title: Influence of inspired oxygen concentration on acceleration atelectasis.
abstract: The USAF is developing an On Board Oxygen Generation System (OBOGS) for use in fighter aircraft. This study was conducted to determine the inert gas dilution requirements of the OBOGS necessary to prevent acceleration atelectasis. Human subjects were exposed to either 21, 50, 70, 82.5, 95 or 100% inspired oxygen, along with an increased +Gz Simulated Aerial Combat Maneuver (SACM) profile using the USAF School of Aerospace Medicine human centrifuge. The SACM profile utilized four +4.5z peaks (136 s at this +Gz) superimposed on a +3 Gz baseline, representing a total ride time of 276 s. A significant reduction in vital capacity (VC) occurred at inspired oxygen concentrations of 70% and greater. The addition of 5% argon (a natural product of OBOGS) to pure oxygen did not reduce the magnitude of acceleration atelectasis observed, nor the severity of breathing symptoms. A 30-s exposure to positive pressure breathing at 30 mm Hg during the end of the SACM reduced the level of VC reduction caused by subjects breathing 100% oxygen during +Gz.
mesh_terms: D000054:Acceleration / Q000009:adverse effects*; D000328:Adult; D000337:Aerospace Medicine; D000401:Aircraft / Q000295:instrumentation; D001128:Argon; D005260:Female; D005676:Gravity Suits; D006801:Humans; D008297:Male; D010102:Oxygen Inhalation Therapy; D011175:Positive-Pressure Respiration; D001261:Pulmonary Atelectasis / Q000517:prevention & control*; D014797:Vital Capacity
chemical_list: D001128:Argon