Obstructive Sleep Apnoea is a condition in which the upper airway becomes partially or completely blocked repeatedly during sleep, resulting in interruptions to normal breathing.

Definitions:

Apnoea (or Apnea), is a temporary pause in breathing for at least 10 seconds, usually when someone is asleep. Pauses in breathing can cause dips in blood oxygen levels and sleep disruption.

Hypopnea is where breathing is temporarily partially reduced, for 10 seconds or longer, often accompanied by a drop in blood oxygen levels. Breathing does not stop, but not enough air reaches the lungs, which can disrupt sleep quality.

Types of Sleep Apnoea

• Obstructive Sleep Apnoea (OSA)

Occurs when the upper airway becomes partially or completely blocked or narrowed during sleep. It is the most common type of sleep apnoea. Anything that makes the throat narrower to start with (for example enlarged tonsils or a set-back lower jaw) makes it OSA more likely. A blocked (or partially blocked) nose also makes OSA slightly more likely

People with Obstructive Sleep Apnoea (OSA) may be unable to sleep properly. Their sleep can be constantly disrupted, and they can experience breathing disturbances many times each hour. Sufferers can fall asleep during the day even whilst working or driving.

• Central Sleep Apnoea (CSA)

Occurs when the brain temporarily fails to send the appropriate signals to the muscles responsible for breathing. Unlike OSA, there is no physical obstruction of the airway.

The incidence of CSA is far lower that OSA In simple terms, OSA is a mechanical blockage treated by increasing air pressure to overcome the blockage while CSA is when there is irregularity of breathing without an airway blockage.

• Mixed Sleep Apnoea

Involves a combination of obstructive and central sleep apnoea, meaning that both physical airway obstruction and irregularity of breathing contribute to interruptions in breathing.

The Sleep Apnoea Trust has produced a leaflet titled ‘What is Obstructive Sleep Apnoea‘.

A BBC article titled ‘I snore, but didn’t know I stop breathing 10 times an hour in my sleep‘ may help you to understand sleep apnoea.

Condition associated with Obstructive Sleep Apnoea

Obesity Hypoventilation Syndrome (OHS)

Obesity Hypoventilation Syndrome (OHS) – also known as ‘Pickwickian Syndrome’ – is a breathing disorder that occurs in individuals with obesity, in which inadequate ventilation leads to an abnormally elevated level of carbon dioxide (CO₂) in the blood, particularly during wakefulness. OHS frequently coexists with Obstructive Sleep Apnoea (OSA), with approximately 90% of individuals with OHS also having OSA.

Written by Jennifer Troath, Advanced Clinical Physiologist in Respiratory and Sleep Medicine with input from Claire Allen, Annabel Nickol and Chris Turnbull from SATA.

Last updated on 24 September 2026

Jennifer Troath – AHCS Registration No. 69167
Volunteer Clinical Adviser, Sleep Apnoea Trust