The differences between pulmonary embolism and chronic obstructive pulmonary disease (COPD) mainly include the following aspects: 1. Different mechanisms of onset: Pulmonary embolism refers to the blockage of the pulmonary arteries by thrombi, while COPD is a disease of the small airways, primarily characterized by the narrowing of these airways. 2. Different clinical manifestations: Pulmonary embolism is often acute, with symptoms such as chest tightness, difficulty breathing, and may also include chest pain, coughing up blood, and fainting. COPD is a chronic disease, usually presenting with chronic chest tightness and difficulty breathing, and may also include symptoms such as coughing and expectoration. 3. Different diagnostics: Pulmonary embolism can often be diagnosed through CT pulmonary angiography, whereas COPD typically requires lung function tests for diagnosis.