Obstructive Sleep Apnea (OSA)

Definition and Key Terms

• Apnea: cessation of breathing lasting >10 seconds
• Hypopnea: reduction in airflow associated with either oxygen desaturation or a microarousal from sleep
• RERA (Respiratory Effort-Related Arousal): mild upper airway narrowing with flow limitation (seen as inspiratory flattening on nasal pressure tracing) that terminates in a microarousal, but does not meet hypopnea criteria
• Mixed apnea: begins as central (no effort) but becomes obstructive
• AHI (Apnea-Hypopnea Index): total apneas + hypopneas per hour of sleep - the standard severity metric

Pathogenesis

Structural/Anatomic

• Narrow oropharyngeal airway from bony structure (retrognathia, micrognathia) or excess soft tissue (enlarged tonsils, tongue, lateral pharyngeal walls)
• Obesity deposits fat in parapharyngeal spaces, reducing airway lumen
• Reduced lung volumes (especially in the supine position) reduce caudal traction on the pharynx, increasing airway collapsibility

Neuromuscular

• During sleep, tonic and phasic activity of upper airway dilator muscles (especially genioglossus) decreases
• Negative pressure reflexes that normally recruit dilators are impaired in OSA patients
• The airway collapses when dilator activity can no longer offset the critical closing pressure (Pcrit) - the intraluminal pressure at which the airway collapses. In OSA patients, Pcrit is near or above atmospheric pressure (vs. markedly negative in normal individuals)

Other Factors

• Fluid redistribution: overnight rostral fluid shift from legs to the neck increases neck circumference and pharyngeal soft tissue pressure
• Upper airway inflammation: chronic snoring-induced mucosal edema and neural injury impair reflex dilator activation
• Loop gain: high ventilatory control instability can predispose to oscillating airflow

Predisposing Factors / Risk Factors

Epidemiology

• Murray & Nadel's Textbook of Respiratory Medicine notes that prevalence estimates using older thermistor-only technology are lower than those from studies that also recorded nasal pressure
• Sex differences may narrow after menopause

Clinical Presentation

Nocturnal Symptoms

• Heavy, habitual snoring (high prevalence, but not specific for OSA)
• Witnessed apneas by bed partner (most specific symptom - description of breathing stops followed by loud gasps)
• Nocturnal choking or awakening gasping
• Nocturia
• Restless sleep, sweating
• Gastroesophageal reflux
• Erectile dysfunction
• Unrefreshing sleep, morning headache
• Insomnia

Daytime Symptoms

• Excessive daytime sleepiness (EDS) - the most common complaint
• Difficulty concentrating, memory loss
• Irritability, personality change
• Depressive symptoms
• Fatigue

Important: OSA is heterogeneous. Some patients with even moderate-to-severe OSA may have few or no symptoms. Different symptom clusters exist - some patients have predominantly insomnia/nocturnal symptoms, others predominantly EDS, others minimal symptoms.

Diagnosis

Questionnaires / Screening Tools

• Epworth Sleepiness Scale (ESS): subjective sleepiness across 8 daily situations; scores >10 indicate excessive sleepiness
• STOP-BANG questionnaire: 8 yes/no items (Snoring, Tiredness, Observed apnea, blood Pressure, BMI, Age, Neck circumference, Gender); useful pre-operative screening
• Berlin Questionnaire: identifies high-risk patients

Objective Testing

• Full multichannel study: EEG, EOG, EMG, airflow (nasal pressure + thermistor), respiratory effort (inductance plethysmography bands), pulse oximetry, ECG, leg movements
• Attended by technician overnight
• Obstructive apneas show paradoxical thoracoabdominal motion during the event (effort present, but no flow)

• Limited-channel devices (typically airflow, oximetry, respiratory effort, position)
• Appropriate for adults with high pre-test probability of moderate-to-severe OSA without significant comorbidities
• May underestimate severity (lower sensitivity for mild OSA, no sleep staging)

Consequences and Complications

Neurocognitive

• EDS leading to impaired driving performance (increased motor vehicle accidents - a major public health concern)
• Cognitive impairment: attention, memory, executive function
• Mood disturbance: depression, anxiety
• Reduced quality of life

Cardiometabolic

Management

Behavioral / Lifestyle

• Strongly recommended for all overweight/obese patients (BMI typically 30-40 in sleep clinic populations)
• Even a 10% weight loss reduces AHI by ~26%; dose-response relationship
• Comprehensive program: calorie-restricted diet + exercise + behavioral counseling
• Bariatric surgery can markedly improve or resolve OSA by reducing tongue fat and parapharyngeal soft tissue volumes
• Weight loss changes more pronounced in men

• For patients with predominantly positional (supine) OSA
• Can be used standalone or as adjunct to other therapies
• Devices range from positional alarms to special pillows/vests

• Alcohol, sedatives, opioids (reduce upper airway muscle tone)
• Sleep deprivation
• Smoking cessation

Positive Airway Pressure (PAP) - First-line treatment

• Mask leak/discomfort: trial different mask types (nasal, nasal pillow, full-face)
• Nasal congestion: heated humidifier, nasal saline, topical nasal steroids
• Claustrophobia / hesitancy: PAP desensitization nap, motivational interviewing, cognitive-behavioral therapy, peer support
• Aerophagia: reduce pressure, try BiPAP
• Optimal adherence: disease education, early follow-up, patient support networks, remote monitoring

Oral Appliance Therapy (OAT)

• Mandibular advancement devices (MADs) protrude the mandible, pulling the tongue and genioglossus forward
• Effective alternative for mild-to-moderate OSA or for patients who refuse/cannot tolerate CPAP
• Requires adequate dentition
• Takes 3 months for full evaluation, fabrication, and adjustment
• Less effective than CPAP in severe OSA but better tolerated, so adherence may partially offset efficacy gap

Surgical Options

• Uvulopalatopharyngoplasty (UPPP): removes uvula, tonsils, and redundant soft palate tissue
• Expansion sphincter pharyngoplasty, lateral pharyngoplasty: variations improving on UPPP
• Tonsillectomy/adenoidectomy: highly effective in children and adults with tonsillar hypertrophy

• Maxillomandibular advancement (MMA): most effective surgery for OSA; advances both jaws forward, permanently enlarging the pharyngeal airspace; considered when medical therapies fail
• Genioglossus advancement, hyoid suspension

• Implanted neurostimulator activates the hypoglossal nerve during inspiration, protracting the tongue
• FDA-approved for moderate-to-severe OSA in patients with AHI 15-65 who cannot tolerate CPAP
• Requires absence of complete concentric palatal collapse on drug-induced sleep endoscopy (DISE)
• Growing evidence base; avoids CPAP altogether

Other / Emerging Therapies

• Continuous Negative External Pressure (cNEP): applies negative pressure via a neck collar, pulling pharyngeal walls anteriorly; currently approved for procedural sedation settings
• Combination therapy: CPAP + oral appliance simultaneously; PAP + positional therapy
• Pharmacotherapy: No FDA-approved drug for OSA currently (as of textbook publication); research ongoing into agents targeting loop gain, arousal threshold, or muscle tone

Recent Evidence (2024-2025)

1. CPAP and cardiometabolic risk - A 2024 systematic review and meta-analysis found that CPAP improves cardiometabolic risk factors in OSA patients. (PMID 39515623)
2. CPAP and blood pressure - A 2025 individual patient data meta-analysis in the European Respiratory Journal found a statistically significant reduction in blood pressure with CPAP therapy in OSA, with the effect size depending on OSA severity and baseline BP. (PMID 39401854)
3. PAP therapy and mortality - A landmark 2025 meta-analysis in Lancet Respiratory Medicine found that positive airway pressure therapy is associated with reductions in all-cause and cardiovascular mortality in OSA, particularly from non-randomized controlled studies with confounder adjustment. The RCT data alone remained inconclusive on mortality, underscoring the challenge of CPAP adherence in trial settings. (PMID 40118084)

Key Clinical Points Summary

• OSA is defined by repetitive upper airway obstruction during sleep; the AHI from PSG grades severity
• The cardinal symptom is excessive daytime sleepiness, but many patients are asymptomatic despite significant disease
• Witnessed apneas by a bed partner are the most specific symptom
• Risk factors: obesity, male sex, age, craniofacial anatomy, menopause, alcohol/sedatives
• Untreated OSA drives systemic hypertension, atrial fibrillation, stroke, coronary disease, metabolic syndrome, and neurocognitive decline
• CPAP is first-line; adherence optimization is as important as prescription
• Alternatives (oral appliances, HNS, surgery) exist for CPAP-intolerant patients
• Weight loss is always recommended as an adjunct and can be primary treatment in significant obesity
• Murray & Nadel's Textbook of Respiratory Medicine, Ch. 120, 122