RNS supra maximal CMAP

3–5 stimuli to a mixed or motor nerve at a rate of 2–3 Hz.

slow enough to prevent calcium accumulation, high enough to deplete the quanta

maximal decrease in Ach release occur after the first four stimuli

reproducible decrement

exercises for 10 seconds to demonstrate repair of the decrement (‘‘post-exercise facilitation’’)

No decrement-1 minute max voluntary exercise –post exercise exhaustion

LOW RATE RNS

HIGH RATE RNS

optimal frequency is 20–50 Hz,for 2–10 seconds

brief (10-second) period of maximal voluntary

isometric exercise has,the same effect as rapid

RNS

Depletion of quanta vs calcium accumulation

Incremental response in LEMS

HIGH RATE RNS

RNS IN PRE AND POST SYNAPTIC DISORDERS

Parameter Pre-synaptic Post-synaptic

CMAP amplitude Small Normal

Low rate RNS Decrement Decrement

High rate RNS Increment Decrement or normal

MYASTHENIA GRAVIS

THANK YOU