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

COIMBATORE – 14.

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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, Coimbatore – 14.

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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:

Dr.A.RAJKUMAR

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ACKNOWLEDGEMENT

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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 encouragement throughout my study. I express my gratitude to her for

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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.

My family and friends have stood by me, during my times of need. Above all I thank the Lord Almighty for His kindness and benevolence.

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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

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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 injury.

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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 if the peripheral nerve damage occurs.

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AIM & OBJECTIVES

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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 effect of vibration on the nerve conduction velocity.

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REVIEW OF LITERATURE

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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 force¹¹.

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5 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 and he had documented it in a book¹⁵. In 1850 Helmholtz for the first

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Picture 1: Resting Membrane Potential

Picture 2: Recording of 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 technique to study the potential difference. They observed that 20000

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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 cells²⁷. 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⁺ movements outside and voltage gradient which allows influx, are

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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 nerve is formed by flat cells called neurolemma or Schwann cell

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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 reach the value of +35mV then falls to the resting level (-70mV)³⁵.

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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⁺ concentration is more inside. The K⁺ can move out but Na+

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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 diameter fibre and latter portion represents small diameter fibre⁴².

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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 to the propagation of action potential. When a nerve fibre is excited its

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Picture 3: Action Potential

Picture 4: Propagation of 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.

Along myelin sheath, at every 1-3mm, there is node of Ranvier⁵⁰.

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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 another end. The distance between the electrode is measured⁵².

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Picture 5: Median Nerve

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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 supplies the muscles, flexor digitorum superficialis, palmaris longus and

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Picture 6: Ulnar Nerve

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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 deep branch⁵⁷.

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Picture 7: Radial Nerve

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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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18 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 the nerve in the dorsal root ganglion⁶².

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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 difference in potential. The generator of electric potentials, the type 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 recording electrodes are away from the generator source usually.

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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 from source.

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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 clinical conduction⁷⁵. The NCV identifies conduction block,

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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 are available.

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MATERIALS & METHODS

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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 and clinical examination was done.

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25 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 automatically on string.

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26 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 communication between Central processing unit and hardware unit.

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Picture 8: Recording of Median Nerve Motor Conduction Velocity

Picture 9: Recording of Median Nerve Sensory Conduction Velocity

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27

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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28

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 5^th metacarpo phalangeal joint and pisiform bone. Electrode was placed over hypothenar eminence in this point.

Reference Electrode (R): It was placed near 5^th 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, cathode was placed. Anode was kept proximal to it.

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Picture 10: Recording of Ulnar Nerve Motor Conduction Velocity

Picture 11: Recording of Ulnar Nerve Sensory Conduction Velocity

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Picture 12: Recording of Radial Nerve Motor Conduction Velocity

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29

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 the posterior division in the posterior cord of brachial plexus.

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Picture 13: Recording of Nerve Conduction Velocity

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30

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 medians, numbers and percentages

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RESULTS

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31 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 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

50 49.98 5.49

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32

Table: 3.Left ulnar motor nerve Nerve

Involved

N Mean

Velocity

P value Left

Ulnar Motor Nerve

Chainsaw workers

50 51.67 5.78 0.39

(>0.05) Non

Workers

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

P value Right

Median Motor Nerve

Chainsaw Workers

50 49.71 6.51 0.86

(>0.05) Non

Workers

50 49.93 6.13

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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

50 50.30 4.79

Table: 7. Left median motor nerve Nerve

Involved

N Mean

Velocity

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

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34

Table: 9. Right radial motor nerve Nerve

Involved

N Mean

Velocity

P value Right

Radial Motor Nerve

Chainsaw Workers

50 50.79 5.58 0.22

(>0.05) Non

Workers

50 52.19 5.78

Table: 10. Left radial motor nerve Nerve

Involved

N Mean

Velocity

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

5.5 2-8 - -

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35

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 50.95 m/sec. Both the values are in 97% confidence limits.

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36

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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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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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

Sensory Conduction Velocity

Right Ulnar Left Ulnar Right Median Left Median

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39

Controls (Non Exposed) Motor Conduction Velocity

Table: 14

Mean Velocity Standard Deviation

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

Motor Conduction Velocity

A Study on Nerve Conduction study in Vibratory Tool Users

ACKNOWLEDGEMENT

CONTENTS

INTRODUCTION

AIM & OBJECTIVES

REVIEW OF LITERATURE

MATERIALS & METHODS

RESULTS