Cml And Other Myeloproliferative Disorders

A 75-year-old man presents to clinic as a new patient. He has hypertension and obstructive lung disease but has otherwise been healthy. He takes hydrochlorothiazide and uses a metered-dose inhaler. He continues to smoke one pack of cigarettes a day despite multiple attempts at quitting. His family history is positive for diabetes and heart disease. His physical examination is remarkable for a prolonged expiratory phase with some wheezing diffusely. Oxygen saturation on room air is found to be 92% at rest but drops to 87% with exertion. The results of laboratory testing, which was done 2 days ago, are normal with the exception of a hematocrit of 58%. You do not have any prior blood counts for comparison.   Which of the following is the most likely cause of this patient's erythrocytosis?