Rapid Nerve Stimulation study

1. Repetitive Nerve Stimulation :
Dr.Roopchand.PS
Senior Resident Neurology
TDMCH, Alappuzha

2. Neuro-Muscular Junction:
• Ach released in quanta.
• Each quanta – 10000
Ach
• Three stores of Ach
quanta.
– Primary(1000 quanta)
– Secondary(10000)
– Reserve(100000)

3. • 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)

4. • 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.

5. 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.

6. Modeling of slow RNS:

9. 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.

10. 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.

11. 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.

16. Typical Pattern in Myesthenia:

17. 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.