What Parameters Does In-lab Polysomnography Measure?

Introduction

In-lab polysomnography (PSG) is the gold-standard sleep study used to diagnose a wide range of sleep disorders. What sets it apart from at-home tests is the depth of information it provides. During the study, several physiological parameters are measured simultaneously to give a comprehensive view of how your body behaves during sleep. Understanding these parameters not only helps in accurate diagnosis but also allows doctors to tailor specific treatments based on your unique sleep profile.

In-lab Sleep Study (Source: CLM Sleep)

1. Brain Waves (EEG - Electroencephalogram)

Electrodes are placed on your scalp to monitor brain activity throughout the sleep cycle. The EEG helps identify different sleep stages: N1, N2, N3 (deep sleep), and REM (rapid eye movement). These patterns indicate sleep architecture and help detect abnormalities such as:

• Difficulty reaching deep sleep
• Frequent awakenings
• Disrupted REM cycles (linked to disorders like REM Sleep Behaviour Disorder)

EEG data is crucial in diagnosing narcolepsy or parasomnias, where brain activity does not align with normal sleep behaviour.

2. Eye Movements (EOG - Electrooculogram)

Sensors placed beside the eyes detect eye movement, particularly important for identifying REM sleep, where most vivid dreaming occurs. Eye movement signals help distinguish between wakefulness and REM and ensure the accurate staging of sleep. Abnormal REM patterns can suggest REM behaviour disorder or fragmented sleep.

3. Muscle Activity (EMG - Electromyogram)

EMG electrodes are attached to the chin, legs, and sometimes arms to record muscle tone and movement:

• Chin EMG shows reduced muscle tone during REM sleep.
• Leg EMG helps detect Periodic Limb Movement Disorder (PLMD) or Restless Legs Syndrome (RLS).
• Any abnormal muscle activity may point to parasomnias like sleep talking or acting out dreams.
• Muscle tone is essential for identifying disorders where the body fails to paralyse itself during REM.

4. Breathing Patterns and Airflow

Breathing is monitored using a combination of:

• Nasal airflow sensors
• Thermistors
• Respiratory belts around the chest and abdomen

These tools detect apnoeas (complete pauses in breathing), hypopnoeas (partial obstructions), and snoring. They help diagnose:

• Obstructive Sleep Apnoea (OSA) – blocked upper airway
• Central Sleep Apnoea – brain fails to send breathing signals
• Complex Sleep Apnoea – combination of both

Breathing disruptions are often linked with low oxygen levels and sleep fragmentation.

5. Blood Oxygen Saturation (SpO₂) and Heart Rate

A pulse oximeter, typically clipped to your finger, continuously monitors:

• SpO₂ (oxygen saturation) – shows how well oxygen is circulating
• Heart rate variability – reveals stress response or arrhythmias during sleep

Sudden drops in oxygen often indicate apnoeic events. Low oxygen for extended periods may increase the risk of high blood pressure, heart disease, or stroke. This data helps assess the severity of sleep apnoea and whether CPAP or other treatment is needed.

Other Optional Parameters

Depending on clinical suspicion, additional measurements may be included:

• CO₂ monitoring (capnography) – for suspected hypoventilation
• Video recording – for abnormal movements or seizures
• Body position sensors – to track whether events worsen when lying flat

Why These Measurements Matter

Each parameter tells a piece of the story. Combined, they offer a 360-degree view of your sleep:

• Brain waves show when you’re asleep and in what stage.
• Eye and muscle movements help confirm REM sleep and detect movement disorders.
• Airflow and oxygen levels reveal breathing quality.
• Heart rate reflects how sleep impacts cardiovascular function.

By measuring all these elements simultaneously, in-lab PSG provides a precise, multidimensional analysis, allowing for highly accurate diagnoses.

Conclusion

In-lab polysomnography is not just about watching you sleep — it’s about gathering detailed information from across your body to understand what goes wrong during the night. From brain activity and breathing to oxygen levels and leg movement, every parameter plays a role in painting a full picture of your sleep health. If you're experiencing unexplained tiredness, disrupted sleep, or snoring, talk to your healthcare provider about whether an in-lab sleep study could uncover the root of the issue.

Source: "In Lab Polysomnography: Precise Sleep Disorder Diagnosis (CLM Sleep) https://www.clmsleep.com/in-lab-polysomnography/