pitfalls in measuring jitter: drink deep, or taste not the pierian … · 2019. 10. 8. · pitfalls...
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Pitfalls in Measuring Jitter: Drink deep, or taste not the Pierian springDonald B. SandersDuke University Medical Center, Durham, NC
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Pitfalls of voluntary jitter studies• Mis-triggering• VRF effects due to inconstant firing rate• Triangular after-potentials• Low jitter due to split fibers• Riding potentials• Jitter in the triggering potential of multispike
potentials• Bimodal IPI latency (e.g., ”flip-flop”)• Unacceptable CN electrode signals
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Mis-triggering
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Inconstant Firing Rate
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Riding Potentials
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Riding signals: IPIs measured at
amplitude levels vs peaks
Acquisitiontrig level
startVoltage
levels
peaks
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Jitter in the Triggering Potential
Stålberg, Sanders & Kouyoumdjian: Pitfalls & errors in measuring jitter, 2017
1 to 2 1 to 3
2 to 1 2 to 3
3 to 1 3 to 2
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Stålberg
Bimodal Jitter – “Flip-Flop”
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Acceptable CNE Signals
OK
No No
ok
nono
ok
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Unacceptable CNE signals
Composite spikes
Rising phase not smooth (visible notches or “shoulders”
Shape not constant in consecutive discharges
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Unacceptable CNE Signals
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Pitfalls of stimulated jitter studies
• Liminal stimulation• Direct muscle fiber stimulation• VRF effect
o at beginning of traino with change in stimulation rate
• F-waves• Axon reflex
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Liminal Stimulation
Kouyoumdjian
b
b
bb
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Liminal Stimulation
Kouyoumdjian
b
b
bb
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Axonal stim.Jitter > 5 µs
Direct muscle fiber stimulation
Jitter < 5 µsdirect stimulation axonal stimulation
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VRF effect at change in stimulation rate
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F-Waves
Effect of occasional F-waves on the following M-latency
Stålberg, Trontelj & Sanders: Single Fiber EMG, 2010
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“Axon Reflexes”
Weak axonal stimulation produces retrogradeactivation of the recorded fiber ( ).
Stålberg, Trontelj & Sanders: Single Fiber EMG, 2010
recordingelectrode
Stronger stimulation ( ) directly activates thebranch with shorter latency.
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Quality control while recording
• Acquire clean sharp signals meeting SFAP criteria.
• Maintain stable electrode position.
• Set good trigger position.
• Look & listen for blocking.
• Maintain steady firing rate.
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• Review data – look at:• Superimposed signals• Sequential histogram
• Confirm stable trigger point.• Confirm blocking.• Calculated values should be consistent
with subjective impression.
Quality control during analysis
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Quality control during interpretation
• Should be consistent with clinical and other neurophysiological findings.
• Increased jitter ≠ MG. Other conditions must be excluded.
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Drink deep, or taste not the Pierian spring
• A little learning is a dangerous thing;drink deep, or taste not the Pierian* spring:there shallow draughts intoxicate the brain,and drinking largely sobers us again. Alexander Pope, An Essay on Criticism, 1709
*A fountain in Pieria, sacred to the Muses and supposedlyconferring inspiration or learning on anyone who drank from it.
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