Strength Duration Curves Flashcards

1
Q

A ____-_____ test is an electrodiagnostic technique used to identify the state of injury or recovery of a motor nerve or muscle

A

strength duration

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2
Q

SD testing = stimulation of a motor nerve with electrical pulses of varying ______ and detecting the _____ of current necessary to get a minimally palpable contraction.

A

duration; amplitude

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3
Q

Can SD testing be used for both motor and sensory nerves?

A

YES

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4
Q

When doing SD testing, you start with the (shortest/longest) pulse and progress to the (shortest/longest)

A

longest; shortest

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5
Q

An external electric charge musts reach a certain minimum value to ______ a nerve.

A

depolarize

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6
Q

______ ____ (Q) = current intensity x current duration.

A

phase charge

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7
Q

______ _____ = area under the curve

A

phase charge

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8
Q

For constant current stimulation using a _______ square wave pulse, the phase charge = mA.msec

A

monophasic

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9
Q

What are 3 important concepts for nerve depolarization in terms of estim?

A
  1. Intensity of electrical stimulus
  2. pulse duration of stimulus
  3. rise time of stimulus
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10
Q

The intensity of a stimulus must be sufficient to depolarize the nerve or muscle cell membrane to threshold, a change of ~ __-__ mV.

A

10-15

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11
Q

Very ___ current intensity cannot depolarize nerve, no matter how long it is applied

A

low

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12
Q

There is a _____ current intensity required to depolarize a nerve.

A

minimum

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13
Q

Pulse duration must be sufficiently long to allow _____ balance to be disturbed.

A

ionic

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14
Q

The ____ ____ must be short enough to reach critical excitation level before accommodation can occur.

A

rise time

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15
Q

We use ___ or ______ waveform in practice.

A

square; rectangular

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16
Q

_______ _____ _____ = the current intensity at a given pulse width at which a just perceptible motor contraction disappears.

A

minimum effective charge

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17
Q

______ = the minimum current needed to fire a nerve impulse at a long duration.

A

Rheobase

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18
Q

In practice, the rheobase is the minimum _____ intensity required to get a just perceptible contraction when using a pulse width greater than or equal to ___msec.

A

100

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19
Q

_______ = the minimum duration of impulse (ie. minimum pulse width) that will produce a response in the nerve at a current intensity of double the rheobase intensity

A

chronaxie

20
Q

Would innervated or denervated muscle have a greater chronaxie?

A

denervated

21
Q

The chronaxie corresponds to the pulse length requiring the minimum ______ (not charge) for excitation.

A

energy

22
Q

Will a sensory or motor nerve require less current strength at a given pulse duration to depolarize?

A

sensory

23
Q

In terms of recruitment, largest diameter nerves will ______ first.

A

depolarize

24
Q

Is location of the nerve with respect to the electrode important in practice?

A

YES; the closer the nerve to the electrode, the more readily it will depolarize because there is a greater current intensity

25
Q

For monophasic or asymmetric biphasic current, negatively charged cathode is (more/less) effective at causing depolarization.

A

more

26
Q

Black cathode = _____ ; red anode = _____.

A

active; inactive

27
Q

The inactive red anode causes are near membrane to become more _____.

A

+

28
Q

The active black cathode causes area near membrane to become more ____.

A

-

29
Q

____ ____ = point of entry of a peripheral nerve into a muscle

A

motor point

30
Q

The motor point is usually at the junction between the proximal ___ and distal ___-___ of the muscle belly.

A

third; two-thirds

31
Q

Current applied at the _____ _____ = greatest number of motor nerve fibres; muscle contraction using ___ current intensity.

A

motor point; lower

32
Q

Normally innervate muscle responds to short duration pulses (___-___msec) via the nerves

A

0.05-0.1

33
Q

Denervated muscle requires long duration pulses (__-__ms) to depolarize muscle sarcolemma directly.

A

50-100

34
Q

What are 3 factors that could affect outcome of SD curve?

A
  1. Skin resistance (clean, warm, wet)
  2. Adipose tissue
  3. Position of electrodes
35
Q

What are 4 advantages of SD testing?

A
  1. able to monitor pt progress
  2. non-invasive
  3. simple, fast and inexpensive
  4. remarkably high inter-rater reliability
36
Q

What are 3 disadvantages of SD testing?

A
  1. Poor repeatability
  2. Unable to localize lesion along nerve trunk
  3. Less valuable for testing large muscle groups
37
Q

What does the kink indication in the curve of a partially denervated muscle?

A

first sign of re-innervation

38
Q

The location of the kink in the SD curve of a partially denervated muscle is not significant (T/F)./

A

TRUE

39
Q

Can you have >1 kink in the SD curve of a partially denervated muscle?

A

YES

40
Q

The portion ____ of the kink in in the SD curve of a partially denervated muscle represents innervated fibres.

A

left

41
Q

The potion to the _____ of the kink in the SD curve of a partially denervated muscle represents innervated AND denervated fibres.

A

right

42
Q

Changes in the curve of partially denervated muscle can precede clinical changes by up to __ weeks.

A

6

43
Q

if there is not recovery in the curve of a partially denervated muscle by __ months = poor prognosis.

A

5

44
Q

The curve of a partially denervated muscle gradually becomes ____ steep as the kink moves downwards.

A

LESS

45
Q

In general, lower current amplitude and shorter pulse durations can depolarize ____ nerves, whereas higher amplitude or longer pulses are needed to depolarize ___ nerves.

A

sensory; motor