Strength Duration Curves

Question 1

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

Answer 1

strength duration

Question 2

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

Answer 2

duration; amplitude

Question 3

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

Answer 3

YES

Question 4

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

Answer 4

longest; shortest

Question 5

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

Answer 5

depolarize

Question 6

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

Answer 6

phase charge

Question 7

______ _____ = area under the curve

Answer 7

phase charge

Question 8

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

Answer 8

monophasic

Question 9

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

Answer 9

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

Question 10

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

Answer 10

10-15

Question 11

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

Answer 11

low

Question 12

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

Answer 12

minimum

Question 13

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

Answer 13

ionic

Question 14

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

Answer 14

rise time

Question 15

We use ___ or ______ waveform in practice.

Answer 15

square; rectangular

Question 16

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

Answer 16

minimum effective charge

Question 17

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

Answer 17

Rheobase

Question 18

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.

Answer 18

100

Question 19

_______ = 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

Answer 19

chronaxie

Question 20

Would innervated or denervated muscle have a greater chronaxie?

Answer 20

denervated

Question 21

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

Answer 21

energy

Question 22

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

Answer 22

sensory

Question 23

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

Answer 23

depolarize

Question 24

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

Answer 24

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

Question 25

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

Answer 25

more

Question 26

Black cathode = _____ ; red anode = _____.

Answer 26

active; inactive

Question 27

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

Answer 27

+

Question 28

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

Answer 28

-

Question 29

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

Answer 29

motor point

Question 30

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

Answer 30

third; two-thirds

Question 31

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

Answer 31

motor point; lower

Question 32

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

Answer 32

0.05-0.1

Question 33

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

Answer 33

50-100

Question 34

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

Answer 34

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

Question 35

What are 4 advantages of SD testing?

Answer 35

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

Question 36

What are 3 disadvantages of SD testing?

Answer 36

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

Question 37

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

Answer 37

first sign of re-innervation

Question 38

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

Answer 38

TRUE

Question 39

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

Answer 39

YES

Question 40

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

Answer 40

left

Question 41

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

Answer 41

right

Question 42

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

Answer 42

6

Question 43

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

Answer 43

5

Question 44

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

Answer 44

LESS

Question 45

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

Answer 45

sensory; motor