Definition of Obstructive Sleep Apnea
Obstructive sleep apnea (OSA) is a disorder of breathing during sleep characterized by prolonged partial upper airway obstruction and/or intermittent complete obstruction (obstructive apnea) that disrupts normal ventilation during sleep and normal sleep patterns. 1
Core Pathophysiologic Features
OSA is fundamentally a syndrome of periodic, partial, or complete obstruction of the upper airway during sleep that causes repetitive arousals from sleep to restore airway patency. 1 The key distinguishing feature is that airway obstruction occurs despite continued respiratory efforts, which differentiates it from central sleep apnea where ventilatory effort is absent. 1, 2
Essential Components of the Definition
The complete definition encompasses several critical elements:
- Recurrent episodes of complete (apnea) or partial (hypopnea) upper airway collapse during sleep 3, 4
- Ongoing respiratory efforts that distinguish OSA from central apnea 1, 2
- Episodic oxygen desaturation and hypercapnia resulting from airway obstruction 1
- Sleep fragmentation due to repetitive arousals or microarousals that terminate obstructive events 1, 2
- Disruption of normal sleep architecture and ventilation patterns 1
Clinical Manifestations Required for Diagnosis
The definition must be accompanied by symptoms or signs to constitute the full syndrome. 1 These include:
- Habitual snoring (often with intermittent pauses, snorts, or gasps) 1
- Witnessed apneas or choking episodes during sleep 1, 3
- Daytime consequences such as excessive sleepiness, though this may be uncommon in young children 1
- Neurobehavioral problems including aggressive or distractible behavior in children 1
Distinction from Primary Snoring
OSA syndrome must be distinguished from primary snoring, which is snoring without obstructive apnea, frequent arousals from sleep, or gas-exchange abnormalities. 1 This distinction is critical because primary snoring does not carry the same morbidity and mortality risks.
Quantitative Diagnostic Criteria
While the qualitative definition is consistent across guidelines, OSA is formally diagnosed by combining symptoms with objective sleep study findings:
- RDI ≥5 events per hour with symptoms, or 3
- RDI ≥15 events per hour without symptoms 3
- The Apnea-Hypopnea Index (AHI) measures the frequency of apneas and hypopneas per hour of sleep 2, 3
- Apneas are defined as complete cessation of airflow for ≥10 seconds despite ongoing respiratory efforts 2
Pathophysiologic Consequences
The repetitive nature of OSA leads to:
- Intermittent hypoxia and hypercapnia from recurrent airway obstruction 5, 2
- Marked swings in intrathoracic pressure during obstructive events 2
- Autonomic nervous system activation with increases in systemic and pulmonary arterial pressure 1
- Changes in cerebral blood flow during obstructive episodes 1
These physiologic derangements explain why untreated OSA increases risk for cardiovascular disease, metabolic dysfunction, neurocognitive impairment, and mortality. 1, 5