NERVE CONDUCTION
VELOCITY

 PRINCIPLES
 ACTION POTENTIAL
 AXONAL TRANSPORT
 TYPES OF CONDUCTION
 CMAP
 SNAP
 VARIABLES
BASICS

PRINCIPLES
 Proximal and distal rule
 Same nerve roots but different peripheral
nerves to localize the changes to one or the
other
 Until normal values

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
 PHYSIOLOGICAL
 AGE
 TEMPARATURE
 SEX
 DIGIT
CIRCUMFERANCE
 UPPER VERSUS
LOWER LIMB
 TECHNICAL :
 STIMULATION;
 FAULTY LOCATION
OF STIMULATOR
 FAT AND OEDEMA
 BRIDGE
FORMATION
BETWEEN ANODE
AND CATHODE

TECH………CONTD…….
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
 The speed at which the nerve conduct an
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
 STIMULATING :
 Cathode – active – black - closer to pick up
 Anode – inactive - red

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 :
 Pick up – proximal point
 Reference – 3cm proximal
 Ground – in b/w stimulating and recording

ANTIDROMIC STUDY (REVERSE)
 Surface electrodes – stimulating
 Ring electrode – recording
 Stimulating :
 Cathode –proximal point
 Anode -3 cm proximal
 Recording :
 Pick up – 1st pip joint
 reference -3 cm distal
 Ground –in b/w stimulating and recording

MACHINE SETTINGS
 Filter – 10 Hz – 2kHz
 Sweep speed -1-2ms/div
 Gain – 1-5 µV /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
Distance
 CV =
latency
 Meters / seconds

ABNORMAL NCV
 Degeneration – amplitude reduction
 Demyelination – latency prolongation

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
 Renshaw cell inhibition
 Maximum voluntary contraction
 Tension

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 =
( F – M – 1 )

CLINICAL APPLICATIONS
 Proximal motor pathway
 Segmental motor neuron excitability
 It is more precise for assessment of
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
 Inhibited by stronger 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 30.3 +/- 1.7
Amplitude 9.8 +/- 6.1
M wave 24.6 +/- 6.6
H/M ratio 0.4 +/- 0.2
H vib 42.9 +/- 18.2
H - TA 39.9 +/- 31.1

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
VIBIRATORY INHIBITION
 Achilles tendon is vibrated for 1 minute at 100
Hz
 Normal – amplitude decreases
 UMN lesion – there is no decrease in
amplitude
 Due to the vibratory inhibition is less than
normal

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 F wave
Nature Monosynaptic
reflex
Not a reflex but
due to antidromic
activation of alpha
motor neuron
Best elicited in Soleus, FCR,VM Any distal muscle
Stimulus Sub maximal Supra maximal
Persistence Persistent Variable
Amplitude 50 – 100 % of M
wave
5 % M wave
Useful in Neuropathy,radicul
opathy,spaticity
Neuropathy,radicul
opathy

BLINK REFLEX

BLINK REFLEX
 The electrical analog of corneal reflex
 Kugelberg in 1952
 To evaluate trigeminal and facial
 Supra orbital nerve
 Orbicularis oculi

REFLEX ARC
 Afferent – trigeminal nerve
 Centre – pons
 Efferent – facial nerve

PHYSIOLOGY OF BLINK REFLEX

METHOD

ELECTRODE PLACEMENTS
Recording :
 Recording - bilaterally over orbicularis oculi
 Reference - side of nasal bone
 Ground - over chin
Stimulating :
 Cathode - supra orbital notch over supra
orbital nerve
 Anode - directed somewhat laterally

MACHINE SETTINGS
 Gain - 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

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