A Study on Nerve Conduction study in Vibratory Tool Users

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A STUDY ON NERVE CONDUCTION STUDY IN VIBRATORY TOOL USERS

Dissertation submitted to

THE TAMILNADU DR. M.G.R MEDICAL UNIVERSITY,

CHENNAI – 600032

In partial fulfillment of the requirement for the degree of Doctor of Medicine in Physiology ( Branch V )

M.D. ( PHYSIOLOGY ) APRIL 2019

DEPARTMENT OF PHYSIOLOGY COIMBATORE MEDICAL COLLEGE

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CERTIFICATE

This dissertation entitled A STUDY ON NERVE CONDUCTION

STUDY IN VIBRATORY TOOL USERS” is submitted to The Tamil Nadu Dr.M.G.R Medical University, Chennai, in partial fulfillment of

regulations for the award of M.D. Degree in Physiology in the

examinations to be held during April 2019.

This dissertation is a record of fresh work done by the candidate

Dr.A. RAJKUMAR, during the course of the study ( 2016 – 2019 ). This work was carried out by the candidate himself under my supervision.

GUIDE:

Dr.D.SELVAM. M.D.,DCH,

Associate Professor,

Department of Physiology,

Coimbatore Medical College,

Coimbatore – 14.

PROFESSOR & HOD:

Dr.R.SHANMUGHAVADIVU. M.D.,

Professor,

Department of Physiology,

Coimbatore Medical College,

Coimbatore – 14.

DEAN:

Dr.B. ASOKAN M.S., M.Ch.,

Coimbatore Medical College & Hospital,

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DECLARATION

I, Dr.A.RAJKUMAR solemnly declare that the dissertation entitled

“A STUDY ON NERVE CONDUCTION STUDY IN VIBRATORY TOOL

USERS” was done by me at Coimbatore Medical College, during the

period from July 2017 to June 2018 under the guidance and supervision

of Dr.D.SELVAM M.D.,DCH., Associate Professor, Department of

Physiology, Coimbatore Medical College, Coimbatore.

This dissertation is submitted to The Tamilnadu Dr. M.G.R. Medical

University towards the partial fulfillment of the requirement for the award

of M.D. Degree (Branch - V) in Physiology. I have not submitted this

dissertation on any previous occasion to any University for the award of

any degree.

Place:

Date:

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ACKNOWLEDGEMENT

I express my sincere thanks to our respected Dean,

Dr.B.ASOKAN M.S., MCh., Coimbatore Medical College, Coimbatore for permitting me to conduct the study.

I thank Dr.P.KALIDAS M.D., Vice Principal, Coimbatore Medical

College, Coimbatore for his encouragement and suggestions in completing

the study.

I am extremely grateful to my beloved and respected Head of the

Department of Physiology, Professor Dr. R.SHANMUGHAVADIVU, M.D.,

for her encouragement in helping me to take up this study. I express my

heart - felt gratitude to her, for her moral support and encouragement

throughout the conduct of the study and also during my post graduate

course. I owe my sincere thanks to her.

I will ever remain in gratitude to Dr.D.SELVAM, M.D.,DCH.,

Associate Professor, Department of Physiology for his valuable support

and guidance for my study.

I am highly obliged to Dr.B. SUJATHA, M.D.,DA., Associate Professor, Department of Physiology, for her motivation to perform this

work.

I sincerely thank Dr.R.THENMOZHI, M.D., D.C.P., Associate

Professor, Department of Physiology for her valuable suggestions and

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sparing her valuable time and patience, which helped me a lot to complete

this study under her expert guidance

My sincere thanks to beloved teachers Dr.S.Kavitha M.D., Dr.A.Abbas, M.D., Dr.A.Moorthy, M.D., Dr.E.S.Manikandan M.D., Dr.S.Kanchana Bobby M.D., Dr.P.Mohan.,M.D., Dr.S.Subhashini M.D., Mrs.D.Revathy M.sc., Dr.C.N.Angel Deepa, M.D., Dr.N.Latha M.D., Dr.K.Archanaa M.D., Assistant Professors, Department of Physiology for their valuable opinion and help to complete this study. I would like to

thank all my tutors for their support in completing this study.

I would grossly fail in my duty, if I do not mention here of my

subjects who gave full cooperation while doing my study.

My sincere thanks to all my fellow postgraduates for their involvement in helping me in this work.

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CERTIFICATE - II

This is to certify that this dissertation work titled “A STUDY ON NERVE

CONDUCTION STUDY IN VIBRATORY TOOL USERS” of the

candidate Dr. A.Rajkumar with registration Number 201615253 for the

award of Doctor of Medicine in the branch of Physiology. I personally verified the urkund.com website for the purpose of plagiarism Check. I

found that the uploaded thesis file contains from introduction to conclusion

pages and result shows 3% percentage of plagiarism in the dissertation.

Guide sign with Seal.

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INTRODUCTION

In this modern day, industrialization, consequent urbanisation and

the development of infrastructure have undergone mechanisation. To

reduce the manual labour due to scarcity of workers, save the time and

money, many industrial tools have been developed which had brought

in significant changes in the pattern of working in construction industry.

The construction of buildings involves massive work of cutting of

wood, timber and concrete into various shapes and sizes to be fit into

the buildings especially prefabricated structures. The cutting tools used

are chainsaws, hand drills, rock drill and the tamper which are hand

held. Among them the chainsaws are the commonly used instruments.

The chainsaws when held in the hand and operated, produce

vibration. When there is a change in the environmental stimulus, the living

cells get excited. The nerve is one such important excitable tissue1_{. In humans}

conduction of nerve impulse is the specialised function of nerves2_{. The hands}

and forearm are exposed to vibrations when the persons handle the

tools for many years and chronic vibration exposure occurs. This

vibrations can damage the muscles, tendons, joints , arteries, veins and

peripheral nerves. The vascular injury commonly seen is Raynauds

phenomenon3_{. The symptoms that are produced due to vibration}

exposure is called vibration syndrome and it is related to vascular

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As the chronic vibration exposure continues, the peripheral nerve

fibres can undergo damage. When a peripheral nerve gets damaged, the

myelination and axons are affected4. As the damage becomes significant,

the injury becomes irreversible and cumulative. When the nerve is

finally damaged, complete symptoms of peripheral neuropathy and its

complications develop5_.

As the nerve injury starts occurring, axon and myelin sheath get

injured, and the nerve conduction is affected. When this nerve

conduction is studied electrophysiologically in the form of motor and

sensory nerve conduction velocities of peripheral nerves in upper limbs,

the results show changes in vibration exposed individuals, before the

development of established vibration syndrome6_{. Hence it will be of}

immense use in early identification of nerve damage and plan for

alternate works for the individuals and to apply preventive measures in

the field of occupational vibration exposure.

The research reports on the nerve conduction velocity which is

an useful electrophysiological study to know the effect on peripheral

nerves are varying and less.

Hence this study is undertaken to study the motor and sensory

nerve conduction velocities of median, ulnar nerves and motor conduction

velocity of radial nerves of both upper limbs in chainsaw users and the

individuals not exposed to vibration and the data are compared to evaluate

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AIM AND OBJECTIVES

AIM:

To study the nerve conduction study in vibratory tool users.

OBJECTIVES:

Cross sectional study is done on the persons working with the

chainsaw which is a vibratory industrial tool. The nerve conduction

velocity study is conducted on median, ulnar, radial nerves on both

forearms. Nerve conduction study is conducted in individuals who are

not working with chainsaws. Both the data are compared to study the

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REVIEW OF LITERATURE

Vibration induced nerve injury was initially reported in 1911 by

Loriga in the mines of Italy. Later in 1918 by Hamilton in Indiana7_{. In}

due course , the musculo skeletal and neurological abnormalities became

established side effects of vibration. The latency of injury may vary

from less than a year to four decades depending on the degree of

vibration8.The vibration exposure is prevalent in construction industry,

forestry, mining, foundry, automobile and metal works.

The pathogenesis appears to be due to local endothelial damage

by a mechanical trauma and oxidative stress that can produce nerve

damage and vaso constriction by sympathetic discharge9_{. The vibration}

damage occurs in large myelinated fibres and small unmyelinated and

myelinated fibres disproportionately . Local nerve damage can result in

muscle damage also.

High frequency vibration is produced by drills, milling machines,

chisels, sanding-cutting-polishing machines10_{. This can also produce}

sensory neural damage and vascular damage. The low frequency vibration

is transmitted to the shoulders and arms which can cause musculo

skeletal abnormalities. The vibration is related to duration intensity, type

of the tools, work place, temperature, posture, rest breaks and grip

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HISTORY

After the discovery of electricity, rapid advancement in the field

of electrical neurophysiology was made possible. Many researchers

specialised in the field of neurophysiology and had done animal

experiments and discovered the functions of nerves and muscles.

Benjamin Franklin (1745 – 1791), a scientist from Philadelphia

described positive and negative electrical charges12_.

HISTORY OF NERVE CONDUCTION STUDY;

Galvani (in 1791) of Bologna University found out that the

nerves act as the conductors of electricity. He described the appearance of

spark during the handling of the amphibian nerve with a knife13_{. He}

described that the electricity currents originate in the body and

channelled in the nerves. He also showed that when free nerve endings

were placed between 2 plates of metals, muscle contraction occurred in

amphibian muscle preparation. In 1838 Matteucci showed that following

the sciatic nerve stimulation, gastrocnemius contraction occurred in

sciatic nerve preparation14. In 1932 Charles Scott Sherrington explained

the Stretch reflex and its role in running and walking. In 1944, an

American Scientist Joseph Erlanger stated that the diameter of nerve

fibres too had contributed to the nerve conduction. Herber S. Gasser in

1944 classified the nerve fibres based on the diameter. Raymond found

that changes in the nerve potential, travel as impulse, down the nerve

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Picture 1: Resting Membrane Potential

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time documented the nerve conduction velocity by recording muscle

contraction. Tustin had described that median nerve conduction velocity

for motor component was 61 m/sec and sensory component was 60

m/sec16.

History of neurophysiology is a mixture of human intelligence,

advancements in technology and instrumentation with positive and

negative responses. Prior to a mechanical contraction response in a

muscle, a wave of electrical excitation occurs. This was first

demonstrated by Burden Sandarson in 189517. Duchenne undertook

studies on neuromuscular diseases based on this observation18.

When Erb in 1861 introduced the different patterns of current, it

became possible to conduct animal studies19_{. The patterns are two types.}

One is Indirect or alternating current which is of high voltage and low

ampere and the second is galvanic current which is direct, having low

voltage and high ampere20.

Potential difference across the cell membrane was measured by

using the micropipette of 0.5µm in size which was developed by John

Eccles of Australia in 196321_.

Squid and Cattle fish have giant axons. Utilising this fact, Alan

Lloyd Helghin and Andrews Huxley of United Kingdom studied the

nerve fibre electrical conduction22. They developed the voltage clamp

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ions enter and same amount exit during the first half and second half

of voltage peak respectively per micrometer23_.

They used radio active Na+ions and demonstrated that nearly

20,000 ions enter the cells per µm2 for each nerve impulse during first

half of voltage peak and same amount of ions come out in second half

of voltage peak24_{. They both described voltage clamp technique to}

measure the potential difference across cell membrane. In 1970, British

Scientist Bernard Katz explained the synaptic transmission25_.

NERVE CELL PHYSIOLOGY:

Nerve cell membrane is made up of lipid bilayer where protein

molecules are embedded. Electrically charged ions cannot pass through

it. The embedded proteins provide channels for the passage. The

proteins are called voltage gated ion channels. The most excitable part

in a nerve is axon hillock, the point at which axon leaves the cell body26_.

The membrane potential in quiescent cells is called the resting membrane

potential( RMP).

RMP is the voltage difference between the two electrodes placed

inside and outside of the axon. Na+_{- K}+_{ATPase is the enzyme that}

pumps 3 Na+_{ions out of the cells and 2 K}+_{ions into the cells}27_.

Potassium leak channels also allow K+_{ions to move out of the cells.}

This results in the negative charge inside the cell membrane compared

to exterior. When the concentration gradient which allows K+

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balanced, equilibrium is achieved28_{. Now the potential is called}

equilibrium potential. It is calculated by Nernst Equation29_.

R – gas constant (1.987 cal/molK), T-Temperature, [X] out –

concentration outside, [X] in – concentration inside, Z- Charge of the ion,

F – Faradays constant. Resting membrane potential of axon is – 70Mv30.

NERVE FIBRE

As the nerve fibre leaves the cell body, it is covered by myelin

sheath. When the nerve fibre leaves the central nervous system, it is

covered by a second covering called neurolemma. As the fibre ends at

the periphery, the neurolemma is lost first, next the myelin sheath and

finally the axis cylinder. The axis cylinder ends as a naked process

without any covering31_.

At the nerve ending, motor fibre splits into 150 branches which

end in muscle fibres. Motor unit is defined as the one nerve fibre along

with all the muscle fibres it supplies.

Myelination in peripheral nerve fibres.

Axon is the central core and the conducting membrane is the

surface of axon. The tissue fills the inter cellular area of axon. It is

called axoplasm32_.

The myelin sheath is a lipid material that surrounds the axon.

The sheath is present in all somatic nerves. Myelin sheath of somatic

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sheath. The nucleus of this cell is present near outer membrane of the

cells. This Schwann cells deposit myelin sheath33_.

Physiological properties of nerve fibre are studied by Cathode

Ray Oscilloscope (CRO).

The study of action potential;

A micro electrode is placed inside the nerve fibre and at outside,

a differential electrode is placed. The micro electrode contains

concentrated potassium chloride solution34_.

The two important properties of nerve fibres are; excitability and

conductivity.

Excitability:

The mechanical, thermal, chemical or electrical stimulus can

stimulate a nerve fibre. The stimulated part becomes electrically negative.

This can be detected by galvanometer or Cathode ray oscilloscope. When

this changes reach a threshold level, depolarisation occurs rapidly to

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ERLANGER AND GASSER CLASSIFICATION OF NERVE FIBRES: MOTOR FIBRES Type Erlanger-Gasser Classification

Diameter Myelin Conduction

velocity

Associated muscle fibers

α Aα 13–20

µm Yes 80–120 m/s

Extrafusal muscle fibers

γ Aγ 5–8 µm Yes 4–24 m/s [2][3]

Intrafusal muscle fibers SENSORY FIBRES Type Erlanger-Gasser Classification

Diameter Myelin Conduction

velocity

Associated sensory receptors

Ia Aα 13–20

µm Yes

80–120 m/s[4]

Responsible for proprioception

Ib Aα 13–20

µm Yes 80–120 m/s Golgi tendon organ

II Aβ 6–12 µm Yes 33–75 m/s

Secondary receptors of muscle spindle. All

cutaneous mechanoreceptors

III Aδ 1–5 µm Thin 3–30 m/s

Free nerve endings of touch and pressure.

Nociceptors of neospinothalamic tract

old thermoreceptors

IV C 0.2–1.5

µm No 0.5–2.0 m/s

Nociceptors of paleospinothalamic tract. Warmth receptor

ACTION POTENTIAL

At resting stage; the negative potential exists inside the cell and

outside is positive. Na+_{concentration is more outside and K}+

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cannot move in. the membrane pores are bound by calcium and Na+

cannot enter. When excited by an action potential, Ca+_{moves out of the}

binding site and tremendous Na+ conduction entry occurs. This is called

activation of membrane37. So, reversal of potential occurs with negative

outside. As the action potential reaches +35mV, calcium binds to the

pores and sodium ion entry is prevented. The stage of repolarisation

occurs37_{. The K}+_{conductance increases and K}+_{comes out of cell. At}

the later stage, this K+_{conductance is slowed down, and it is called}

negative after potential. The active Na+ pump mechanism utilises ATP

for energy, Na+ is pumped out and K+ into the cell and resting

membrane potential is reached38_.

Compound Action Potential

When the potential is recorded in a group of nerve fibres or

trunk of nerve, it is called compound action potential40_{. It is a}

summated potential of nerve fibres with different conduction velocities.

Most of the nerves have myelinated nerve fibres with various diameter41.

This was studied in frog by Erlanger and Gasser. When

maximum shock is given, pressure is given between recording and

stimulating electrode, the pressure stops the conduction in thick fibres

initially. In an evoked potential, the earlier portion represents large

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The conduction amplitude height represents all of the axon

bundles in the nerve .So first α wave appears then β, γ, δ and Β and

finally C wave of unmyelinated fibres occur serially43.

Conductivity:

This happens by the ubiquitously ATP utilising process of nervous

axons for the maintenance of metabolic integrity to provide nutrients to

the axons. The axons transport occur in anterograde and retrograde

fashion44_{. The velocity can be varying. The stages of axonal transport of}

Signalling proteins are;

1) The synthesised new proteins are packed into organelles and sent

to the proximal axon.

2) The distally directed movement which is occur with the pauses

and transient reversal.

3) Arriving at the destination and get incorporated into axolemma.

4) Turn around

5) Dynein driven transport which is retrograde.

6) Lysosomes digest during transit or at arrival in cell body.

Nerve growth factors are transported in retrograde fashion from

nerve ending to cell bodies after entering by endocytosis45_.

Propagation of Action Potential

At one point on the membrane , action potential occurs. The

action potential then excites the adjacent portion of membrane leading

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Picture 3: Action Potential

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permeability to sodium is increased46_{. The sodium ions diffuse in and}

positive charges move in through depolarised membrane. Inside the

myelinated fibre, the voltage in increased by these positive charges

above threshold level and initiate action potential47.

Now in the new areas, sodium channels open and the spread of

action potential occurs. The new current flow and local circuit occurs

along the membrane. The depolarisation travels across the entire length.

This transmission is called Nerve Impulse48_.

Direction

The action potential can travel in all directors in all branches of

nerve fibre till whole membrane is depolarised49_.

All or none principle:

The process of depolarisation travels in the membrane if

environment is favourable, and does not travel if not favourable. When

action potential cannot generate voltage sufficient enough to stimulate

the next area, depolarisation process ceases. So, action potential to

threshold ratio should be more than 1 and it is the safety factor49_.

The large nerve fibres are myelinated and small are unmyelinated.

A nerve trunk has 2 times of unmyelinated fibres than myelinated

fibres. In myelinated axon, the membrane conducts action potential.

Axon is filled with axoplasm. Axon is surrounded by myelin sheath.

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The Schwann cell membrane rotates around the axon many times

by the lipid substance - sphingomyelin, which is an insulator which

reduces the ion flow by 5000 fold. Nodes of Ranvier occur at every

1-3 micrometer in the nerve which is uninsulated50.

SALTATORY CONDUCTION

In myelinated fibres, action potential occurs at the Nodes of

Ranvier only. The current flows in extracellular fluid outside and

axoplasm inside and reach the next node in an axon, exciting

subsequent nodes one by one. Hence impulse jumps from node to

another node51.

This mechanism increases the conduction velocity by 5-50 fold.

Also it causes conservation of energy by 100 times . So it requires low

metabolism for re-establishment of sodium and potassium concentration.

The velocity is 0.25 m/sec in unmyelinated fibres and 100 m/sec in

myelinated fibres51.

The impulse gets propagated in both the directions. When

diameter of nerve increases, velocity of conduction also increases.

Conductivity Hursh factor is 6 for humans, which is the ratio of

velocity to diameter. So when diameter of nerve is known , velocity can

be calculated52_.

Conduction velocity of nerve bundle is calculated by giving

electrical stimulation at one end and recording the action potential at

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Myelinated fibres have conduction velocity depending on their

diameter. In the unmyelinated nerve fibre, conduction is proportional to

the square root of diameter.

Other factors that influence conduction velocity are;

1. Temperature; cooling decreases the conduction,

2. Pressure; Increased pressure decreases conductivity,

3. Blood supply; if reduced , conductivity is reduced,

4. Chemicals; CO2 and narcosis diminish the conduction,

5. H+_{ion Concentration; increased H}+_{ion, decreases conductivity,}

6. O2; decreased O2, decreases the conductivity

Anatomy – Median Nerve

Median nerve has both motor and sensory components. It is

derived from the spinal nerve roots C5 to T1 through the lateral and

medial cords in brachial plexus.

It is motor to flexors of forearm and muscles of thenar

eminence. It provides sensory fibres to the palm on its lateral aspect,

terminal phalanges on dorsal surface along with thumb, index finger,

middle finger and half of the ring finger53_.

Between the heads of pronator teres, it enters the forearm. It

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flexor carpi radialis. Its anterior interosseous branch is a muscular

branch for flexor digitorum profundus, pronator quadratus and flexor

pollicis longus54.

Then it enters carpel tunnel. In the hand, first and second

lumbricals, flexor pollicis brevis, opponens pollicis and abductor pollicis

brevis are supplied55_.

Before entering the carpel tunnel, a sensory branch called palmar

cutaneous branch is given that supplies thenar muscles56_.

Ulnar Nerve

Brachial plexus gives medial cord from which the C7, C8, T1

root fibres form ulnar nerve. It lies close to brachial artery and median

nerve in the arm. Posterior to the epicondyle, it is located at condylar

groove. It enters cubital tunnel (Feindel and Straford 1958).

The cubital tunnel is formed by the medial ligament of elbow on the

floor and flexor carpi ulnaris aponeurosis on the roof56.

Here, flexor carpi ulnaris branch arises, then branches to flexor

digitorum profundus arise. In the Guyon’s Canal , between hook of

hamate and pisiform bone, it passes into the wrist57_.

The fourth digit on its ulnar border and fifth digit receive

sensory supply. The hypothenar muscles that is; flexor digiti minimi,

abductor digiti minimi and opponens digiti minimi are supplied by the

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At the lateral aspect of the hand, it supplies III and IV

lumbricals, interossei, flexor pollicis and adductor pollcis58_.

The dorsal and palmar cutaneous branches do not pass through

the Guyon’s Canal58.

Radial Nerve

Brachial plexus gives posterior cord that continues as radial

nerve,. The spinal nerve roots are C5 to T1. All the three heads of the

triceps are supplied. Then it passes around spiral groove in humerus.

Posterior antibrachial branch is given in the spiral groove. It is

superficial distal to the deltoid insertion59_.

It supplies extensor carpi radialis longus and brevis and brachio

radialis. Between branchioradials and brachialis, it enters forearm.

Posterior interossei branch in the forearm, gives branch to supinator

muscle. The nerve passes in between the superficial and deep parts of

muscle, piercing the arcade of Frohse. Then branches are given to

extensor indicis, extensor pollicis brevis, extensor pollicis longus,

extensor digiti minimi, extensor digitorum, extensor carpi ulnaris and

abductor pollicis longus. The cutaneous nerve passes on the lateral

aspect of forearm and supplies the hand on dorsal aspect59_.

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PERIPHERAL NERVES;

The peripheral nerves are surrounded by successive layers of

connective tissue. The axons are surrounded by perineurium.

Perineurium pack the axons into fascicles. The nerve is composed of

fascicles packed by epineurium. The blood vessels to the nerves are

called Vasa Vasorum. The nerves to the nerves are called Nervi

Nervorum. The axon is a cytoplasmic protrusion from the body of

neuron. The axon has a constant radius and longer than dendrites and

they transmit signals60.

The axolemma cover the axons. They are membranes. The

axoplasm is the cytoplasm. Telodendria are the end branches of axon.

The axon terminal is called telodendron which synapse with the other

cell body61_.

When it forms synapse with the dendrite of same neuron, it is

called autapse. At synapse, the junction is formed with glands and

muscles. When synapse appear at the entire length of the axon it is

called en passant synapse61_.

Discussion on nerves

The sensory nerves are the cable like bundles from the different

fibres that originate in sensory receptors of the peripheral nerves. The

fibres are usually paired with the efferent fibre of motor nerves and

put together to form the peripheral nerves. These different nerves leave

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Some sensory neurons called pseudounipolar neurons, that

transmit warmth and touch, conduct the impulse from periphery to cell

body. Again the impulse conducted from cell body to spinal cord

through another branch of same axon. The myelinated nerve fibres are

group A and group B fibres. The unmyelinated nerve fibres are group

C fibres. The sensory fibres alone are separately grouped into type I,

type II, type III and type IV62_.

BIOELECTRIC POTENTIALS

Bioelectric potentials are generated from the sources inside the

body that is peripheral nerves, muscles, and brain. They are recorded

by electrodes which are placed in same distance away. The potentials

originate from neuronal membranes which allows current flow from in

and out of the cell by capacitative effects and passive leakage. These

current lead to extracellular currents that flow in the conducting

medium in the body which is called as volume conductor. Volume

conduction is the transfer of potentials to a distance. In clinical

neurophysiology, the human body acts as nonhomogenous volume

conductor. These currents reach the surface in the skin. Hence potential

difference is created across the two electrodes placed over the skin. The

differential amplifier can be used for detection and amplification of

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volume conductor, recording electrodes, propagation through volume

conductor, distance of propagation, all decide the effect of recording.

The potential in neurons is the sum of potentials generated by

individual neurons.

In a macroscopic level, the cortical pyramidal cells behave like

dipole layer and their synchronous activation generates potential field.

This is called open field configuration. But in the neurons with

dendritic arborizations, the fields generated are distributed radially

around cell body and called closed fields. Set of radially oriented

dipoles on the surface of the sphere produce fields that produce closed

field potentials. Such field is negligible at the distance because radial

and tangential current flow cancel each other.

Motor cortex or peripheral motor and sensory nerves are

stimulated and initiate peripheral evoked potentials. Motor cortex

potentials travel peripherally to anterior horn cells and muscles. These

potentials can be recorded in spinal cord, peripheral nerves and muscles.

Peripherally generated sensory nerve impulse travel in central direction

to cortex via dorsal nerve roots and spinal cord dorsal columns.

The peripheral nerve potentials have unique properties in volume

conductors. The nerve potentials are recorded from overlying skin

electrode as close to the generating source as possible. But the

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The peripheral nerve fibres can be recorded individually, but the

synchronous volley of potentials are recorded from multiple grouped

parallel fibres which produce the nerve potentials that are recorded

clinically. The wave forms generate nerve action potential. The

travelling potential in a nerve fibre is represented in two dipoles placed

end to end. The configuration and size of the potential depends on the

recording electrode and generator and seen as positive wave forms.

Sensory evoked potentials at the cortex are the summated potentials

from cortical neurons.

A single source of current is called monopole. The magnitude of

current decreases with the distance away from current source can be

measured along the equipotential lines. Each such line represents a

constant potential along the line.

In a nervous system, adjacent monopoles of opposite polarity

define the dipole. Here, current flows from positive to negative pole.

Potential lines are generated away from dipole. The magnitude of

current falls off inversely in relation to distance from source.

The electrical activity in cortical neurons is contributed by the

excitatory and inhibitory post synaptic potentials in dendritic trees of

pyramidal neurons.

The potential of dipole fall of inversely with square of distance

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The dipole records in relation to distant reference at points

perpendicular to dipole axis, appears as a single peak. This has sharps

that increases with decreasing distance from source.

In peripheral recordings in resistive-capacitive medium, the

volume conduction is a frequency dependent factor. The potentials are

out of phase. The latency recorded in a distance is shorter than that

recorded over nerve.

When potential difference is large, a high spatial gradient is

present. When it is high the potential is called a near field potential. In

motor conduction study, the typical recording G1 Montage over the

motor end plate and G2 over muscle tendon. It allows for initial

negative wave form with high amplitude. A negative positive biphasic

wave form is recorded.

Sensory nerve conduction studies produce biphasic or triphasic

wave forms. Triphasic wave forms are seen in sensory nerve

conduction. In motor conduction study, the electrodes are placed over

site of action potential generation. In sensory nerve conduction study

the action potential is always generated away from the recording

electrode.

Nerve conduction studies record the evoked response in response

to stimulation of peripheral nerves. The Nerve conduction velocity study

(NCV) are used as confirmatory tests in the suspicious neuropathy in

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demyelination, acute, chronic or sub acute disease. The prediction of

prognosis of disease is also possible. Several factors determine the

accurate value of results.

CHAINSAW;

Chainsaw is a movable, mechanical instrument. It has a chain

with attached teeth. This can rotate on a guide bar. It is commonly

used in the construction industry for cutting of wood into various

shapes and sizes. At first , an instrument called Osteotome was invented

by Bernhar Heinean an orthopaedist in 1830. In 1783, hand saw with

serrated chain was invented. In 1927, first gasoline powered chain saw

was developed by EMIL LERP. It is a two stroke petrol engine using

internal combustion system. It has an elongated guide bar with alloy

steel which is 90 cm in length. It has tooth which is made up of

chromium plated steel. The instrument has chain brake and rear handle

guard. The chain saws produce vibrations and emit carbon monoxide63.

Now the electrically operated chainsaws and diesel operated chainsaws

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24

MATERIALS AND METHODS

The design of the study is cross sectional study. The study was

conducted during the year 2017-2018. Ethical committee approval was

obtained from the Ethics committee of the Coimbatore Medical

College.

Cases / Exposed to vibration:

The subjects were selected from those working in the

construction sites in the Coimbatore area. These workers were selected

in their morning assembling area. The age range set was 20-35 years.

All the workers were males. Those workers who are on duty for 8

hours per day and using the hand held electrically operated chainsaw

for a minimum duration of 3 hours per day, working for atleast 5

days per week and handling the instrument for atleast 5 years of

duration were selected. Among them 50 cases were included for the

study. Written informed consent was obtained form each individual.

Their name, age, sex, height and weight were recorded. History

was taken and clinical examination was done .

Controls / Non exposed:

About 50 males in the age group of 20-35 years working in the

nearby areas not using the hand held vibratory tools in their profession

were selected. Written informed consent was taken. History was taken

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Exclusion criteria:

In both the cases and controls, those persons having diabetes

mellitus, hypertension, neurological disorders, peripheral nerve diseases,

chronic smokers, chronic alcoholics, obesity, spinal cord diseases, cardio

vascular diseases, chronic respiratory diseases, fever were excluded.

RECORDING OF NERVE CONDUCTION:

Neuroperfect was placed in smooth levelled surface, it was kept

away from transformers, DC motors, Powers appliances to eliminate

electromagnetic interference. Proper grounding of AC outlets was done.

MOTOR CONDUCTION:

Electrode was applied at appropriate position. Nerve was

stimulated by pressing the foot switch corresponding to single. The

strength stimulus was increased or decreased by adjusting the control

provided on the stimulus electrode.

On getting satisfactory waves form, it was recorded.

SENSORY CONDUCTION;

Electrode was applied at appropriate position. Nerve was

stimulated by pressing the foot switch. The stimulus was adjusted by

adjusting the control provided on the stimulating electrode. The nerve

was stimulated till the averaged wave becomes smooth and sensory

nerve action potential became prominent.

Cursors for voltage and latency measurement get marked

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Settings:

Motor nerve conduction velocity;

Sweep speed : 2ms/div,

Sensitivity : 3mV/div,

Hi filter : 10 khz ,

Lo filter : 2kh

Notch filter : One

Sensory nerve conduction velocity;

Sweep speed : 2 ms/div;

Sensitivity : 10µv/div;

Hi filter : 3khz;

Lo filter : 20 hz

Notch filter : On

Settings:

The interface between the hardware unit (neuroperfect) and

computer is done by using 9 pins D type connector. This connector can

be interfaced at any two of the serial ports available at PC side (com1,

and com2). In order to make the software settings, where the interface

connector is placed, port setting is done using the settings button.

Selecting this button, a new window pops up. The port where the

interface connector is placed must be appropriately selected for proper

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Picture 8: Recording of Median Nerve Motor Conduction Velocity

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Median nerve to the abductor pollicis brevis,(motor component);

Position: Subject was in supine position.

Active electrode(A): It was placed between the first metacarpo

phalangeal joint and the distal wrist crease in its midpoint , that is over

the abductor pollicis brevis.

Reference electrode: It was placed little distal to the first metacarpo

phalangeal joint that is over the tendon.

Ground electrode: It was placed near active electrode between the cathode

and active electrode.

Stimulation Point (1): The flexor carpi radialis tendon was located. A

point ulnar to the tendon was noted. It was the first point. Midpoint of

the distal wrist crease was the second point. A line was drawn between

the points. Isolated stimulator cathode was placed 3cm proximally from

active electrode in this line. Anode is placed proximally.

Stimulation point (2): In the anticubital region, brachial pulse was felt.

Medial to this pulse, cathode was placed.

Instrument settings: 3mV division is the sensitivity, 2-3 Hz is low

frequency filter, 10kz is high frequency filter. 2m sec/division is the

sweep speed.

Tested fibres: Brachial plexus medial cord - anterior division in lower

trunk- C8 to T1 nerve roots.

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Median nerve; Sensory Nerve Conduction study;

Ring electrode nerve conduction study was performed. Recording

electrode was placed at first interphalangeal joint in the second digit.

Stimulating electrode was placed at 3cm from distal wrist crease

proximally. Reference electrode was placed 3cm proximally. The distant

latency, conduction velocity and action potential were measured.

Ulnar nerve: motor nerve conduction velocity:

It is motor nerve to the muscle abductor digiti minimi.

Position: The arm was kept abducted, externally rotated at 45˚. The

elbow was flexed to 90˚. Thumb pointing to the ear was the neutral

position of forearm.

Active Electrode(A): A midpoint was marked between the 5th_metacarpo

phalangeal joint and pisiform bone. Electrode was placed over

hypothenar eminence in this point.

Reference Electrode (R): It was placed near 5th metacarpo phalangeal

joint distally.

Ground Electrode: It was kept between the active electrode and cathode.

Stimulation Point (S1): Cathode was placed near active electrode 8cm

proximally over a line that is radially running near the tendon of

flexor carpi ulnaris. Anode was located proximal to it.

Stimulation Point(S2): Near the medial epicondyle, about 4cm distally,

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Picture 10: Recording of Ulnar Nerve Motor Conduction Velocity

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Settings: 3mV/division was sensitivity, 2-3Hz is low frequency filter,

10Hz was the high frequency filter, 2mS division was sweep speed.

Tested Nerve: C8, T1 roots in lower trunk and anterior division in the medial cord of brachial plexus.

ULNAR NERVE Sensory Nerve Conduction Study

Antidromic nerve conduction study was carried out. Cathode was

placed near distal wrist crease 3cm proximally. Nerve conduction was

recorded from fifth digit inter phalangeal ring electrode

RADIAL NERVE Motor nerve conduction study Motor nerve to the extensor carpi ulnaris

Position: The subject was kept in supine position.

Active Electrode(A): A midpoint was marked between the lateral

epicondyle and ulnar styloid process in the midforearm. Active electrode

was placed here.

Reference Electrode: It was placed over thumb.

Stimulation Point: The electrode was unipolar cathode and kept 6cm

proximal to the lateral epicondyle in the lateral upper arm. Anode was

placed 2cm proximally.

Machine setting: 3 mV/division was the sensitivity, sweep speed was

2msec/division.

Fibres Tested: C6, C7, C8 roots through lower middle, upper trunks in

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International tobacco association has classified smokers as;

(i) Smokers who has used more than 100 cigarettes in his life time

and is continuing smoking.

(ii) Non smokers who has not smoked 100 cigarettes in his life time

and currently not smoking for 6 months.

(iii) Ex-smokers, who has smoked 100 cigarettes in his life time and

currently not smoking for 6 months.

In this study only non smokers have been included to prevent

the nicotine related nerve injury that can interfere with the study

results.

STATISTICAL ANALAYSIS

To test the mean value difference between the two groups, paired

‘t’ test and unpaired ‘t’ test were used. The data were compared by

chi-square(x2)test. The linear regression analysis was done to calculate

the correlation between the conduction velocities. The significance of

statistical value was considered when ‘p’ value was less than 0.05 (5%).

The descriptive statistics for nerve conduction and study

population are given as means and standard deviations, ranges or

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RESULTS

Among the selected individuals, 100 subjects willing to participate

were included in the study. Results are depicted in the tables 1 to 10.

Anthropometric particulars are given in Table:9. In the results, the data

is depicted for each nerve and each side.

Cases : Exposed / Chainsaw workers

[image:58.595.109.531.339.480.2]

Controls : Non exposed / Non workers

Table:1. Right ulnar motor nerve Nerve

Involved

Worker Category

N Mean

Velocity

Standard Deviation

P value

Right Ulnar

Motor Nerve

Chainsaw

Workers

50 49.71 6.05 0.34

(>0.05)

Non

Workers

50 50.90 6.30

Table:2. Right ulnar sensory nerve Nerve

Involved

N Mean

Velocity

P value

Right Ulnar

Sensory

Nerve

Chainsaw

workers

50 39.81 5.90 0.000

(<0.001)

Non

Workers

[image:58.595.105.532.565.704.2]

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[image:59.595.108.528.132.270.2]

32

Table: 3.Left ulnar motor nerve Nerve

Involved

N Mean

Velocity Standard Deviation P value Left Ulnar Motor Nerve Chainsaw workers

50 51.67 5.78 0.39

(>0.05)

Non

Workers

[image:59.595.106.530.326.466.2]

50 50.65 6.07

Table: 4. Left ulnar sensory nerve Nerve

Involved

N Mean

Velocity

P value

Left Ulnar Sensory Nerve Chainsaw Workers

50 37.57 4.97 0.000

(<0.001)

Non

Workers

50 50.25 6.47

Table: 5. Right median motor nerve Nerve

Involved

N Mean

Velocity Standard Deviation P value Right Median Motor Nerve Chainsaw Workers

50 49.71 6.51 0.86

(>0.05)

Non

Workers

[image:59.595.108.530.522.663.2]

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[image:60.595.108.530.126.264.2]

33

Table: 6. Right median sensory nerve Nerve

Involved

N Mean

Velocity

P value

Right Median Sensory Nerve Chainsaw Workers

50 40.58 6.17 0.000

(<0.001)

Non

Workers

[image:60.595.106.531.320.463.2]

50 50.30 4.79

Table: 7. Left median motor nerve Nerve

Involved

N Mean

Velocity Standard Deviation P value Left Median Motor Nerve Chainsaw Workers

50 50.76 6.02 0.87

(>0.05)

Non

Workers

50 50.95 5.59

Table: 8. Left median sensory nerve Nerve

Involved

N Mean

Velocity

P value

Left Median Sensory Nerve Chainsaw Workers

50 41.26 5.27 0.000

(<0.001)

Non

Workers

50 51.22 5.57

[image:60.595.107.533.518.657.2]

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[image:61.595.108.533.102.225.2]

34

Table: 9. Right radial motor nerve Nerve

Involved

N Mean

Velocity Standard Deviation P value Right Radial Motor Nerve Chainsaw Workers

50 50.79 5.58 0.22

(>0.05)

Non Workers

[image:61.595.111.529.304.429.2]

50 52.19 5.78

Table: 10. Left radial motor nerve

Nerve Involved

N Mean

Velocity Standard Deviation P value Left Radial Motor Nerve Chainsaw Workers

50 51.79 5.43 0.12

(>0.05)

Non Workers

50 50.19 4.99

Table: 11. Anthropometric particulars

Cases Control

Mean Range Mean Range

Age (Years) 31.0 20-35 33 20-35

Height (cm) 164 154-176 162.5 151-171

Weight (kg) 55 42-72 52 46-72

No.of years in present employment

[image:61.595.107.530.494.685.2]

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Right Ulnar Nerve; Motor Nerve Conduction Velocity

In the 50 volunteers from the chain saw users, the motor nerve

conduction velocities, fall within the range of 45.05 to 57.32 m/sec.

The mean value of the resulting data shows 49.7 m/sec. with standard

deviation of 6.05 with 97% confidence limits.

For the 50 healthy volunteers from controls, the motor conduction

results lie in the range between 42.08 to 60.01 and the mean of all the

fifty values is 49.98 with standard deviation of 5.49 with confidence

limits 97%.

Left Ulnar Nerve; motor Nerve Conduction Velocity

The controls who are not exposed to vibration have velocity

range 46.05 to 58.34 m/sec. The mean value is 50.67 with 6.07

standard deviation falling within the 97% confidence limits.

The exposed have a velocity range of 44.44 to 57.33 m/sec. the

average conduction velocity is 51.67 m/sec.

Right Median Nerve; Motor Conduction Velocity

The conduction velocity for right upper limb for median nerve is

distributed in between the values 42.04 and 61.04 m/sec with a mean

of 49.93 m/sec for controls.

The left upper limb motor velocity of median nerve has the

values in the range of 41.44 to 58.33 m/sec. The mean value lies at

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Left Median nerve; Motor conduction velocity

Motor conduction velocity mean value is 50.76 m/sec with

standard deviation 6.02 for exposed and for non exposed 50.95±5.9 m/sec.

‘p’ value is >0.05.

Right Radial Motor Nerve conduction velocity;

In the non exposed, the mean is 50.79 with standard deviation

5.58. In the exposed, the mean is 52.19 with standard deviation 5.78.

Left Radial Motor Nerve conduction velocity;

For cases the mean falls in 49.15 with standard deviation 6.04 for

exposed and mean is 49.61with standard deviation 6.09 for unexposed.

Sensory Conduction Velocity

Right Ulnar Nerve: The mean value is 39.81±5.90 m/sec for exposed and 49.98±5.49 m/sec for non exposed with ‘p’ value < 0.001.

Left Ulnar Nerve: The mean value is 31.57±4.97 m/sec in non exposed individuals and 50.25±6.47 m/sec in exposed with ‘p’ value <0.001.

Right Median Nerve: Mean nerve conduction velocity is 40.58 ±6.17 m/sec for exposed and 50.30±4.79 m/sec for non exposed with ‘p’ value <0.001.

Left Median Nerve: Mean value is 41.26±5.27 m/sec in exposed and 51.22±5.57 m/sec in non exposed with ‘p’ value <0.001.

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[image:64.595.114.560.347.649.2]

37

TABLE ; 12. VIBRATION EXPOSED (Cases) Motor Conduction Velocity

Mean Velocity Standard Deviation

Right Ulnar 49.71 6.05

Left Ulnar 51.67 5.78

Right Median 49.61 6.51

Left Median 50.76 6.02

Right Radial 50.79 5.58

Left Radial 49.15 6.08

Graph: 1

49.71 51.67 49.61 50.76 50.79 49.15

0 10 20 30 40 50 60

Right Ulnar Left Ulnar Right Median Left Median Right Radial Left Radial

Motor Conduction Velocity

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[image:65.595.113.560.371.704.2]

38

TABLE : 13

VIBRATION EXPOSED Sensory Conduction Velocity

Mean Velocity Standard Deviation

Graph: 2

39.81

37.57

40.58 41.26

0 10 20 30 40 50

Right Ulnar Left Ulnar Right Median Left Median

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Controls (Non Exposed) Motor Conduction Velocity

Table: 14

Right Radial 52.19 5.78

Left Radial 49.61 6.09

Graph: 3

50.9 50.65 _49.93 50.95 52.19 _49.61

0 10 20 30 40 50 60

Right Ulnar Left Ulnar Right Median Left Median Right Radial Left Radial

Motor Conduction Velocity

[image:66.595.114.561.429.708.2]

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Controls (Non Exposed) Sensory Conduction Velocity

Table: 15

Graph: 5

49.98 50.25 50.3 51.22

0 10 20 30 40 50 60

Right Ulnar Left Ulnar Right Median Left Median

[image:67.595.113.562.315.644.2]

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Results in motor nerve conduction velocity Table: 16

Right Motor Conduction velocity Significant

Cases Controls

Median 49.74 49.93

p>0.05

Ulnar 49.71 50.90

Radial 50.79 52.19

Results in motor nerve conduction velocity Table: 17

Left Motor nerve conduction velocity Significant

Median 50.76 50.95

p>0.05

Ulnar 51.67 50.65

Radial 49.15 49.61

Results in sensory conduction velocity Table: 18

Right Sensory conduction velocity Significant

Median 40.58 50.30

P<0.001

[image:68.595.106.532.132.285.2] [image:68.595.106.531.366.522.2] [image:68.595.107.534.599.725.2]

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Results in sensory conduction velocity Table: 19

Left Sensory conduction velocity Significant

Median 41.26 51.22

P<0.001

Ulnar 37.57 50.25

From the table 14, the motor nerve conduction velocities in

median, ulnar and radial nerves on the right upper limb showed no

significant difference between the exposed and non exposed. All the

comparative values have ‘p’ value of >0.05 which shows statistically no

significant difference.

From the table 14, the left upper limb motor conduction velocities

for median, ulnar and radial nerves show little difference that too is

statistically insignificant with ‘p’ value of >0.05.

From the table 15, the conduction velocities for sensory

component of right median nerve and right ulnar nerves show a gross

difference. When the values of exposed are compared with non

exposed, the ‘p’ value is <0.001 which is statistically more significant.

Hence, the sensory conduction velocities of median and ulnar nerves are

delayed.

From the table 18 and 19, the sensory conduction velocity on left

side, and right side of median and ulnar nerves are compared. Both the

[image:69.595.107.533.126.250.2]

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43

individuals with more significant ‘p’ value of <0.001. Hence sensory

nerve conduction velocities are delayed.

Sensory Conduction Velocity Table: 20

Right Left Significant

Median Ulnar Median Ulnar

Exposed 40.58 39.81 41.26 37.57

p>0.05

Non-exposed 50.30 49.98 51.22 50.25

Graph: 6

In the vibration exposed subjects , right median sensory conduction

velocity is little more delayed than left median nerve but not

significant. In case of ulnar nerve, left side sensory conduction is more

[image:70.595.110.550.229.622.2]

A Study on Nerve Conduction study in Vibratory Tool Users

CERTIFICATE

DECLARATION

ACKNOWLEDGEMENT

CONTENTS

INTRODUCTION

AIM AND OBJECTIVES

REVIEW OF LITERATURE

The study of action potential;