Snoring & Sleep Apnoea

I think I have sleep apnoea – Which type of sleep study is suitable for me?

February 1, 2020

In his ENT practice, Dr Gan often sees patients who suffer from loud snoring, choking or gasping episodes during sleep and excessive daytime sleepiness. These are symptoms that are suggestive of a condition called obstructive sleep apnoea (OSA). OSA is a condition in which a person repeatedly stop breathing or chokes for a brief period of time during their sleep. As a result, they do not get enough oxygen carried to their lungs, heart and brain. This can have severe health consequences (refer to for more information). The only way to confirm the absence or presence of OSA is to undergo a Sleep Study. However, with so many types of sleep study available, patients and some doctors are confused. In this article, Dr Gan explains the different types of sleep study for diagnosing OSA and their indications.



What is a sleep study?


A sleep study is an overnight study which involves the placement of different sensors on the body to monitor the amount and quality of sleep as well as the body’s physiological activities during sleep. It also monitors whether the patient chokes or stop breathing during sleep (collective index is known as Apnoea-Hypopnoea Index or AHI, which is used to diagnose OSA).



What are the types of sleep study available for the diagnosis of OSA?


Level 1 sleep study (Polysomnography – PSG)


  • Done overnight in a Sleep Laboratory or Hospital
  • Attended by a trained Sleep Technologist
  • Monitors at least 7 parameters – e.g. brain waves, heartbeats, breathing, oxygen level in your blood, eye movement and arms/legs movements during sleep (Figure 1)



Figure 1 – A full level 1 Sleep Study done in a hospital 



Level 2 sleep study


  • Done at home
  • Unattended by a trained Sleep Technologist
  • Monitors the same parameters as a Level 1 sleep study



Level 3 sleep study (e.g WatchPAT study)


  • Done at home
  • Unattended by a trained Sleep Technologist
  • Monitors at least 4 parameters – e.g oxygen level, heart rate body position, snoring and other parameters while you sleep



Level 4 sleep study (Sleep Apnoea Screening)


  • Done at home
  • Unattended by a trained Sleep Technologist
  • Monitors 2 parameters –  e.g blood oxygen level, heart rate or airflow  



Can my sleep study be done at home?


If you’ve been asked to do any of the level 2 to 4 sleep study, it can be done at home. Having a sleep study performed at home has the advantage of eliminating anxiety associated with sleeping in a foreign environment.



Who should undergo a level 1or 2 sleep study?


A level 1 sleep study (done in the hospital or a sleep laboratory and is attended by a Sleep Technologist) is the gold standard in the diagnosis of OSA. However, if the patient has no major neuromuscular disease, communication issues or other suspected sleep disorders (e.g. sleep walking or abnormal body movements during sleep), a level 2 study (which monitors the same parameter as a level 1 study but can be done at home and is unattended by a Sleep Technologist) is an option. This allows patients to be tested in the comfort of their own home in their usual sleep environment and likely provides the same accuracy as a level 1 sleep study.



What if I can’t sleep with so many sensors attached to me?


Level 1 & 2 sleep studies involved wearing at least 7 sensors (meaning more wires attached to the patient’s head and body during sleep). Some patients are light sleepers and may not be able to sleep well due to the discomfort from wearing these wires. Hence for such patients, a level 3 or level 4 sleep study may be an option.


Level 3 & 4 sleep studies involves less sensors attached to the body and monitor less information during sleep. Hence, it is usually more comfortable and tolerable for most patients. A statistical analysis of data from multiple studies (meta-analysis) have shown that the measurement of AHI (Apnoea-Hypopnoea Index), which is used to assess OSA from a WatchPAT study (Level 3 study), has been shown to match the findings of a full level 1 Sleep Study (~89% of the time). A WatchPAT measures the AHI indirectly by looking at the body’s stress response to choking episodes during sleep (Figure 2).



Figure 2 – A WatchPAT Study (Level 3 sleep study) which is performed at home and tolerable by most patients


A level 3 or 4 sleep study may be suitable for patients who have the following criteria:


  1. Have symptoms that are very suggestive of OSA
  2. Do not report any abnormal body movements or sleep walking during sleep
  3. Do not have significant heart or lung conditions that may complicate interpretation of the sleep study
  4. If your doctor does not suspect that you have central sleep apnoea (a condition in which your brain signals to tell your body to breathe during sleep are not working properly)



Most patients have no problems sleeping with a level 3 or 4 sleep study. However, for light/sensitive sleepers or anxious patients, practicing good sleep hygiene measures will help. These include:


  1. Avoiding naps during the day
  2. Avoiding caffeine on the day of the sleep study
  3. Avoiding exercising in the evening of the sleep study



Sedatives (sleeping pills) are in general discouraged as some may affect the results of the sleep study.

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