Obstructive Sleep Apnea (OSA) - MD Examination Answer (10 Marks)

DEFINITION

• Apnea: Cessation of airflow for >10 seconds with persistent respiratory effort
• Hypopnea: Reduction in airflow (>30%) for >10 seconds with >3-4% oxygen desaturation or arousal
• RERA (Respiratory Effort-Related Arousal): Increasing respiratory effort terminating in arousal but not meeting apnea/hypopnea criteria

EPIDEMIOLOGY

• Prevalence: ~15-30% of males, ~5-15% of females using modern AHI ≥5 criteria
• Increases with age; peaks in 5th-6th decade
• Male:Female ratio ~2:1 (narrows post-menopause)
• Risk significantly higher in obesity, with ~40-90% of morbidly obese individuals affected
• Ethnic variation: Asian patients develop OSA at lower BMI due to craniofacial differences

PATHOGENESIS

1. Upper Airway Anatomy and Collapsibility

2. Neuromuscular Factors

• During sleep, activity of upper airway dilator muscles (especially genioglossus) decreases, particularly during REM sleep
• Muscle loading leads to myoadaptive changes - fiber type shifts, increased fatigability
• Protective reflexes (response to negative pressure) are attenuated during sleep
• Sensory neuropathy from repeated mechanical trauma worsens compensatory reflexes

3. Fluid Shift

• In recumbency, fluid shifts from the legs (particularly in heart failure or venous insufficiency) to the neck, increasing pharyngeal tissue volume and narrowing the airway

4. Reduced Lung Volume

• Supine position reduces functional residual capacity (FRC), decreasing tracheal traction that normally stents the pharynx open

5. Upper Airway Inflammation

• Repeated mechanical trauma causes local edema and inflammation, worsening airway narrowing over time

PREDISPOSING FACTORS / RISK FACTORS

CLINICAL FEATURES

Nocturnal Symptoms

• Loud, habitual snoring (most common presenting complaint, often reported by bed partner)
• Witnessed apneas (highly specific - partner reports breath stopping then loud gasp)
• Nocturnal choking or gasping
• Restless sleep / frequent position changes
• Nocturia (due to atrial natriuretic peptide release)
• Diaphoresis (night sweats)
• Gastroesophageal reflux
• Morning headaches (due to nocturnal CO₂ retention)
• Erectile dysfunction / decreased libido
• Insomnia / fragmented sleep

Daytime Symptoms

• Excessive daytime sleepiness (EDS) - the cardinal symptom; uncontrollable sleep in inappropriate situations (watching TV, driving, meetings)
• Cognitive impairment: poor concentration, memory deficits
• Mood disturbances: irritability, depression, anxiety
• Fatigue and lack of energy
• Impaired quality of life

Physical Examination Findings

• Obesity, high BMI, increased neck circumference
• Mallampati class III-IV oropharynx
• Retrognathia, micrognathia
• Tonsillar hypertrophy
• Deviated nasal septum, nasal polyps
• Systemic hypertension (often resistant)
• Signs of right heart failure in severe/chronic cases (cor pulmonale)

DIAGNOSIS

Severity Classification (by Apnea-Hypopnea Index - AHI)

Diagnostic Criteria (AASM/ICSD-3)

• AHI ≥5 with OSA symptoms or comorbidities (HTN, CAD, stroke, AF, HF, T2DM, mood disorder), OR
• AHI ≥15 regardless of symptoms

Screening Questionnaires

• Epworth Sleepiness Scale (ESS): ≥10 indicates excessive sleepiness
• STOP-BANG questionnaire: Snoring, Tiredness, Observed apneas, blood Pressure, BMI >35, Age >50, Neck >40 cm, Gender (male) - score ≥3 = high risk
• Berlin Questionnaire: Categorizes into high/low risk groups

Diagnostic Studies

• Performed in-lab, attended
• Monitors: EEG, EOG (eye movements), EMG, ECG, airflow (thermistor + nasal pressure), respiratory effort (inductance plethysmography), oxygen saturation (SpO₂), body position, leg movements
• Identifies: sleep stages, apneas, hypopneas, RERAs, oxygen desaturation, arousal index

• Portable, unattended, lower channel count
• Appropriate for patients with high pre-test probability of moderate-severe OSA without major comorbidities
• Does not measure sleep time (uses recording time), so may underestimate severity

• Measures objective daytime sleepiness; mean sleep latency <8 min is pathological

PATHOPHYSIOLOGY OF CONSEQUENCES

1. Hypoxemia + Hypercapnia → chemoreceptor stimulation → cortical arousal → airway reopening
2. Sympathetic activation (repetitive surges) → hypertension, tachycardia, endothelial dysfunction
3. Intrathoracic pressure swings (up to -80 cmH₂O) → increased cardiac afterload, RV stress
4. Oxidative stress and inflammation (intermittent hypoxia activates HIF-1α, NF-κB) → pro-inflammatory cytokines (IL-6, TNF-α, CRP elevation)
5. Endothelial dysfunction → atherosclerosis, platelet aggregation
6. Sleep fragmentation → HPA axis dysregulation, insulin resistance, impaired leptin signaling

COMPLICATIONS

Cardiovascular

• Systemic hypertension: OSA is the most common secondary cause of resistant HTN; odds ratio ~1.5-2.5
• Atrial fibrillation: OSA strongly associated; CPAP reduces AF recurrence post-cardioversion
• Coronary artery disease: Independent risk factor
• Heart failure: Bidirectional relationship; OSA worsens and is worsened by HF
• Stroke: ~3-fold increased risk in severe OSA
• Pulmonary hypertension (in severe/chronic cases)

Metabolic

• Type 2 Diabetes Mellitus: Intermittent hypoxia promotes insulin resistance
• Metabolic syndrome
• Non-alcoholic fatty liver disease (NAFLD)

Neurocognitive

• Impaired attention, processing speed, executive function
• Depression and anxiety
• Dementia risk (impaired sleep-dependent memory consolidation; Alzheimer's pathology accumulation)

Other

• Motor vehicle accidents (2-7x increased risk)
• Perioperative complications (anesthetic risk)
• Polycythemia (in chronic severe hypoxemia)
• Cor pulmonale (in severe, untreated long-standing OSA)

MANAGEMENT

1. Behavioral / Lifestyle Measures

• Weight loss: First-line; 10% body weight reduction can reduce AHI by ~26%; bariatric surgery in morbidly obese
• Positional therapy: Supine avoidance devices/positional pillows (for positional OSA where AHI doubles in supine position)
• Avoid alcohol, sedatives, and opioids (worsen pharyngeal tone)
• Smoking cessation
• Treat underlying conditions (hypothyroidism, nasal congestion)
• Sleep hygiene

2. Positive Airway Pressure (PAP) - First-line treatment

• Gold standard for moderate-severe OSA
• Provides pneumatic splinting of the airway
• Pressure range typically 4-20 cmH₂O; titrated in lab or auto-CPAP
• Reduces AHI, improves EDS, blood pressure, quality of life
• Adherence is the major challenge (goal: >4 hours/night on >70% of nights)
• Common side effects: mask leak, nasal dryness, aerophagia, claustrophobia

• Automatically adjusts pressure based on detected events
• Suitable for uncomplicated OSA without significant central apneas or hypoventilation

• Separate inspiratory (IPAP) and expiratory (EPAP) pressures
• Used for: CPAP intolerance, OSA with hypoventilation, complex/central sleep apnea, neuromuscular disease

• For complex/central sleep apnea
• Contraindicated in HF with reduced EF (LVEF <45%) - increased mortality shown in SERVE-HF trial

3. Oral Appliances (Mandibular Advancement Devices - MAD)

• Reposition mandible and tongue anteriorly, increasing retroglossal airway space
• Effective for mild-moderate OSA; less effective than CPAP but better tolerated/adherence
• Indicated when CPAP is refused or not tolerated
• Requires intact dentition; made by dental specialist
• Side effects: TMJ discomfort, tooth movement, excess salivation

4. Surgical Options

5. Pharmacological Therapy (adjunctive)

• No FDA-approved pharmacotherapy specifically for OSA
• Solriamfetol / Modafinil / Armodafinil: For residual EDS despite adequate CPAP (not for OSA itself)
• Tirzepatide / GLP-1 agonists: Emerging evidence - weight loss reduces OSA severity (recent trials 2024-2025)
• Nasal steroids: For allergic rhinitis contributing to nasal obstruction

6. New/Emerging Therapies

• Dasotraline/Combination pharmacotherapy targeting loop gain and arousal threshold (investigational)
• Hypoglossal nerve stimulation expanding indications
• Machine learning for CPAP adherence prediction and personalized therapy selection

MONITORING AND FOLLOW-UP

• Repeat PSG/HSAT if symptoms recur after treatment
• CPAP compliance monitoring via device data (hours of use, AHI on therapy, leak rate)
• Annual reassessment; weight changes alter OSA severity
• Blood pressure monitoring; cardiovascular risk factor management

KEY POINTS SUMMARY TABLE