 Impaired arterial blood gas (oxygen) tensions during intense exercise, increased blood lactate, and rarely death have been noted (likely due to ruptured chordae tendinae or a different mechanism of lung hemorrhage).Epistaxis is diagnosed when blood is visible at either or both nostrils during or following exercise.To confirm whether the blood is coming from the upper or lower airway requires further examination by endoscopy, although in some cases it is not possible to determine the location.