This document discusses techniques for performing blink reflex testing, H-reflex testing, and single-fiber electromyography (SFEMG). It provides details on electrode placement, machine settings, normal values, and clinical implications for each test. The blink reflex assesses the trigeminal and facial nerves, while the H-reflex evaluates the tibial nerve and S1 root. SFEMG precisely detects abnormalities in individual motor unit action potentials, such as increased jitter or blocking, which can localize neuropathies or myopathies.

1. Blink Reflex, H Reflex,
SFEMG
~Dr VAIBHAV KUMAR SOMVANSHI
DM Neurology Resident

2. Blink Reflex
 1. Position - supine with the eyes either open or gently closed.
 2. Recording - both orbicularis oculi muscles simultaneously.
 3. Active electrodes - below the eye just lateral and inferior to the pupil at mid-
position
 4. Reference electrodes - lateral to the lateral canthus.
 5. Ground electrode - mid-forehead or chin.
 6. Stimulation - supraorbital nerve over the medial eyebrow
 7. Recording - orbicularis oculi bilaterally.
 9. For each side, four to six stimuli are obtained and superimposed to determine
the shortest response latencies.

3. Schematic Representation
Chusid JC. Correlative Neuroanatomy and Functional Neurology. 18th ed. Stamford, CT: Appleton & Lange; 1982, with permission.

4. Settings of machine
Technical factors Recording parameter
Nerve to be stimulated Supraorbital nerve
Site o stimulation Supraorbital notch
Stimulating electrde Active midway below lower eyelid
Reference nasal bone
Ground chin
stimulator Cathode in the notch anode laterally
Stimulus rate 0.2-0.3 Hz
gain 200-500 µV/division
Sweep 5-10ms/division
Filter High pass- 10 hz
Low pass – 10k Hz
Total stimulus 4-6 stimulus for each side

5. Normal vs Abnormal Patterns
Normal Values:
Absolute-
R1 latency <13ms
I/L R2 <41ms
C/L R2 <44ms
Comparative-
R1<1.2ms
I/L R2 <5ms
C/L R2 <7ms

6. Clinical implication
 Electrical analogue of corneal reflex
 Unilateral trigeminal or facial lesion
 Unilateral mid-pontine lesion
 Unilateral medullary lesion
 Demyelinating peripheral neuropathy

7. Lesion localization with Blink Reflex

8. H-Reflex
 Paul Hoffmann – first evoked the response in 1918.
 Unlike the F response that can be elicited from all motor nerves, the distribution of
the H reflex is much more limited.
 In newborns, H reflexes are widely present in motor nerves, but beyond the age of
2 years, they can only be routinely elicited by stimulating the tibial nerve in the
popliteal fossa and recording the gastroc-soleus muscle.

9. G1 is placed over the soleus, 2–3 fingerbreadths distal to the gastrocnemius
muscle
G2 over the Achilles tendon
The tibial nerve is stimulated submaximally in the popliteal fossa
Cathode placed proximal to the anode.

10. Position
 Pt should be lie in prone position with thigh and leg supported
 Feet should hang freely with dorsum hang at right angle to tibia

11. Machine settings
Technical factors Recording parameter
Nerve to be stimulated tibial nerve
Site o stimulation Popliteal fossa
stimulator Cathode proximal to anode
Stimulus rate 0.2-0.5 Hz
gain 200-500 µV/division
Sweep 10ms/division
Filter High pass- 10 hz
Low pass – 10k Hz
Total stimulus 10 stimulus

12. With increasing stimulation, the H wave grows
and the M response appears.
At higher stimulation, the M potential continues
to grow and the H reflex diminishes, due to
collision between the H reflex and antidromic
motor potentials

13. Reference Normal value

14. Clinical Implications
 GBS
 S1 radiculopathy
 C6-C7 radiculopathy – FCR

16. SFEMG
 Single-fiber EMG method of recording AP of Single muscle
fiber
 Muscle fiber diameter – 40-70 µm
 Recording area - 25µm2
 Needle insertion – 20-30 degree to skin
 Most commonly tested muscle – EDC – superficial, easily
acccesible
 Patient should be alert, co-operative and able to maintain 3
minute contraction

18. Machine settings
Technical factors Recording parameter
Muscles EDC, frontalis
Angle of insertion 20-30 degree to skin and inserted till hub and then
retracted little
electrode Active over the target muscle
Reference near by to active electrode
SFEMG 2cm distal to eectrode over visible twitch
stimulator Less than 5mA
Stimulus rate 2-10 Hz
gain 200-500 µV/division
Sweep 10ms/division – fiber density
100-500 µs/division - jitter
Filter High pass- 500hz
Low pass – 10k Hz
Constant contractions – Motor unit firing rate 15-18 Hz

19. Jitter
 Time interval between two potentials –
trigger, slave  varies from one discharge
to another.
 This interpotential variability is K/a jitter
 Jitter considered abnormal if either of
following present

20. Blocking
 Increase in jitter so much that leads to failure of impulse transmission – Blocking 
absence of one potential of pair
 Blocking typically occurs when jitter value exceed – 80-100ms

21. Fiber density
 Number of fibers from 1 motor unit within 300µm2 radius of SF needle.
 increases with age
 Sweep speed – 10ms/division
 Calculation  total number of spiky potential/ total number of potentials

22. Duration of SF potential
 Onset of 1st deflection of the 1st potential to return of the last component to
baseline
 Normal  below 4ms
 Duration and amplitude is proportional to fiber density.

23. Clinical Implications
 NMJ discorder – increased jitter with or without increased in density
 Neuropathy – increased jitter with increased density
 ALS - increased jitter with modest increased density (denervation excedds
reinnevration)
 Myopathy (DMD) - increased jitter with
modest increased density.

25. Schematic representation showing
relationship b/w jitter & fiber density

26. Learning Points

28. References
 Electromyography and Neuromuscular Disorders; David C. Preston, MD; Barbara
E. Shapiro, MD, PhD chapter 6,23,24,25.
 Boonyapisit K, Katirji B, Shapiro BE, et al. Lumbrical and interossei recording in
severe carpal tunnel syndrome. Muscle Nerve. 2002;25:102–105.
 Cartwright MS, Walker FO. Neuromuscular ultrasound in common entrapment
neuropathies. Muscle Nerve. 2013;48(5):696–704.