What is the pathophysiology of pulmonary hypertension in COPD?

• A. Decreased right heart output
• B. Pulmonary vessel vasoconstriction due to alveolar hypoxia increases pulmonary vascular resistance
• C. Increased alveolar ventilation
• D. Decreased hemoglobin affinity

Answer: (B)

Chronic alveolar hypoxia from COPD triggers hypoxic pulmonary vasoconstriction, a key response that increases the resistance in the pulmonary arteries. When many regions of the lung are hypoxic, this vasoconstrictive effect becomes widespread, pushing up pulmonary vascular resistance and raising pulmonary arterial pressures. Over time, the vessels undergo remodeling—smooth muscle hypertrophy and intimal thickening—so the high pressure becomes more fixed and persistent. This higher afterload on the right ventricle can lead to right heart strain and eventual cor pulmonale.

This mechanism explains why pulmonary hypertension develops in COPD: it's driven by the vascular response to low oxygen in the lungs, not by a primary decrease in cardiac output, increased ventilation, or changes in hemoglobin oxygen affinity.