Artifact Recognition and Troubleshooting

2017 Focus Fall Super Session

The Best of the Best For Respiratory Therapists and Sleep Technologists

The Doubletree Hilton Hotel

Pittsburgh, PA

Thursday Sept. 28, 2017

LAURA A. LINLEY CRTT/RPSGT

Conflict of Interest Disclosures for Speakers

1. I do not have any potential conflicts to disclose.

2. I wish to disclose the following potential conflicts of interest:

Type of Potential Conflict Details of Potential Conflict

Grant/Research Support

Consultant

Speakers’ Bureaus

Financial support

Other

3. The material presented in this lecture has no relationship with any of these potential conflicts, OR

4. This talk presents material that is related to one or more of these potential conflicts, and the following

objective references are provided as support for this lecture:

1.

2.

3.

X

OBJECTIVES

1. Physiology, Instrument and environmental artifacts

2. Discuss and demonstrate the appropriateness of filter changes vs. referencing

3. Recognition of high frequency artifacts

4. Recognition of low frequency artifacts

5. Troubleshooting

4

WHAT'S KEY TO AN ARTIFACT FREE RECORDING

• Good, clean prep

• Balanced impedances

• Good hook-up, neatly bundled electrodes

• Place jack-box close to patients head

• Keep patient cool, not cold

• Unplug all electrical items close to patient, i.e. bed, radio, fan, etc.

PHYSIOLOGIC VS. NON-PHYSIOLOGIC

• Heart

• Muscles

• Eyes

• Sweat

• Respiratory

• Electrical

• Impedance

• Noise

• Electrode Popping

NOT ALL ARTIFACT IS BAD

• SNORING ARTIFACT: helps identify sleep onset

• MUSCLE ARTIFACT: helps identify movement in sleep

GENERAL GUIDELINES

• DOCUMENT and CORRECT

• If artifact is localized to just one channel, it typically indicates the problem lies with one electrode.

• If problem is detected during the impedence/biocalibrations, every effort should be made to resolve prior to lights out.

• If problems presents after patient is asleep, reference or change derivation first with documentation and replace when patient awakes

• CLINICAL JUDGEMENT

Eye Movement

The eye has a significant polar electrical field known as the corneoretinal potential (CRP).

The front (cornea) of the eye is

positive with to the back (retina).

8

.

AAST Technologist Guide to Sleep Studies Second Edition. Fig 35

Look Left: LEOG Positive– Downward Deflection

Verify Eye Movement

Look Left ( 1) . Look Right (2) Blink (3)

NOTE: positive part of the eye (the cornea) rotates closer to the right EOG electrode, resulting in a downward deflection. When the eyes open they rotate down, resulting in an upward deflection in the right EOG channel. Voluntary blink artifact in the frontal channels is slower and much higher in amplitude than the spontaneous blinking

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EOG Artifact in EEG seen in biocals.

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Eye Movement Facts

• Drowsiness and Stage 1 are noted to have slow rolling eye movements.

• REM (rapid eye movements)

• The CRP is often diminished or absent in blind individuals.

• This artifact cannot be eliminated.

12

Eye movement in the EEG, during REMNormal phasic twitching of legs duringNormal variation in respirations associated with REM.

13

ECG Artifact

• This artifact is prominent in patients who are obese or have short, thick necks.

• Common Mode Rejection will eliminate if impedance levels among the electrodes are low and equal

• This occurs most often when using a referential montage, particularly if the input impedances are unbalanced.

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ECG artifact in EOG, EEG, & EMG.

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ECG ARTIFACT FIX

If the offending electrode is one of the mastoid reference electrodes (M1 or M2)

• Solution #1: Re-apply these leads by raising the placement higher up on the mastoid (behind the point of the ear) to minimize the artifact

• Solution #2: Double-reference M1 and M2 to minimize the ECG artifact• Any M1/M2 artifacts will now contaminate all linked channels

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DOUBLE REFERENCE

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Cardiac Oscillation

• Usually seen when using respiratory channels.

• This artifact often occurs during prolonged central apneas and it is often incorrectly considered to indicate a patent airway.

18

Cardiac-oscillation in the flow channel

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Glossokinetic Potentials

• The tongue, like the eye, is electrically charged. The tip of the tongue is more negative than the root.

• The movement will change the electrical field around the face; this artifact in the EEG is call a glossokinetic potential.

• Commonly seen in very young patients and is due to sucking or chewing.

• Document what the patient is doing.

• Elimination of the artifact is difficult.

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INFANT SUCKING ON PACIFIER-ARTIFACT EEG

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Infant Sucking-EEG clean

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Muscle Artifact• Caused by localized muscle activity in the vicinity of an exploring or

reference electrode. Common in tense or anxious patients.

• There is no correction of the artifact in a sleeping patient

• Muscle artifact may appear in any channel that records a physiological signal. It can also be used to identify bruxism, movement arousals, vocalization, etc.

• Depending on the particular channel filter settings, such as with EEG channels, this artifact can mimic cortical spikes.

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Movement artifact, associated with bruxism

MOVEMENT IN SLOW WAVE SLEEP

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Muscle artifact in EOG & EEG

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Electrode “Pop”

• May simulate a spike or sharp wave.

• Caused by an electrically unstable electrode, by a drying electrode, or by a slight mechanical instability that changes the area of electrode surface in contact with the skin.

28

Bad Ground-popping

Movement artifact

Chin popping

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M1 electrode popping

Leg lead popping/off

No.

ELECTRODE “POP” FIX

• Bad O2 electrode (no common referential lead)

• Check lead security as well as pin input in head box

• Solution: Re-apply and/or replace the lead

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60 Hz Artifact

1. Appears as a regular, sinusoidal wave and it obscures the physiologic signal.

2. Common Mode Rejection will eliminate if impedance levels among the electrodes are low and equal.

3. Patient Ground Electrode helps dissipate 50/60Hz interference

Causes of 60 Hz

• High Electrode Impedances

• Excessive Current Leakage: • Ancillary Equipment

• Extension Cords

• TV/Fans

• Long Leg EMG Leads

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Intermittent 60 Hz

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Vagal nerve stimulator, cycling on for 7

seconds and off for 15 seconds.

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60 Hz Artifact-Fix

1. NOTCH Filter (Leg EMG)

2. Replace: Normalize Impedances

3. Electromagnetic-may be reduced by minimizing loops in electrode wires (ponytail).

4. Multiple grounds must be avoided. Unplug anything that could be the cause.

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Movement Artifact

• This artifact occurs most often during a position change but can also be produced by limb movement or the characteristic head, neck and mandible movements seen in OSA.

• Patient movement may cause electrode popping and amplifier blocking artifact, particularly if an electrode becomes loose during the study.

• In many cases, movement artifact can be useful when scoring events because it helps to identify arousals when accompanied by an EEG frequency shift.

38

Movement Artifact Seen in EEG

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Awakening-movement artifact

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Movement Artifact-Fix

• Usually disappears when patient falls asleep.

• Identify problem electrode and change derivation to back up configuration.

• Bundle the electrodes together to form a neat ponytail. Try to avoid suspending the jack-box over the headboard. It is better if the electrode bundle rests on the bed and the patient does not lay on the wires.

41

Respiration Artifact

• Respiration artifact in the EEG and EKG appears as a low frequency baseline sway that occurs in phase with the respirations. It is mostly positional.

• It frequently arises in patients with severe OSA & COPD.

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Respiratory artifact primarily in M1 & ECG

Leg electrode popping.

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Respiratory Artifact in M1

60 Hz in legs

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Respiration Artifact-Fix

• The LRR in the EEG/EPG can be raised from 0.3 to 1Hz to decrease the slow wave artifact—document and address when able.

• Reposition the electrode wires or the patient’s head by either raising or lowering it by taking or giving an extra pillow.

• Wrap the electrodes together in a neat bundle to help prevent this.

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Sweat Artifact

• Sweat artifact is best described as a low frequency baseline sway that often affects one or more channels.

• Sweat is an electrolyte that increases the conductivity of the skin surface creating a short circuit between two electrodes.

• Profuse perspiration can loosen electrodes making them susceptible to electrode popping severe enough to often cause amplifier blocking artifact.

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Sweat Artifact in the EOG & EEG

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Sweat Artifact-Fix

• Try to cool the patient, either by reducing the room temperature or removing a blanket.

• Placing a fan in the patient’s room helps but can also be a potential source of 60 Hz artifact.

• Wipe electrodes sites with alcohol

• As a last resort, reduce the low-frequency filter to minimize the effect of sweat artifact. .

IDENTIFY PROBLEM

PREVIOUS SLIDE DISCUSSION

• Previous slide shows a run of quadrigemenal PVCs

• This can be also seen on the EMG channels

• Solution: Document your findings

IDENTIFY PROBLEM

PREVIOUS SLIDE DISCUSSION• The C3 electrode was off; there was no common

reference electrode (M1, M2)• Solution: Re-apply C3 electrode

• ECG artifact was seen in the EEG and EOG leads• Solution: Double-reference M1 + M2 to attenuate the EKG

artifact

IDENTIFY PROBLEM

PREVIOUS SLIDE DISCUSSION

• Respiratory artifact was seen in the occipital leads (O1 and O2)

• Solution: Increase your LFF from 0.3 Hz to either 0.5 Hz, 0.8 Hz or no higher than 1.0 Hz to attenuate the respiratory artifact

QUESTION 1

If the positive side of the eye is the cornea, and the negative side of the eye is the retina, when the patient moves his eyes to the left, the left EOG electrode becomes more:

a. Positive

b. Negative

c. Stable

d. Upward

QUESTION 1 ANSWERLook Left….LEOG Positive---Downward Deflectiona. Positive

QUESTION 2:What’s occurring in this picture?

a. Sweat Artifact EOG

b. ECG Artifact

c. Paradoxical Breathing

QUESTION 2:What’s occurring in this picture?

B. ECG Artifact

Seen in M1 and M2

QUESTION 3 : WHAT IS OCCURING?

a. Electrode popping

b. No nasal/oral airflow sensor

c. Paradoxical breathing

d. All the above

Question 3 Answer

ALL THE ABOVE