A patient with pulmonary embolism develops hemoptysis. What is the pathophysiologic cause?

Hemoptysis in pulmonary embolism occurs as a result of pulmonary tissue infarction. When an embolus occludes a pulmonary artery or one of its branches, blood flow to the distal lung tissue is cut off. If the collateral bronchial circulation is insufficient to maintain viability, ischemia and subsequent infarction of lung parenchyma develop. This necrotic lung tissue bleeds into the alveoli and airways, producing the characteristic blood-tinged or frankly bloody sputum known as hemoptysis. Pulmonary infarction occurs in a minority of PE cases — roughly 10 to 15 percent — and is more likely when there is pre-existing cardiopulmonary disease reducing collateral flow. Bronchospasm can occur with PE due to mediator release and causes wheezing and airway obstruction, but it does not directly cause hemoptysis. Pleural effusion can accompany PE, particularly with infarction, and may cause pleuritic chest pain, but it does not itself cause coughing up blood. Infection is not a primary pathophysiologic feature of PE-related hemoptysis. Recognizing that hemoptysis in the context of PE indicates infarction helps guide clinical severity assessment and management decisions.