Aero-atelectasis has developed in aircrew flying routine peacetime flights on the latest generation high-performance aircraft, when undergoing excessive oxygen supply. To single out the effects of hyperoxia and hypergravity on lung tissue compression, and on ventilation and perfusion, eight subjects were studied before and after 1h15 min exposure to 1-3.5Gz in a human centrifuge. They performed the protocol three times, breathing air, 44.5%O2 or 100%O2 and underwent functional and topographical imaging of the whole lung by ultrasound and SPECT/CT. Ultrasound lung comets (ULC) and atelectasis both increased after exposure. The number of ULC was <1 pre-protocol (i.e. normal lung) and larger post-100%O2 (22 ± 3, mean ± SD) than in all other conditions (P<0.001). Post-44.5%O2 differed from air (P <0.05). Seven subjects showed low to medium grade atelectasis post-100%O2. There was an effect on grade of gas mixture and hypergravity, with interaction (P < 0.001 respectively). 100%O2, 44.5% O2 and air differed from each other (P < 0.05). SPECT ventilation and perfusion was always normal. Ultrasound concurred with CT for showing normal lung in the upper third and ULC/atelectasis in posterior and inferior areas, not for other localizations. In conclusion, hyperoxia and hypergravity are independent risk factors of reversible atelectasis formation. Ultrasound is a useful screening tool. Together with electrical impedance tomography measurements (reported separately), these findings show that zones with decreased ventilation prone to transient airway closure are present above atelectatic areas.
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