Influence of inspired oxygen concentration on acceleration atelectasis

Area of Science:

• Aerospace Medicine
• Physiology
• Respiratory System

Background:

• The U.S. Air Force is developing an On Board Oxygen Generation System (OBOGS) for fighter aircraft.
• Acceleration atelectasis is a potential risk associated with high inspired oxygen concentrations during high-G maneuvers.

Purpose of the Study:

• To determine the inert gas dilution requirements for OBOGS to prevent acceleration atelectasis.
• To assess the impact of varying inspired oxygen concentrations on vital capacity during simulated combat maneuvers.

Main Methods:

• Human subjects were exposed to varying inspired oxygen concentrations (21-100%) during a Simulated Aerial Combat Maneuver (SACM) profile on a human centrifuge.
• The SACM profile included +4.5 Gz peaks superimposed on a +3 Gz baseline.
• Vital capacity (VC) and breathing symptoms were measured.

Main Results:

• A significant reduction in vital capacity (VC) was observed at inspired oxygen concentrations of 70% and greater.
• The addition of 5% argon to pure oxygen did not mitigate acceleration atelectasis or breathing symptoms.
• A 30-second exposure to positive pressure breathing (30 mm Hg) at the end of the SACM reduced VC reduction in subjects breathing 100% oxygen.

Conclusions:

• Inspired oxygen concentrations of 70% or higher during high-G maneuvers can lead to significant vital capacity reduction.
• Inert gas addition (5% argon) does not appear to prevent acceleration atelectasis.
• Positive pressure breathing may be a viable countermeasure to reduce lung volume reduction during high-G exposure with high oxygen concentrations.