Obstructive sleep apnoea

Obstructive sleep apnoea (OSA), also known as obstructive sleep apnoea syndrome (OSAS), is a disorder characterised by repetitive episodes of total (i.e. apnoeas) or reduction (i.e. hypopnoeas) in ventilation due to total or partial collapse of the upper airway during sleep.

This condition is distinct from central sleep apnoea.

Epidemiology

Obstructive sleep apnoea is very common, affecting both paediatric and adult populations ^1-3. The disorder is more common in men and in adults, its incidence increases with age ^1-3.

Risk factors

• male sex ^1-5

• increased age ^1-5

• obesity ^1-5

• hypothyroidism ^1,2

• acromegaly ^1,2

• craniofacial anaomalies: micrognathia, retrognathia

• adenoidal hypertrophy

• various genetic syndromes (e.g. Down syndrome, Marfan syndrome) ^1,6

Clinical presentation

Obstructive sleep apnoea has a varied clinical presentation ^1-3. Signs and symptoms include daytime somnolence, gasping or choking awakenings, pauses in breathing during sleep, snoring during sleep (less prominent in paediatrics), nocturnal bradyarrhythmias, morning headache, and behavioural sequela of poor sleep such as lack of concentration and irritability (more prominent in paediatrics) ^1-3. Given many of these clinical features occur during sleep, affected patients may often be unaware of these, even in severe cases of obstructive sleep apnoea ².

These clinical features can be detected formally in a diagnostic polysomnogram ^1-3. This test may include all or some of electroencephalography (EEG), electrooculography (EOG), chin electromyography (EMG), electrocardiography (ECG), respiratory inductance plethysmography, nasal oral airflow measurements, pulse oximetry, expired carbon dioxide monitoring, transcutaneous carbon dioxide monitoring, and video monitoring ^1-3. Such monitoring allows for the detection of apnoeas and hypopnoeas, which are utilised in the apnoea-hypopnoea index (AHI) to determine the number of breathing abnormalities per hour of sleep ^1-3. Obstructive sleep apnoea is defined as an AHI of five or more ^1-3.

Pathology

During sleep, especially REM sleep, there is relaxation of the upper airway muscles, including the tongue and pharyngeal dilator muscles (e.g. genioglossus) ^1-4. In those with anatomical risk factors for obstructive sleep apnoea, relaxation of upper airway muscles while supine may lead to decreased pharyngeal cross-sectional area ^1-4. When this obstruction is complete there is clinical apnoeas with hypoxaemia and hypercarbia. These events in turn lead to arousal from sleep in order to increase the tone of the upper airway ^1-4. This leads to the cessation of the apnoea or hypopnoea, and return to normal unobstructed upper airway flow ^1-4. When sleep recommences, this cycle may repeat itself ^1-4.

This cycle leads to fragmentation of sleep, resulting in daytime sleepiness and associated behavioural symptoms ^1-4. Furthermore, episodic oxygen desaturations lead to episodic sympathetic overactivity and loss of normal blood pressure nocturnal dipping, leading to an increased cardiovascular risk ^1-3,7.

Radiographic features

Imaging is not utilised as a tool to diagnose obstructive sleep apnoea, but rather, has a role in evaluating the upper airway for anatomical factors that may be contributing to sleep apnoea, and for purposes of pre-operative planning ^4,5.

Generally, features that may indicate risk of obstructive sleep apnoea on cross-sectional imaging (e.g. CT or MRI) of the head and neck:

• narrowing of upper airway ^4,5

  • one study highlights a risk associated with a transverse dimension of the upper oropharyngeal airway <10 mm and an elongation of the oropharynx >70 mm ⁴

• excess soft tissue surrounding the upper airway, including tonsil and/or adenoid hypertrophy, fat, or muscle ^4,5

• pharyngeal tumours or cysts ^4,5

• tongue anomalies (e.g. macroglossia, glossoptosis) ^4,5

• palatal anomalies (e.g. high arched palate) ^4,5

• jaw anomalies (e.g. micrognathia, retrognathia) ^4,5

• nasal anomalies (e.g. nasal polyps, septal deviation) ^4,5

• hyoid anomalies (e.g. inferiorly situated) ^4,5

• thyroid anomalies (e.g. ectopic thyroid, goitre) ^4,5

• other craniofacial anomalies ^4,5

Treatment and prognosis

Management encompasses lifestyle changes as well as non-invasive and potentially invasive treatments ^1-3.

In regard to lifestyle, weight loss, sleeping on one’s side, avoiding alcohol, and smoking cessation are recommended ^1-3. Additionally, the diagnosis of obstructive sleep apnoea may have implications on driving (depending on country of residence), especially if driving commercially ^1,2.

Non-invasive management includes mandibular advancement splints, and, what is considered to be the gold-standard treatment – continuous positive airway pressure (CPAP) ^1-3. Generally, CPAP should be offered to all patients with at least moderate disease ^1-3.

Invasive management includes device implantation such as a hypoglossal nerve stimulator (e.g. Inspire® device), and surgery such as uvulopalatopharyngoplasty, adenotonsillectomy, or nasal surgery ^1,3,8. Utility of these surgical options depend on patient's invdividual anatomical risk factors for obstructive sleep apnoea ^1,3.

Differential diagnosis

• obesity hypoventilation syndrome