Obstructive Sleep Apnea (OSA) — MD Examination Answer (15 Marks)

1. DEFINITION

• Apnea: ≥10-second cessation of airflow with ≥90% reduction from baseline, with continued respiratory effort
• Hypopnea: ≥10-second, ≥30% reduction in nasal pressure airflow, associated with ≥3% SpO₂ drop (Def. 1A) or ≥4% SpO₂ drop (Def. 1B) or microarousal
• RERA (Respiratory Effort-Related Arousal): ≥10-second sequence with increasing respiratory effort or inspiratory flow flattening, terminating in microarousal — not meeting criteria for apnea/hypopnea
• AHI (Apnea-Hypopnea Index): Total apneas + hypopneas per hour of sleep (scored from PSG)

2. SEVERITY CLASSIFICATION (AASM)

3. EPIDEMIOLOGY

• Prevalence: ~15–30% of men and 5–15% of women in the general adult population (higher with updated AASM scoring criteria using nasal pressure)
• Most common in middle-aged, obese males
• Sex difference: Men have 2–3× higher risk than pre-menopausal women; gap narrows post-menopause
• Increases with age, obesity, and in specific ethnic populations (East Asians have OSA at lower BMI due to craniofacial differences)
• Highly prevalent in pregnancy (especially 3rd trimester)

4. PATHOGENESIS

A. Upper Airway Anatomy & Dimensions

• Narrowed oropharyngeal lumen from tonsillar hypertrophy, macroglossia, retrognathia, craniofacial disproportion
• Adipose infiltration in obese patients narrows airway and reduces lung volume-mediated tracheal traction

B. Upper Airway Collapsibility

• The pharynx is a collapsible tube; collapsibility is quantified as Pcrit (critical closing pressure)
• In OSA, Pcrit is elevated (less negative), meaning the airway collapses at lower driving pressures
• Normal awake neuromuscular compensation is lost during sleep

C. Neuromuscular Factors

• Upper airway dilator muscles (genioglossus, tensor palatini) normally activate reflexively to maintain patency
• During sleep, especially REM, these reflexes are diminished → pharyngeal collapse
• Loop gain (ventilatory control instability) and arousal threshold (low in OSA) also contribute

D. Upper Airway Inflammation

• Repeated mechanical trauma from snoring and apneas → mucosal edema, local inflammation → further narrowing

E. Fluid Redistribution

• In supine position during sleep, rostral fluid shift from legs → neck → increases pharyngeal tissue pressure and narrows airway
• More pronounced in heart failure and CKD patients

5. PREDISPOSING FACTORS / RISK FACTORS

6. CLINICAL FEATURES

Nocturnal Symptoms

• Loud, habitual snoring (cardinal symptom; bed-partner history essential)
• Witnessed apneas (gasping, choking, breath-holding)
• Restless sleep, nocturia (due to ↑ ANP from intrathoracic pressure changes)
• Nocturnal diaphoresis, GERD symptoms

Daytime Symptoms

• Excessive daytime somnolence (EDS) — most common daytime complaint
• Non-restorative, unrefreshing sleep
• Morning headaches (CO₂ retention)
• Cognitive impairment: poor concentration, memory deficits
• Mood disturbances: irritability, depression
• Sexual dysfunction/impotence

Clinical Signs

• Obesity (especially central/neck obesity; neck circumference >43 cm in men, >38 cm in women)
• Short, thick neck
• Retrognathia/micrognathia
• Tonsillar hypertrophy (Mallampati class III/IV)
• Hypertension (often refractory)
• Crowded oropharynx

7. DIAGNOSIS

Screening Questionnaires

• Epworth Sleepiness Scale (ESS): Score ≥10 indicates significant EDS
• STOP-BANG questionnaire: Validated screening tool (Snoring, Tiredness, Observed apneas, Pressure [HTN], BMI >35, Age >50, Neck >40 cm, Gender male); score ≥3 = high risk

Gold Standard: Polysomnography (PSG) — Level I study

• Full overnight, in-laboratory, multichannel recording
• Records: EEG (sleep staging), EOG, EMG, ECG, airflow (thermistor + nasal pressure), thoracoabdominal effort (RIP bands), SpO₂, body position
• Identifies apneas, hypopneas, RERAs, oxygen desaturations, arousals, sleep stages
• Required for complex patients (heart failure, COPD overlap, neuromuscular disease, suspected central apnea)

AASM Diagnostic Criteria for OSA

• A: Symptoms (EDS, unrefreshing sleep, insomnia, witnessed apneas, gasping/choking) OR comorbidities (HTN, mood disorder, cognitive dysfunction, CAD, CHF, stroke, AF, T2DM)
• B: Sleep recording ≥5 predominantly obstructive events/hour
• C: Sleep recording ≥15 predominantly obstructive events/hour (even without symptoms)

Home Sleep Apnea Testing (HSAT) — Level III/IV

• Portable, out-of-laboratory devices
• Records airflow, SpO₂, respiratory effort, heart rate
• Cannot score sleep stages → uses Recording Time (not TST), so tends to underestimate AHI vs. PSG
• Appropriate for patients with high pre-test probability of moderate-severe OSA without significant comorbidities

Additional Investigations

• Thyroid function tests (exclude hypothyroidism)
• ABG (assess daytime hypoventilation in severe OSA)
• Fasting glucose, HbA1c (metabolic comorbidities)
• Overnight oximetry (screening tool; not diagnostic)

8. PATHOPHYSIOLOGY OF COMPLICATIONS

1. Intermittent hypoxia → oxidative stress → endothelial dysfunction → systemic hypertension, atherosclerosis
2. Sympathetic activation (hypoxia + arousals) → ↑ catecholamines → ↑ HR, BP; chronic activation → sustained HTN
3. Intrathoracic pressure swings (large negative pressure against obstructed airway) → ↑ cardiac afterload, risk of arrhythmias
4. Sleep fragmentation → neurocognitive impairment, EDS, mood disorders
5. Metabolic dysregulation → insulin resistance, leptin resistance, adipokine dysfunction

9. COMPLICATIONS

Neurobehavioral

• Excessive daytime sleepiness → ↑ motor vehicle accidents (2–7× increased risk)
• Cognitive impairment (working memory, attention, executive function)
• Depression, anxiety, personality changes

Cardiovascular

• Systemic hypertension: OSA is the most common secondary cause of HTN; 30–50% of OSA patients have HTN
• Atrial fibrillation: ↑ risk 2–4× (hypoxia, autonomic changes, atrial stretch)
• Coronary artery disease, myocardial infarction
• Congestive heart failure (both cause and effect)
• Stroke (↑ risk ~2×)
• Pulmonary hypertension (in severe/untreated cases)

Metabolic

• Type 2 diabetes mellitus / insulin resistance
• Non-alcoholic fatty liver disease
• Metabolic syndrome

Other

• Pulmonary hypertension, cor pulmonale (in obesity-hypoventilation overlap)
• Nocturia, sexual dysfunction
• GERD exacerbation

10. MANAGEMENT

A. General/Behavioral Measures (All Patients)

• Weight loss: 10% weight reduction → ~26% reduction in AHI; most effective for long-term
• Positional therapy: Avoidance of supine sleep (positional OSA: AHI supine ≥2× lateral AHI); positional devices/tennis ball technique
• Alcohol and sedative avoidance (especially 2–3 hours before sleep)
• Smoking cessation
• Sleep hygiene optimization
• Treat underlying conditions (hypothyroidism, nasal congestion)

B. Positive Airway Pressure (PAP) Therapy — FIRST-LINE

• Gold-standard treatment for moderate-severe OSA
• Creates a pneumatic splint preventing upper airway collapse
• Pressure typically 6–14 cmH₂O (titrated in lab or auto-titrating)
• Reduces AHI to near-normal, improves EDS, BP, quality of life, cognitive function
• Limitations: Adherence (~50–70% at 1 year); side effects: nasal dryness, mask leak, claustrophobia → humidifiers, mask fitting address these

• Automatically adjusts pressure breath-by-breath; equivalent efficacy to fixed CPAP; better tolerated

• For patients unable to tolerate CPAP, OSA-hypoventilation overlap, or central component

C. Oral Appliances (Mandibular Advancement Devices — MAD)

• Indicated for mild-moderate OSA or patients intolerant of CPAP
• Advance mandible 50–75% forward, enlarging retroglossal airspace
• Less efficacious than CPAP (↓ AHI by ~50%) but better adherence in some
• Requires intact dentition; dental/TMJ side effects

D. Surgical Options

• Uvulopalatopharyngoplasty (UPPP): Removes redundant soft palate/uvula/tonsils — cures ~50%; less effective for severe OSA
• Tonsillectomy/adenoidectomy: Highly effective in children with OSA
• Maxillomandibular Advancement (MMA): Most effective surgical option (~85–90% success); for craniofacial contributors
• Hypoglossal nerve stimulation (Inspire therapy): For moderate-severe OSA with CPAP intolerance; implantable neurostimulator activates genioglossus during inspiration
• Bariatric surgery: Indicated for morbidly obese patients — significant OSA improvement
• Nasal surgery: Septoplasty/turbinectomy — adjunctive; rarely curative alone
• Tracheostomy: Definitive but reserved for life-threatening, refractory OSA

E. Pharmacological (Limited Role)

• No FDA-approved drug for OSA per se
• Solriamfetol / Modafinil / Armodafinil: Adjuncts for residual EDS despite adequate PAP use
• Carbonic anhydrase inhibitors (acetazolamide): Used in central/high-altitude components
• Treat comorbidities (antihypertensives, thyroid replacement)

11. MONITORING AND FOLLOW-UP

• CPAP download data (AHI, leak, hours of use) at 1 month then every 6–12 months
• Repeat PSG if symptoms recur or significant weight change
• Cardiovascular risk factor surveillance
• Reassess after weight loss (may no longer need therapy)
• Driving risk counseling mandatory (especially professional drivers)

12. SPECIAL SITUATIONS

SUMMARY TABLE