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NORMATIVE DATA FOR MEDIAN NERVE CONDUCTION STUDY IN TRICHY SOUTH INDIA.
DISSERTATION SUBMITTED FOR M.D., [PHYSIOLOGY] DEGREE - BRANCH V
THE TAMILNADU DR. MGR MEDICAL UNIVERSITY, CHENNAI – 600 032.
MAY – 2020
Registration Number - 201715551 DEPARTMENT OF PHYSIOLOGY
TRICHY SRM MEDICAL COLLEGE HOSPITAL AND RESEARCH CENTRE
TRICHY – 621 105.
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CERTIFICATE
This Dissertation titled “NORMATIVE DATA FOR MEDIAN NERVE CONDUCTION STUDY IN TRICHY SOUTH INDIA ” 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 May 2020.
This Dissertation is a record of fresh work done by the candidate, DR.K.G.KARTHICKEYAN., during the course of the study (2017-2020).
This work was carried out by the candidate himself under my supervision.
DR. NACHAL ANNAMALAI M.D., Guide & HOD,
Professor, Department of Physiology, Trichy SRM Medical College Hospital &
Research Centre Trichy – 621 105.
DR. A.JESUDOSS M.S., DLO.,
DEAN
Trichy SRM Medical College Hospital & Research Centre, Trichy – 621 105.
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ACKNOWLEDGEMENT
It is my honour and privilege to thank Prof. Dr. NACHAL ANNAMALAI M.D., Professor, Department of Physiology, my guide, who has been helping me and guiding me at every stage since the genesis of idea for this study. I owe my sincere thanks to her suggestions, timely help throughout the conduct of the study and also during my postgraduate course.
I express my sincere gratitude to our respected Dean Dr. A. Jesudoss MS., DLO., Trichy SRM Medical College Hospital & Research Centre, Trichy for permitting me to conduct this study.
I thank Dr. P. Thirumalaikolundhu Subramanian M.D., Medical superintendent, Trichy SRM Medical College Hospital & Research Centre, Trichy for his encouragement and suggestion in completing this study.
I express my deep sense of gratitude towards Dr, Muhil, M. M.D., Associate Professor, Department of Physiology, Dr.Swarnalatha M.D, Associate Professor, Department of Physiology, Trichy SRM Medical College Hospital & Research Centre, Trichy, for their constant encouragement and timely advice with respect to this study of mine.
I thank Dr.M.Rajajeyakumar, M.D. Assistant Professor, Department of Physiology, Trichy SRM Medical College Hospital & Research Centre, for always being a constant encouragement, and advice in completing the study. I also thank Dr. Niranjana M.D., Assistant professor Department of Physiology, Trichy SRM Medical College Hospital &
Research Centre , for her help in completing the study.
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I also thank Dr.S.V.Ajantha M.D., Tutor , Department of physiology , Mr. R. A.
Suresh Balaji, M.Sc., Tutor , Department of physiology Mrs. H. Petricia, M.Sc., Tutor , Department of physiology, for their constant encouragement and timely help during my postgraduate period.
I extend my gratitude towards Dr .Hema M.D Associate Professor , and Dr. Prabha Thangaraj M.D , Assistant Professor Department of community medicine for their timely help in solving the statistical part of this study.
I express my heartfelt thanks towards Dr. Ramu M.D, D.M (Neuro ) Professor Department of neurology, Dr.Revathy M.D, D.M ( Neuro ) Assistant professor Department of neurology , Mrs. Shanthi NCV & EEG lab technician, Trichy SRM Medical College Hospital & Research Centre, Trichy , for their constant support throughout this study.
I express my deep sense of gratitude and thanks to my Postgraduate seniors Dr.
Tamilsudar M.D , Dr. Ajantha M.D , Dr. Preetha M.D , Dr. Lavanya AV, Juniors Dr.Lavanya G , Dr. Tharani G , for their support and help during the study.
I thank the lab technicians and non-teaching fraternity of Physiology department, who have been a significant support throughout my course.
Last but not least, I would grossly fail in my duty, if I do not thank My Parents , wife, Children, family members and the Participants, who have supported whole heartedly and helped me in every aspects in completing this study.
Above all my sincere thanks to the Almighty.
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DECLARATION
I Dr.K.G.KARTHICKEYAN hereby solemnly declare that the dissertation entitled
“NORMATIVE DATA FOR MEDIAN NERVE CONDUCTION STUDY IN TRICHY SOUTH INDIA” was done by me at Trichy SRM Medical College Hospital And Research Centre, Irungalur, Trichy, under the supervision and guidance of DR.NACHAL ANNAMALAI. M.D. (PHYSIOLOGY), Professor and Head of the Department of Physiology, Trichy SRM Medical College Hospital And Research Center , Irungalur , Trichy.
This dissertation is submitted to The Tamilnadu Dr. M.G.R Medical University, towards partial fulfilment required 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.K.G.KARTHICKEYAN
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CERTIFICATE
This is to certify that this dissertation work titled “NORMATIVE DATA FOR MEDIAN NERVE CONDUCTION STUDY IN TRICHY SOUTH INDIA” of the candidate
DR. K.G.KARTHICKEYAN with registration Number 201715551 for the award of M.D.
Degree in the branch of Physiology (Branch-V). 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 6 percentage of plagiarism in the dissertation.
DR. NACHAL ANNAMALAI M.D., Guide & HOD,
Professor, Department of Physiology, Trichy SRM Medical College Hospital &
Research Centre Trichy – 621 105.
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ORIGINALITY CHECK
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ORIGINALITY CHECK
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CONTENTS
S. No. TITLE PAGE NO
1. INTRODUCTION 1
2. AIM & OBJECTIVES 4
3. REVIEW OF LITERATURE 5
4. MATERIALS AND METHODS 54
5. RESULTS 63
6. DISCUSSION 74
7. CONCLUSION 78
8. SUMMARY 79
9. LIMITATIONS 80
10. RECOMMENDATION 81
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ANNEXURES
1. BIBLIOGRAPHY
2. PROFORMA
3. CONSENT FORM
4. KEY TO MASTER CHART 5. MASTER CHART
xix xxx xxxii xxxiv xxxv
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LIST OF ABBREVIATIONS
NCS - Nerve conduction study.
NCV- Nerve conduction velocity.
EMG - Electro myogram.
DL – Distal latency.
ms - Milliseconds.
m /s - Meter per second.
mv - Milli volt.
SNAP- Sensory nerve action potential.
MNCV – Motor nerve conduction velocity.
SNCV - Sensory Nerve Conduction Velocity .
Na / K ATPase Sodium Potassium Adenosine Tri Phosphatase enzyme pump Rt – Right side.
Lt – Left side.
S.D - Standard deviation.
Na+ - sodium ion.
K + - Potassium ion.
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LIST OF FIGURES
Figure.
No TITLE Pg. No
1. First EMG Machine demonstrated by James Golseth. 13 2. Schematic representation of nerve conduction instrument 16 3. Active and Reference Disc electrodes 17
4. Ground Electrodes 17
5. Ring Electrodes 18
6. Needle Electrodes 18
7. Surface Electrodes 19
8. Structure of a Neuron 22
9. Structure of peripheral nerve 23
10. Saltatory conduction in Myelinated Neuron 27
11. Action Potential in a Neuron. 29
12. Electrode Placement. 34
13. Optimisation Of Stimulator Position 35
14. Compound Muscle Action Potential 36
15. Motor action potential stimulation 37 16. Motor Conduction Velocity Calculation 40 17. Sensory action potential stimulation 42 18. Graph of sensory nerve action potential 43
19. Anatomy of median nerve 47
20. RMS EMG ALERON 201 channel machine 57
21. Median nerve motor conduction disc electrode placement 59 22 Median nerve sensory conduction ring electrode placement 60
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LIST OF TABLES
Table.
No TITLE
Pg. No
1. Filter settings for Electrodiagnostic studies. 20
2. Classification of Nerve fibers. 25
3. Causes of Carpal tunnel syndrome. 49
4. Demographic characteristics of study population 63
5. Demographic data of male and female subjects. 64
6. Median motor nerve parameters in males and females. 65
7. Median sensory nerve parameters in male and female. 67
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LIST OF CHARTS
Chart.
No TITLE
Pg. No
1 Schematic Supply of Median nerve. 48
2 Percentage distribution of study population as per BMI. 69
3 Age distribution in study population 71
4 Height Distribution in study population 72
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INTRODUCTION
Nerve Conduction Studies :
Nerve Conduction Studies are part of electro diagnostic methods utilised in the clinics for assessing the normal functioning status of the peripheral nerves. The
development of nerve conduction study dates back to the early part of the 20 th century.1 Nerve conduction studies play a vital role in describing the disease conditions of the peripheral nerves. The basic technique consists of an electrical stimulation of nerves and the recording of the evoked potentials, either from the muscles or from the nerves themselves.2,3 In clinics NCS plays an important role in identifying the limit of damage and the point of neural injuries. Demyelination and axonal degeneration are the two main peripheral nerve diseases which can be distinguished with the help of nerve conduction velocity.
Nerve conduction velocity is an invasive simple procedure to evaluate the peripheral nerve fiber status. They are now commonly used for the precise localization of injured nerve fiber and exact description of the peripheral nerve functions.
Nerve conduction studies are part of routine tests in the present scenario which help in identifying and defining the condition of the tested nerve fiber. The peripheral nervous system can be completely examined by the NCS.
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Nerve conduction study involves the examination of motor, sensory and mixed nerves . The examined nerve fiber is activated by applying a small milli amperes of electric current on the skin overlying the nerve and the obtained action potential is recorded for interpretation of its function. The values from the conduction velocity is compared with the existing normative data available in the literature and research works for its interpretations.1,4
Normative data :
Normative data can be defined as a value or range of parameters common for a population at a point of time. These data describes the normal values which is below or above gives us the result of the test for diagnosis. Normative data plays an
essential role for clinicians in making decisions differentiating from normal conditions and pathological conditions.
Normative data are necessary for clinicians for the following reasons.
Defining the history of a disease condition in a particular population.
Improving quality of patient care by clinicians.
Instituting the proper definitions of diseases for primary physicians.
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The researchers should concentrate on methodologies to develop normative data. A cross sectional study can be utilised for making normative data in stipulated time.
Normative data can also be obtained from longitudinal studies, case control studies and existing data sets. The data should be precisely interpreted with clear
methodology and the results should be simplified for benefit of patients and to provide a good quality primary care.5
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Aim and Objective
To establish the normative data for conduction velocity of motor and sensory division of median nerve in population of Trichy ,South India.
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Review of literature
Normative Data
Normative data consist of observations which characterize what is common in a distinct population, ethnicity, institution or health system at a particular point of time.
These information are of great significance to physicians and researchers.They provide the basic description of phenomena related to health, illness and also helps in finding variation in different population in due course of time.
Applications
Normative data are used to define an illness condition from a normal . They are considered as the most relevant and important for the primary care physicians to distinguish between disease and a normal condition. It forms the basis for analytical studies of researchers. Some of the uses are listed below.
1. Normative data with proper interpretations describes precisely the natural history of conditions related to diseases in clinics.
2. They play a major role in the development of suitable standards of care for physicians.
3. Helpful in the improvement and substantiation of illness nosologies for primary care physician, education and in research.
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Methods of accomplishing Normative Data
Numerous potential epidemiological observations are used to obtain normative data. Some of the methods are
1. Cross sectional study.
2. Case control study.
3. Longitudinal study.
4. Existing data sets.
Cross sectional studies
.A cross sectional study determines the prevalence of one or more variables and the associations between such variables in a specific population at a single point of time. When the association of phenomena with age or time are not over interpreted cross sectional studies are effective in describing normative phenomena.
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Case control studies.
The researcher spots the series of cases with matched conditions. One or more control groups are then selected consisting of subjects from the same population at risk of the condition but who do not have disease. Then the researcher ascertains prior exposure of both groups to different factors that might relate to the condition of interest. Case control studies cannot estimate incidence rates, proportions or trends because of unspecified populations. Therefore it never represents what is usual in a specified population, so case control studies are not effective in obtaining normative data.
Longitudinal designs.
Longitudinal studies are the most excellent design to obtain normative data, but the effect of time and aging on biological phenomenon should be taken into account to reveal the relative significant of aging effects , cohort effects and epoch effects. Three types of such studies are employed with varying strength and limitations.
Existing Data sets.
Existing data sets are useful sources of normative data. Several large data sets are collected for this purpose using various study designs, sometimes it gives the desired results to clinicians and researchers who are in search of normative data.
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A clearly defined and measured phenomenon with the methods of interpretation of the obtained data prior to the study yields a specified normative data. Normative data are often taken from various observational epidemiologic study designs, importance is given to methodological issues.
Normative data add better clinical and research nosologies, improved recognization of the natural history of common problems and growth of appropriate standards of clinical care for primary physicians.5
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Electrodiagnostic studies
Historical review
EARLY DEVELOPMENTS IN NEUROPHYSIOLOGY.
The progress of clinical neurophysiology was closely related to the invention of electricity.
1745-1791 – There was fast development in the field of electricity. Due to the ability to store electricity, experiments are done based on it by stimulating nerves and muscles. The scientist contributed to this success are Pieter Van Musschenvorock , Benjamin Franklin and Luigi Galvani . The famous kite experiment, which was electrified due to induction was demonstrated by Benjamin Franklin in 1752. By the use of “ Kite experiment ” charged the Leyden jar. Electricity was a source of wonder and delight prior to his research.1
Evolution of neurophysiology.
Luigi Galvani revealed that the nerves were good conductors of electricity.
Galvani distinguished a spark from the conductor when he touched the frog's nerve with a knife during a trial. This illustration correlated the connection between nerve muscle contraction and electrical stimulation of nerves. He assumed that electricity was generated by the body and conducted through the nerves.
Francois Magendie in 1822 separated anterior and posterior spinal roots. By his demonstration stimulation of posterior root resulted in pain and anterior root resulted in motor activity. This work was the basis of peripheral nerve functional classification.
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In 1829 Marianini established that ascending negative current was more efficient than the descending current in obtaining muscle contraction.Carlo Matteucci a physics professor illustrated the electrophysiological based working of the nervous system.
Helmholtz in 1850 measured the conduction velocity of nerve in the frog on recording muscle twitch. By using a similar procedure median motor and sensory nerve
conduction was found to be 61.0 ± 5.1 m/s and 60 m/s.
Dubois Raymond in 1851 recorded action potential of voluntarily contracting muscle by placing jars of liquid as electrode. This lead to the commencement new era of electromyography.
Remak in 1858 determined that the entry point of nerve to muscle was easy to
stimulate. Krause portrayed the endplate transmission of motor impulses. Keningsberg in 1864 detailed the duration of current and its relation with muscle contraction.
In 1861 Erb introduced the electrodiagnostic method using faradic and galvanic current. Duchennne (1806- 1875) was the first to orderly study the diseases which affect neuromuscular system . He was the one who build up equipments and
techniques for electrical stimulation. He also experimented with medical applications of photography. Herman in 1878 activated the brachial plexus and recorded the action potential from the of forearm and named it as action current. In 1895 Burden Sanderson was the first who demonstrated that wave of excitation precedes the mechanical response.
In 1907 Lapicque developed a circuit breaker equipment operated by gravity. He defined rheobase as minimal intensity of continuous current required for muscle
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excitation. He defined chronaxie as the minimal current duration twice the intensity of rheobase. In 1916 Adrian reported the strength duration curve and noted that healthy muscles showed a constant curve than the degenerative muscle showed predictable shift.
In 1907 Bordet stated that during the passage of sustained current the electrical activity levels changed less frequently in denervated muscle compared to a normal muscle. In 1912 Piper recorded the voluntary activity of the muscle using string galvanometer.1,6
ELECTROMYOGRAPHY AND NERVE STIMULATION TECHNIQUE.
Braun in 1897 invented the cathode ray tube. In 1903 Einthoven designed the string galvanometer. In the year 1920 Fobers and Thacker amplified the action potential using electron tube and recorded it using string galvanometer. Edgar Douglas Adrain Investigated the nature of stimulus on nerve tissue, with the help of cathode ray tube, capillary electrometer and thermiotic valve, he was able to amplify the signal 5000 times and recorded the action potential of single nerve fiber.
In 1929 Denny Brown studied the motor unit potentials. Joseph Erlanger and Herbert Spencer Gasser in 1922 with the help of an oscilloscope examined nerve
transmission in different types of the nerve fibers. They determined that the nerve conduction velocity was proportional to its diameter. They classified nerves as per the conduction velocity which was dependent on its diameter. Both were awarded Noble prize in 1944 for their work.
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John Eccles described synaptic transmission, he further described ionic mechanism and depolarizing abilities of ions . His experiments on chemical and electrical activity of synaptic transmission together with Katz developed new insights. In 1963 along with Hodgkin and Huxley received Noble prize. Alan LIoyd Hodgkin and Andrew F.
Huxley investigated electrical conduction of nerves. They measured resting action potentials in squid and cattle fish studied the change in sodium and potassium ions across cell membranes. They devised a method for measuring and controlling potential across cell membrane “Voltage clamp”. In 1949 Huxley recorded conduction in myelinated nerve fibers and described saltatory conduction. He also described physiology of muscle contraction , anisotropic ( A ) and isotropic ( I ) bands and sliding filament theory of muscle contraction.
Bernard Katz described miniature endplate potentials and attributed it to release of acetylcholine quanta in the synaptic transmission. He also described the role of calcium in the release of neurotransmitter. His contribution provided insights in neuromuscular junction and CNS. In 1970 received Noble prize for his contribution.
Fritz Buchthal worked on electromyography and established electromyography lab in Riggs military hospital. He documented the motor unit potentials of different muscles at different ages. He developed near nerve technique of stimulation and recorded the changes in axonal and demyelinating neuropathies.
In 1942 James Goldseth documented the clinical values of electrodiagnostic tests, collaboration with James Fizell an electronic engineer he found a constant current stimulator. In between Herbert Jasper found a monopolar needle electrode after
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treating the war injured patients. In the yaer 1948 Combined work of these three researchers paved the way for introduction of clinically useful electromyography equipment.
FIGURE 1 : FIRST EMG MACHINE DEMONSTRATED BY JAMES GOLSETH (centre)6
Motor nerve conduction velocity using muscle action potential was measured by Piper and Munnich. Hoffmann encouraged by Sherringtons work on stretch reflex
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displayed monosynaptic reflex by stimulating tibial nerve and recorded it from soleus muscle.This reflex named after him as H reflex.
In 1944 Harvey and Kutfer used nerve conduction studies in patients with peripheral neuropathy.In 1948 Hodes , Laravee and German first estimated conduction velocity by exciting the nerve at different levels.In 1944 Kugelberg and In 1954 Cobb and Marshall revealed the slowing of impulse propogation in ischemic nerves. Simpson displayed the slowing of impulse in carpal tunnel syndrome. Lambert and Kaeser came out with differentiating axonal and demyelinating neuropathies.
In 1937 Eichler published the first report of median and ulnar nerve action potential.
Dawson used photographic superimposition technique to improve the resolution of cortical somatosensory potential. This principle was used for measuring sensory nerve conduction velocity. In 1956 Dawson developed digital nerve stimulation technique to differentiate with motor conduction.1,6
In 1950 Magladery and McDougal described F wave, Blink reflex was described by Kugelberg in 1952 are commonly used in neurophysiological studies.
In 1963 Ekstedt and Stalberg developed the method of single fiber electromyography.
In 1980 Merton and Morton described transcranial electrical stimulation for better understanding of motor pathway conductions.
Rossini developed the method of unifocal stimulation.
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In 1985 Barker along with his colleagues stated that magnetic stimulation was painless technique. which paved the way for exploring remote parts of the central nervous system.
ELECTRODIAGNOSTIC SIGNALS AND MEASURMENTS
Electrodiagnostic studies used in the clinical setup comprises of certain elements such as display, measurement and its interpretations of action potentials which are recorded from central nervous system , peripheral nerves and muscles. The equipments are available in the market with simple programs.
The components of the machines are 1. Electrodes.
2. Filters 3. Stimulator.
4. Display.
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Figure 2 : Schematic representation of nerve conduction instrument
. 1Electrodes :
Active , Reference and Ground electrodes are used in nerve conduction studies.
Action potential is calculated in between active and reference electrodes. The ground electrode is the zero voltage point. The cup or disc electrodes are used in evoked potentials , ring electrodes are used in measuring sensory conduction velocity and needle electrodes are used in electromyography. Several metals and alloys such as stainless steel , platinum , nickel, chromium, silver and gold are used for making electrodes. 1,7,8
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Figure 3 : Active and Reference Disc electrodes.9
Figure 4 :Ground electrode.9
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Figure 5 : Ring electrodes.9
Figure 6 : Needle electrodes.9
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Figure 7 : Surface electrodes.9
Filter :
Filters helps in careful control of frequency domain of a signal. Pass band is said to be the frequency range of a signal which pass through the filter, where as the stop band is the frequency range which is not transmitted through the filter. Transision band lies between the pass band and stop band. Filtering is needed for removing the noise and optimizing the recordings. Low frequency filters eliminate the slow changing low frequencies and permit higher frequencies, hence called as high pass filters. High frequency filters behaves opposite and permits low frequencies and blocks high frequencies hence named as low pass filters.1
The recommended low and high cut filter settings for electrodiagnostic studies are tabulated in table 1.
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Table 1 : Filter settings for electrodiagnostic studies
1TEST LOW CUT
(Hz)
HIGH CUT (kHz)
Motor nerve conductions 2 - 5 10
Sensory nerve conduction 5- 10 2 – 3
EMG
Insertional activity Quantitative analysis
10 -20 2 – 5
10 10 Somatosensory evoked potential 5 - 20 1 – 2
Auditory brainstem evoked Potential
10 - 100 3
Visual evoked potential 1 - 3 0.1 – 0.3
Motor evoked potential 20 2
Stimulator:
Stimulators are necessary for evoked potentials and nerve conduction velocities. 50 - 1000µs stimulus duration is used , equipments have controls to regulate the
voltage.Constant current and constant voltage are the two types of stimulators used
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in electrodiagnostic studies. The range of voltage starts from 0v to 300 v and current of 0 mA to 100mA. Stimulators used in routine nerve conduction studies have a cathode and an anode they are bipolar nature. The cathode is negatively charged, whereas the anode is positively charged.cathode and anode are kept apart 2-3cm in standard nerve stimulators.1,7
Display :
Wave form displays are usually used which may be of analog oscilloscope or computer based digital video display.
Analog oscilloscope - After amplification and filtering signals are displayed straight away.
Digital display - A specialized device termed as (ADC ) analog to digital converter is used for displaying the signal.
Gain and sweep time :
Gain and sweep speed alters the latency and duration of an action potential. Pixel size determines the minimal latency and duration of the action potential.1ANATOMY OF PERIPHERAL NERVES
A basic knowledge of anatomy and physiology of peripheral nervous system is needed to differentiate its pathophysiology and principles of nerve conduction study.
Peripheral nerves are made up of multiplefascicles, each fascicle is a bundle of nerve fibers . Peripheral nerves are covered by three sheaths of connective tissue,
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endoneurium, perineurium and epineurium from inside out. Endoneurium comprises of collagen and few fibrocytes.. Perineurium forms blood nerve barrier. The
outermost sheath covering is epineurium. The blood vessels and lymphatics are
present in it. It continues with the duramater of the spinal root. Peripheral nerves gains it strength and flexibility from all these three layers.1,8
Figure 8 : Structure of a neuron
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Figure 9 : Structure of a peripheral nerve.
11PHYSIOLOGICAL PARAMETERS
The conduction speed of the nerve depends on certain factors such as nerve fiber diameter, myelination extent of the nerve fiber and the distance between the two successive nodes in a nerve fiber. The thickness of myelin sheath becomes more and more with increasing size of the axon which further makes the distance between two successive nodes further apart from each other. This yields faster conduction velocity.
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The thickness of the nerve axons varies from 0.2 µ to 20 µ. The nerve fibers are divided in to myelinated nerve fibers and unmyelinated nerve fibers. The presence of Schwann cells a protective covering sheath around the nerve fibers differentiates myleniated nerve fibers from the un mylineated ones. Node of Ranvier is the distance between two Schwann cells. At this point the axons are un insulated.
The spacing of Schwann cells at the point of development determines the inter nodal distance. There is no Proliferation of Schwann cells after the initial development but the growth of the nerve increases the inter nodal distance. The characteristic features of early myelinated fibers are , increased inter nodal distance, larger thickness and broad spacing at the nodes of ranvier. 12,13,14.
CLASSIFICATION OF NERVE FIBERS
Erlanger and Gasser classified nerve fibers on the basis of fiber diameter into A , B , and C .
Group
A
fiber consist of somatic myelinated fibers of afferent and efferent nerves of varying length from 1 µ to 20 µ.It is further subdivided into α , β , γ and δ in the descending order of declining diameter and conduction speed.Group B fibers are the ones with the small preganglionic myelinated axons of the autonomic nervous system. The fibers are of varying length from 1 µ to 3 µ.
Group C fibers are the components of the visceral afferents , pain , temperature afferents and in preganglionic autonomic efferents. The fibers are of varying length from 2 µ to 2 . 2 µ. 12.13,14
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Table – 2 Classification of nerve fibers
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IMPULSE CONDUCTION :
The formed action potential in the axons moves in either direction from its point of formation. The impulse movement is continuous in unmylineated fibers. The impulse movement is not continuous in myelineated fibers it is saltatory in nature, it jumps from one node to the other.12
MYELINATED FIBERS :
The Conduction velocity is more rapid in myelinated fibers when compared to that of unmyelinated fibers. The inter nodal capacitance and conductance is inversely
proportional to the thickness of myelin membrane.The conduction speed increases with increase in myelination of axon.
The increased conductance and capacitance in internodal segments due to decrese myelination as seen in demyelinating diseases results in local potential loss. This leads to failure of activation of successive nodes of ranvier and eventually ends in
conduction block.12,13.
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Figure 10 : Saltatory conduction in myelineated neuron
15UNMYELINATED FIBERS :
The conduction speed is very slow in unmyelinated fibers when compared to that of myelinated fibers. The main reason behind it is the continuous form of impulse transmission. In certain clinical conditions such as focal compression and decrease in diameter of nerve fiber further slows the impulse transmission across the nerve fiber.
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The basic knowledge of resting membrane potential and action potential of the nerve fiber is required to analysis the pathology behind it.12,13
RESTING MEMBRANE POTENTIAL
At the resting state,the ions Na+ and K+ has slight permeability. The K+ leaky channels present in the plasma membrane is the reason behind potassium escape from it. which allow K+ to move out against its electrochemical gradient. This is the reason for K+ being close to electrochemical equilibrium, and the membrane potential is close to the potassium equilibrium potential of -90 mV. At rest sodium ions have a very low permeability, which means sodium is far from electrochemical equilibrium and the membrane potential is far from the Na+ equilibrium potential of +65 mV. The combination of above two factors that is the selective permeability of the cell membrane and the different concentration of various ions inside and outside the cell give rise to a potential difference across the membrane.
Na+ and K+ do not reach equilibrium. Even after a small amount of Na+ can enter the cell and a current of K+ can leave the cell by means of K+ leak channels, these
potential difference is maintained by the Na+/K+ pump By using a molecule of ATP, this pump can takes out three Na+ ions from the cell and bring two K+ ions into the cell. The resting membrane potential is maintained by
“Diffusion potassium ions.
Difussion of potassium and sodium ions.
By Na+/K+ pump ( pumping 3 Na+ out of the cell & 2 K+ inside the cell)”.
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The potential of K+ is about -70mV to -90mV and the potential of Na+ is +60 mV.
Here we are concerned with the resting membrane potential of neurons , it is about -70mV, which is close to the equilibrium potential for K+.
Clinically the generation and maintenance of the resting membrane potential are important in neurons and muscle. Conditions that change the resting membrane potential of these cells interfere on proper functioning of these cells.16,17,18 ,19.
ACTION POTENTIAL
The electrical current produced by the neuron for propagating the impulse along it is named as action potential , it needs a electric or chemical stimulus for it. This changes the ion flow in and out of the cell. The net movement of positive charge is on the direction of current and the movement of negative ions is in opposite direction.
In a neuron the resting membrane potential is -70 mv, when it reaches -55mv to -60 mv it opens the voltage gated Na+ channels this is said to be threshold potential. This movement of more number of positive ions in to the cell makes it more positive. This inflow of more Na+ ions opens more number of voltage gated Na+ channels results in positive feed back cycle to initate a action potential known as all or none potential.
The increased potassium ion flow out of the cell and the decreased inflow of sodium results in net loss of positive charge inside the cell . It continues until the cell has repolarised to its resting membrane potential.8,19
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Figure 11 : Action potential in a neuron.
20FACTORS AFFECTING NERVE CONDUCTION :
Factors which interfere in the transmission of impulse through the nerve fibers can be described under two headings.
1. Physiological factors 2. Technical factors
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1. PHYSIOLOGICAL FACTORS:
TEMPERATURE :
The conduction velocity through the nerve fiber is affected by temperature. The internal body temperature regulates the intra neuronal temperature12,13,14 . For each degree Celsius rise in body temperature, there is a increases five percent rise in conduction velocity. The reverse is also true at low temperatures the conduction velocity is decreased. The latency increases by 0.3milli seconds (ms) and velocity decreases by 2.4 meters / seconds (m/s) for decrease in each degree celcius.21,22 The change in conduction velocity due to alteration in body temperature is connected to effect of temperature on sodium channels in the nerves. The temperature in the neurophysiology laboratory should be in the range of 20° C to 25° C . 12,23.
AGE :
Nerve conduction velocity varies with age groups. It is less in infants and childrens. In neonates it is half the adult value. Adult value is reached by three to five years of age and then remains relatively stable until 60 years of age.1.5 % of the conduction velocity is decreased for each decade after 60 years. This is connected to gradual loss of larger neurons with increase in age.12,24,25,26
HEIGHT :
An inverse relationship exists between the height of the individual and the velocity of nerve conduction . The main reason behind it is the shorter nerves conduct faster than
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the longer nerves in the equal age group. Slowing down of conduction occurs in taller subjects which is attributed to greater axonal tapering and lesser myelination in them.12,25,26,27.
LIMB:
The conduction velocity is greater in the upper limb when compared to lower limbs.
The length of the nerve going to lower limb is longer than the upper limb , this affects the conduction velocity. This leads to decreased conduction by
1. Distal axonal tapering . 2. Shorter internodal distance.
3. Gradual decrease in axonal diameter.
4. Temperature differences are low in feet when compared to hands.
GENDER:
There exist a significant differences in nerve conduction in males and females. This due to the increased body fat mass in females. 12.
2. TECHNICAL FACTORS
Factors affecting nerve conduction can be due to a defect in the stimulating system or in the recording system.
STIMULATING SYSTEM
Malfunction of the stimulating system may yield less response or no response.12,13
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ABNORMAL LOCATION OF STIMULATOR
The stimulator may be placed in the wrong position on the skin surface or the nerve may be stimulated minimally .The position of the stimulator should be corrected and placed in proper position for optimal stimulation.
FAT OR EDEMA BETWEEN STIMULATOR AND NERVE
In subjects of obesity or edema , when needle electrodes are used the fat tissue and edematous tissues are hinderance for the impulse to reach the target.
BRIDGE FORMATION BETWEEN ANODE AND CATHODE
The main reason for failure of the stimulating system is the shunting of current between anode and cathode. The cause may be sweat or the formation of a bridge by conducting jelly used for nerve conduction stimulators.
RECORDING SYSTEMS
The defects in the recording systems yields an incorrect display if they are connected in a improper way.
DAMAGE IN THE ELECTRODE WIRE
Proper positioning and attachment of the recording system is vital for the correct
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response it is tested by contracting the muscle below the electrodes. The cables should also be checked for recording correct responses.12,13.
INCORRECT POSITION OF ACTIVE OR REFERENCE ELECTRODE An Initial positivity prior to the peak of compound muscle action potential put
forwards a incorrect positioning of the active electrode . The recorded potential is also altered if the reference electrode is misplaced in an active electrode position rather than a remote region in relation to muscle action potential . 12.13.
WRONGLY CONNECTED SETTINGS
The recorded response would be faulty if placements of amplifiers and filters are not set properly . 12.
Figure 12 : ELECTRODE PLACEMENT 28
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STIMULATION
In order to obtain a proper and traceable amplitude in NCSs , it is important that all fibers are stimulated with in a nerve. A correct intensity of current is required for it, low current results in not desired level of stimulation of nerve fibers and a high current results in co stimulation nearby nerves. Supramaximal stimulation is necessary for depolarising the all axons of the stimulating nerve fibers.
Supramaximal stimulation is given by progressively increasing the stimulus intensity until a plateau is achieved by the amplitude , then increasing the
intensity further by 20 – 25 % for the stimulation will not excite.29
FIGURE 13 : OPTIMISATION OF STIMULATOR POSITION 29
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COMPOUND MUSCLE ACTION POTENTIAL ( CMAP )
The response after stimulation is a biphasic action potential with initial negative deflection , when the active electrode is placed properly over the motor end point of the muscle . When the electrode is misplaced from the motor end point the initial deflection will be positive, followed by a negative deflection . CMAP is the summated response of all the muscle fibers that lie within the stimulated area of the electrode.29
Figure 14 : Compound muscle action potential
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Motor nerve conduction Principle:
The principle behind the motor nerve conduction is stimulating the nerve fiber at proximal and at distal point . The following things are calculated latency, amplitude, duration, compound muscle action potential and conduction velocity.12
Figure 15 : Motor action potential stimulation
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Components in motor nerve conduction study
1. Latency 2. Amplitude 3. Area 4. Duration
5. Conduction velocity 1. LATENCY
It is said to be the time from the point of stimulus to the point of CMAP on the base line.
Causes for latency are
1. The time between the stimulus and its reaching time to neuro muscular junction.
2. Neuromuscular junction ( NMJ ) delay time.
3. Muscle depolarisation time .
Latency is short in fastest conducting motor fibers.
2. AMPLITUDE :
It is a measure of the deflection from the baseline to the negative peak or the first negative peak to the next positive peak. The amount of muscle fibers depolarised yields the amplitude. A reduction in amplitude is commonly because of axonal loss. 29
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Other causes which corresponds to it are conduction block ,neuromuscular disorders and myopathies.
3.AREA
The space above the baseline to the negative peak is the area of compound muscle action potential. Determination of it manually is not possible and it is calculated automatically in the computers of the recording devices. The number of muscle fibers depolarised is given by negative peak CMAP area. The proximal and distal stimulation differences helps in describing conduction block from demyelinating diseases.
4. DURATION
The initial deflection from the baseline to the negative peak is measured as duration. It is the measure of equality of firing of each nerve fibers in a point of time. In demyelinating diseases the duration is increased because of the slowing down of motor fibers.
5. CONDUCTION VELOCITY
Nerve conduction velocity (NCV) can be determined by stimulating the nerve at two sites ( separated by a known distance ) . NCV is calculated by measuring the distance in millimeter between two points of stimulation ,which is divided by the latency difference in millisecond.Conduction velocity ( CV ) is measured in meter/ second (m / s). 29
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Figure 16 : Motor conduction velocity calculation
29Distance from distal to proximal stimuli NCV ( m/s ) =
Proximal latency – distal latency
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SENSORY NERVE CONDUCTION
PRINCIPLES :
Sensory nerve conduction studies are performed by stimulating the nerve and recording the sensory nerve action potential ( SNAP ) directly by electrodes placed over the nerve . It can be done either antidromically or orthodromically .
In orthodromic conduction , the distal portion of the nerve is stimulated and sensory nerve action potential is recorded proximally along the nerve . It is orthodromic because the impulses are travelling in the same direction as would sensory impulses . In antidromic conduction , the stimulation is given at proximal part of the nerve and sensory nerve action potential is recorded at the distal part of the nerve that is the impulses travel in the opposite direction . Antidromic techniques are preferred over orthodromic techniques .In sensory studies nerve fibers alone are accessed.12.
ELECTRODE PLACEMENT
Ring electrodes are used for orthodromic digital nerve stimulation or recording antidromic responses . The active electrode is placed proximally and reference electrode is placed distal to the active electrode . The ground electrode is placed between active and stimulating electrode . The distance between the active electrode and reference electrode is critical because the summated SNAP amplitude is the sum of the electrical activity recorded at the two electrodes . If the two electrodes are close both become active which distorts the waveform and decreases the amplitude of action potential.12,13
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The inter electrode distance should be at least 3 cm for the potentialto clear the active electrode before the activity begins at the reference electrode .
Sensory nerve conduction can be done by both stimulating and recording from a pure sensory nerve, stimulating a mixed nerve and recording from its sensory branch (e.g.
Median antidromic digital ) , or stimulating a sensory nerve and recording from a mixed nerve ( e.g. Median orthodromic digital ).30
Figure 17 : Sensory action potential stimulation
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Figure 18 : GRAPH OF SENSORY NERVE ACTION POTENTIAL29
SNAP is a triphasic potential with an initial and a terminal positivity and a negative deflection in the middle . The negative deflection indicates the time of arrival of the impulses beneath the active electrode .
Components calculated in sensory nerve conduction study :
1. Latency 2. Amplitude 3. Duration
4. Nerve conduction velocity :
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1. LATENCY
For Biphasic sensory nerve action potentials onset latency is time between intial negative peak from the stimulus. For the triphasic sensory nerve action potentials it extends up to the initial positive peak. The midpoint of the first negative peak is the peak latency. The peak latency is not affected by stimulus artifact and noise.29
2. AMPLITUDE
The amplitude is measured from baseline to negative peak or can be calculated from negative peak to the positive peak. It represents the total of each sensory fibers that are depolarised. Decreased sensory nerve action potential describes the pathology or abnormal functioning of the sensory part of the peripheral nerve.
3. DURATION
onset of baseline to the first negative peak is calculated as duration, it can also be calculated from the initial to the end of the wave back to the baseline.sensory nerve action potential is much smaller than compound muscle action potential.it is a precise of only a nerve potential alone.
4. SENSORY NERVE CONDUCTION VELOCITY ( SNCV ) :
SNCV can be determined by stimulation at a single point unlike motor nerve
conduction velocity which requires a multiple points for stimulation.it is calculated by dividing the total distance travelled by onset latency.29
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CLINICAL APPLICATIONS OF NERVE CONDUCTION STUDY.
1. For accessing the peripheral nerve disease of the nerve fibers.
2. To distinguish between nerve lesions from muscular disorders and neuromuscular junction abnormalities.
3. Differentiate axonal degeneration from segmental demyelination.12,13,14..
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MEDIAN NERVE
Anatomy :
Median nerve derived from the medial and lateral cords of brachial plexus is a mixed nerve with root value of C5 to T1 .Median nerve mainly gives supply to the flexor muscles of forearm and thenar muscles. The lateral portion of palm and the dorsal surface of terminal phalanges receives its sensory supply via median nerve. The median nerve pass through the two heads of pronator teres in the forearm to supply it and then it also supplies flexor carpi radialis, Palmaris longus , flexor digitorum superficialis ,flexor digitorum profundum, flexor pollicus longus and pronator quadrates with its branches.
The median nerve enters the hand via carpal tunnel to supply lumbricals I and II ,opponens pollicis , flexor pollicis brevis and abductor pollicis brevis. Thenar eminence supplied by the palmar cutaneous branch receives its sensory innervations from the median nerve. 1,7.
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Figure 19 : ANATOMY OF MEDIAN NERVE
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Chart 1 : Schematic supply of median nerve
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The compression of median nerve leads to the following syndromes.
1. Carpal tunnel syndrome.
2. Anterior interosseous syndrome.
3. Pronator teres syndrome.
The above said conditions slows down the conduction along the median nerve resulting in conduction block.most common among these is the carpal tunnel syndrome. The possible cause for carpal tunnel syndrome has been listed in the table 3.
Table : 3 Causes of carpal tunnel syndrome.1,33,34.
1. Disorders reducing the space of carpal tunnel
Thickening of synovium.
Rheumatoid arthritis.
Osteophyte.
Callus.
Ganglion.
Dialysis.
Pregnancy.
Hypothyroidism.
Acromeagaly.
Amyloidosis.
Myeloma.
Over use of wrist.
Occupational.
2. Increased susceptibility to pressure.
Diabetes mellitus.
Hereditary susceptibility to pressure palsy.
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Anterior interosseous syndrome:
It is one of the branches of the median nerve.
It supplies Flexor pollicis longus, flexor digitorum profundum I II and pronator quadratus.
Clinical symptoms are Pain in forearm & elbow.
Complaints of weakness in the muscles supplied by it.
The conduction velocity is recorded in pronator quadratus by stimulating the nerve at elbow.
The results of conduction velocity helps in the diagnosis.1
Pronator Teres syndrome:
The median nerve passes through the two heads of pronator teres .
Any damage during this course leads to pronator teres syndrome the cause might be trauma, hypertrophy of muscles or any fibrous band formation.
Median conduction in this conditions reveals slowing down in proximal side.
But the latency and conduction is normal at wrist.1,
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Other Related nerve conduction research works
.In the study conducted by Hennessey WJ et al in 1994, they studied the variations in Nerve conduction study of upper limb which included 44 healthy subjects
consisting of 23 males and 21 females between age group of 19 to 43 years of age.
They explained that there exist a gender differences in nerve conduction velocities and concluded that it may be due to the circumference difference of fingers in male and female genders.35 In another study conducted by Hennessey WJ , MD Frank et al in 1994 with 44 carefully examined subjects consisting of 23 men and 21 women subjects. They found out that dominance of hand has no significant change in nerve conduction parameters. Ageing has less changes but more apparent for median nerve conduction, ageing caused a decrease in amplitude for sensory nerve action potential with increasing age.36
In a study by Mohammed Saufi Awang et al in 2007 studied the effect of ageing on nerve conduction in 250 healthy subjects. They divided them in to four groups according to their age and found that only median motor conduction had significant change.They concluded that further criteria such as height and body mass index has to be taken in to account for further studies.26 In the year 2010 Dilip Thakur et al
studied the effect of gender in nerve conduction with 34 healthy subjects consisting of 19 male subjects and 15 female subjects came out with results that males had higher compound muscle action potential, longer latencies and duration ,SNAP latencies and duration were also longer in males ,when compared to females. They suggested that
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adjustments in values should be made between male and female to increase the sensitivity and specificity of nerve conduction studies.37
In the year 2011 Sachin M Pawar et al studied nerve conduction parameters of upper limb in 175 healthy subjects consisting of 144 males and 31 females between age group of 18 to 66 years and established normative data for upper limb nerve conduction study and have founded that gender differences in SNAP amplitude of median and ulnar nerves in population of central parts of india.38
In the year 2013 Shaikh Shahabuddin et al studied nerve conduction among 90 healthy subjects comprising 45 males and 45 females aged 20 years and above found gender differences in nerve conduction velocities .In their study the results suggested that age and height had inverse relation with nerve conduction study parameters.39 In a study Ruchika G et al in 2013 studied nerve conduction velocity in upper limb in malwa region with 100 subjects consisting of 50 males and 50 females with in age group of 20 to 60 years found out gender differences in sensory potential amplitude in median and ulnar nerves established normative data for upper limb nerve conduction study.40
In 2014 Gakhar et al published a study comparing nerve conduction properties in males and female of 20 to 30 years age group with 70 subjects comprising of 35 males and 35 females found that gender had definite effects on latency, amplitude and
conduction velocity on motor and sensory nerve conduction velocities.41
In 2015 Dipti Bania et al studied nerve conduction in upper limb on 100 healthy subjects comprising of 40 males and 60 females between age group of 20 to 60 years.
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They found their nerve conduction velocities of median and ulnar motor and sensory were in similar with other previous studies in respect with gender , age and height parameters.42
In 2016 LF Owolabi et al in their cross sectional study of 200 healthy individuals comprising of 116 males and 84 females established normative data for median nerve conduction velocity in Nigerian population. They found similarities with other
existing normative data of median nerve conduction velocities.43
In 2017 Manjinder singh et al in their cross sectional study of 290 subjects
comprising of 150 males and 140 females aged 17 to 21 years. They found no gender differences which was not similar to previous studies, but their median nerve latency and amplitude was higher in males compared to the females which was in correlation with other previous existing studies.44
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MATERIALS AND METHODS
Study Design: Cross Sectional Study Study Setting:
This study was conducted during the period of December 2017 to June 2019 at Trichy SRM Medical Hospital & Research center, Irungalur, Trichy. Anthropometric measurements & Nerve conduction study were performed at the clinical physiology laboratory in the hospital.
Study Duration: one & half years.
Selection of Subjects:
The healthy volunteers were selected for this study using simple randomization technique.
Sample Size:
The calculated sample size was 200 ( 100 male subjects and 100 female subjects.) with 95% confidence interval.
Using the formula = Z 2 σ2 d 2
where Z - calculated table value for confidence interval with 95 % is 1.96.
σ - standard deviation from previous study.44 d - absolute error taken as 1 %.
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Study Population: 100 Male and 100 Female subjects from trichy population.
Inclusion criteria:
100 healthy male and 100 healthy female volunteers.
Age group - 17 years to 60 years of age.
Exclusion criteria:
A known case of systemic and neurological disorders such as ( Diabetes mellitus, systemic hypertension, and hypothyroidism.)
Neuropathy.
Myopathy.
History of upper limb injury.
Alcoholism.
Subjects with drugs affecting nerve conduction (eg: antidepressants).
Estimation of height ,weight and Body Mass Index:
The participants height and weight were recorded before the nerve conduction study in the laboratory. Height was measured in erect posture using a stadiometer to the nearest cm. Weight was measured in a standard weighing machine to the nearest kg without footwear. Body mass index (BMI) was calculated by “Quetelet’s Index”, as the ratio of weight in kg and height in meter square.
BMI = Weight ( kilograms )
Height 2 (meters)
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Subjects were divided into 3 groups according to WHO classification of BMI.
Category I Underweight: <18.5
Category II Normal: 18.5 to 24.9
Category III Overweight : >25.0
Percentage of study population were categorised as per BMI.
Methodology
The study was conducted using nerve conduction machine RMS ( Recoders medicare system ) EMG ALERON 201 channel machine in the clinical physiology
laboratory located in the hospital block of Trichy SRM Medical College Hospital and Research Centre, Trichy.
MEDIAN NERVE - MOTOR COMPONENT
The procedure was to activate the median nerve by a supra maximal stimulus at the wrist and elbow. A Compound Muscle Action Potential (CMAP) was recorded using surface electrodes and then the values are interpreted.
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Figure 20 : RMS EMG ALERON 201 CHANNEL MACHINE
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ELECTRODE PLACEMENT:
Three electrodes were used
1. Active or Recording electrode was placed close to the motor point of Abductor Pollicis brevis muscle.
2. Reference electrode was placed 3 cm distal to active electrode at first metacarpo phalangeal joint.
3.Ground electrode was placed in the palmar surface.
A supramaximal stimulus was used to stimulate the nerves . Surface stimulation was performed as per the following steps.12,13,14
Stimulation point 1:
At wrist in between the tendons of palmaris longus and flexorcarpi radialis.
Stimulation point 2:
At elbow medial to biceps tendon and brachial artery.
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Figure 21 : Median nerve motor conduction Disc electrode placement.
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MEDIAN NERVE – SENSORY COMPONENT
Median nerve is stimulated at wrist and sensory nerve action potentials are recorded from digital nerve of index finger antidromically using ring electrodes.
ELECTRODE PLACEMENT
1. Active or Recording electrode was placed at proximal inter phalangeal joint of index finger.
2. Reference electrode was placed at distal inter phalangeal joint of index finger.
The inter electrode distance should be at least 3cm.
3. Ground electrode was placed in the palmar surface.17,18
Figure 22 : Median nerve sensory conduction ring electrode placement
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NERVE STIMULATION
A supramaximal stimulus was used to stimulate the nerves.
Site : At wrist , between the tendons of palmaris longus and flexor carpi radialis approximately 1 cm proximal to the most distal wrist crease .
COMPONENTS MEASURED IN NERVE CONDUCTION STUDY 1. Proximal and distal latency of the action potential
2. Amplitude of the action potential 3. Nerve Conduction Velocity
The distal latency and nerve conduction velocity was calculated and displayed in the computer .The distal latency was measured in milliseconds (ms) and the conduction velocity was measured in meters per second ( m / s ).
Procedure :
• All the subjects who will be selected are asked to fill the data sheet with informed written consent.
• After obtaining written informed consent from the participants, The nerve conduction study was Performed using RMS EMG ALERON 201 channel machine in the clinical physiology lab .
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The proximal and distal ends of the overlying skin is cleaned with spirit.
Electrode should be fixed properly disc electrodes for motor conduction and ring electrodes for sensory conduction.
Check the connecting elements in the recording machine.
Sweep speed maintained at 5ms/cm.
Supramaximal stimulus is used in the distal and proximal end to obtain a desired amplitude .
The distance between the two stimulation points is measured and entered in the computer.
The conduction velocity and distal latency is calculated by the computer.12,13,14.
PRECAUTIONS TAKEN
1. Detailed instructions was given to the selected subjects of the study procedure before conducting the study and a informed written consent was obtained.
2. Before stimulation the subjects were relaxed.
3. Optimum temperature was maintained in clinical physiological laboratory.
4. Electrode placements were checked before to stimulation.12,13.
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Result
A total of 200 subjects were included in the nerve conduction study, out of which were 100 male subjects and 100 female subjects. The demographic characteristics are shown in table 4.
TABLE 4 . Demographic characteristics of study population ( n = 200 ).
S.no Variable Mean S.D Min Max
1 Age ( years ) 27.44 7.85 17 53
2 Height (meters ) 1.61 0.07 1.42 1.83
3 Weight (kilograms) 59.70 11.63 35 98
4 BMI 22.72 3.49 15.24 35.99
Among the individuals included in the present study , the mean age of the study group was found to be 27.44 ± 7.85 years with the range of 17 to 60 years. The mean height of the study group was found to be 161.73 ± 7.73 cm.The mean weight
