Instrumentation and Common Errors Flashcards
A low frequency filter with too high of frequency limit may:
______ amplitude
____ peak latency
____the negative spike duration
______ a phase
and ____ total waveform duration
decrease amplitude
shorten peak latency
decrease the negative spike duration
add a phase
increase total waveform duration
A high frequency filter with too low a cut-off may:
_____ amplitude
______ onset and peak latency
decrease amplitude
prolong onset and peak latency
sweep speeds that are too slow may ____
omit phases, turns, or entire potentials when using digital equipment
name the equipment that comprises electrodiagnostics (5)
electrode
amplifier
microprocessor
stimulator
cathode ray tube (CRT)
when an event happens 1000 times in a second it has a frequency of ______
1kHz
equation for voltage
voltage (Volts) = current (amperes) x resistance (Ohms)
V=IR
equation for power
power = volts x amperage (current)
or P=VI or I^2 x R
equation for work
work/energy (E) = P x T or I^2 x R x t
____ measures energy stored in magnetic field set up by a conductor
Inductance - measured in Henrys (L)
____ measures the electric field that surrounds the conductor
capacitance (measured in Ferads)
_____ refers to the effects of resistance, capacitance, and inductance, not just the resistance. So it takes into account the associated magnetic field of the process, unlike resistance
impedance - there is a meter on the EMG machine to tell you how much leakage is in the system; twice a year someone should check to make sure there is no leakage in the system
_____ is cycles per second
frequency; 1 cycle per second is 1 Hz
a low filter (___ pass) allows the _____ frequencies to go through, and filters out the _____ fequencies
high pass, high, low
a high frequency filter (_____ pass) allows the ____ frequencies to go through and filters out the _____ frequencies
low pass, low, high
What are the normal settings for sensory NCS
Low freq
High freq
low 20Hz
High 2 kHz
what are the normal settings for motor NCS
Low freq
High freq
2 Hz
10 kHz
what are the normal settings for EMG
Low freq
high freq
20 Hz
10 kHz
what are the normal settings for single fiber EMG
low freq
high freq
500Hz
10Hz
elevating the low frequency filter on SNAP does what 4 things?
shortens peak latency
reduces the amplitude
changes potentials from bi-to tri-phasic
does not change onset latency
reducing the high frequency filter on SNAP does what 4 things
prolongs peak latency
reduces amplitudes
creates longer negative spike
prolongs onset latency
decreasing the low frequency filter on SNAP does what 4 things
onset latency - no change
peak latency - increases
negative spike duration - increases
amplitude - increases
increasing high frequency filter on SNAP does what 4 thigns
onset latency - shortens
peak latency - decreases
negative spike duration
amplitude - increases
CMAP if you increase low frequency filter:
same as SNAP
shortens peak latency
reduces the amplitude
changes potentials from bi-to tri-phasic
does not change onset latency
CMAP decreasing high frequency filter: (4)
less change in amplitude
prolonged onset latency
prolonged peak latency - rightward shift
not nearly as effective (as sensory nerve study) b/c motor studies have more low frequency wave forms, so fewer are eliminated
What should you do if you have simulus artifact? 4
- decrease skin impedence - remove lotions
- decrease resistance of the skin - pumous stone on callus
- make sure ground is between stim and pickup
- rotate the anode - changes isoelectric potential lines
Monopolar needle measures ______ degrees
reference where ?
360
over inert point
Concentric measures _____ degrees
reference where?
270 degrees - must spin electrode to get appropriate response “aiming periscope”
Reference is in steel shaft
If cathode and anode are reversed ____ and ____ are affected
prolongs distal latency
increases conduction velocity
what is the formula for conduction velocity
distance/prox lat - distal latency
if proximal stim cathode reversed, CV will _____
decrease
If cold, ______ stays open longer and ______ is less.
wave form gets _____.
Amplitude _____
Latency _____
CV ______
_____ per degree
Na channels
inactivation
larger
increases
decreases
decreases
2-4 m/sec per degree slowing
if you increase the gain _______
smaller differences become larger
decreased onset latency
no change in amplitude
Must have the same _____ for prox and distal stimulation
gains
if you get a positive deflection during stimulation, you _______
If persistent + deflection, ______
not over motor point
measure where leaves baseline.
Velocity =
distance/time.
there are 4cm between active and reference electrodes. If less, will get a _____ shift.
____ peak latency
_____ onset latency
______ amplictude
______ duration
left
decreased peak latency
no effect on onset latency
decreased amplitude
increased duration
constant voltage stimulation is inconsistent due to ____
skin resistance
Constant current is _____ consistent and will get _____ irrespective of skin resistence
more, same stimulation
latency and amplitude:
SNAP:
CMAP:
snap: latency to peak onset, amplitude peak to peak
CMAP onset latency when leaves the baseline. Amplitude is baseline to peak
CmAP studies must subtract out distal stim point to extrude ______
NMJ elements
which needle?
increased amplitudes
no change in duration in most studies
more phases
monopolar
Turn the machine on first then _____
hook up the patient
Nevere have ____ on the patient
2 grounds
Plug all components into ____
the same electrical bed
Absolute contraindication:
external pacemaker, no LVAds
central and deep lines okay just use opposite limb
do not use extension cords due to ______
leakage of current
Use ____ table
wooden exam table
Can do study if on anticoagulation but avoiding ____ and ____
absolute contraindication if inr is > ____
deep muscles to avoid compartment syndrome and paraspinals/multifidi
3.5
Do not place needle through ____
active cellulitis
or a nerve
PTX “at risk muscles”
(4)
C&T paraspinals - no perpendicular - aim for lamina
Supraspinatus aim towards scapula, not perpendicular
Serratus anterior - aim for rib if not palpable
rhoboids - dont do study
lymphedema is a _____ contraindication to EMG
relative - dont do it if the risk seems to be too much or if theyre having a lot of swelling. If it will change the treatment then its okay.
