NCV Flashcards
Definition of anode and cathode?
Anode = positive = reference
Cathode = negative = recording / active
Definition of threshold, maximal, and supramaximal stimulus?
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.
Which kind of axons are evaluated by the onset latency
Onset latency: conduction time of the fastest conducting axons.
Which nerve has the greatest MNCV between ulnar, peroneal, and tibial nerves?
peroneal > tibial > ulnar
What is the definition of physiologic temporal dispersion?
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)
What is the definition of phase cancelation?
the increase in latency difference may line up the positive peaks of fastest axons with the negative peaks of slower axons.
What is the definition of residual latency?
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
What is the effect of age on MNC?
- MNCV reach adult value between 6-12 months in dogs (10x) and 3 months in cats.
- Dogs > 7 yo show a gradual decreased in MNCV ; by 10 yo, decreased by 10-15%
- 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
What are the differences between large and thin diameter sensory fibers?
Large diameter sensory fibers have lower threshold and conduct faster (10-15%)
What is the effect of temperature on MNC?
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
What is the effect of age on SNC?
SNCV reduced by 10 m/s over 9 yo
What are the causes of decreased distal tibial SNCV?
Reduced temperature
Decreased internodal distance
Decreased myelinated fibers diameter
Give 5 causes of decreased CMAP amplitude.
Decreased number of axons (axonopathy)
Decreased release of Ach (botulism)
Decreased number of myofibers (myopathy)
Severe temporal dispersion with phase cancellation
Conduction block
SNCV can be reliably recorded in mixed sensorimotor nerves: true or false?
True
Larger diameter sensory fibres have a lower threshold for activation and conduct 5-10% faster than antidromic motor conduction.
In which muscle should be placed the recording electrode for median nerve NCV?
Flexor carpi radialis
The size of the CMAP (amplitude and area) is determined by:
The number of myofibers contributing to it
The number of motor axons stimulated
Another name for a threshold stimulus is:
Submaximal
Supramaximal
Maximal
Ubermaximal
Submaximal
In severely affected patients, which parameters may need to be adjusted to record?
Sweep speed
Sensitivity
Stimulus intensity
Sensory NCV studies are important because:
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
