Polysomnography: A Comprehensive Overview of Sleep Stages and Physiological Monitoring

Study Notes

Polysomnography: A Comprehensive Overview of Sleep Stages, EEG, EMG, EOG, and Respiratory Monitoring

Polysomnography, commonly known as a sleep study, is a non-invasive diagnostic test that evaluates various physiological parameters during sleep. It is the gold standard for diagnosing sleep disorders, particularly obstructive sleep apnea syndrome (OSAS). This article provides an overview of polysomnography, focusing on the subtopics of sleep stages, EEG, EMG, EOG, and respiratory monitoring.

Sleep Stages

Sleep is staged in 30-second epochs, with detailed criteria and definitions for wakefulness and each stage of sleep. Electroencephalography (EEG) is recorded at the frontal, central, and occipital regions and is used to define sleep stages.

Wakefulness: This is characterized by high-frequency, low-amplitude EEG waves, and muscle activity as measured by electromyography (EMG).
Stage 1: Transition from wakefulness to sleep, with slow eye movements and muscle tone reduction.
Stage 2: Light sleep with moderate muscle tone reduction and the presence of sleep spindles and K-complexes.
Stage 3: Deep sleep, also known as slow-wave sleep, with even lower muscle tone and slower EEG waves.
Stage 4: Deepest level of sleep, with even slower EEG waves and increased muscle tone.
Rapid Eye Movement (REM) sleep: This stage is characterized by rapid eye movements, low muscle tone, and dreams.

EEG

Electroencephalography (EEG) is a key component of polysomnography, used to monitor sleep staging, arousals, and abnormal or epileptiform activity. EEG is recorded at the frontal, central, and occipital regions, with at least three channels required to stage sleep. EEG montages may include F4-M1, C4-M1, and O2-M1, with backup electrodes also placed for possible malfunctions.

EMG

Surface electromyography (EMG) is used to evaluate muscle tone, assist with sleep staging, and detect periodic limb movements in sleep (PLMS). At least three electrodes are typically used, with chin electrodes for REM sleep without atonia (RSWA) and additional electrodes on anterior tibialis muscles for PLMS.

EOG

Electrooculography (EOG) is used to monitor horizontal and vertical eye movements, which assist in sleep staging and demonstrate in-phase eye movements. Electrodes are placed at the right and left outer canthi, 1 cm above and below the eye axis.

Respiratory Monitoring

Polysomnography includes channels to monitor respiratory activity.

Airflow: Nasal pressure sensors detect partial airflow limitation or hypopneas, while oronasal thermal flow sensors detect complete airflow obstruction or apneas.
Respiratory effort: Chest and abdominal sensors are used to evaluate respiratory effort, aiding in the distinction between obstructive, central, and mixed events.
Pulse oximetry: This detects the arterial oxygen saturation, providing information about the patient's oxygen levels during sleep.
ECG: An electrocardiogram (ECG) is included to assess for arrhythmias and heart rate.
End-tidal PCO2: This can assist with the detection of hypoventilation.
Body position sensor: An optional parameter, typically included, evaluates body position via position sensors or by examining video recordings.

In conclusion, polysomnography is a valuable tool for diagnosing and managing sleep disorders, providing an objective measure of sleep quality and physiological activity during sleep. The simultaneous recording of multiple physiologic parameters, such as EEG, EMG, EOG, respiratory monitoring, and cardiac activity, allows for a comprehensive understanding of sleep patterns and disorders.

Description

Polysomnography is a non-invasive diagnostic test that evaluates various physiological parameters during sleep. This quiz covers the overview of polysomnography, including sleep stages, EEG, EMG, EOG, and respiratory monitoring.