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A (quick) overview of polysomnographic artefacts. Jo Tiete. Centre Hospitalier Luxembourg. polysomnographic artefacts. 1 Subject Induced Art e facts or Physiological Artefacts. Skin artefact. Symptoms

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A (quick) overview of polysomnographic artefacts

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A quick overview of polysomnographic artefacts l.jpg

A (quick) overview of polysomnographic artefacts

Jo Tiete

Centre Hospitalier Luxembourg


Polysomnographic artefacts l.jpg

polysomnographic artefacts

1

Subject Induced Artefacts

or

Physiological

Artefacts


Skin artefact l.jpg

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.

7th ESST Meeting - Jo Tiete CHL


Skin artefact4 l.jpg

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).

7th ESST Meeting - Jo Tiete CHL


Sweat artefact l.jpg

Sweat artefact

Symptoms

  • Low frequency baseline swings that may affect one or more channels.

  • Is due to transpiration and is a combination of a salt-bridge between electrodes and the skin.

7th ESST Meeting - Jo Tiete CHL


Sweat artefact6 l.jpg

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.

7th ESST Meeting - Jo Tiete CHL


Ecg artefact l.jpg

ECG artefact

Symptoms

  • Is most prominent in subjects who are obese or have short, thick necks.

  • Often when using ear reference montages (A1-A2) and if the input impedance is unbalanced.

  • If EKG occurs on the EEG channels, you need toeliminate it to avoid misinterpretation.

7th ESST Meeting - Jo Tiete CHL


Ecg artefact8 l.jpg

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!

7th ESST Meeting - Jo Tiete CHL


Pulse artefact l.jpg

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.

7th ESST Meeting - Jo Tiete CHL


Pulse artefact10 l.jpg

Pulse artefact

Actions

  • Reposition the subject’s head.

  • Switch the amplifier’s input configuration.

  • Ad more electrolyte gel to the electrode.

  • Reposition the electrode.

7th ESST Meeting - Jo Tiete CHL


Cardio ballistic artefact l.jpg

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.

7th ESST Meeting - Jo Tiete CHL


Cardio ballistic artefact12 l.jpg

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.

7th ESST Meeting - Jo Tiete CHL


Pacemaker artefact l.jpg

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.

7th ESST Meeting - Jo Tiete CHL


Pacemaker artefact14 l.jpg

Pacemaker artefact

Actions

  • Can not be eliminated without stopping the pacemaker.

  • Monitor the ECG channel to identify.

7th ESST Meeting - Jo Tiete CHL


Eye movement artefact l.jpg

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.

7th ESST Meeting - Jo Tiete CHL


Eye movement artefact16 l.jpg

Eye movement artefact

Actions

  • There is no correction for this artefact.

7th ESST Meeting - Jo Tiete CHL


Eye blink artefact l.jpg

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.

7th ESST Meeting - Jo Tiete CHL


Eye blink artefact18 l.jpg

Eye blink artefact

Actions

  • There is no correction for this artefact.

7th ESST Meeting - Jo Tiete CHL


Unilateral rem l.jpg

Unilateral REM

Symptoms

  • Subject has lost functionality of one eye.

  • One EOG electrode is suspected of poor quality or high impedance.

7th ESST Meeting - Jo Tiete CHL


Unilateral rem20 l.jpg

Unilateral REM

Actions

  • Ophtalmic exploring (glass eye ?).

  • Verify or change bad electrode, if electrode is the cause.

7th ESST Meeting - Jo Tiete CHL


Movement artefact l.jpg

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.

7th ESST Meeting - Jo Tiete CHL


Movement artefact22 l.jpg

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.

7th ESST Meeting - Jo Tiete CHL


Tremor artefact l.jpg

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.

7th ESST Meeting - Jo Tiete CHL


Tremor artefact24 l.jpg

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.

7th ESST Meeting - Jo Tiete CHL


Body rocking head banging artefact l.jpg

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.

7th ESST Meeting - Jo Tiete CHL


Body rocking head banging artefact26 l.jpg

Body rocking & Head banging artefact

Actions

  • There is no correction for this artefact.

  • Bundle electrode wires.

7th ESST Meeting - Jo Tiete CHL


Muscle artefact l.jpg

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.

7th ESST Meeting - Jo Tiete CHL


Muscle artefact28 l.jpg

Muscle artefact

Actions

  • There is no correction for this artefact.

7th ESST Meeting - Jo Tiete CHL


Respiration artefact l.jpg

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.

7th ESST Meeting - Jo Tiete CHL


Respiration artefact30 l.jpg

Respiration artefact

Actions

  • repositioning the subject’s head or the electrode wires.

  • Keep wires bundled and from under the subject’s head or body.

7th ESST Meeting - Jo Tiete CHL


Fish mouthing artefact l.jpg

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.

7th ESST Meeting - Jo Tiete CHL


Fish mouthing artefact32 l.jpg

Fish-mouthing artefact

Actions

  • There is no correction for this artefact.

7th ESST Meeting - Jo Tiete CHL


Snoring artefact l.jpg

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.

7th ESST Meeting - Jo Tiete CHL


Snoring artefact34 l.jpg

Snoring artefact

Actions

  • There is no correction for this artefact.

7th ESST Meeting - Jo Tiete CHL


Gurgle artefact l.jpg

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).

7th ESST Meeting - Jo Tiete CHL


Gurgle artefact36 l.jpg

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.

7th ESST Meeting - Jo Tiete CHL


Genioglossal artefact l.jpg

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.

7th ESST Meeting - Jo Tiete CHL


Genioglossal artefact38 l.jpg

Genioglossal artefact

Actions

  • There is nothing you can do to prevent this artefact.

7th ESST Meeting - Jo Tiete CHL


Polysomnographic artefacts39 l.jpg

polysomnographic artefacts

2

Artefacts that arise

from subject

or

the recording

Equipment.


Bi metallic artefact l.jpg

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).

7th ESST Meeting - Jo Tiete CHL


Bi metallic artefact41 l.jpg

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.

7th ESST Meeting - Jo Tiete CHL


Polysomnographic artefacts42 l.jpg

polysomnographic artefacts

3

Recording Equipment

or

Environmental

Induced Artefacts.


50 or 60 hz artefact l.jpg

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 installedequipment. 

  • Electromagnetic radiation from the building’s electric wiring and from devices powered with these wires.

  • At the frequency of the alternating current.

7th ESST Meeting - Jo Tiete CHL


50 hz artefact l.jpg

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.

7th ESST Meeting - Jo Tiete CHL


Salt bridge artefact l.jpg

Salt-bridge Artefact

Symptoms

  • When excessive amount of electrode gel spreads between two electrodes forming a conductive pathway.

7th ESST Meeting - Jo Tiete CHL


Salt bridge artefact46 l.jpg

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.

7th ESST Meeting - Jo Tiete CHL


Amplifier blocking artefact l.jpg

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.

7th ESST Meeting - Jo Tiete CHL


Amplifier blocking artefact48 l.jpg

Amplifier-blocking artefact

Actions

  • Reduce the channel’s sensitivity.

  • Wait till channels set.

7th ESST Meeting - Jo Tiete CHL


Electrode popping artefact l.jpg

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).

7th ESST Meeting - Jo Tiete CHL


Electrode popping artefact50 l.jpg

Electrode-popping artefact

Actions

  • Switch the input to a backupelectrode. 

  • Repair or replace the electrode who suffer from high impedance.

  • Change the broken or corroded electrode lead.

7th ESST Meeting - Jo Tiete CHL


Supply line artefact l.jpg

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).

7th ESST Meeting - Jo Tiete CHL


Supply line artefact52 l.jpg

Supply line artefact

Actions

  • Inexpensive commercial filters are available and recommended.

  • Unplug devices that share the polygraphs power source.

7th ESST Meeting - Jo Tiete CHL


Static electricity artefact l.jpg

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.

7th ESST Meeting - Jo Tiete CHL


Static electricity artefact54 l.jpg

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.

7th ESST Meeting - Jo Tiete CHL


Aliasing artefact l.jpg

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.

7th ESST Meeting - Jo Tiete CHL


Aliasing artefact56 l.jpg

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.

7th ESST Meeting - Jo Tiete CHL


Mobile phone artefact l.jpg

Mobile phone artefact

Symptoms

  • When mobile phone is near headbox and not switched off.

  • Intermittant, when cellular contact operators antenna or visa versa.

7th ESST Meeting - Jo Tiete CHL


Mobile phone artefact58 l.jpg

Mobile phone artefact

Actions

  • Switch off cellular or keep away from headbox.

7th ESST Meeting - Jo Tiete CHL


Telemetry artefact l.jpg

Telemetry artefact

Symptoms

  • Generated by the local propagation of radio waves (intensive care).

  • Occur in periodic bursts.

  • Frequently present in Inductive plethysmography belts.

7th ESST Meeting - Jo Tiete CHL


Telemetry artefact60 l.jpg

Telemetry artefact

Actions

  • Balance and / or lower electrode impedances.

  • Change old or corroded Inductive plethysmography belts.

  • Shielding the laboratory may be required.

7th ESST Meeting - Jo Tiete CHL


Photonic artefact l.jpg

Photonic artefact

Symptoms

  • Applies to transducers that utilizephotonic 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.

7th ESST Meeting - Jo Tiete CHL


Photonic artefact62 l.jpg

Photonic artefact

  • Photonic transducers should be shielded from exposure to extraneous photons.

  • Commercial wraps for shielding oxymetry probes are available.

7th ESST Meeting - Jo Tiete CHL


Slide63 l.jpg

From your

« Artefact Buster »

Thank you for your attention.

Email: [email protected]

7th ESST Meeting - Jo Tiete CHL


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