NCV

Question 1

Definition of anode and cathode?

Answer 1

Anode = positive = reference​

Cathode = negative = recording / active​

Question 2

Definition of threshold, maximal, and supramaximal stimulus?

Answer 2

Threshold stimulus: one that barely elicits a response in some, but not all, axons in a nerve​

Maximal stimulus: one that activates the entire group of axons, further increase does not cause additional increase in amplitude.​

Supramaximal stimulus: greater than maximal stimulus.

Question 3

Which kind of axons are evaluated by the onset latency​

Answer 3

Onset latency: conduction time of the fastest conducting axons.​

Question 4

Which nerve has the greatest MNCV between ulnar, peroneal, and tibial nerves?

Answer 4

peroneal > tibial > ulnar​

Question 5

What is the definition of physiologic temporal dispersion?​

Answer 5

proximal stimulation gives an evoked potential of slightly longer duration and lower amplitude than distal stimulus. Not seen in distal because axons already tapered and represented very similar axon population (synchronized)​

Question 6

What is the definition of phase cancelation?​

Answer 6

the increase in latency difference may line up the positive peaks of fastest axons with the negative peaks of slower axons.

Question 7

What is the definition of residual latency?​

Answer 7

collective delay through the fine intramuscular nerve branch and at the neuromuscular junction

RL= observed CMAP latency - (distal stimul to recording elect distance)/calclulated distal MNCV

normal in dog/cat <2.5ms

Question 8

What is the effect of age on MNC?​

Answer 8

1. MNCV reach adult value between 6-12 months in dogs (10x) and 3 months in cats.
2. Dogs > 7 yo show a gradual decreased in MNCV ; by 10 yo, decreased by 10-15%​
3. With maturity, CMAP increase in duration due to increase in width and size of the endplate zone and in amplitude due to increase myofiber size​

Question 9

What are the differences between large and thin diameter sensory fibers?​

Answer 9

Large diameter sensory fibers have lower threshold and conduct faster (10-15%)​

Question 9

What is the effect of temperature on MNC?​

Answer 9

1°C decreased in temperature = MNCV decrease by 1.7-1.8 m/s in dogs​

Cold-induced slowing of Na+ channel inactivation -> increase amplitude of nerve and muscle potential​

Question 10

What is the effect of age on SNC?

Answer 10

SNCV reduced by 10 m/s over 9 yo​

Question 11

What are the causes of decreased distal tibial SNCV?​

Answer 11

Reduced temperature​

Decreased internodal distance​

Decreased myelinated fibers diameter​

Question 12

Give 5 causes of decreased CMAP amplitude.​

Answer 12

Decreased number of axons (axonopathy)​

Decreased release of Ach (botulism)​

Decreased number of myofibers (myopathy)​

Severe temporal dispersion with phase cancellation​

Conduction block​

Question 13

SNCV can be reliably recorded in mixed sensorimotor nerves: true or false?​

Answer 13

True​
​
Larger diameter sensory fibres have a lower threshold for activation and conduct 5-10% faster than antidromic motor conduction.​

Question 14

In which muscle should be placed the recording electrode for median nerve NCV?​

Answer 14

Flexor carpi radialis​

Question 15

The size of the CMAP (amplitude and area) is determined by:

Answer 15

The number of myofibers contributing to it​

The number of motor axons stimulated​

Question 16

Another name for a threshold stimulus is:​

Submaximal​
Supramaximal​
Maximal​
Ubermaximal​

Answer 16

Submaximal​

Question 17

In severely affected patients, which parameters may need to be adjusted to record?

Answer 17

Sweep speed​

Sensitivity​

Stimulus intensity​

Question 18

Sensory NCV studies are important because:​

Answer 18

They are quite sensitive, thus able to detect mild or early disease​

They can differentiate neuropathies that are strictly motor or sensory from those that involve both pathways​

They can be performed on several sensory and/or mixed nerves to determine the extent of neuromuscular disease in a given patient​