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Obesity Hypoventilation Syndrome

Obesity Hypoventilation Syndrome: Pathogenesis and clinical findings Obesity (BMI ≥ 30 kg/m2) risk factors: Poor eating patterns, sedentary lifestyle, genetic predisposition, hypothyroidism, Cushing’s syndrome, socio-economic factors, age Sleep-disordered breathing risk factors: Family history, tonsillar or adenoidal hypertrophy, ↑ neck circumference, type 2 diabetes, HTN Authors: Mohammad Omer Mujtaba Siddique Reviewers: Ali Babwani Luiza Radu Jonathan Liu* MD at time of publication* ↑ Adipose deposition in abdomen Abdominal fat pushes against diaphragm ↑ Diaphragmatic displacement ↑ Resistance to chest wall expansion ↑Leptin resistance High pressure Pharyngeal on upper airway dilations unable Secondary depression ↓ Chest wall ↓ Leptins ability to stimulate ↑ lung to compensate Narrowing of (compromised function) of Poor ventilation to expansion ventilation (mechanism unknown) collapsibility for weight upper airways respiratory system lower lobes of lungs ↓ Tidal volume (air that moves in/out of lungs in a respiratory cycle) ↑ Respiratory rate ↑ Chest wall thickness ↑ Leptin (a hormone released by adipose tissues that controls hunger by signaling fullness) ↑ Adipose deposition near upper airways ↑ Buildup of edema in lower extremities ↑ Respiratory workload ↓ Chest wall compliance (ability to stretch) ↓ Leptin receptor expression ↓ Leptin through blood-brain barrier ↓ Pharyngeal space Respiratory system is unable to compensate to ↑ Fluid shifts from demands legs to neck during sleep Hypoventilation in sleep ↓ Ventilation (air exchange in lungs) ↑ PaCO₂ (partial pressure of arterial carbon dioxide) ↑ Serum [H+] ↑ Serum [HCO3 -] by renal reabsorption buffers [H+] rise ↓ PaO₂ (partial pressure of arterial oxygen) Hypoxia (low O₂ in tissue) Higher PaCO₂ required to reduce pH ↓ O₂ levels in alveoli triggers pulmonary vessel vasoconstriction PaCO₂ > 45 mmHG Respiratory acidosis ↓ response to CO₂ in central chemoreceptors in brain Pulmonary hypertension (high pressure in pulmonary arteries) ↓ Neural drive ↓ Ventilatory responsiveness ) Right heart pumps against higher pulmonary pressure leading to cardiomyocyte hypertrophy Cor pulmonale (right-sided heart failure) Fatigue Chronic hypercapnia (↑ CO2 retention) Pathophysiology Legend: Mechanism Sign/Symptom/Lab Finding Complications Morning headaches Daytime lethargy Published Jun 16, 2025 on www.thecalgaryguide.com