Pulmonary Hypertension (see Pulmonary Hypertension): Chronic myeloproliferative disorders can cause pulmonary HTN by various potential mechanisms
High cardiac output, auto or surgical asplenia, direct obstruction of pulmonary arteries by circulating megakaryocytes (99), CTEPH (100), portopulmonary HTN, and congestive heart failure may all play a role.
References
Unexplained pulmonary hypertension in chronic myeloproliferative disorders. Chest 2001;120:801-8
Pulmonary hypertension secondary to thrombocytosis in a patient with myeloid metaplasia. Chest 1993; 103:642-4