Faradic and faradic type of currents moreover IDC can be used for electro diagnosis in neuromuscular problem.

1. Dr Mubarak Muhammad Ali
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2. STRENGTH DURATION
CURVE
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3. OBJECTIVES
• What is Electro diagnosis
• What is Chronaxie & Rheobase
• Reaction of innervation and denervation
• Strength duration test
• Factors influencing strength duration curve test.
Dr Mubarak Muhammad Ali
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4. ELECTRO DIAGNOSIS
• Faradic and faradic type of currents
moreover IDC can be used for electro
diagnosis in neuromuscular problem.
• The mechanism underlying normal
electrical activity of muscle and nerves,
when stimulated with electrical current
forms the basis of electro diagnosis
Dr Mubarak Muhammad Ali
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5. CHRONAXIE
• The shorter the duration of impulse more will be the
intensity of current require to obtain minimal contraction.
• The chronaxie of an intact nerve healthy innervated muscle
is much lower approximately 0.03ms then that of
denervated muscle approx. 10ms
Dr Mubarak Muhammad Ali
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6. RHEOBASE
• Longer the duration of impulse lesser will be the intensity of current
needed to obtain minimal contraction.
• Generally 10 impulses of 300,100,30,10,3,1,0.3,0.1,0.03and0.01 are
used.
Dr Mubarak Muhammad Ali
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7. Dr Mubarak Muhammad Ali
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8. PARTIAL REACTION OF DENERVATION
• Faradic response will be that more current or a
higher rheobase will require to produce minimal
contraction.
• Denervated fibers will fail to respond and only
innervated fibers will respond to shorter duration of
impulse 0.2-1 ms of faradic current.
• Interrupted direct current will bring about
contractions through nerve in the innervated fibers
and directly stimulate the denervated fibers. The
response will be in the form of a sluggish muscle
twitch in the normal muscle.
Dr Mubarak Muhammad Ali
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9. COMPLETE REACTION OF DENERVATION
• No response to faradic or faradic type current
is obtain since the whole nerve will not be
conducting.
• To the interrupted direct current there will be
slow and sluggish muscle twitch response.
Dr Mubarak Muhammad Ali
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10. ABSOLUTE REACTION OF DENERVATION
•Because of progressive atrophy of
denervated muscle and ultimate
fibrosis, no response to even the
interrupted direct current is obtained.
Dr Mubarak Muhammad Ali
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11. STRENGTH DURATION CURVE
• Is also known as intensity duration curve
• Intensity time test & Amplitude time curve
• Its principal is based on the fact that both
nerve and the muscle response depends on
intensity of the current and duration of
impulse used and the fact that the intensity
of current require to excite a nerve or a
muscle has a relationship with duration of
the impulse
Dr Mubarak Muhammad Ali
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12. • By varying the strength and duration of electrical
impulse a graph can be plotted called SD Curve.
• Curve provide valuable information on the state of
excitability of nerve and muscle
Dr Mubarak Muhammad Ali
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13. NORMAL CURVE
• Two components respond to electrical stimulation in
the normal (innervated muscle).
• The intramuscular nerve fiber – and
• The muscle fibers
• Because nerve fibers can appreciate and respond to
shorter duration of impulses where as the muscles
respond only to longer duration of stimuli the curve
depicts the short time constant characteristics of nerve
fiber.
• A normal muscle continue to respond without
increasing the intensity until the duration of impulse is
reduced to 0.3-0.1ms the intensity must be increased to
obtain contraction.
Dr Mubarak Muhammad Ali
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14. PARTIALLY DENERVATED MUSCLE CURVE
• Partially denervated muscle response to electrical
current also depicts the long time constant
characteristics.
• The muscle will require higher intensity of current then
normal muscle to produce a rheobasic response.
• The intensity will depend on the degree or extent of
denervation.
• The muscle response to longer duration of stimuli usually
up to 3 and 10 MS pulse
• If the Duration of shorter then 3 MS then only innervated
fibers will respond.
Dr Mubarak Muhammad Ali
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15. • This is reflected in
the from of kink.
the kink divide the
curve into two
parts, one which
depicts short time
constant of nerve
fiber and other
depicting the long
time constant of
muscle fiber.
Dr Mubarak Muhammad Ali
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16. COMPLETE DENERVATION MUSCLE CURVE
• A completely denervated muscle response to electrical current
depicts the longer time constant characteristic of muscle fiber.
• A completely denervated muscle fails to shorter duration of
stimulus.
• The initial minimal response to long duration of stimuli is higher in
intensity then the normal muscle.
• For every shorter duration of stimulus the intensity must be
increased to obtain rheobasic response.
• There is steeply rising curve is obtained.
Dr Mubarak Muhammad Ali
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17. REGENERATING AND DEGENERATING CURVES.
Repeated strength duration curve tests at appropriate
intervals can reveal the regeneration of a completely
denervated or a partially denervated muscle.
Similarly a partially innervated muscle can be tested
to know whether the innervation is improving or
deteriorating.
The appearance of a kink in a completely denervated
curve is a sign of improved innervation
Dr Mubarak Muhammad Ali
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18. FACTORS INFLUENCING
STRENGTH DURATION CURVE TEST.
• 1. SKIN TEMPERATURE.
Temperature of the skin over the muscle test plays an
important role.
Decreased temperature (cold skin) raises the rheobase
values where as increased temperature reduces the
rheobase value.
It is thus important to keep the skin temperature
constant during the test.
• 2. OEDEMA.
• Presence of oedema beneath the electrodes will
increase the rheobasic values and thus affect graph.
Dr Mubarak Muhammad Ali
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19. 3. Deeper muscles can not be stimulated by
electrical current and thus invalid results.
4. Larger muscles having sections or groups
should be tested in sections e.g deltoid,
quadriceps. Only smaller muscles can be
tested wholly.
5.FATTY SKIN.
Fatty tissues offer maximum resistance to
electrical current.
Even the normal muscle will require a higher
rheobasic values.
Dr Mubarak Muhammad Ali
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20. Dr Mubarak Muhammad Ali
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21. Dr Mubarak Muhammad Ali
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