Strength Duration Curves Flashcards
A ____-_____ test is an electrodiagnostic technique used to identify the state of injury or recovery of a motor nerve or muscle
strength duration
SD testing = stimulation of a motor nerve with electrical pulses of varying ______ and detecting the _____ of current necessary to get a minimally palpable contraction.
duration; amplitude
Can SD testing be used for both motor and sensory nerves?
YES
When doing SD testing, you start with the (shortest/longest) pulse and progress to the (shortest/longest)
longest; shortest
An external electric charge musts reach a certain minimum value to ______ a nerve.
depolarize
______ ____ (Q) = current intensity x current duration.
phase charge
______ _____ = area under the curve
phase charge
For constant current stimulation using a _______ square wave pulse, the phase charge = mA.msec
monophasic
What are 3 important concepts for nerve depolarization in terms of estim?
- Intensity of electrical stimulus
- pulse duration of stimulus
- rise time of stimulus
The intensity of a stimulus must be sufficient to depolarize the nerve or muscle cell membrane to threshold, a change of ~ __-__ mV.
10-15
Very ___ current intensity cannot depolarize nerve, no matter how long it is applied
low
There is a _____ current intensity required to depolarize a nerve.
minimum
Pulse duration must be sufficiently long to allow _____ balance to be disturbed.
ionic
The ____ ____ must be short enough to reach critical excitation level before accommodation can occur.
rise time
We use ___ or ______ waveform in practice.
square; rectangular
_______ _____ _____ = the current intensity at a given pulse width at which a just perceptible motor contraction disappears.
minimum effective charge
______ = the minimum current needed to fire a nerve impulse at a long duration.
Rheobase
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.
100
_______ = 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
chronaxie
Would innervated or denervated muscle have a greater chronaxie?
denervated
The chronaxie corresponds to the pulse length requiring the minimum ______ (not charge) for excitation.
energy
Will a sensory or motor nerve require less current strength at a given pulse duration to depolarize?
sensory
In terms of recruitment, largest diameter nerves will ______ first.
depolarize
Is location of the nerve with respect to the electrode important in practice?
YES; the closer the nerve to the electrode, the more readily it will depolarize because there is a greater current intensity
For monophasic or asymmetric biphasic current, negatively charged cathode is (more/less) effective at causing depolarization.
more
Black cathode = _____ ; red anode = _____.
active; inactive
The inactive red anode causes are near membrane to become more _____.
+
The active black cathode causes area near membrane to become more ____.
-
____ ____ = point of entry of a peripheral nerve into a muscle
motor point
The motor point is usually at the junction between the proximal ___ and distal ___-___ of the muscle belly.
third; two-thirds
Current applied at the _____ _____ = greatest number of motor nerve fibres; muscle contraction using ___ current intensity.
motor point; lower
Normally innervate muscle responds to short duration pulses (___-___msec) via the nerves
0.05-0.1
Denervated muscle requires long duration pulses (__-__ms) to depolarize muscle sarcolemma directly.
50-100
What are 3 factors that could affect outcome of SD curve?
- Skin resistance (clean, warm, wet)
- Adipose tissue
- Position of electrodes
What are 4 advantages of SD testing?
- able to monitor pt progress
- non-invasive
- simple, fast and inexpensive
- remarkably high inter-rater reliability
What are 3 disadvantages of SD testing?
- Poor repeatability
- Unable to localize lesion along nerve trunk
- Less valuable for testing large muscle groups
What does the kink indication in the curve of a partially denervated muscle?
first sign of re-innervation
The location of the kink in the SD curve of a partially denervated muscle is not significant (T/F)./
TRUE
Can you have >1 kink in the SD curve of a partially denervated muscle?
YES
The portion ____ of the kink in in the SD curve of a partially denervated muscle represents innervated fibres.
left
The potion to the _____ of the kink in the SD curve of a partially denervated muscle represents innervated AND denervated fibres.
right
Changes in the curve of partially denervated muscle can precede clinical changes by up to __ weeks.
6
if there is not recovery in the curve of a partially denervated muscle by __ months = poor prognosis.
5
The curve of a partially denervated muscle gradually becomes ____ steep as the kink moves downwards.
LESS
In general, lower current amplitude and shorter pulse durations can depolarize ____ nerves, whereas higher amplitude or longer pulses are needed to depolarize ___ nerves.
sensory; motor
