Aviation medicine is a branch of medicine that applies medical knowledge to the human factors in aviation. Broadly defined, this subdiscipline endeavors to discover and prevent various adverse physiological responses to hostile biologic and physical stresses encountered in the aerospace environment. Problems range from life support measures for astronauts to recognizing an ear block in an infant traveling on an airliner with elevated cabin pressure altitude. Aeromedical certification of pilots, aircrew and patients is also part of Aviation Medicine. A final subdivision is the AeroMedical Transportation Specialy. These military and civilian specialists are concerned with protecting aircrew and patients who are transported by AirEvac aircraft (helicopters or fixed-wing airplanes).