A decrease in the level of dioxygen in blood.
http://purl.obolibrary.org/obo/UPHENO_0076014
http://purl.obolibrary.org/obo/HP_0012418
http://purl.obolibrary.org/obo/UPHENO_0079822
http://purl.obolibrary.org/obo/UPHENO_0085961