Sleep Apnoea is a sleep-related breathing disorder characterised by repeated episodes during sleep in which breathing stops completely or becomes markedly reduced, usually because the upper airway collapses, respiratory drive temporarily ceases or both mechanisms interact. The most common form is obstructive sleep apnoea, in which the airway narrows or closes despite ongoing respiratory effort. Central sleep apnoea involves reduced or absent respiratory effort during episodes and is associated with altered control of breathing.
Some people have mixed or complex patterns containing both obstructive and central events. Repeated interruptions of ventilation can cause oxygen desaturation, fluctuations in carbon dioxide, brief arousals from sleep and activation of the sympathetic nervous system. The person may not remember these arousals, yet sleep becomes fragmented and restorative sleep is impaired. Common manifestations include loud habitual snoring, witnessed pauses in breathing, gasping during sleep, morning headache, dry mouth, nocturia, excessive daytime sleepiness and impaired concentration, although not everyone with clinically important disease is sleepy.
Obstructive Sleep Apnoea develops when anatomical and physiological factors make the upper airway susceptible to collapse during sleep. Sleep reduces activity in several muscles that help maintain airway patency, while gravity, craniofacial anatomy, tissue volume and airway shape influence the available space. Increased body fat around the neck and upper airway can increase collapsibility, making obesity a major risk factor, but obstructive disease also occurs in people who are not overweight.
Craniofacial structure, enlarged tonsillar tissue, nasal obstruction, ageing and certain genetic characteristics can contribute. Alcohol and sedative medicines can worsen airway collapse in susceptible individuals by altering muscle tone and arousal responses. Supine sleeping can increase obstruction in some people because gravity promotes posterior displacement of soft tissues. The condition is therefore not simply caused by obesity or snoring; it results from an interaction between airway anatomy, neuromuscular control, sleep state and mechanical forces.
During an obstructive apnoeic event, inspiratory effort continues against a closed or severely narrowed upper airway. Negative pressure generated by the respiratory muscles can further promote airway collapse. Oxygen levels fall while carbon dioxide rises, and the resulting physiological stress activates sympathetic pathways. Eventually an arousal from sleep restores upper-airway muscle activity and breathing resumes, often with a loud gasp or snort. These cycles may occur many times per hour, repeatedly interrupting normal sleep architecture.
The frequency of events is commonly expressed through an apnoea-hypopnoea index or related respiratory event measure, but clinical severity is not determined by this number alone. The depth and duration of oxygen desaturation, symptom burden, cardiovascular disease, sleepiness and event timing all matter. Repeated intermittent hypoxaemia and sympathetic surges can contribute to vascular dysfunction, blood-pressure elevation and metabolic disturbances. Sleep fragmentation can impair attention, memory, mood and reaction time even when daytime oxygen levels are normal.
Diagnosis requires assessment of symptoms, risk factors and objective sleep-related breathing measurements. Overnight polysomnography is a comprehensive diagnostic study that can record airflow, respiratory effort, oxygen saturation, heart rhythm, brain activity and other physiological variables. Home sleep-apnoea testing can be appropriate for selected adults with a sufficiently high pre-test probability of uncomplicated obstructive disease, but it provides less physiological information than full polysomnography and may miss some forms of sleep-related breathing disorder.
The apnoea-hypopnoea index quantifies the number of apnoeic and hypopnoeic events per hour of sleep or recording time depending on the test, but interpretation should account for the measurement method. Clinical history may include reports from a bed partner because witnessed breathing pauses can be more informative than the patient's own observations. Differential diagnoses include insomnia, circadian disorders, periodic limb movements, narcolepsy, medication effects and other causes of daytime sleepiness.
Treatment of obstructive Sleep Apnoea depends on severity, symptoms, anatomy, comorbidity and patient circumstances. Continuous positive airway pressure delivers pressurised air through a mask and acts as a pneumatic splint that prevents upper-airway collapse during sleep. It is highly effective when used consistently, but adherence can be limited by mask discomfort, nasal symptoms, pressure intolerance or other practical barriers.
Mandibular advancement devices can reposition the lower jaw and tongue and are an alternative for selected people, particularly when disease is suitable for oral-appliance treatment. Weight reduction can improve obstructive disease in people for whom excess body weight contributes, although it is not an adequate assumption that weight loss alone will resolve every case. Positional therapy can help when events occur predominantly while sleeping supine. Management of nasal obstruction, avoidance of alcohol near bedtime and review of sedating medicines may also be useful. Selected anatomical problems can be treated surgically or with other specialist interventions.
Untreated clinically significant Sleep Apnoea can have consequences extending beyond disturbed sleep. Repeated sympathetic activation and intermittent hypoxaemia are associated with hypertension and increased cardiovascular risk, while severe sleepiness can impair driving and occupational safety. Metabolic associations include impaired glucose regulation and increased risk of metabolic disease, although causal relationships are complex and influenced by obesity and other factors.
In children, obstructive disease can present differently, with behavioural problems, poor school performance, mouth breathing, growth concerns or enlarged tonsils and adenoids rather than obvious daytime sleepiness. Central sleep apnoea may occur in association with heart failure, neurological disorders, high altitude exposure, opioid use or instability of respiratory control. Treatment of central disease therefore depends heavily on the underlying mechanism, and therapies effective for obstructive disease cannot simply be assumed to work in every central disorder.
Sleep Apnoea has important terminology distinctions. An apnoea is a substantial cessation of airflow, whereas a hypopnoea is a partial reduction in airflow meeting specified criteria, usually accompanied by an oxygen desaturation or arousal depending on the scoring rules. Obstructive events involve continued or increased respiratory effort against an obstructed airway, while central events involve absent or markedly reduced effort. Snoring is common in obstructive disease but is neither necessary nor sufficient for diagnosis.
Daytime sleepiness is also important but can be absent, particularly in people who have adapted to chronic sleep disruption or whose primary manifestations are cardiovascular or cognitive. The disorder should not be confused with ordinary occasional snoring or brief pauses that do not produce clinically significant physiological disturbance. Accurate interpretation requires the sleep-study data to be considered alongside symptoms, comorbidities and the individual's circumstances rather than treating a single numerical index as the entire diagnosis.
The history of Sleep Apnoea research reflects growing recognition that sleep is an active physiological state with major effects on airway control and systemic health. Early descriptions focused on dramatic nocturnal breathing interruptions, while modern sleep medicine has developed objective physiological monitoring and several treatment modalities. Technological developments have made positive-airway-pressure devices smaller, quieter and more adaptable, while home diagnostic testing has increased access to evaluation in appropriate populations.
Nevertheless, treatment success depends not only on physiological efficacy but also on long-term use, comfort and behavioural adaptation. A major misconception is that Sleep Apnoea is merely a sleep-quality problem; repeated respiratory events can produce measurable cardiovascular, metabolic and neurocognitive effects. Another is that only people with obesity develop obstructive disease. The disorder is better understood as a multifactorial interaction between airway anatomy, sleep-related neuromuscular changes, respiratory control and systemic health, with treatment selected according to the specific physiological subtype and individual risk.
