Artifacts

James D. Geyer, MD

Paul R. Carney, MD

Key for Channels Used in the Examples Provided

The standard polysomnogram montage was used and included the following:

Electro-oculogram (left, LOC-A2; right, ROC-A1): LOC and ROC, left and right outer canthus electro-oculogram (EOG) electrodes

Electroencephalogram (EEG), C3-A2, C4-A1, F3-A2, F4-A1, O1-A2, and O2-A1, left central, right central, left frontal, right frontal, left occipital, and right occipital; electrode location, ground (FPZ), reference (CZ), and A1 and A2 (mastoids)

E1: Left outer canthus eye electrode

E2: Right outer canthus eye electrode

Chin1-Chin2: Submental electromyogram (EMG) signal

M1: Left mastoid electrode location

M2: Right mastoid electrode location

C3, F3, and O1: Left central, frontal, and occipital EEG electrodes

C4, F4, and O2: Right central, frontal, and occipital EEG electrodes

EMG electrodes: LAT1-LAT2 and RAT1-RAT2, left and right lower limb electrodes

Two standard electrocardiogram (ECG) leads are included: ECG1-ECG2, ECG2-ECG3

SNORE: Snore sensor sound

N/O: Nasal/oral thermistor

ORAL/N/O AIR-flow: Nasal-oral airflow

NPRE: Nasal pressure signal

THOR/CHEST and ABD: Chest and abdominal walls motion effort

MFLO: Mask flow of CPAP

Pco₂: Pressure in mm Hg of carbon dioxide

Spo₂: Percent oxygen desaturation by pulse oximetry with a finger probe

Pt Position: Patient position (supine, left, right, prone)

NPRE: Nasal pressure

Pleth: Plethysmography

EEG electrodes:

Fp: Frontopolar or prefrontal

F: Frontal

C: Central

T: Temporal

P: Parietal

O: Occipital

A: Ear or mastoid

F3: Left midfrontal

P3: Left parietal

T4: Right temporal

A1: Right ear

Cz: Vertex

FIGURE 8-1 ECG artifact in the EEG, EOG, and chin EMG.

These sharply contoured waveforms can be confirmed as an ECG artifact by their correlation with the ECG channel. (Copyright James Geyer and JNP Media, 2016. Used with permission.)

FIGURE 8-2 Eye movement artifact, otherwise known as an ocular artifact is demarcated by the stars.

The eye is a charged dipole (much like a battery). The positive pole is at the cornea and the negative pole is at the retina. The EOG consists of a bipolar linkage from the ROC electrode, 1 cm lateral and 1 cm superior to one outer canthus, to the LOC electrode, 1 cm lateral and 1 cm inferior to the other outer canthus. The electrode toward which the eyes move becomes relatively positive and the other relatively negative. (Copyright James Geyer and Neurotexion, 2016. Used with permission.)

FIGURE 8-3 Bruxism.

Bruxism or tooth grinding is a prevalent type of parafunctional oromotor activity and is categorized as a sleeprelated movement disorder. Sleep bruxism is a stereotyped movement disorder characterized by grinding or clenching of the teeth during sleep. (Copyright James Geyer and JNP Media, 2016. Used with permission.)

FIGURE 8-4 Cough artifact.

The patient has a history of lung cancer which predisposes the patient to coughing. The findings associated with a cough relate in part to the forcefulness of the cough. A hiccup has some similarities but occurs with a sudden contraction of the muscles of inspiration and closure of the glottis, which produces the characteristic sound. (Copyright James Geyer and JNP Media, 2016. Used with permission.)

FIGURE 8-5 Sweat artifact.

Sweat artifact is identified by a high amplitude and slow-frequency waveforms typically with superimposed EEG activity. This may sometimes be erroneously labeled as slow-wave sleep (stage N3) by an inexperienced technologist or polysomnographer. The electro-oculogram (EOG) and EEG electrodes are the regions most frequently affected by sweat artifact. The slow frequencies seen with sweat artifact are typically much slower than stage N3 and usually have superimposed faster frequencies. The most appropriate way to correct the artifact is by cooling the patient, removing the electrode or electrodes affected by sweating and drying the area, or even applying an antiperspirant. (Copyright James Geyer and JNP Media, 2016. Used with permission.)

FIGURE 8-6 Left artificial eye with metallic components and eyelid dysfunction.

An ocular prosthesis results in a loss of the dipole and therefore the loss of the left EOG signal. Some patients with prosthetic eyes have prosthetic hardware containing metallic components that may act as a dipole generating a typically smaller electrical potential that may appear as a low-amplitude eye movement when compared with the normal eye. (Copyright James Geyer and JNP Media, 2016. Used with permission.)

FIGURE 8-7 Eye flutter.

This may be seen with certain ocular disorders and in psychiatric conditions including anxiety and panic. (Copyright James Geyer and JNP Media, 2016. Used with permission.)

FIGURE 8-8 Abnormal eye movements related to selective serotonin reuptake inhibitor use, revealed in the EOG channels.

Prominent eye movements are seen during non-REM (NREM) stage N2 sleep. These abnormal eye movements during NREM sleep have been described in patients taking SSRIs such as fluoxetine, paroxetine, citalopram, and escitalopram. (Copyright James Geyer and JNP Media, 2016. Used with permission.)

FIGURE 8-9 Reading artifact in the ocular leads.

The unique feature of this artifact is demonstrated by the repetitive rhythmic pattern compatible with reading. (Copyright James Geyer and JNP Media, 2016. Used with permission.)

FIGURE 8-10 Mask flow artifact.

The morphology of the mask flow channel displays the characteristic sharp dip at the end of each breath below the baseline level. (Copyright James Geyer and JNP Media, 2016. Used with permission.)

FIGURE 8-11 Chewing artifact from the patient eating.

The chewing motion, occurring during wakefulness, originates in the chin with spread to the other EEG electrodes, which is similar to the pattern seen with bruxism. (Copyright James Geyer and JNP Media, 2016. Used with permission.)