Short Answer Physics Test Flashcards

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1
Q

Electrodiagnostics

A
  • it is a method of obtaining information about diseases by passively recording the electrical activity of body parts or by measuring their response to external electrical stimulus.
  • is a branch of medical practice in which electrical tests are performed to evaluate excitability of nerves and muscles using DC and PC.
  • The aim of electrodiagnositcs is to demonstrate the changes in excitability, occuring in the neuromuscular system which is sick
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2
Q

Electrodiagnostic testing

A
  • Is a powerful tool for diagnosing and developing treatment plans for patients with diseases of the peripheral nervous system and muscles
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3
Q

The Electrodiagnostic examinations

A
  • can provide essential information in cases of suspected peripheral nervous system disorders or injury
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4
Q

Electrical stimulation should not be used under 3 conditions

A
  • with patients having a pacemaker
  • over the carotid sinus
  • over the abdominal area during pregnancy
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5
Q

Qualitative techniques

A
  • involve observation of a type of muscle contraction in response to specific electrical pulses
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6
Q

Quantitative Techniques

A
  • are based on a quantitative determination of physical quantities, which are measurement of muscle excitability. Examples: strength-duration curve, chronaxie measurements
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7
Q

Motor point

A
  • a small area overlying muscle where aslight visible contraction is most easily elicited with a minimal amplitude(intensity) electrical stimulus
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8
Q

A motor point of a nerve

A
  • corresponds to a point on the skin, at which a nerve lies closest to skin surface
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9
Q

A motor point of a muscle

A
  • a point where a nerve enters into a muscle
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10
Q

Traditional clinical electrical evaluation tests

A
  • Reaction of degeneration test(RD)
  • Strength-duration curve and chronaxie test
  • nerve conducting tests
  • clinical electromygraphy(EMG)
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11
Q

Reaction of degeneration test(RD)

A
  • This tests is a useful screening procedure for assessment of problems that may involve lower motor neurons
  • Reaction of normally innervated muscle=it will respond with a brisk twitch when stimulated with a short-duration pulse lasting less than 1 ms and also when stimulated with longer pulse durations (for example 100 ms)
  • Reaction of normally innervated muscle- it will respond with sustained or tetanic contraction if the pulses are applied in rapid succession
  • Reaction of a muscle with peripheral denervation - it will not respond to a stimulus of 1 ms or shorter but will contract in a sluggish manner when the longer pulse duration stimulus is applied
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12
Q

RD Test - using electrodes

A
  • The electrode is used to search as precisely as possiible or the motor point of the muscle of interest
  • The negative(cathode) electrode- is used as the active stimulating electrode over the motor point
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13
Q

The first part of Classical RD test

A
  • the motor point area is stimulated with a series of short-duration(less than 1ms) pulses
  • a frequency of the stimulus-greater than 20Hz (a tetanic or sustained contraction)
  • a waveform- monophasic or biphasic(assymmetrical)
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14
Q

Reaction of a muscle in the first part of the classical RD test

A
  • a tetanic contraction- a muscle is normally innervated
  • a sluggish response or no response- peripheral denervation is likely to occur
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15
Q

The second part of the classical RD test

A
  • the involved muscle is stimulated with a long-duration pulse
  • a monophasic pulse of atleast 100 ms duration or preferably longer
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16
Q

Reaction of a muscle in the second part of the classical RD test

A
  • a slow or sluggish response-contractile muscle tissue is present but the muscle is either partially or completely denervated
17
Q

Reaction of degeneration test(RD)-Part 2

A
  • The RD test is usually not done until atleast 10 days after onset of the problem, so that the process of neural degenration can progress to a stage in which electrical changes would appear
  • An abbreviated form of the test for reaction of degeneration may be used as a quick screening test for differentiating a muscle with normal peripheral innervation from a muscle with peripheral denervation
  • The RD test is only a gross screening procedure and should not be expected to differentiate or precisely identify the location of pathology. The test may be indicated in conditions of unexplained paralysis
18
Q

Strength - Duration Curve and Chronaxie test

A
  • 1930-1960 - strength - duration curves and chronaxie measurements were widely used for electrodiagnosis of peripheral nervous system disorders in these years
  • Their frequency of use sharply declined with the development of nerve conduction testing and electromyography
  • Three tests provide a reliable means of assessing the locatio,n, severity and progress of peripheral nerve - nerve degeneration and regeneration
19
Q

Chronaxie

A
  • a minimal pulse duration of stimulus of twice rheobase strength that will cause the excitable cell membrane to discharge
20
Q

Strength - Duration Curve

A
  • is obtained by imposition of values of the time and values of the intensity which produce the minimal muscle contraction in the coordinate system
  • Plotting an S-D curve requires pulse duration ranging from 0.01 ms to 1000ms
  • To plot the strength - duration curve rectangular pulses are use
21
Q

Rheobase

A
  • a minimal intensity of stimulus amplitude(strength) required to eleicit a minimal visually perceptible muscle contraction (for 1000 ms impulse)
22
Q

Strength - Duration Curve Uses

A

Can be used for:

  • evolution of variety of lower motor neuron pathologies
  • Assessment of peripheral nerve injuries

These tests can provide reliable and accurate information on the status of peripheral innervation and denervation

23
Q

The intensity of the Stimulus (criteria of the intensity (amplitude) or strength and pulse duration or time of the stimulus)

A

must be strong to depolarize the membrane to its threshold level for excitability

24
Q

Time of the stimulus ( criteria of the intensity(amplitude) or strength and pulse duration or time of the stimulus)

A

the stimulus be of suffiecient duration to overcome the capacitance of the membrane

Q= i• t= constant

25
Q

To plot the strength- duration curve

A
  • triangular pulses can be used
  • using progressively shorter pulse durations , the values of stimulus amplitude which produce a minimal muscle contraction are recorded and then plotted on the graph
  • chronaxie and rheobase can be determined from S-D curve
  • Chronaxie
    • 0.1-1ms (a muscle is normally innervated)
    • 30-50ms ( fully denervated muscle)
26
Q

Strength- Duration Curve and Chronaxie Testing:

A
  • Are as objective as nerve conducting testing and electromyography
  • are non-invasive
  • can provide valuable information on the status and progress peripheral nerve injuries
27
Q

Strength- Duration Curve and Chronaxie Testing, other applications:

A
  • Can be for evaluation of peripheral neuritis, other peripheral nerve disease that may involve axonal degeneration and motor-neuron disease conditions
  • the tests may be used to complement other evaluative procedures in differentiating between normal nerve tissue and neuropathology
28
Q

Electromygraphy (EMG)

A
  • an assessment which provides a means of monitoring and evaluating electrical activity of muscle directly-without artificial stimulation
  • advantage: characteristics of muscle can be studied during relaxation and voluntary contraction
  • useful in evaluating electrical activity of lower motor neurons and muscle fibers, because electromygraphy helps in identifying electrical changes consistent with pathologic processes in these anatomic areas
  • instrumentation required is similar to what is used in nerve conduction testing, but an electrical stimulator is not needed
  • a sterile needle electrode is inserted directly into the muscle
  • endogenous electrophysiologic activity produced by depolarization and repolarization of the muscle cell memebrane is transduced from the electrode and displayed on oscilloscope
  • monopolar and concentric needle electrodes are most commonly used in routine EMG
29
Q

Electromygraphy (Electromygraphic activity is studied under the following conditions)

A
  • while the muscle is at rest and is completely relaxed
  • during a mild contraction, just strong enough to produce individual motor unit action potentials
  • during a very strong contraction, held with enough force to recruit as many motor units as possible
30
Q

Nerve Conducting Tests: Purpose

A
  • The purpose of these tests is to assess the time and quality of the conduction of neural impulses in peripheral motor and sensory nerves
  • A controlled monophasic pulsed electrical stimulus is applied to the skin overlying a nerve
31
Q

Nerve Conducting Tests: Instrumentation

A
  • a differential amplifier capable of detecting and accurately amplifying signals in a range from 2 mV to 50 mV
  • an electrical stimulator that provides square wave monophasic pulsed stimulus from 0.05 to 1 ms, and output amplitude up to 500 V or 100 mA
  • an oscilloscope
32
Q

Nerve Conducting Tests: Responses

A
  • the stimulus frequency capability should be variable from signal to pulse trains of 50 Hz
  • The responses are recorded from the specific sites of interest, which may be from:

>Muscle in the motor nerve conduction tests

>peripheral sensory nerves

>the scalp in evokes potential studies

33
Q

Nerve Conducting Tests: Tests

A

The following tests are distinguished:

-motor nerve conduction

-f wave nerve conduction

-sensory nerve conduction

-h reflex response

These tests are useful in establishing or rulingout the presence of a peripheral neuropathy and determining and localizing a peripheral nerve entrapment or a plexopathy

34
Q

Nerve Conducting Tests: Another Feature of Assessment

A

Another Feature of the assessment of nerve conduction test results is differentiation, when possible between nerve conduction changes consistent with a demyelinating process and those seen with an axonal disorder.