What is Obstructive Sleep Apnea (OSA)?

Definition of Obstructive Sleep Apnea

Obstructive Sleep Apnea (OSA) is a disorder of breathing during sleep characterized by repetitive episodes of complete or partial upper airway obstruction that disrupt normal ventilation and sleep patterns, despite ongoing respiratory efforts. 1

Core Pathophysiologic Features

OSA occurs when the upper airway periodically narrows or collapses during sleep, causing:

• Complete obstruction (apnea): Total cessation of airflow for ≥10 seconds while respiratory efforts continue 2, 3
• Partial obstruction (hypopnea): Reduction in airflow that causes oxygen desaturation or arousal from sleep 2, 3
• Repetitive arousals: Brief awakenings or microarousals that fragment sleep architecture and restore airway patency 1, 2

The key distinguishing feature is that respiratory efforts persist during obstruction, differentiating OSA from central sleep apnea where respiratory drive ceases. 2

Clinical Manifestations

Nighttime Symptoms

• Habitual snoring, often with intermittent pauses, snorts, or gasps 1
• Witnessed apneas or choking episodes during sleep 1, 4
• Disturbed or restless sleep 1
• Nocturia 3

Daytime Symptoms

• Excessive daytime sleepiness (common in adults, less common in young children) 1, 3
• Neurocognitive impairment including reduced concentration and memory 4, 5
• Behavioral problems or aggressive/distractible behavior, particularly in children 1
• Mood disorders and fatigue 3, 4

Physiologic Consequences

The repetitive obstruction causes:

• Intermittent hypoxia and hypercapnia: Episodic oxygen desaturation and carbon dioxide retention 1, 6
• Marked intrathoracic pressure swings: Increased respiratory efforts against a closed airway 2, 7
• Sympathetic activation: Secondary cardiovascular stress response 6
• Oxidative stress and systemic inflammation: Contributing to long-term complications 6

Serious Sequelae

Untreated OSA is associated with significant morbidity and mortality:

• Cardiovascular: Hypertension, arrhythmias, stroke, coronary heart disease, heart failure, and increased cardiovascular mortality 1, 6, 5
• Metabolic: Metabolic dysfunction and systemic inflammation 1, 5
• Neurocognitive: Cognitive impairment and behavioral problems 1, 4
• Pediatric-specific: Failure to thrive and cor pulmonale 1
• Quality of life: Motor vehicle and industrial accidents, decreased social and professional performance 3, 4

Epidemiology and Risk Factors

Prevalence

• Adult prevalence of sleep-disordered breathing: 9% in women, 24% in men 1
• Overt OSA with symptoms: 2% in women, 4% in men 1
• Pediatric prevalence: 1.2% to 5.7% 1
• Much higher prevalence (≥50%) in patients with cardiac or metabolic disorders 3

Major Risk Factors

• Obesity: The strongest and most prevalent risk factor, present in 60-90% of adult patients 8, 3
• Adenotonsillar hypertrophy: Primary cause in children 1, 8
• Male gender: 2-3 times higher prevalence than women 8, 3
• Age: Prevalence increases with age, peaking around 55 years 8, 3
• Craniofacial anomalies: Micrognatia, macroglosia, narrow upper airway 1, 8
• Neuromuscular disorders: Affecting upper airway muscle function 1, 8

Diagnostic Criteria

OSA is defined by:

• Apnea-Hypopnea Index (AHI): Number of apneas and hypopneas per hour of sleep 2, 3
• Clinical definition: AHI ≥5 with symptoms OR AHI ≥15 without symptoms 3
• Severity stratification: Mild, moderate, or severe based on laboratory-specific indices, as specific AHI cutoffs vary between laboratories 1

Critical Clinical Pitfall

OSA must be distinguished from primary snoring, which involves snoring without obstructive apnea, frequent arousals, or gas-exchange abnormalities. 1 History and physical examination alone are poor at differentiating between the two, making objective sleep testing essential for diagnosis. 1