pulmonary embolism risk factorslung damage after pulmonary embolismsudden pulmonary embolismmultiple pulmonary embolismspulmonary embolism positionpulmonary embolism diagnosisrecurrent pulmonary embolismpulmonary embolism prognosisunprovoked pulmonary embolismchronic pulmonary embolism treatmentdefine pulmonary embolismbilateral pulmonary embolism