Cold agglutinin disease is a type of autoimmune hemolytic anemia (see this term) defined by the presence of cold autoantibodies (autoantibodies which are active at temperatures below 30°C).
An embolus (that is, an abnormal particle circulating in the blood) located in the pulmonary artery and thereby blocking blood circulation to the lung. Usually the embolus is a blood clot that has developed in an extremity (for instance, a deep venous thrombosis), detached, and traveled through the circulation before becoming trapped in the pulmonary artery.