Pathogenesis: The emboli has separated from its site of origin travels through the circulation to the inferior vena cava. The right ventricle pumps this emboli obstructed pulmonary artery. increase in resistance to blood flow in the pulmonary vessels. Severe pulmonary hypertension, Residual volume strain, and cardiac heart failure ->50-60% decrease in perfusion. -v/Q mismatch in which there is "dead space" ventilation in some parts of the lung and overperfusion in others. right-to-left intrapulmonary shunting with insufficient oxygenation of a large portion of perfused blood.