What causes sleep apnea?

What Causes Sleep Apnea

Sleep apnea is caused by upper airway collapse during sleep (obstructive type) or loss of respiratory drive from the brain (central type), with obesity being the single most important modifiable risk factor present in 60-90% of adult cases. 1

Two Distinct Types with Different Mechanisms

Obstructive Sleep Apnea (OSA)

• The primary pathophysiologic event is physical obstruction of the upper airway during sleep while breathing effort continues, resulting from an imbalance between anatomic narrowing and inadequate compensatory neuromuscular responses. 2, 1
• The fundamental problem occurs when muscle tone naturally decreases during sleep, allowing anatomically vulnerable airways to collapse completely (apnea) or partially (hypopnea). 1

Central Sleep Apnea (CSA)

• CSA results from temporary loss of ventilatory effort due to central nervous system or cardiac dysfunction, with the brain failing to signal respiratory muscles to breathe. 2
• This type commonly occurs in patients with congestive heart failure. 2

Anatomic Causes

Craniofacial and Structural Abnormalities

• Small or recessed jaw, narrow airway structures, and altered facial bone structure significantly increase OSA risk. 1
• Posterior pharyngeal crowding (Modified Mallampati score 3 or 4) reflects anatomic predisposition to collapse. 1
• Macroglossia (enlarged tongue) and tonsillar hypertrophy physically encroach on the pharyngeal lumen. 1
• Increased neck circumference reflects soft tissue crowding around the airway. 1

Obesity: The Dominant Modifiable Cause

• Obesity is present in 60-90% of adult OSA patients and represents the most important modifiable risk factor. 1
• Adipose tissue deposits around the pharynx mechanically narrow the airway and increase collapsibility. 1
• Systemic inflammatory mediators associated with obesity exacerbate pharyngeal collapse mechanisms. 1
• Weight gain directly induces or worsens OSA, creating a bidirectional relationship where OSA may also predispose to further weight gain. 1

Neuromuscular and Functional Causes

• Inadequate upper airway dilator muscle response during sleep fails to maintain airway patency. 1
• Impaired mechanoreceptor sensitivity and reflexes that normally maintain pharyngeal patency contribute to collapse. 1
• Reduced muscle tone during sleep allows anatomically vulnerable airways to collapse. 1
• High loop gain (unstable ventilatory control system) and increased controller gain contribute to both obstructive and central apnea. 3

Medications That Cause or Worsen OSA

• Opioids are the most significant pharmacologic cause, activating μ- and δ-receptors, causing CNS respiratory depression, upper airway muscle relaxation, and tongue collapse. 1
• Testosterone worsens OSA by increasing apnea-hypopnea index and prolonging hypoxemia time, consistent with higher male prevalence. 1
• Benzodiazepines and muscle relaxants may worsen OSA through respiratory depression and muscle relaxation. 1

Demographic and Non-Modifiable Risk Factors

Sex and Hormones

• Male sex confers 2-3 times higher risk than females, related to differences in fat distribution, hormonal influences, and upper airway anatomy. 1
• Postmenopausal status in women increases risk, suggesting protective hormonal effects in premenopausal women. 1

Age

• Aging increases both prevalence and severity of OSA, with age-related changes in upper airway anatomy, muscle function, and respiratory control contributing. 1
• A critical caveat: elderly OSA patients may not be obese, unlike younger patients where obesity is nearly universal. 1

Genetics and Race/Ethnicity

• Genetic factors and family history influence predisposition through inherited craniofacial structure and obesity tendency. 1
• Asian populations have elevated risk at lower BMI levels due to craniofacial differences. 1
• African Americans and Hispanics show higher prevalence independent of obesity. 1

Medical Comorbidities as Contributing Causes

• Untreated hypothyroidism causes myxedematous infiltration of upper airway tissues. 1
• Cardiovascular disease is both a consequence and contributor to OSA, particularly for central sleep apnea. 1
• Type 2 diabetes shows a bidirectional relationship with OSA, possibly through insulin resistance mechanisms. 1
• Resistant hypertension is strongly associated with OSA. 1

Critical Clinical Pitfalls to Avoid

• Over 80% of sleep apnea remains undiagnosed, particularly in women due to provider bias toward screening men. 1
• Absence of reported symptoms does not exclude OSA—objective findings are more reliable than subjective complaints. 1
• Children with OSA are frequently misdiagnosed with ADHD when behavioral symptoms are actually due to sleep fragmentation. 1
• In older adults, look beyond obesity as the sole indicator—anatomic factors become more prominent with age. 2, 1