Review Question - QID 212464

A 31-year-old man presents to his physician with a 4-month history of progressive shortness of breath with exertion. He works for a moving company and is concerned that he will not be able to continue working due to this shortness of breath. His past medical history is significant for childhood asthma but he has not experienced symptoms from asthma for 10 years prior to presentation. He also notes that he gets very frequent nosebleeds, but was not found to have any coagulation disorders on prior workup. Physical exam reveals some clubbing of the fingers and the findings shown in Figure A. Administration of albuterol has no effect on the patient's shortness of breath. Which of the following is most likely responsible for this patient's shortness of breath?