Repetitive Nerve Stimulation :

Dr.Roopchand.PSSenior Resident Neurology

TDMCH, Alappuzha

Neuro-Muscular Junction:

• Ach released in quanta.• Each quanta – 10000

Ach• Three stores of Ach

quanta.– Primary(1000 quanta)– Secondary(10000)– Reserve(100000)

• Calcium influx at depolarized presynaptic junction.

• Calcium influx α Ach released.• Ach binds to AchR on post synaptic membrane

fold crests.• Sodium channels open to produce End Plate

Potentials (EPP)• EPP α Amount of Ach binding to AchR.• EPP above threshold produces an all or none

Muscle Fiber Action Potential (MFAP)

• Safety Factor: The amplitude of EPP above threshold value required to generate a MFAP.

• Ach broken up in the synaptic cleft by Ach esterase.

• Choline taken up in to presynaptic cleft.

Physiologic modeling of RNS:1. M= pn– M: number of quanta released– P : probability of release (0.2)– N: number of quanta in primary store(1000)

2. Secondary store replenishes the primary after 1 to 2 seconds.

3. 100msec required to pump calcium out of presynaptic terminal– Stimulation rated > 10hz cause calcium accumulation.

Modeling of slow RNS:

Modeling of Rapid RNS(30-50Hz):With rapid RNS, the Depletion of quanta is counterbalanced by (1) increased Mobilization of quanta from the

secondary to the primary Store (2) (2) calcium accumulation in the presynaptic

terminal increases p, the probability of release.

Exercise testing:

• Subject asked to voluntarily contract muscle with maximum force.

• Motor units fire at maximal rate (30-50Hz).• Same effects as Rapid RNS.• Effects occur with brief periods of excercise

(typically 10 sec).– Post exercise or post tetanic facilitation.

LAB Practice:• Postexercise facilitation and

exhaustion Three-Hertz repetitive nerve stimulation in a patient with myasthenia gravis

• A: Decrement of compound muscle action potential (CMAP) amplitude at rest.

• B: Postexercise facilitation, Decrement of CMAP immediately following 10 seconds of maximal voluntary exercise has repaired toward normal.

Typical Pattern in Myesthenia:

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.

Thank You