A (quick) overview of polysomnographic artefacts

1. A (quick) overview of polysomnographic artefacts Jo Tiete Centre Hospitalier Luxembourg

2. polysomnographic artefacts 1 Subject Induced Artefacts or Physiological Artefacts

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. Pacemaker artefact Actions • Can not be eliminated without stopping the pacemaker. • Monitor the ECG channel to identify. 7th ESST Meeting - Jo Tiete CHL

15. 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

16. Eye movement artefact Actions • There is no correction for this artefact. 7th ESST Meeting - Jo Tiete CHL

17. 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

18. Eye blink artefact Actions • There is no correction for this artefact. 7th ESST Meeting - Jo Tiete CHL

19. 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

20. Unilateral REM Actions • Ophtalmic exploring (glass eye ?). • Verify or change bad electrode, if electrode is the cause. 7th ESST Meeting - Jo Tiete CHL

21. 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

22. 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

23. 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

24. 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

25. 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

26. Body rocking & Head banging artefact Actions • There is no correction for this artefact. • Bundle electrode wires. 7th ESST Meeting - Jo Tiete CHL

27. 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

28. Muscle artefact Actions • There is no correction for this artefact. 7th ESST Meeting - Jo Tiete CHL

29. 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

30. 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

31. 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

32. Fish-mouthing artefact Actions • There is no correction for this artefact. 7th ESST Meeting - Jo Tiete CHL

33. 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

34. Snoring artefact Actions • There is no correction for this artefact. 7th ESST Meeting - Jo Tiete CHL

35. 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

36. 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

37. 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

38. Genioglossal artefact Actions • There is nothing you can do to prevent this artefact. 7th ESST Meeting - Jo Tiete CHL

39. polysomnographic artefacts 2 Artefacts that arise from subject or the recording Equipment.

40. 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

41. 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

42. polysomnographic artefacts 3 Recording Equipment or Environmental Induced Artefacts.

43. 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

44. 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

45. Salt-bridge Artefact Symptoms • When excessive amount of electrode gel spreads between two electrodes forming a conductive pathway. 7th ESST Meeting - Jo Tiete CHL

46. 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

47. 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

48. Amplifier-blocking artefact Actions • Reduce the channel’s sensitivity. • Wait till channels set. 7th ESST Meeting - Jo Tiete CHL

49. 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

50. 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