A sleep study (polysomnography) is a diagnostic test that monitors your brain, heart, breathing, and movement during sleep to detect disorders like sleep apnea, insomnia, narcolepsy, and restless legs syndrome (RLS).
Types of Sleep Studies
| Type | What It Measures | When Used |
| In-Lab Polysomnography (PSG) | Full monitoring (EEG, EKG, oxygen, muscle activity) | Sleep apnea, narcolepsy, parasomnias |
| Home Sleep Apnea Test (HSAT) | Limited (breathing, oxygen, heart rate) | Suspected obstructive sleep apnea (OSA) |
| Multiple Sleep Latency Test (MSLT) | Daytime naps to assess sleepiness | Narcolepsy, idiopathic hypersomnia |
| Maintenance of Wakefulness Test (MWT) | Ability to stay awake | Assess treatment effectiveness (e.g., for truck drivers) |
Why is a Sleep Study Done?
- Diagnose sleep apnea(pauses in breathing)
- Evaluate excessive daytime sleepiness(narcolepsy)
- Assess abnormal movements(RLS, periodic limb movements)
- Diagnose parasomnias(sleepwalking, night terrors)
- Monitor seizures during sleep
What’s Measured in a Sleep Study?
| Parameter | Sensor Used | Purpose |
| Brain activity (EEG) | Scalp electrodes | Sleep stages (REM vs. non-REM) |
| Eye movements (EOG) | Near-eye electrodes | Detects REM sleep |
| Muscle activity (EMG) | Chin/leg electrodes | Checks for RLS or bruxism |
| Heart rhythm (EKG) | Chest electrodes | Arrhythmias during sleep |
| Breathing effort | Belly/chest bands | Detects apnea/hypopnea |
| Oxygen levels (SpO₂) | Finger probe | Checks for hypoxia |
| Snoring | Microphone | Evaluates sleep apnea severity |
How to Prepare for a Sleep Study
✅ Avoid caffeine & alcohol (can disrupt sleep)
✅ Wash hair (no oils/sprays) for EEG electrodes
✅ Bring comfortable clothes
✅ Take usual medications (unless doctor says otherwise)
❌ No naps on the day of the test
What Happens During the Test?
- Evening Setup (In-Lab PSG):
- Electrodes attached to scalp, face, chest, legs.
- Belly bands & oxygen monitor placed.
- Sleeping in a Clinic Room:
- Technicians monitor you via camera & audio.
- Test runs 6–8 hours(full night).
- Home Sleep Test (HSAT):
- Portable device worn overnight (fewer sensors).
Interpreting Sleep Study Results
Key Metrics:
- Apnea-Hypopnea Index (AHI):
- <5 = Normal
- 5–15 = Mild sleep apnea
- 15–30 = Moderate sleep apnea
- >30 = Severe sleep apnea
- Oxygen Desaturation Index (ODI):Drops in SpO₂ per hour.
- Sleep Efficiency:% of time asleep vs. in bed.
- REM Latency:Time to first REM phase (short in narcolepsy).
Common Diagnoses:
| Disorder | Findings |
| Obstructive Sleep Apnea (OSA) | AHI ≥5, snoring, oxygen drops |
| Central Sleep Apnea | Breathing pauses without effort (heart failure, opioid use) |
| Narcolepsy | Short REM latency (MSLT confirms) |
| Restless Legs Syndrome (RLS) | Leg movements (PLMS >15/hour) |
| Insomnia | Low sleep efficiency, long sleep latency |
Treatment Options Based on Results
- Sleep Apnea:
- CPAP/BiPAP(air pressure machine)
- Oral appliances(for mild OSA)
- Surgery(tonsillectomy, UPPP)
- Narcolepsy:Stimulants (modafinil), sodium oxybate.
- RLS:Iron supplements, dopamine agonists.
- Insomnia:CBT-I (therapy), sleep hygiene, meds (short-term).
Home Sleep Test vs. In-Lab Study
| Factor | Home Test (HSAT) | In-Lab (PSG) |
| Accuracy | Good for OSA only | Gold standard (full data) |
| Comfort | Sleep at home | Clinic environment |
| Cost | Cheaper | More expensive |
| Disorders Detected | Only sleep apnea | All sleep disorders |
HSAT is used first for suspected OSA; PSG if unclear or complex cases.
Key Takeaways
✔ Sleep studies diagnose apnea, narcolepsy, RLS, and insomnia.
✔ AHI ≥5 = Sleep apnea (CPAP is common treatment).
✔ Home tests are simpler but less comprehensive than in-lab PSG.
✔ Abnormal REM sleep may indicate narcolepsy.
