Obstructive Sleep Apnea

Detailed Overview

The airway collapse occurs at the level of the pharynx, often exacerbated by a narrow airway, obesity, or reduced upper airway muscle tone during REM sleep. The repeated drops in blood oxygen and surge in sympathetic nervous system activity during arousals trigger oxidative stress and systemic inflammation. OSA is a massive independent risk factor for cardiovascular diseases, stroke, and metabolic syndrome.

Epidemiology & Demographics

Extremely common; affects roughly 15-30% of males and 10-15% of females in North America. Prevalence sharply increases with age and rising obesity rates.

Etiological Mechanism

Anatomic narrowing of the upper airway (tonsillar hypertrophy, micrognathia) combined with state-dependent loss of neuromuscular compensation during sleep.

Primary Causes

Loss of upper airway dilator muscle tone (especially genioglossus) during sleep, allowing negative inspiratory intrathoracic pressure to collapse the pharyngeal walls.

• Obesity: High BMI, particularly neck circumference (>17 inches in men, >16 in women), leads to fat deposition in pharyngeal tissues.
• Craniofacial abnormalities: Retrognathia, macroglossia, or large tonsils narrow the airway.
• Male Sex: Men have double the risk, though the gap narrows post-menopause.

During wakefulness, pharyngeal dilator muscles maintain airway patency against the negative intraluminal pressure of inspiration. During sleep, muscle tone decreases. In predisposed individuals, this causes the airway to occlude. Ventilation ceases, causing PaO2 to drop and PaCO2 to rise. Chemoreceptors detect this and trigger a central nervous system arousal. The patient briefly wakes up, restoring airway tone, takes a series of hyperventilatory breaths, and falls back asleep. This cycle repeats dozens of times per hour. The intermittent hypoxia causes endothelial dysfunction, sympathetic hyperactivation, and hypertension.

Characteristic Clinical Presentation

• Loud, disruptive snoring: Often punctuated by gasping, choking, or witnessed pauses in breathing.
• Excessive Daytime Sleepiness: Falling asleep during passive activities (driving, meetings). Assessed via Epworth Sleepiness Scale.
• Morning headaches: Dull, generalized headache upon waking, caused by nocturnal hypercapnia causing cerebral vasodilation.
• Nocturia: Frequent urination at night due to increased release of Atrial Natriuretic Peptide (ANP) from negative intrathoracic swings.

Physical Examination Signs

• Crowded oropharynx (Modified Mallampati Score III or IV).
• Thick neck circumference.
• Systemic hypertension, particularly non-dipping nocturnal blood pressure.

• Cor Pulmonale: Right-sided heart failure resulting from hypoxic pulmonary vasoconstriction and pulmonary hypertension.
• Atrial Fibrillation: High incidence due to structural remodeling of the atria from intrathoracic pressure swings.
• Motor Vehicle Accidents: 2-3 times higher risk due to severe daytime somnolence.

Diagnostic Criteria & Guidelines

Diagnosed via Polysomnography (in-lab or Home Sleep Apnea Testing). Diagnostic criteria: >= 15 predominantly obstructive respiratory events (apneas, hypopneas, or RERAs) per hour of sleep OR >= 5 events per hour combined with symptoms (sleepiness, gasping/choking, or comorbid conditions like hypertension/stroke).

Differential Diagnosis

• Central Sleep Apnea
• Narcolepsy
• Periodic Limb Movement Disorder
• Hypothyroidism

Laboratory Tests & Biomarkers

• Polysomnography (PSG): AHI > 5/hr with repeated drops in SpO2 (desaturations) and EEG arousals.
• Complete Blood Count (CBC): Secondary polycythemia (elevated hematocrit > 50%) due to chronic intermittent hypoxia.
• Thyroid Stimulating Hormone (TSH): Check to rule out hypothyroidism which can cause macroglossia and myopathy.

Imaging Modalities & Findings

• Cephalometry or CT upper airway:

• Mild
  Apnea-Hypopnea Index (AHI) of 5 to 14 events per hour.
• Moderate
  AHI of 15 to 29 events per hour.
• Severe
  AHI >= 30 events per hour. Associated with highest cardiovascular risk.

Second-Line & Adjunctive Therapy

Mandibular Advancement Devices (MADs) custom-fitted by a dentist for mild-moderate OSA or CPAP-intolerant patients. Hypoglossal nerve stimulator (Inspire) implantation for moderate-severe OSA patients intolerant to CPAP with BMI < 32.

Surgical & Procedural Management

Uvulopalatopharyngoplasty (UPPP) removes excess tissue from the soft palate and pharynx. Maxillomandibular advancement (MMA) for severe anatomic obstruction. Tracheostomy is curative but reserved for life-threatening, refractory cases.

Recommended Lifestyle Changes

• Avoid alcohol and sedatives 4-6 hours before bedtime as they relax pharyngeal muscles.
• Positional therapy: Sleep on the side rather than the back (supine position exacerbates gravity-induced tongue collapse).

Patient Counseling & Advice

Emphasize that CPAP compliance requires wearing the mask for >= 4 hours per night on >= 70% of nights to achieve cardiovascular benefits. Warn about the legal and safety risks of driving while excessively sleepy.

Follow-Up & Monitoring Schedule

Review CPAP download data (modem compliance report) at 1 month, then annually to check usage hours, mask leak, and residual AHI. Titrate pressure if residual AHI > 5.

Preventive Strategies

Weight maintenance is the primary preventative strategy.

Excellent with CPAP adherence; abolishes daytime sleepiness and normalizes mortality risk. Untreated severe OSA carries a significantly high risk of sudden cardiac death and stroke.