A 58-year-old man with a 40-pack-year smoking history and COPD (FEV₁ 35% predicted) presents with progressive dyspnea, orthopnea, and ankle edema over 6 months. Examination reveals JVD with prominent A waves, a parasternal heave, loud P2, and a pulsatile hepatomegaly. Chest X-ray shows an enlarged main pulmonary artery. The structure marked **C** in the diagram (dilated main pulmonary artery) is a consequence of chronic pulmonary hypertension secondary to his lung disease. Which of the following mechanisms BEST explains the pathophysiology of cor pulmonale in this patient?

Explanation

## Why "Chronic hypoxic pulmonary vasoconstriction and progressive vascular remodeling leading to increased pulmonary vascular resistance and RV afterload" is right Cor pulmonale in COPD is fundamentally driven by chronic hypoxia-induced pulmonary vasoconstriction and structural remodeling of the pulmonary vascular bed. This increases pulmonary vascular resistance (PVR), forcing the RV to work against higher afterload. Over time, the RV hypertrophies (wall thickness >5 mm) and dilates, which then causes the pulmonary artery (structure **C**) to dilate as it accommodates the increased flow and pressure. The clinical findings—JVD with prominent A waves (reflecting concentric RVH), parasternal heave, loud P2, and pulsatile hepatomegaly—all reflect this RV-centered pathophysiology. This mechanism is the hallmark of cor pulmonale from pulmonary disease (WHO group 3 PH), as stated in Robbins 10e Ch 15 and Harrison 21e Ch 277. ## Why each distractor is wrong - **Left ventricular systolic dysfunction causing backward transmission of elevated pressures into the pulmonary circulation**: This describes group 2 pulmonary hypertension (PH due to left heart disease), which is explicitly EXCLUDED from the definition of cor pulmonale. Cor pulmonale by definition arises from pulmonary disease or pulmonary vascular disease, not left heart disease. The LV in pure cor pulmonale remains normal in size. - **Acute pulmonary embolism causing mechanical obstruction of the pulmonary vascular bed**: While acute PE can cause acute pulmonary hypertension and RV strain, cor pulmonale is a chronic condition requiring sustained pulmonary hypertension. Acute PE does not produce the chronic RV hypertrophy and remodeling seen here. Chronic thromboembolic PH (CTEPH, group 4) can cause cor pulmonale, but this patient has COPD with hypoxic mechanisms, not recurrent thromboembolism. - **Mitral stenosis causing pulmonary venous congestion and secondary pulmonary hypertension**: Mitral stenosis causes postcapillary (group 2) PH via elevated left atrial pressure, not precapillary PH from pulmonary vascular disease. This is again excluded from cor pulmonale by definition and does not explain the RV-centric pathology in this COPD patient. **High-Yield:** Cor pulmonale = RV disease from pulmonary (not cardiac) cause; COPD is the most common etiology; hypoxic vasoconstriction + vascular remodeling → increased PVR → RVH + RV dilation → PA dilation; LV stays normal. [cite:Robbins 10e Ch 15; Harrison 21e Ch 277]