Transcript Let's talk about polysomnographic artefacts

A (quick) overview of
polysomnographic artefacts
Jo Tiete
Centre Hospitalier Luxembourg
polysomnographic
artefacts
1
Subject Induced
Artefacts
or
Physiological
Artefacts
Skin artefact
Symptoms
• The skin is considered to
contribute the greatest
possible distortion of brain
potentials.
• The factors that effect skin
impedance are its:
– thickness,
– the degree of cellular
hydration,
– the number of sweat
glands
– and hair follicles which
provide low-resistance
pathways into the skin.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
3
Skin artefact
Actions:
• Proper preparation of the skin is the sleeptech
most important concern.
• Degreasing with aceton/ether.
• Rubbing the skin (peeling), but with care… for
the subject and for the sleeptech! (blood born
viruses).
15/07/2015
7th ESST Meeting - Jo Tiete CHL
4
Sweat artefact
Symptoms
• Low frequency baseline
swings that may affect one
or more channels.
• Is due to transpiration and is
a combination of a saltbridge between electrodes
and the skin.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
5
Sweat artefact
Actions:
• Identify the electrode and eliminate it by making
appropriate changes to the channel’s input selector or
replace electrode.
• Cool the subject, by reducing the room T°, use a fan or
remove blankets.
• Place an absorbing towel under the subject’s head.
• Use an anti-perspirant aerosol on the area around the
electrode.
• As last resort, you can reduce the low-frequency filter.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
6
ECG artefact
Symptoms
• Is most prominent in
subjects who are obese or
have short, thick necks.
• Often when using ear
reference montages (A1A2) and if the input
impedance is unbalanced.
• If EKG occurs on the EEG
channels, you need to
eliminate it to avoid
misinterpretation.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
7
ECG artefact
Actions
• Reposition or move the mastoid reference (A1 &
A2) electrodes to the ear lob.
• Link the 2 mastoids (A1<->A2) with a jumper
cable, doing so will most likely alter the
amplitude of the waveforms.
• Lowering the high-freq filter is not a good
practice!
15/07/2015
7th ESST Meeting - Jo Tiete CHL
8
Pulse artefact
Symptoms
• It is a mechanical artefact
that is picked up because
the recording electrode is
positioned over an artery.
• Monitoring EKG is useful.
• R phase of EKG wave
occurs at the same point
in each EEG slow wave.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
9
Pulse artefact
Actions
• Reposition the subject’s head.
• Switch the amplifier’s input configuration.
• Ad more electrolyte gel to the electrode.
• Reposition the electrode.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
10
Cardio ballistic artefact
Symptoms
• Cardiac pumping is detected
on respiratory flow/effort
channels during apneas.
• Related to pulse artefact.
• Also on oesophagial
pressure channels but
sometimes on any high
impedance EEG channel.
• Mostly seen in thin/skinny
individuals.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
11
Cardio ballistic artefact
Actions
• Repositioning the subject’s head.
• Raising the subject’s head off the bed with a roll of
towels may eliminate it.
• Eliminate artefact by repositioning the
oesophageal pressure catheter.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
12
Pacemaker artefact
Symptoms
• This artefact is due to an
electrical pulse of the
pacemaker.
• Can be periodic or
intermittent and may
appear in one or more
channels.
• May look like spikes or
sharp waves in the EEG.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
13
Pacemaker artefact
Actions
• Can not be eliminated without stopping the
pacemaker.
• Monitor the ECG channel to identify.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
14
Eye movement artefact
Symptoms
• Eyes have a strong polar
field (cornea-fundal &
cornea-retinal potential).
• Is of sufficient strength to
introduce slow wave
artefact into frontal &
temporal EEG signals.
• But useful for detecting
stage 1 or REM.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
15
Eye movement artefact
Actions
• There is no correction for this artefact.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
16
Eye blink artefact
Symptoms
• Same process as eye
movement artefact, but
always in awake.
• Blinking artefact can
pollute the EEG tracings
but are useful because
the frequency of eye
blinks decrease with
drowsiness prior to sleep
onset.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
17
Eye blink artefact
Actions
• There is no correction for this artefact.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
18
Unilateral REM
Symptoms
• Subject has lost
functionality of one eye.
• One EOG electrode is
suspected of poor quality
or high impedance.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
19
Unilateral REM
Actions
• Ophtalmic exploring (glass eye ?).
• Verify or change bad electrode, if electrode is the
cause.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
20
Movement artefact
Symptoms
• High amplitude slow
waves sometimes with
amplifier blocking in the
EEG channels.
• During a position change
or limb movement or the
characteristic head, neck
and mandible movements
seen in OSA.
• Cause electrode popping
and amplifier blocking.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
21
Movement artefact
Actions
• Wrap electrodes and transducers together and form a
neat bundle (poney tail) to reduce this type of
artefact.
• Avoid suspending the head box over the bed’s
headboard with all wires in bed.
• Better have the electrode wire bundle rest on the bed
without the subject laying on the wires.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
22
Tremor artefact
Symptoms
• 4-8 Hz that can be
confused with theta.
• In Parkinson’s disease.
• Decrease with sleep onset
but tremors may remain
present during stage two
or reappear during REM.
• Plethysmography belts
can also pick up this
artefact.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
23
Tremor artefact
Actions
• Repositioning the subject’s head to avoid contact
with the bed will reduce but not eliminate this
artefact.
• Nothing that can be done to eliminate tremors
detected by inductive plethysmography belts.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
24
Body rocking & Head
banging artefact
Symptoms
• Both disorders produce a
periodic occurrence of
movement artefacts.
• Sometimes with amplifier
blocking which in most
cases affects all EEG
channels.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
25
Body rocking & Head
banging artefact
Actions
• There is no correction for this artefact.
• Bundle electrode wires.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
26
Muscle artefact
Symptoms
• Can appear in all channel.
• Can mimic cortical spikes
If continuously present.
• Can be used to identify
bruxism, movement
arousals, vocalization,
motion, tension, etc.
• Can render portions of the
record unscorable.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
27
Muscle artefact
Actions
• There is no correction for this artefact.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
28
Respiration artefact
Symptoms
• Low frequency baseline
sway in EEG.
• Occurs in-phase with the
respiration tracing.
• Artefact is positional.
• Caused by body
movements associated
with respiration.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
29
Respiration artefact
Actions
• repositioning the subject’s head or the electrode
wires.
• Keep wires bundled and from under the subject’s
head or body.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
30
Fish-mouthing artefact
Symptoms
• False "breaths" recorded
by thermal airflow probes.
• Misclassify obstructive
apnoea as an obstructive
hypopnoea.
• Produced by air being
drawn into the mouth as
the mandible retracts
during a blocked
inspiration.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
31
Fish-mouthing artefact
Actions
• There is no correction for this artefact.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
32
Snoring artefact
Symptoms
• Mostly, but not only, in
EMG.
• Indicate an increase in
respiratory drive.
• Sufficient to incorporate a
secondary inspiratory
musculature.
• Is considered as a
physiological response to
increased pCO2 levels.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
33
Snoring artefact
Actions
• There is no correction for this artefact.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
34
Gurgle artefact
Symptoms
• Appears as spindle-like
activity in the EEG
channels on each inhale
or exhale.
• Seen in comatose
subjects.
• Can affect the estimated
airflow signal.
• Can occur when CPAP
machine is used with a
humidifier in a cold room
(condensation).
15/07/2015
7th ESST Meeting - Jo Tiete CHL
35
Gurgle artefact
Actions
• Swallowing clear the airway, but comatose
subject may require suctioning of the airway.
• When present in the estimated airflow channel of
a CPAP you need to drain the condensed water
from the hose.
• It may also be helpful to insulate a portion of the
CPAP tubing (decrease condensation).
• Increase the room temperature in order to reduce
condensation.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
36
Genioglossal artefact
Symptoms
• The subject’s tongue is an
electrically polarized mass
that can introduce slow wave
artefact into EEG channels.
• Raising the tip of the tongue
to the roof of the mouth can
generate a potential of 100
micro volts at the vertex.
• This artefact has been
described as resembling
intermittent, rhythmic delta.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
37
Genioglossal artefact
Actions
• There is nothing you can do to prevent this
artefact.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
38
polysomnographic
artefacts
2
Artefacts that arise
from subject
or
the recording
Equipment.
Bi-metallic artefact
Symptoms
• Blocked Ionic flow between
different metals that
discharge suddenly.
• Oral appliances, dental
fillings can produce an
intermittent artefact that
presents as sharp waves or
spikes. (=subject).
• If different metals, scratched
silverchloride or gold
electrode are used. (=
environment).
15/07/2015
7th ESST Meeting - Jo Tiete CHL
40
Bi-metallic artefact
Actions
• Record the discharges on a separate channel by
positioning electrodes over the location of the
dental fillings, or metal components of appliances
to identify the artefact.
• Chloride the scratched (silver) electrode.
• Discard scratched gold electrodes.
• Use of « disposable » electrodes.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
41
polysomnographic
artefacts
3
Recording Equipment
or
Environmental
Induced Artefacts.
50 or 60 Hz Artefact
Symptoms
• 50 (60Hz) interference was
very common on analog
amplifiers (bad common
mode rejection).
• Source is environmental, but
can also indicate malfunction
or improper installed
equipment.
• Electromagnetic radiation
from the building’s electric
wiring and from devices
powered with these wires.
• At the frequency of the
alternating current.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
43
50 Hz Artefact
Actions
• Check impedance and balance impedance between
electrodes, specially Ref. or ground.
• Apply gel or place fresh electrode(s).
• Verify if electrode cables are not lose and bundle them.
• All conductive surfaces (antennas!) and electric
appliances near subject should be grounded to the same
ground.
• Keep bio-signals and power leads far away.
• Better a non-motorized wooden than a metal bed.
• Don’t make loops in power cords.
• Use a « Fahraday cage ».
• As a last resort, you can use the 50/60Hz notch filter.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
44
Salt-bridge Artefact
Symptoms
• When excessive amount
of electrode gel spreads
between two electrodes
forming a conductive
pathway.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
45
Salt-bridge Artefact
Actions
• Switch to a backup electrode.
• Cleaning the skin surface between the
electrodes.
• Remove the electrodes, clean the skin then,
reapply the electrodes.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
46
Amplifier-blocking
artefact
Symptoms
• Excessif amplification
leads to signal clipping or
amplifier blocking.
• Pen deflection is maximal
for an amount of time.
• No interpretation possible
on one or more channels.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
47
Amplifier-blocking
artefact
Actions
• Reduce the channel’s sensitivity.
• Wait till channels set.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
48
Electrode-popping
artefact
Symptoms
• Is usually intermittent.
• Can be mistaken as spike
trains, sharp waves and
even K-Complexes.
• The cause is most often a
loose electrode or broken
electrode wire (corrosion).
15/07/2015
7th ESST Meeting - Jo Tiete CHL
49
Electrode-popping
artefact
Actions
• Switch the input to a backup electrode.
• Repair or replace the electrode who suffer from
high impedance.
• Change the broken or corroded electrode lead.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
50
Supply line artefact
Symptoms
• Resemble as a spike and
may affect one or all of
the channels.
• Referred to as a power
surge.
• Power supply is unstable
or is placed under heavy
load by the current
demand (on/off switch).
15/07/2015
7th ESST Meeting - Jo Tiete CHL
51
Supply line artefact
Actions
• Inexpensive commercial filters are available and
recommended.
• Unplug devices that share the polygraphs power
source.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
52
Static electricity
artefact
Symptoms
• Surrounds us and on a
polygraphic recording.
• An environmental artifact
that can appear on
differential channels.
• Isolated slight baseline
sway or as a spike.
• It may also appear as a
spike on any DC channel.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
53
Static electricity
artefact
Actions
• Increase the relative humidity in room.
• Use commercial aerosol sprays designed to
neutralize static charges (on the blankets).
• Use proper grounding techniques.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
54
Aliasing artefact
Symptoms
• results when frequencies
from separate sources
combine to produce an
interference pattern at
lower frequencies.
• Typical sources include
hospital paging systems,
telemetry, television and
radio signals.
• In digital recordings when
too low sampling rate are
used.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
55
Aliasing artefact
Actions
• Proper grounding reduces aliasing from
electromagnetic radiation.
• Shielding the laboratory may be required.
• Appropriate sampling rate (>= 2 x value of the
highest frequency) is needed to properly
reconstruct the original waveforms in digital
recording systems.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
56
Mobile phone artefact
Symptoms
• When mobile phone is
near headbox and not
switched off.
• Intermittant, when cellular
contact operators antenna
or visa versa.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
57
Mobile phone artefact
Actions
• Switch off cellular or keep away from headbox.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
58
Telemetry artefact
Symptoms
• Generated by the local
propagation of radio
waves (intensive care).
• Occur in periodic bursts.
• Frequently present in
Inductive
plethysmography belts.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
59
Telemetry artefact
Actions
• Balance and / or lower electrode impedances.
• Change old or corroded Inductive
plethysmography belts.
• Shielding the laboratory may be required.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
60
Photonic artefact
Symptoms
• Applies to transducers
that utilize photonic
technology (oximetry,
transcutaneous CO2 and
photoplethysmography).
• introduced by any device
that emits near-IR to IR
light (camera infra-red
light, ambient light).
• Degrade accurate reading
of subjects pulse or
SAO2.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
61
Photonic artefact
• Photonic transducers should be shielded from
exposure to extraneous photons.
• Commercial wraps for shielding oxymetry probes
are available.
15/07/2015
7th ESST Meeting - Jo Tiete CHL
62
From your
« Artefact Buster »
Thank you for your attention.
Email: [email protected]
15/07/2015
7th ESST Meeting - Jo Tiete CHL
63