Sleep apnea is a disorder characterized by repeated episodes of partial or complete upper airway obstruction during sleep, leading to intermittent hypoxia, sleep fragmentation, and increased cardiovascular risk.
Obstructive Sleep Apnea
OSA is caused by collapse of the pharyngeal airway during sleep. The pharynx is a collapsible tube with no rigid skeletal support. During wakefulness, pharyngeal dilator muscles (genioglossus, tensor palatini) maintain patency. During sleep, muscle tone decreases, and in susceptible individuals, the airway narrows or collapses. Obstruction typically occurs at the level of the soft palate (velopharynx) or tongue base (oropharynx). Apnea is defined as complete cessation of airflow for 10 or more seconds. Hypopnea is a reduction in airflow of 30% or more for 10 seconds accompanied by oxygen desaturation (3-4%) or arousal. Severity is measured by the apnea-hypopnea index (AHI): mild (5-15 events/hour), moderate (15-30), and severe (over 30).
Risk Factors
Obesity is the strongest risk factor — a 10% weight gain increases AHI by 32%, and 60-70% of OSA patients are obese. Neck circumference over 17 inches (men) or 16 inches (women) increases risk. Male sex: 2-3 times more common in men. Age: prevalence increases with age until about age 65, then plateaus. Family history: genetic component (craniofacial anatomy, fat distribution). Craniofacial anatomy: retrogenia (recessed chin), retrognathia, macroglossia (large tongue), tonsillar hypertrophy, narrow palate, and increased pharyngeal soft tissue. Menopause: risk increases in postmenopausal women. Endocrine conditions: hypothyroidism, acromegaly. Lifestyle: alcohol before bed (relaxes pharyngeal muscles), smoking (airway inflammation), and supine sleep position (gravity worsens collapse).
Symptoms and Screening
The cardinal symptom is excessive daytime sleepiness — falling asleep inappropriately during sedentary activities (watching TV, reading, driving). The Epworth Sleepiness Scale quantifies sleepiness (score over 10 of 24 indicates excessive sleepiness). Witnessed apneas (bed partner reports breathing pauses or gasping) are reported by 75% of patients. Additional symptoms: loud snoring (disruptive, witnessed), choking or gasping during sleep, restless sleep, nocturia (increased nighttime urination — due to atrial natriuretic peptide release from negative intrathoracic pressure), morning headache (from nocturnal hypercapnia and vasodilation), dry mouth on waking (mouth breathing), and cognitive symptoms (impaired concentration, memory, executive function).
The STOP-Bang questionnaire screens for OSA. Snoring (loud enough to be heard through closed doors), Tiredness (daytime fatigue or sleepiness), Observed apnea (witnessed breathing pauses or choking), Pressure (high blood pressure, treated or untreated). Plus BMI over 35, Age over 50, Neck circumference over 17 inches (men) or 16 inches (women), Gender male. Score 0-2: low risk. Score 3-4: intermediate risk. Score 5-8: high risk of moderate to severe OSA.
Consequences of Untreated OSA
Untreated OSA increases the risk of systemic hypertension (2-3 fold), resistant hypertension, pulmonary hypertension, atrial fibrillation (risk increases with AHI severity), stroke (2-4 fold increase), coronary artery disease, heart failure (OSA increases left ventricular afterload), type 2 diabetes (independent association even after adjusting for obesity), cognitive impairment and dementia risk, mood disorders (depression, irritability), and motor vehicle accidents (2-3 fold increase — from sleepiness).
Diagnosis
The gold standard is attended in-laboratory polysomnography (PSG): EEG (sleep staging), airflow (nasal pressure transducer, thermistor), respiratory effort (chest and abdominal belts), pulse oximetry (oxygen saturation), heart rate (ECG), leg movements (EMG), snoring (microphone), and body position. Home sleep apnea testing (HSAT) is an alternative for patients with high pretest probability of moderate to severe OSA without significant comorbidities. HSAT records airflow, respiratory effort, and oxygen saturation but not EEG (cannot quantify sleep time or detect non-respiratory sleep disorders). PSG is indicated when HSAT is negative but suspicion remains, or in patients with cardiopulmonary disease, neuromuscular disease, or comorbid sleep disorders.
Treatment: Positive Airway Pressure
Continuous positive airway pressure (CPAP) is the first-line treatment for moderate to severe OSA and is effective for mild OSA with symptoms. CPAP delivers a constant pressure throughout the respiratory cycle, creating a pneumatic splint that keeps the airway open. CPAP is highly effective (normalizes AHI in most patients), reduces blood pressure by 3-5 mmHg, improves daytime sleepiness (Epworth score drops from 14-16 to 6-8), improves quality of life and cognitive function, and reduces cardiovascular events with consistent use.
Optimal CPAP therapy requires proper mask fitting (nasal vs full-face vs nasal pillow), appropriate pressure (determined by attended titration PSG or auto-titrating CPAP), heated humidification (prevents nasal dryness and congestion), and adherence support. CPAP adherence is the greatest challenge — 30-50% of patients discontinue therapy within 2 years. Factors improving adherence include patient education, mask comfort, heated humidification, gradual acclimation (wearing mask awake, using ramp feature), and follow-up support.
Bi-level PAP (BiPAP) delivers higher pressure during inspiration and lower during expiration. It is used for patients who cannot tolerate CPAP (pressure discomfort) or who have central sleep apnea or obesity hypoventilation syndrome. Auto-titrating CPAP automatically adjusts pressure based on detected airflow limitation, snoring, and apnea.
Alternative Treatments
Weight loss is the most effective disease-modifying intervention. A 10-15% weight loss reduces AHI by 30-50%. Bariatric surgery produces significant sustained weight loss and clinical improvement (AHI reduction as high as 70%). Oral appliances (mandibular advancement devices) advance the mandible and tongue, increasing pharyngeal airway dimensions. They are effective for mild to moderate OSA (50-70% success rate) and can be used as an alternative to CPAP when CPAP intolerance occurs. Positional therapy (sleeping on the side using positional devices) is effective for patients whose OSA is primarily position-dependent (AHI in supine position at least 2 times AHI in non-supine). Upper airway surgery (uvulopalatopharyngoplasty, tonsillectomy, hypoglossal nerve stimulation) is reserved for patients who cannot tolerate CPAP and have specific anatomical targets.
Central Sleep Apnea
CSA is characterized by repetitive cessation or reduction of airflow without respiratory effort — the brain fails to send signals to the respiratory muscles. CSA is much less common than OSA, accounting for approximately 5-10% of sleep apnea cases. Causes include Cheyne-Stokes respiration (heart failure, stroke), opioid-induced central apnea (mu-receptor activation depresses respiratory drive), high-altitude periodic breathing, and idiopathic central sleep apnea. Treatment involves treating the underlying cause (optimize heart failure management, reduce opioid dose), adaptive servo-ventilation (ASV) for CSA associated with heart failure, supplemental oxygen, and acetazolamide for high-altitude CSA.
Summary
OSA is caused by pharyngeal airway collapse during sleep, driven primarily by obesity (60-70% of patients). The STOP-Bang questionnaire screens effectively. Polysomnography is the diagnostic standard. CPAP is the first-line treatment, effective but with adherence challenges. Weight loss is the most effective disease-modifying therapy. Oral appliances and positional therapy are alternatives for mild to moderate OSA. Untreated OSA causes hypertension, atrial fibrillation, stroke, and sleepiness-related accidents. Central sleep apnea is a separate disorder of respiratory drive, treated by addressing the underlying cause.