In a patient with chronic obstructive pulmonary disease developing cor pulmonale, the initial trigger for right ventricular hypertrophy is best explained by:

• A Polycythemia-induced hyperviscosity raising pulmonary vascular resistance
• B Increased venous return from peripheral edema
• C Left ventricular diastolic dysfunction causing back-pressure
• D Hypoxic pulmonary vasoconstriction causing sustained elevation in pulmonary arterial pressure ✓

Explanation

Alveolar hypoxia triggers hypoxic pulmonary vasoconstriction (HPV) through a mechanism involving inhibition of voltage-gated K+ channels in pulmonary artery smooth muscle cells, causing sustained depolarization and contraction. Chronic HPV leads to pulmonary arterial remodeling and persistently elevated pulmonary artery pressure, increasing right ventricular afterload and ultimately causing cor pulmonale. Polycythemia does contribute but is secondary; left ventricular dysfunction is excluded in primary cor pulmonale.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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