Artifacts and Troubleshooting Flashcards
____ refers to an extraneous
signal appearing in a recording
channel on the PSG.
Artifact
____ are electrical signals
recorded in a channel that cause
the desired signal to become
harder to read.
Artifacts
After electrodes are placed on the patient, an _____
should be performed to assess the quality of the signals.
impedance check
______ refers to
resistance to a current.
Electrical impedance
When electrical flow is impeded or resisted, a signal is more likely to be contaminated with ___ or extraneous electrical activity.
artifact
Impedance values should be __
and fairly ___ in measurement.
low / equal
The AASM recommends that
impedance values below _____ be achieved.
5 kiloohm
Low and equal impedance values
are associated with _____ that are less likely to contain artifacts.
higher-quality recordings
______ are associated with an increased chance of contamination with
artifacts and occur when an
electrode is not securely placed
against the skin or scalp, when the electrode site has not been
properly cleaned, or when the
sensor is faulty, broken, or dirty.
High impedance values
Artifacts can originate from the
____, the ____, or ____, and _____
vary.
patient, equipment, external
sources, corrective methods
_____ is a fast-wave
activity that depicts the
electrical activity of the
patient’s heart and appears in a
channel other than the ECG
channel.
ECG artifact
This is a common artifact in
patients with hypertension. The
increased blood pressure in
hypertensive patients causes
the ____ to be felt easily in
areas of the body away from
the heart.
pulse / ECG Artifact
_____ is most commonly
seen in the EEG,
electrooculogram (EOG), chin
EMG, and leg EMG channels
and presents itself as a single
fast wave appearing
approximately every ___,
depending on the underlying
heart rate.
ECG artifact / second
The ____ can be easily
identified by lining up the
extraneous signal with the
patient’s QRS complex in the
ECG channel.
artifact
The primary cause of ECG
artifact is _____
poor electrode
placement.
An electrode that is placed
directly over a ____ or an
_____ is likely to detect the
pulse and transmit this signal
to the polysomnograph.
large vein / artery
Correction of ECG artifact
relies on identification of the
_____.
source electrode
Because the ____ is usually associated with poor electrode placement, the best method of correction is to move any affected electrode to an appropriate ______.
artifact / alternate
location
For example, the reference
electrodes M1 and M2 are
usually placed on the ___
process behind the ear. If they
are recording the ECG, these
electrodes can be moved
higher up behind the ear or to
the earlobes.
mastoid
If ECG artifact is identified after
the patient falls asleep, it can
be corrected by either _____ or ____
re- referencing or double
referencing.
____
is accomplished by changing one of the channel’s inputs
(G2) to an alternate electrode.
Re-referencing
_____ is characterized by high-amplitude, high-frequency signals that obscure many or all of the channels and occur as a result of a body movement.
Movement artifact
_____ is probably the most
frequently occurring artifact during a sleep study.
Movement
Even small muscle
movements can cause ____, ____ changes as the skin moves across the tissues underneath it.
high- amplitude, high-frequency
During ____ and
_____ procedures, the
technologist should instruct the
patient to lie still, preferably in the supine position, reducing or
eliminating movement artifact.
impedance checks and calibration
_____ can be subdivided into several types that include sweat, respiratory, and sway artifact.
Slow-wave artifact
Slow-frequency artifacts are
characterized by a _____, usually _____ waveforms intruding into one or several channels.
slow frequency / high-amplitude
_____ is a type of slow-
frequency artifact caused by sweat on the patient’s skin.
Sweat artifact
___ from sweat causes a chemical reaction
that, in turn, causes slow changes in the frequency of electrical signals.
Salt
The ___ and ___
channels are most frequently
affected by sweat artifact.
EOG and EEG
As the patient sweats from the
forehead, often the ground lead is affected, which serves as a
reference for all the ___ and ___ channels.
EOG and EEG
______ is a slow-frequency artifact that it caused by slow, subtle head movements
associated with breathing.
Respiratory artifact
____ is commonly caused by swinging movements of the electrode wires or the headbox.
Sway artifact
This artifact is usually recognized
by ruling out the other two causes or visualizing motion of the head box. (____)
Sway artifact
Slow-wave artifacts can be
masked by increasing the ______
low-frequency filter (LFF).
If the artifact is caused by
breathing, as in a respiratory
artifact, repositioning the patient’s head on the ___ can be helpful.
pillow
if a patient is sweating and slow artifact is noted, it is appropriate to ______ affected by the sweat, dry the area, replace them, and use a fan to keep the patient cool.
remove electrodes
Lastly, resecuring the head box
can effectively eliminate ____ if
that is the source of the artifact.
sway
____ is an artifact caused by snoring.
Snore artifact
This usually appears in the EEG
channels or in the chin EMG.
Snore Artifact
____ appear as high-
amplitude, high frequency bursts of activity for a short period of time, corresponding with and ending when the snore ends.
Snore artifacts
Snore artifact is not correctable by changing filter or gain settings, but it will correct itself when the patient ___.
stops snoring
When an electrode is broken or
disconnected from the patient or
head box, it works as an ___
and detects electrical activity from ____.
antenna / external sources
This electrical activity is often
referred to as ___ and is usually in the frequency range of ___, because
this is the frequency used by most electrical devices and outlets in the United
States.
electrical noise , 60 Hz
This ____ usually ___ signal appears to dominate any affected channel,
obscuring relevant waveforms.
high frequency, / high-amplitude
Occasionally ______
may be present when all
connections are stable, but an
electrical device resides close to
the diagnostic equipment.
60-Hz interference
Today’s sleep diagnostic systems
include a built-in 60-Hz filter, also called a ___ or a ____.
notch filter / line filter
This sets a special frequency filter from _____ to help reduce 60-Hz artifact.
59 Hz to 61 Hz
____ filters merely
attenuate signals outside the filter ranges rather than completely eliminate them.
frequency
Therefore, if a ___ signal is present, it will likely
affect the quality of the tracing
even if the notch filter is applied.
As with other artifacts, the optimal method of correction is at the ___.
60- Hz / source
The most common cause of 60-Hz artifact is ____ or improper cleaning of the site.
poor electrode application
Faulty, broken, or disconnected
electrodes can permit the entrance of _____ into the pathway, as can loose cable connections or electrical devices sitting close to the diagnostic equipment.
60-Hz signals
_____ and other ____
items touching the electrode also can be potential sources of 60-Hz interference.
Metal jewelry and other metal
_____ occurs when high- frequency muscle activity
contaminates a channel that is not designed to collect muscle activity.
Muscle artifact
___ appears to mimic the
activity that is collected in the EMG channels.
artifact
On a sleep study, muscle artifact is commonly seen in the __ and ___ channels when a patient is
anxious or clenches the jaw or
grinds his or her teeth.
EEG and EOG
______ is most often
observed when the patient is
awake and tends to gradually
disappear as the patient relaxes
and enters sleep.
Muscle artifact
______ is characterized by occasional pops or bursts of 60- Hz activity in a channel.
Electrode popping
This is usually caused by a loose
connection in the signal pathway or a faulty or broken wire.
Electrode Popping
_______ often displays
itself as just one fast high-
amplitude wave, or it may pop for a few seconds at a time before returning to normal.
Electrode popping
______ is characterized by a blocking of the pens at the highest and lowest points of the channel parameters.
Pen blocking
This artifact occurs when the gain setting in a channel is too high, causing the pen to attempt to reach beyond the upper and lower parameters of the channel.
Pen blocking
_____ are two terms used interchangeably to describe the amplitude settings on the polysomnograph.
Gain and sensitivity
Although the _____ of
the signal remains unchanged and is defined at the source of the signal (the patient), the display of the height of the signal can be adjusted.
actual amplitude
When the ____ is increased, the height of the waveform display increases.
gain setting
The sensitivity setting is
measured in terms of _____
microvolts
per vertical millimeter (μV/mm).
the ______ is
increased, the waveform appears shorter in height.
sensitivity setting
Some polysomnographs use a
_____, some use a _____, and some have options to use either one or both.
gain setting / sensitivity setting
Changing the gain setting
from _____ would double the height of the waveform, while changing the sensitivity from ____ μV/mm would half the display of the waveform.
1 to 2 / 20 to 40
______ can also
negatively affect the signals on a
PSG.
Improper filter settings
As a general rule, ____ should not be used to correct artifacts
because it is likely to eliminate
relevant waveforms intended to be recorded from the patient.
filters
If the LFF on an EEG channel is
increased from the recommended setting of ____, it will attenuate the ____ and _____ will be missed.
0.3 to 3 Hz / slow EEG waves / delta waves
If the HFF is decreased from the
recommended setting of ____, it will attenuate _____, _____, and other _______.
35 to 10 Hz / alpha waves, spindles, and other fast EEG waveforms.
Because of the potential effects of over ____, frequency filters
should be used conservatively.
filtering
