13th January 2024

Components of a full Polysomnogram

A full sleep study will include all the components below and be done overnight in a centre.

Staging Sleep

• Electroencephalography (EEG): to monitor brain waves and help stage sleep.
• Electrooculogram (EOG): to pick up the movement and activity of the eyes
• Electromyogram (EMG): to measure muscle tension and movement

They measure for:

• Arousals: changes in sleep stage to full wakefulness or a lighter stage of sleeping. These are counted and then divided by total sleep time to give an Arousal Index (AI)

Monitor Respiratory Airflow

• Oronasal thermistor and nasal pressure transduction: to monitor for changes to airflow

They measure for:

• Apnoeas: absence or near-complete absence of airflow. These are classified as obstructive (apnoea with evidence of respiratory effort), central (apnoea with absence of any respiratory effort) or mixed (apnoea with a period of absent respiratory effort followed by evidence of some effort).
• Hypopnea: Reduction of airflow, not sufficient to be classified as an apnoea

Respiratory Effort

• Thoracic and abdominal Respiratory Inductance Plethysmography (RIP): bands across the abdomen and thorax to measure chest and abdominal wall movement and thus respiratory effort

Oximetry

• Pulse oximeters: the most basic element to measure the oxygen saturations through sleep

They measure for:

• Hypoxaemia during sleep 

Cardiac Rate and rhythm

• Electrocardiogram (ECG): 1-3 lead ECG to measure heart rate and monitor for any cardiac dysrhythmias

Ventilation

Monitoring of ventilation is often only performed if there is a high clinical suspicion of hypoventilation.

• Transcutaneous CO2 monitoring
• End-tidal CO2 monitoring

From the above measures, one can make interpretations on:

• Sleep quality: disturbance/ fragmented sleep will exhibit a higher proportion of N1 or N2 sleep. The timing of apnoeas can also help differentiate central from obstructive apnoeas.
• Apnoea- Hypopnea Index (AHI): Apnoea + hypopneas divided by the total sleep time. This can be subdivided into an obstructive AHI and central AHI.
• Degree of Hypoxaemia