repetitive nerve stimulation
TRANSCRIPT
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Repetitive Nerve Stimulation
Centre for converging technologies
UOR, Jaipur
Name: Mohit kumar pate
IX sem
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PLAN OF THE TALK
Physiology of Neuromuscular junction
Procedure, technical aspects
Interpretation
Application in various conditions
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RNS-TECHNIQUE
RNS study is one of the most useful electro
diagnostic test for diagnosing pre- and postsynaptic
neuromuscular transmissions.
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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
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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
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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.
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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
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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.
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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
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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.
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STIMULUS TECHNIQUE
Best at 3-5 hz
Decrement increases with stimulus rates up to
10hz.
Higher rates cause movement artifacts and painful
Pseudo facilitation
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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
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LOW RATE RNS
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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
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HIGH RATE RNS
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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
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MYASTHENIA GRAVIS
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THANK YOU