Obstructive Sleep Apnoea (OSA)
A mechanical failure of the upper airway during sleep, resulting in oxygen desaturation and sympathetic nervous system activation.
Pathophysiology
During sleep, muscle tone in the upper airway naturally relaxes. In OSA, this relaxation combined with anatomical factors (such as a large tongue, excess parapharyngeal tissue, or a retrognathic jaw) causes the airway to collapse completely (apnoea) or partially (hypopnea).
The resulting drop in blood oxygen triggers a micro-arousal in the brain to restore breathing, severely fragmenting sleep architecture and preventing restorative deep and REM sleep.
Diagnostic Criteria (AHI)
Severity is classified by the Apnoea-Hypopnea Index (AHI)—the average number of events per hour of sleep.
| Severity | AHI Score | Clinical Impact |
|---|---|---|
| Normal | < 5 | Baseline physiological range. |
| Mild OSA | 5 - 14.9 | May present with daytime fatigue; treatment depends on symptoms. |
| Moderate OSA | 15 - 29.9 | Increased cardiovascular risk; treatment highly recommended. |
| Severe OSA | ≥ 30 | Significant mortality risk if untreated; urgent intervention required. |
Primary Treatment Modalities
- CPAP (Continuous Positive Airway Pressure): The gold standard. Uses a pneumatic splint to keep the airway open.
- MAD (Mandibular Advancement Device): An oral appliance that holds the lower jaw forward, suitable for mild to moderate cases.
- Hypoglossal Nerve Stimulation: An implantable device that stimulates the tongue nerve during inhalation.