Polygraphy vs. Polysomnography: What’s the Difference?

Sleep testing can be confusing—especially when the names sound so similar.Here’s a simple breakdown of polygraphy and polysomnography, and when each one is used.

🛏️ Polysomnography (PSG): The Full Sleep Study

Polysomnography is the gold-standard, overnight sleep study performed in a sleep lab. It measures many signals at once to give a complete picture of how your brain and body behave during sleep.

What it measures:

• Brain waves (EEG)

• Eye movements

• Muscle tone

• Heart rhythm

• Breathing effort & airflow

• Oxygen levels

• Leg movements

• Sleep stages (REM, deep sleep, light sleep)

What it’s used for:

• Sleep apnea (all types)

• Narcolepsy

• REM Sleep Behavior Disorder

• Parasomnias (night terrors, sleepwalking)

• Periodic limb movement disorder

• Complex insomnia

👉 Think of it as a full diagnostic work-up that analyzes both sleep quality and breathing.

😴 Polygraphy (PG): The Focused Home Sleep Test

Polygraphy—often called a home sleep apnea test (HSAT)—is a simpler device used at home. It focuses mainly on breathing patterns, not sleep stages.

What it measures:

• Airflow

• Breathing effort

• Oxygen saturation

• Heart rate

• Sometimes snoring & body position

What it’s used for:

• Suspected obstructive sleep apnea in otherwise healthy adults

What it does not measure:

• Brain activity

• Sleep stages

• Limb movements

• Neurological sleep disorders

👉 Think of polygraphy as a quick breathing assessment, not a full look at sleep.

🔍 The Key Difference

Feature	Polysomnography	Polygraphy
Measures sleep stages	✔ Yes	✘ No
Measures brain waves	✔ Yes	✘ No
Number of sensors	Many	Few
Location	Sleep lab	Home
Best for	Broad sleep evaluation	Screening for sleep apnea

🧠 In one sentence:

Polysomnography is a comprehensive sleep study that measures brain and body activity; polygraphy is a simpler home test focused mainly on breathing to detect sleep apnea.