Obstructive Sleep Apnea (OSA) - PG Exam Essay (with flowcharts/diagrams)

Etiopathogenesis / Pathophysiology

1. Anatomical narrowing of pharyngeal airway
   • Obesity, enlarged tongue/soft tissues, craniofacial abnormalities (retrognathia), longer airway
2. Increased airway collapsibility (critical closing pressure, Pcrit)
3. Sleep-related fall in pharyngeal dilator muscle tone
4. Reduced lung volume in supine posture (less tracheal traction)
5. Fluid shift and upper airway edema/inflammation
6. Instability of ventilatory control in some patients

• Intermittent hypoxemia
• Hypercapnia
• Recurrent arousals and sleep fragmentation
• Sympathetic activation, oxidative stress, endothelial dysfunction
  leading to cardiovascular and metabolic morbidity.
  (Murray and Nadel’s Textbook of Respiratory Medicine, p. 2760)

Risk factors

• Obesity (most important modifiable factor)
• Male sex, increasing age
• Craniofacial crowding, adenotonsillar hypertrophy
• Alcohol/sedatives, smoking
• Nasal obstruction
• Endocrine/metabolic factors (e.g., hypothyroidism, acromegaly)
• Family/genetic predisposition

Clinical features

Diagnostic approach (Flowchart)

Clinical suspicion (snoring + daytime sleepiness/witnessed apneas)
                |
                v
Risk assessment (history, exam, Epworth score, comorbidity screen)
                |
                v
Objective sleep test mandatory
(PSG preferred / HSAT in selected uncomplicated adults)
                |
                v
AHI/RDI-based severity + oxygen desaturation burden + symptom burden
                |
                v
Phenotype/endotype + comorbidities + patient preference
                |
                v
Individualized treatment plan + long-term follow-up

Investigations

• Gold standard: attended overnight PSG
  Records airflow, respiratory effort, oxygen saturation, sleep stages, ECG, limb movements, etc.
• Indices: AHI, RDI, oxygen desaturation, arousal index, sleep architecture
• HSAT: alternative in selected adults without major cardiorespiratory/neuromuscular complexity
• Ancillary: thyroid function, metabolic/cardiovascular risk evaluation, ENT evaluation where relevant

Management

1) General and behavioral

• Weight reduction (diet, exercise, bariatric approach when indicated)
• Avoid alcohol/sedatives at bedtime
• Sleep hygiene and positional therapy
• Treat nasal obstruction and contributing factors

2) Positive airway pressure (PAP)

• CPAP is first-line in moderate-severe OSA and symptomatic disease
• Reduces obstructive events, improves sleepiness and quality of life
• Improves BP and may reduce cardiovascular risk in adherent patients

3) Oral appliance therapy

• Mandibular advancement devices in mild-moderate OSA or CPAP intolerance

4) Surgery (selected patients)

• Upper airway surgery for anatomical obstruction (e.g., multilevel approaches)
• Maxillomandibular advancement in selected refractory cases
• Therapy often individualized and combination treatment may be needed
  (Murray and Nadel’s Respiratory Medicine, p. 2818)

5) Follow-up

• Assess adherence, residual symptoms, machine data, side effects
• Reassess comorbidities and repeat sleep study when indicated

Complications

• Systemic hypertension, coronary artery disease, arrhythmia, heart failure, stroke
• Insulin resistance/metabolic syndrome
• Neurocognitive impairment, depression
• Increased risk of motor vehicle and occupational accidents

Prognosis

Exam-ready management flowchart

Diagnosed OSA
   |
   +--> Mild (AHI 5-15): lifestyle +/- positional therapy +/- oral appliance
   |
   +--> Moderate-Severe (AHI >=15): CPAP first-line + lifestyle
   |
   +--> CPAP intolerance/non-response:
           reassess mask/interface, pressure titration, adherence barriers
           consider oral appliance / surgery / combination therapy
   |
   --> periodic follow-up: symptoms + AHI control + comorbidity control

Diagrams for answer sheet / viva discussion

1) PSG tracing showing obstructive events (apnea/hypopnea/RERA concept):

2) Cardiovascular pathophysiology flowchart in OSA: