Introduction 

What is sleep apnoea? 

Sleep apnoea is a chronic sleep disorder where patients experience episodes of waking up and gasping for air during sleep. This is because breathing suddenly stops and starts at an irregular rate throughout the night. This disorder can prevent the normal flow of oxygen to the brain and body.^1,2 This can lead to other associated physical and mental disorders like stroke, type 2 diabetes, hypertension, heart disorders, or depression.^3,4,5

A study by the British Lung Foundation in 2014 revealed that only 330,000 adults diagnosed with obstructive sleep apnoea (OSA) were undergoing treatment out of an estimated 1.5 million adults in the UK with OSA. In other words, more than 85% of people in the UK are living with untreated sleep apnoea. But why is this important? To find out, this article will illustrate the effects of untreated sleep apnoea on your cognitive health and the link between sleep apnoea and neurocognitive disorders.

Types of sleep apnoea

Obstructive sleep apnoea (OSA)

OSA occurs when the throat muscles supporting the soft palate and tongue in the mouth relax and block the upper airway causing irregular breathing throughout the night. This lowers the oxygen level in the blood and signals the brain to wake you up to open the airway.

Central sleep apnoea (CSA)

CSA occurs when the brain does not send signals for the normal movement of chest muscles involved in breathing and causes the patient to wake up gasping for air. This could be due to an underlying medical condition affecting the brainstem, which is the control centre in the brain responsible for breathing.⁶

Complex or treatment-emergent central sleep apnoea

Complex sleep apnoea is an extremely special case where patients undergoing treatment for OSA develop CSA (when the brain does not signal the muscles involved in breathing). 

OSA is the most common type of sleep apnoea seen in most patients and is therefore the focus of most scientific research available today. 

Common symptoms of sleep apnoea

• Frequent and loud snoring, snorting or choking noises
• Shortness of breath 
• Insomnia and fragmented sleep
• Headaches in the morning
• Inability to focus or pay attention while awake
• Hypersomnia or an uncontrollable level of daytime sleepiness⁷

Risk factors 

• Being male or postmenopausal women
• Being overweight or obese
• Physical abnormalities in respiratory organs like the nose or throat
• Poor lifestyle habits like excessive alcohol consumption, smoking, and consuming sleeping pills regularly
• Hypertension or high blood pressure
• Type 2 diabetes
• Cardiovascular diseases 

Overview of neurocognitive disorders 

Neurocognitive disorder is an umbrella term for mental disorders that are characterised by a decline in previously attained cognitive abilities like attention, learning, memory, language and others.⁸ These include conditions like Alzheimer’s disease (AD), vascular dementia or mild cognitive impairment. 

If we imagine the brain as a tree, just like damage to the roots can cause the tree to weaken, damage or ageing in certain brain regions or pathways can cause a decline in the brain and body’s normal functioning. 

Types of neurocognitive disorders 

• Delirium or sudden and severe confusion
• Mild neurocognitive disorders like mild cognitive impairment
  • A modest decline in cognitive function that does not interfere with one’s independent ability to perform daily tasks
• Major neurocognitive disorders or dementia
  • A significant decline in cognitive function that causes loss of ability to perform daily tasks independently⁸

General symptoms include difficulty in thinking and learning, hallucinations, delusions, fluctuations in mood like anxiety or depression, and behavioural disturbances that can put the patients themselves or others in danger.

Causes of neurocognitive disorders 

• Age-related changes in the brain’s structure
• Brain injuries
• Genetic factors like family history
• Lifestyle factors like excessive alcohol consumption, smoking, and inadequate exercise 

The link between sleep apnoea and neurocognitive disorders 

The quality of sleep has a significant impact on brain health. An average of 7-8 hours of daily sleep for adults has many benefits for cognitive health such as improved memory recall and thinking skills through mechanisms like regeneration and repair of brain cells and the removal of waste products or toxins from brain cells.⁹ Adequate sleep also helps regulate our body’s metabolism, reduces fatigue, and is linked to an improved quality of life overall.

On the other hand, poor sleep has been associated with insomnia, irritability, fatigue, and an increased risk of infection, diabetes, dementia, high blood pressure, and increased vulnerability to accidents and injuries. 

A key feature of sleep apnoea is fragmented or disturbed sleep and insomnia. Studies have shown evidence for the link between sleep apnoea and neurocognitive or neurodegenerative disorders like Alzheimer’s disease, postoperative delirium, stroke and mild cognitive impairment.^10,11,12

Mechanisms underlying sleep apnoea and neurocognitive disorders

Hypoxia

A lack of oxygen flow to the brain can cause brain structure and function changes. In patients with obstructive sleep apnoea (OSA), areas of the brain responsible for attention, visual memory and visual processing are affected due to a lack of communication between the network of brain cells in these regions. Hypoxia and disordered sleep have been found to accelerate the cognitive decline seen in Alzheimer’s disease.

Inflammation

Inflammation is normally a protective mechanism by the brain and body against infections and injuries. However, in OSA, low-level inflammation over a long time can affect the part of the brain responsible for the initial stages and maintenance of sleep and alertness and cause excessive daytime sleepiness. 

High levels of inflammation can lead to the death of brain cells and the tethered communication between brain regions ultimately leads to a decline in memory, attention, and executive functions like thinking, planning and working memory.¹³

Sleep fragmentation

Disturbed sleep or fragmented sleep was found to have a significant impact on mood and memory retention. This was due to damage inflicted in the brain cells of the hippocampus and prefrontal cortex regions which are responsible for memory, emotions, and executive functions.¹⁴

How does untreated sleep apnoea affect cognitive health?

Untreated sleep apnea can contribute to the long-term decline of cognitive health and thus increase the risk of neurocognitive disorders, as illustrated above. Apart from physiological changes, untreated sleep apnea can also affect the overall quality of life. Frequent and loud snoring can harm your partner’s sleep, and other symptoms, such as irritability or the inability to focus when awake, may even lead to problems maintaining relationships. 

Most importantly, symptoms like hypersomnia, headaches or fatigue can lead to serious life-threatening accidents or injuries like car accidents, so it is important to report to the government driver’s department, such as the DVLA UK, if you have been diagnosed with sleep apnoea and refrain from driving when experiencing any symptoms. 

Prevention and treatment

The best ways to prevent sleep apnoea are regular exercise, following a healthy balanced diet, and avoiding the use of alcohol, tobacco, and sleeping pills. 

Sleep apnoea is usually diagnosed in specialised clinics for sleep disorders using a polysomnography test (sleep study). A polysomnography test records activity from the brain, heart, lungs, muscles, and blood oxygen levels while you sleep. 

Continuous positive airway pressure (CPAP) is the recommended treatment for sleep apnoea.¹⁵ This machine pumps air at a constant pressure into a mask worn over the nose and mouth during sleep and helps keep the airway open for breathing. It is normal to experience some discomfort when using the CPAP machine for the first few times, but it improves your breathing and sleep quality. It has also been found to reverse the hypoxic and inflammatory mechanisms leading to neurocognitive disorders.¹⁶ Other lifestyle changes like weight loss, higher exercise engagement, and following a strict sleep routine can alleviate the symptoms of sleep apnoea. 

Summary 

Sleep apnoea is a chronic sleep disorder in which breathing suddenly stops and starts throughout the night, and causes you to wake up gasping for air. The most common type of sleep apnoea is obstructive sleep apnoea, where the throat muscles relax causing a narrower airway for breathing. A common symptom of sleep apnoea is insomnia and disturbed sleep which has been linked to the development of neurocognitive disorders like Alzheimer’s disease, characterised by a decline in cognitive functions such as memory and attention. 

Common mechanisms underlying the development of neurocognitive disorders in OSA patients include hypoxia, inflammation in the brain, and sleep fragmentation. Therefore early diagnosis and treatment of sleep apnoea is important to reverse the negative effects and improve cognitive health and overall quality of life.