CD34 and obstructive sleep apnea syndrome: In OSAHS patients without clear cardiovascular diseases, expression of CD34 and CD31, markers of endothelial progenitor cells (EPCs), is significantly reduced, while vascular endothelial growth factor (VEGF) is markedly elevated, indicating that these vasoactive factors may be involved in the formation of vascular endothelial injuries in OSAHS patients [66].