A hypoperfusion of the BLOOD through an organ or tissue caused by a PATHOLOGIC CONSTRICTION or obstruction of its BLOOD VESSELS, or an absence of BLOOD CIRCULATION. The phenotype is Experimental Factor Ontology entry EFO_0000556 (ischemia). Also known as: Ischaemia, Ischaemia, NOS, Ischemia (disorder), Ischemia, NOS, Ischemias.