Pulmonary vascular disease and myeloid abnormalities in PAH. This study identifies hemangioblast proliferation and fibrosis as key components in the pathophysiology of PAH. Increased levels of HIF-inducible factors, some of which are produced by diseased pulmonary vascular cells, promote hemangioblast proliferation and progenitor cell mobilization. Local production of recruitment factors by pulmonary vascular endothelium attract mobilized progenitor cells into the pulmonary artery wall where these cells fuel vascular remodeling. (Illustration by David Schumick, BS, CMI. Reprinted with permission, Cleveland Clinic Center for Medical Art & Photography, 2010. All rights reserved.)