RV enlargement and/or altered function resulting from primary lung disease; leads to RV hypertrophy and eventually to RV failure. Etiologies include:

• Pulmonary parenchymal or airway disease leading to hypoxemic vasoconstriction: e.g., chronic obstructive pulmonary disease (COPD), interstitial lung diseases, bronchiectasis, cystic fibrosis (Chaps. 133: Chronic Obstructive Pulmonary Disease and 136).
• Diseases of the pulmonary vasculature: e.g., recurrent pulmonary emboli, pulmonary arterial hypertension (PAH) (Chap. 129: Pulmonary Hypertension), vasculitis, sickle cell anemia.
• Inadequate mechanical ventilation (chronic hypoventilation). Kyphoscoliosis, neuromuscular disorders, marked obesity, sleep apnea (Chap. 140: Sleep Apnea).