Breathing and lung function tests

Tests to measure your breathing during sleep

Sleep tests are used to see if symptoms can be explained by things that happen while you’re asleep. These symptoms include:

  • feeling tired or sleepy in the day
  • abnormal oxygen levels
  • high carbon dioxide levels

You may be observed overnight at a sleep clinic, or by using a small monitor worn overnight at home.

If you are referred to a local sleep centre, they will ask about your medical history and symptoms and examine you physically. They will measure your height and weight to find out your body mass index and measure your neck circumference.

The sleep specialists will then arrange for your sleep to be assessed overnight. You may be asked to complete a sleep questionnaire and a medication list. Your doctor may request a:

Respiratory sleep test

A respiratory sleep test is used to diagnose obstructive sleep apnoea (OSA).

While you sleep, you’ll wear some equipment to record your oxygen levels, breathing movements, heart rate and snoring.

Sometimes, if your doctor wants to know about your carbon dioxide levels while asleep, you may wear a small clip in your earlobe and have a blood gas test in the morning when you wake up.  

respiratory sleep test


Polysomnography is a more complex test used to analyse sleep. It’s an overnight study conducted in a quiet hospital room. It’s designed to:

  • assess sleep and wakefulness – it measures your brain waves, eye movements and muscle movements
  • assess your heart and breathing – it measures your air flow, chest wall motion, oxygen levels and heart activity
  • record video and audio footage

If basic tests haven’t given clear results, and also if you make abnormal movements or do strange things while you’re asleep, a polysomnography may be needed. Some equipment will be attached to you with tape, wires and straps to take the measures as you sleep.

Your sleep specialist may ask you to stay in hospital after the overnight stay for a multiple sleep latency test. You’ll be asked to nap for periods of 20 to 30 minutes at set times.

The specialist may want to know how alert you are during the day and how easily you fall asleep. You’ll do a maintenance of wakefulness test during the day following your overnight stay. You’ll be asked to stay awake as long as you can, sitting still in a quiet, relaxing, semi-darkened room.

respiratory sleep test

OSLER test

An Oxford sleep resistance (OSLER) test measures the amount of time you are able to stay awake in conditions that are favourable to fall asleep. This test is performed during the daytime.

You will be asked to lie in a semi-recumbent position in a darkened room isolated from noise. You will have a handheld box that needs to be repeatedly activated every time you see a red light.

If you have concerns or need advice, call our helpline on 03000 030 555 between 9am and 5pm on a weekday or email them.

We'll take good care of your personal info and you can update the way we contact you at any time - check out our privacy policy at to find out more.

Download this information (421KB, PDF)

Last medically reviewed: January 2017. Due for review: January 2020

This information uses the best available medical evidence and was produced with the support of people living with lung conditions. Find out how we produce our information. If you’d like to see our references get in touch.