F-wave, A-wave, H reflex (partially done)

Question 1

What is the F-wave

Answer 1

• Long latencyof motor nerve conduction stimulus (after the M wave of MNCS)
• Generated by supramaximal stimulation
• Due to antidromic motor nerve conduction (antidromic-> ventral horn-> activates motor neuron -> orthodromic -> F wave)
• Allows assessment of the proximal portion of LMN, including the ventral horn
• Purely motor event

See slide 7

Question 2

Clinical applications

Answer 2

• assess ventral nerve root and proximal portion of motor nerves
• measure of motor neuron excitability

more details slide 12

Question 3

More proximal stimulations cause ____ M wave latency and ____ F wave latency

Answer 3

Longer M latency
Shorter F latency

Question 4

F-wave amplitude….

Answer 4

< 3% M wave amplitude in dogs
(only 1-5% neurons are reactivated)

Question 5

F-wave latencies…

Answer 5

Conduction time between the stimulation site and spinal cord.

Shortest latencies = largest/fastest motor axons

Are influenced by limb lenght

Question 6

Delay in F-wave latency suggests…

Answer 6

Slowing of motor axon conduction

Question 7

What is chronodispersion?

Answer 7

• dt between max - min F wave latencies (slowest - fastest nerve conductions)
• Indicates degree of temporal dispersion between stimuli

Question 8

How is measuring F wave conduction velocity clinically useful?

Answer 8

To compare with distal conduction velocities. Useful in peripheral neuropathies.

Question 9

Central latency?

Answer 9

= (Lat F - Lat M - 1) / 2

Question 10

F-wave ratio?

Answer 10

= (Lat F - Lat M - 1) / (2xLat M)

not influenced by limb length

Question 11

What means..

a) ↑ F ratio ?
b) ↓ F ratio ?

vs references values

Answer 11

a) ↑ F ratio = more proximal lesion
b) ↓ F ratio = more distal lesion

Question 12

Axon reflex

What is the A-wave (axon reflex)?

Answer 12

• Intermediate latency component, between M and F waves.
• Small motor potential with identical latency at each stimulation
• Generated by submaximal stimulation
• Due to collateral sprouting in the proximal portion of the nerve in chronic neuropathies (antidromic -> back down the nerve branch).

Slide 34

Question 13

H reflex

H reflex

Answer 13

Slide 35-51

Question 14

CDP

What is the Cord Dorsum Potential (CDP)

Answer 14

• Field potential recorded from spinal cord intumescences
• Generated by supramaximal stimulation of periphearl nerves
• Purely afferent (sensory) events
• Useful to assess:
  — Proximal sensory nerves
  — Dorsal nerve roots
  — Dorsal horns (spinal cord)

Question 15

CDP

3 components of CDP waveforms

Answer 15

A) Small triphasic wave
B) large neg peak (actual CDP) = depolaraization of dorsal horn interneurons
C) Late positive phase

Question 16

CDP

How can we abolish CDP artifacts from muscle contraction?

Answer 16

Atracurium

Question 17

CDP

Define
a) onset latency
b) onset to peak latency

Answer 17

a) from stimulus -> takeoff of initial phase (A)
b) from stimulus -> peak of actual CDP (B)

Slide 66 + 72