U.S. Air Force Lt Col Samuel Mcintyre, NATO Allied Command Transformation deputy chief of staff military assistant, breaths through a mask as he flies a flight simulator during hypoxia training at 1st Operations Group aerospace and operational physiology, Joint Base Langley-Eustis, Va., Dec. 5, 2017. Hypoxia is when the heart and/or lungs can’t provide the blood with the proper amount of oxygen causing the brain and other organs to start failing. (U.S. Air Force photo by Airman 1st Class Tristan Biese)