Sleep apnoea is a sleep-related breathing disorder in which breathing repeatedly stops or becomes markedly reduced during sleep. The term apnoea refers to a cessation of airflow, while hypopnoea refers to a substantial reduction in airflow associated with physiological consequences such as oxygen desaturation or an arousal. The most common form is obstructive sleep apnoea, in which the upper airway repeatedly narrows or collapses despite continued respiratory effort. Central sleep apnoea is different: breathing pauses occur because the brain's respiratory drive temporarily decreases or becomes unstable, so respiratory effort is reduced or absent during the event. Mixed patterns can also occur.
Obstructive sleep apnoea results from interactions between upper-airway anatomy and neuromuscular control. During wakefulness, muscles help maintain airway patency. During sleep, muscle tone changes, and in susceptible people the airway can become sufficiently narrow that inspiratory negative pressure promotes further collapse. Factors such as craniofacial anatomy, enlarged tonsillar tissue, neck circumference, body-fat distribution, age and genetic predisposition can influence susceptibility. Not everyone with obesity develops sleep apnoea, and people who are not obese can also have clinically important obstructive sleep apnoea. Anatomical and physiological risk factors therefore matter alongside body weight.
During an obstructive event, airflow falls or stops while the respiratory muscles continue attempting to breathe. Oxygen levels may fall and carbon dioxide can rise. The brain may then produce a brief arousal that increases upper-airway muscle activity and restores airflow. The person may not consciously remember these arousals, but repeated events can fragment sleep substantially. This pattern can occur dozens or even hundreds of times in a severe case. The result is not simply occasional snoring; it is repeated disruption of normal sleep and breathing physiology.
Sleep apnoea is often associated with loud, persistent snoring, but snoring alone does not establish the diagnosis. Other clues include witnessed pauses in breathing, choking or gasping during sleep, restless sleep, morning headache, dry mouth, nocturia and excessive daytime sleepiness. Some people mainly report insomnia, difficulty concentrating or mood changes rather than obvious sleepiness. Bed partners may notice the breathing abnormalities before the affected person does. Children can present differently, including behavioural problems, learning difficulties, mouth breathing, enlarged tonsils or growth concerns rather than the classic adult presentation.
Diagnosis usually requires assessment of breathing during sleep. Polysomnography is a comprehensive sleep study that can record airflow, respiratory effort, blood oxygen saturation, brain activity, heart rate and other physiological signals. Home sleep-apnoea testing can be appropriate for selected adults with a high probability of uncomplicated obstructive sleep apnoea, although it generally collects fewer signals than laboratory polysomnography. The apnoea-hypopnoea index, or AHI, describes the number of apnoeas and hypopnoeas per hour of sleep or recording time depending on the test. Severity is commonly categorised using AHI thresholds, although symptoms and other physiological findings are also important.
Treatment depends on the type and severity of sleep apnoea and individual circumstances. Continuous positive airway pressure, commonly called CPAP, delivers pressurised air through a mask to splint the upper airway open and is a major treatment for obstructive sleep apnoea. Other options can include mandibular advancement devices, positional therapy, weight management where appropriate, upper-airway surgery, tonsil or adenoid treatment in selected children, and other specialist interventions. Central sleep apnoea requires assessment of the underlying cause and may be managed differently. Simply treating snoring without assessing possible apnoea can therefore miss an important disorder.
Untreated clinically significant sleep apnoea can affect daytime alertness and quality of life and is associated with cardiovascular and metabolic consequences. Repeated oxygen desaturation, arousals and sympathetic activation can contribute to physiological stress. Associations have been reported with hypertension, cardiovascular disease and metabolic disorders, although the causal relationships and treatment effects vary between specific conditions and populations. Excessive sleepiness also creates a direct safety issue because impaired alertness can increase the risk of driving and workplace accidents.
Sleep apnoea is therefore distinct from ordinary snoring and from an occasional pause in breathing. The diagnosis concerns recurrent sleep-related respiratory events with defined physiological consequences. Risk assessment considers symptoms, anatomy, medical history and sleep characteristics rather than body weight alone. Persistent loud snoring accompanied by witnessed pauses, gasping, significant daytime sleepiness or other suggestive symptoms warrants clinical assessment. Prompt assessment is particularly important when sleepiness affects driving or when breathing abnormalities are repeatedly observed during sleep.
