NERVE CONDUCTION VELOCITY

BASICS

PRINCIPLES ACTION POTENTIAL AXONAL TRANSPORT TYPES OF CONDUCTION CMAP SNAP VARIABLES

PRINCIPLES
Proximal and distal rule Same nerve roots but different peripheral

nerves to localize the changes to one or the other

Proximal and Distal Rule

Proximal-distal rule: motor neurons that innervate distal muscles (e.g., hand muscles) are located lateral to motor neurons that innervate proximal muscles (e.g., trunk muscles)

TYPES OF CONDUCTION
ORTHODROMIC:

Normal physiological direction

ANTIDROMIC:

Opposite to normal physiological direction

Motor unit

VARIABLES AFFCTING NCV

TECHNICAL :

AGE TEMPARATURE SEX DIGIT CIRCUMFERANCE UPPER VERSUS LOWER LIMB

STIMULATION; FAULTY LOCATION OF STIMULATOR FAT AND OEDEMA BRIDGE FORMATION BETWEEN ANODE AND CATHODE

TECHCONTD.
RECORDING:

BREAK IN THE CABLE WRONGLY CONNECTED AMPLIFIER WRONG SETTINGS OF GAIN ,SWEEP,FILTER INCORRECT POSITION OF ACTIVE OR REFERANCE

IN ADVRETANT STIMULATION OF UNWANTED NERVE :

VOLUME CONDUCTION ANAMOLUS CONDUCTION

NERVE CONDUCTION VELOCITY

impulse

TYPES OF NCV
MNCV

SNCV
LATE RESPONSES

H REFLEX F WAVE AXON REFLEX

BLINK REFLEX

TYPES

NCV MNCV SNCV LATE RESPONSES

MNCV

PRINCIPLES OF MNCV
Orthodromic
Motor or mixed nerve is stimulated at least at

two points along it course Pulse is adjusted to get CMAP A Biphasic action potential should be recorded Supra maximal stimulation should be used

ELECTRODE PLACEMENTS
RECORING :

PICK UP : Muscle belly (motor points) REFERENCE :Tendon(3 cm distal to pick up) GROUND : In between pickup and stimulating
Cathode active black - closer to pick up Anode inactive - red

STIMULATING :

MACHINE SETTING
Square wave pulse

Duration-0.1ms
Frequency-1 pulse /sec Intensity-5 40mA or 100 -300 V Diseased nerve-75mA or 500 V Filter setting-5HZ 10KHZ Sweep speed-2 -5 ms/div

MEASUREMENTS
Onset latency Duration Amplitude Conduction velocity

WAVE FORMS

LATENCY
Time in ms from the stimulus artifact to the

first negative deflection of CMAP Measure of fastest conducting motor fibers It includes RESIDUAL LATENCY Measured in ms

AMPLITUDE
Base line to negative peak

Peak to peak
Co relates with the number of nerve fibers Measured in mV

DURATION
Initial take off from the base line to final return

to the baseline Co relates with the density of small nerve fibers Measured in ms

CONDUCTION VELOCITY
Conduction velocity is determined by dividing

the distance between the two cathodal stimulation points by the difference between the two latencies Conduction distance CV = Proximal distal latency Meters / seconds

NORMAL VALUES
In between 45-70 m/sec Upper limbs-60 m/sec (average) Lower limbs -50 m/sec (average)

SNCV

PRINCIPLES OF SNCV
Orthodromic or Antidromic Orthodromic:

Digital nerve is stimulated and SNAP recorded at a proximal point along the nerve

Antidromic:

The nerve is stimulated at a proximal point and SNAP recorded distally.

ELECTRODE PLACEMENTS
ORTHODROMIC STUDY Ring electrodes Stimulation Surface electrodes - recording Stimulating :

Cathode 1st IP joint Anode 3cm distal

Recording :

ANTIDROMIC STUDY (REVERSE)

Ring electrode
Stimulating :

recording

Cathode proximal point Anode -3 cm proximal Pick up 1st pip joint reference -3 cm distal Ground in b/w stimulating and recording

Recording :

MACHINE SETTINGS

Filter 10 Hz 2kHz Sweep speed -1-2ms/div

Gain 1-5 V /div

MEASUREMENTS
Onset latency

Amplitude
Duration Conduction velocity

WAVE FORM

ONSET LATENCY
Stimulus artifact to the initial positive or

subsequent negative peak Measured in ms

DURATION
Initial take off from the baseline to final return

to the baseline It represents the number of slow conducting fibers Measured in ms

AMPLITUDE
Base line to negative peak or Positive to

negative peak It represents the density of nerve fibers Measured in mV

CONDUCTION VELOCITY
SNCV is calculated dividing the distance

(mm) between stimulating and recording site by the latency

CV

= latency

Meters / seconds

ABNORMAL NCV
amplitude reduction Demyelination latency prolongation
Degeneration

LATE RESPONSES

 Late responses are the potentials

appearing after motor response (M wave) following a mixed nerve stimulation

TYPES
H reflex F wave Axon reflex

F WAVE

F WAVE
It is a late response resulting from Antidromic activation of alpha motor neuron involving conduction to and from spinal cord and occurs at the interface between the peripheral and central nervous system

PHYSIOLOGY OF F WAVE

WAVE FORMS

HISTORICAL BACKGROUND
Magladery and mc dougal 1950 ( CMT )
Small muscles in the foot

De afferented man Not a reflex Proximal motor pathway

FACTORS AFFECTING F WAVE

METHODS
Supra maximal stimulation ( 25 % )
Stimulus rate more than 0.5 Cathode should be proximal to anode It is recorded from any distal muscle by

stimulating appropriate nerve

RECORDING
Electrode placements same as MNCV

Machine settings: Amplifier gain 200 -300 microvolts /division Sweep speed 5-10 ms / division

PROCEDURE
Relaxed slight voluntary contraction Amplitude of more than 20 micro volts 10 20 responses persistence

PARAMETERS
Latency Chronodispersion

Persistence
Amplitude F/M ratio Conduction velocity

WAVE FORMS

LATENCY
Minimal latency Maximal latency Mean or median latency Age, height, limb length 31 ms in hand, 61 ms in foot Right to left symmetry is more than 2 ms in

hand and 4 ms in foot abnormal

CHRONODISPERSION
Difference between minimal latency and

maximal latency Measure of range of conduction of F wave ABP 3.6 +/- 1.2 ADM 3.3 +/- 1.1 EDB 6.4 +/- 0.8

PERSISTENCE
Number of occurrence divided by number of

stimuli Measure of antidromic excitability of particular motor neuron pool

AMPLITUDE
Depends on the number and size of the

motor unit 5 % of M wave Mean amplitude Excitability of alpha motor neuron

F/M RATIO
Proportion of motor neuron pool activated by

antidromic stimulation To use mean rather than maximum F amplitude for calculating F/M ratio ADM O.8 Ad H 0.9

CONDUCTION VELOCITY
stimulus site to C7 spinous process via the

axilla and mid clavicular point Stimulus site to T12 spinous process via knee and greater trochanter of the femur ( 2D ) FWCV = (FM1)

CLINICAL APPLICATIONS
Proximal motor pathway

Segmental motor neuron excitability

segmental motor neuron excitability than H and T reflex

LMN
latency Changes in peripheral nerve and root lesion F/M ratio Increased in both poly neuropathy and spasticity persistence Absent or reduced in GBS, ALS, proximal nerve root injury choronodispersion Increased in poly neuropathy ( demyelinating )

UMN
Amplitude and Persistence
Initial stage

Decreased

Chronic stage Increased latency also prolonged while duration and

amplitude increased in UMN

H REFLEX

H- REFLEX
The H - reflex is a monosynaptic reflex elicited by sub maximal stimulation of the tibial nerve and recorded from calf muscles

Hoffman 1918

PHYSIOLOGY OF H REFLEX

REFLEX ARC
1 a fibers
Spinal cord Alpha motor neuron

 It does not include muscle spindle

H reflex is larger at submaximal stimulation

Due to collision of orthodromic impulses by antidromic conduction in motor axons

MODIFYING FACTORS
Renshaw cell inhibition
Supraspinal mechanism Inhibition by adjacent motor neuron

VARIATIONS

In normal adults other muscles except small

muscles of hand and feet In childrens below 2 years

METHODS

ELECTRODE PLACEMENTS
Position :

Semi reclining or prone Recording : Active - Distal edge of calf Reference - Tendon Stimulating : popleteal fossa

MACHINE SETTINGS
STIMULATION Square wave pulse of 1 ms Stimuli below 0.1 ms will stimulate motor axons Cathode is kept proximal to anode Stimulus frequency should not exceed 1 in 5 seconds

PROCEDURE
The stimuli is adjusted to evoke maximum H

response amplitude At this strength a small M response may also present M response help to monitor the strength of stimuli At least 5 H response required for analysis By increasing the stimuli strength to supra maximal maximum M responses can be recorded 3 M responses required for analysis

PARAMETERS
latency
H - amplitude M wave H / M ratio H - Vibratory inhibition H TA Conduction velocity

WAVE FORMS

NORMAL VALUES
Latency Amplitude M wave H/M ratio 30.3 +/- 1.7 9.8 +/- 6.1 24.6 +/- 6.6 0.4 +/- 0.2

H vib
H - TA

42.9 +/- 18.2

LATENCY
Measured in ms Soleus 35 ms, FCR 20 ms Age, height, limb length Right to left asymmetry up to 1.5 ms Latency in full term infant is 15.94 +/- 1.45

AMPLITUDE

Base to peak of the negative phase Measured in mV Alpha motor neuron excitability

H / M - RATIO
The ratio of peak to peak maximum H reflex

to maximum M amplitude To estimate the motor neuron pool activation Less than 0.7

TONIC VIBIRATION REFLEX

VIBRATORY INHIBITION

RECIPROCAL INHIBITION

CONDUCTION VELOCITY

The distance between knee and T11 by the

latency difference between H reflex and M response

CLINICAL APPLICATIONS
PNS To evaluate proximal sensory motor pathway Helpful in plexopathies ,radiculopathies and neuropathies latency S1 radiculopathy Absent C5 - C6 radiculopathy Absent GBS - absent or delayed or dispersed

CNS Understanding the patho physiology Excitability of alpha motor neuron Amplitude, H/M ratio, H - vibratory inhibition, H - reciprocal inhibition

DIFFERENCE BETWEEN H REFLEX AND F WAVE

H reflex Nature Monosynaptic reflex

F wave Not a reflex but due to antidromic activation of alpha motor neuron Any distal muscle

Best elicited in

Soleus, FCR,VM

Stimulus
Persistence Amplitude

Sub maximal
Persistent 50 100 % of M wave

Supra maximal
Variable 5 % M wave

Useful in

Neuropathy,radicul Neuropathy,radicul opathy,spaticity opathy

BLINK REFLEX

BLINK REFLEX

The electrical analog of corneal reflex Kugelberg in 1952 To evaluate trigeminal and facial

Supra orbital nerve

REFLEX ARC
Afferent trigeminal nerve

pons Efferent facial nerve

PHYSIOLOGY OF BLINK REFLEX

METHOD

ELECTRODE PLACEMENTS
Recording : Recording Reference Ground Stimulating : Cathode
Anode

- bilaterally over orbicularis oculi - side of nasal bone - over chin

MACHINE SETTINGS
- 200 500 mV/division Sweep speed - 10 ms /division Stimulus rate - 1 in 3 seconds Avoid prolonged studies - R2 Habituated Aberrant innervation - lower facial muscles
Gain

RESPONSES
Ipsilateral side - R1 and R2

Contra lateral - R2

WAVE FORMS

PHYSIOLOGICAL MECHANISM
R 1 - Monosynaptic pathway

R2 - Poly synaptic pathway

NORMAL VALUES
Ipsilateral side R1 less than 13 ms R2 -- less than 40 ms Contra lateral side R2 less than 41 ms

CLINICAL APPLICATIONS
Abnormal R1 and R2 on the paretic side with

normal contra lateral R2 - ipsi lateral facial nerve lesion