Sleep Study & Sleep Lab — What to Expect

What Is a Sleep Study?

A sleep study — medically called polysomnography — records what your body does while you sleep. It is the test that confirms or rules out obstructive sleep apnoea, and it is the single most useful investigation in sleep medicine.

Snoring alone cannot tell you whether you have sleep apnoea. Neither can daytime tiredness, a partner's description, or how you feel in the morning. Only a sleep study measures what actually happens to your breathing overnight.

The test is painless. Nothing is injected, nothing goes inside your body, and you are not sedated. Sensors are placed on the skin and you sleep as normally as you can.

What a Sleep Study Measures

Several body systems are recorded at once, which is why the word polysomnography (many measurements) is used:

Position matters more than most people expect. Some patients have significant apnoea only when sleeping on their back — a finding that changes treatment entirely.

Sleep Lab vs Home Sleep Test

Two formats exist, and they are not interchangeable.

In-lab polysomnography is done overnight in a sleep lab. A technician applies the sensors and monitors the recording through the night. It captures brain activity and sleep staging, so it detects arousals and non-respiratory sleep disorders that a home device cannot.

A home sleep apnoea test uses a smaller device you take home and wear in your own bed. It records breathing, oxygen and heart rate, but usually not EEG — so it cannot measure sleep stages or confirm how long you were actually asleep.

A home test that comes back normal does not rule out sleep apnoea if symptoms are strong — it under-estimates severity when you sleep poorly with the device. In that situation an in-lab study is the correct next step.

Understanding Your AHI Score

The headline number on your report is the AHI — Apnoea-Hypopnoea Index. It is the average number of times per hour that your breathing stopped (apnoea) or became significantly shallow (hypopnoea).

Thresholds differ in children, where an AHI above 1 is already abnormal — one reason paediatric sleep-disordered breathing is assessed differently.

Three other numbers matter:

• Oxygen nadir — the lowest oxygen level reached. Someone with moderate AHI but oxygen dropping into the 70s may need more urgent treatment than the AHI alone suggests.
• ODI (Oxygen Desaturation Index) — how many times per hour your oxygen fell by 3–4% below baseline. It shows how often the events actually cost you oxygen.
• Supine AHI — your AHI while on your back. If it is far higher than your overall AHI, positional therapy may help considerably.

An apnoea is a complete pause of 10 seconds or more; a hypopnoea is a partial blockage reducing airflow by at least 30% with an oxygen drop or arousal. Both count toward your AHI.

AHI is not the whole picture. Two people with an AHI of 20 can need different treatment depending on oxygen levels, symptoms, blood pressure and heart health.

Do You Need a Sleep Study? The STOP-BANG Screen

STOP-BANG is a widely used screening questionnaire. It does not diagnose anything — it estimates whether testing is worthwhile.

• S — Snoring loudly?
• T — Tired during the day?
• O — Observed to stop breathing during sleep?
• P — Pressure: treated for high blood pressure?
• B — BMI over 35?
• A — Age over 50?
• N — Neck circumference over 40 cm?
• G — Gender: male?

Roughly: 0–2 yes = low risk; 3–4 = intermediate; 5–8 = high risk, and a sleep study is clearly indicated.

Consider testing regardless of score if you have loud habitual snoring, witnessed breathing pauses, unrefreshing sleep, morning headaches, difficult-to-control blood pressure, or you feel sleepy while driving.

What Happens on the Night

For an in-lab study at our sleep lab in Kilpauk:

1. Arrive in the evening, usually around 8–9 pm, with your usual night clothes and medication.
2. Sensor placement takes 30–45 minutes. Small sensors are taped or clipped on — scalp, face, chest, a finger probe, and soft bands around chest and abdomen.
3. You sleep. Most people sleep less well than at home; that is expected and does not invalidate the test. You can turn over, and staff will help if you need the bathroom.
4. Morning removal, typically by 6–7 am. There is no recovery period — go straight to work if you wish.
5. Report and consultation. Raw data is scored and interpreted, and results are explained alongside your symptoms.

Practical points: avoid caffeine after mid-afternoon and alcohol that evening, skip hair oil or heavy creams so sensors stick, and continue regular medication unless told otherwise.

When DISE Is Needed

A sleep study tells you how severe the obstruction is. It does not tell you where it is happening — and that matters if surgery is being considered.

Drug-induced sleep endoscopy (DISE) answers the "where". Under light sedation that mimics natural sleep, a flexible endoscope views the airway while you are actually obstructing. It shows whether collapse is at the soft palate, the tonsils, the tongue base, or several levels together.

Findings are usually recorded using the VOTE classification, which grades collapse at four levels:

Many patients collapse at more than one level, which is precisely why single-site surgery sometimes disappoints.

This is what makes surgery targeted rather than speculative. Palate surgery will not solve tongue-base collapse, and the reverse is equally true. DISE findings guide the choice between uvulopalatopharyngoplasty, tongue base reduction, jaw advancement surgery, or a combination.

DISE is usually recommended when CPAP has not been tolerated and surgical alternatives are being planned.

After Your Results

• AHI under 5 with symptoms — the cause may be simple snoring without apnoea, positional, or another sleep disorder.
• Mild OSA — weight management, positional therapy, treating nasal obstruction, and an oral appliance are often tried first.
• Moderate to severe OSA — CPAP is usually first-line. Where it is not tolerated, DISE-guided sleep apnoea surgery is the alternative.

Untreated moderate-to-severe sleep apnoea is linked to hypertension, heart rhythm problems, stroke, poor diabetic control and road-traffic accidents. Testing is worth doing.

Sleep Care at THANC

Sleep medicine at THANC is led by Dr. Mahalakshmi Rangabashyam Shetty, MBBS, DipNB (ENT), MRCS (ENT) Edinburgh — Senior Consultant and Sleep Lead, Department of Sleep Health. Her practice covers snoring, obstructive sleep apnoea and circadian sleep disorders, using sleep studies and DISE-guided assessment to match treatment to the individual airway.

Because sleep-disordered breathing often involves the nose, palate, tongue base or jaw together, assessment is shared across the sleep and snoring service, ENT, and oral & maxillofacial surgery — so the diagnosis leads to the right treatment rather than the most available one.

Book a consultation to discuss whether a sleep study is right for you.