Dussault C, Gontier E, Verret C, Soret M, Boussuges A, Hedenstierna G, Montmerle-Borgdorff S. Hyperoxia and hypergravity are independent risk factors of atelectasis in healthy sitting humans: a pulmonary ultrasound and SPECT/CT study. Aeroatelectasis 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

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... tion and perfusion, eight subjects were studied before and after 1 h 15 min exposure to ϩ1 to ϩ3.5 G z 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 single-photon emission computed tomography combined with computed tomography (SPECT/CT). Ultrasound lung comets (ULC) and atelectasis both increased after exposure. The number of ULC was Ͻ1 pre protocol (i.e., normal lung) and larger post 100% O 2 (22 Ϯ 3, mean Ϯ SD) than in all other conditions (P Ͻ 0.001). Post 44.5% O2 differed from air (P Ͻ 0.05). Seven subjects showed low-to mediumgrade atelectasis post 100% O 2. There was an effect on grade of gas mixture and hypergravity, with interaction (P Ͻ 0.001, respectively); 100% O 2, 44.5% O2, and air differed from each other (P Ͻ 0.05). SPECT ventilation and perfusion were always normal. Ultrasound concurred with CT in 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. ϩG z accelerations; lung collapse; echography; computerized tomography; excessive oxygen supply