Indices of acceleration atelectasis and the effect of hypergravity duration on its development

Abstract

New Findings What is the central question of the study To determine the effects of +Gz acceleration duration on acceleration atelectasis and identify measurement techniques that can be used to assess it. What is the main finding and its importance Non‐invasive measurement of acceleration atelectasis using electrical impedance tomography and estimates of pulmonary shunt provide more detailed assessment of acceleration atelectasis than traditional forced vital capacity measures. Using these techniques, it was found that as little as 30 s of +Gz acceleration exposure can cause acceleration atelectasis. The results of the present study will allow a more accurate and detailed assessment of acceleration atelectasis in the future. Abstract Background Recently there have been reports of acceleration atelectasis during fast jet flight despite the use of systems designed to minimise this. Prior to further investigation of this, indices suitable for use in applied settings and identification of acceleration durations which elicit it are required. Methods Fifteen non‐aircrew subjects performed five centrifuge exposures lasting 15, 30, 60 and 2 × 90 s with a plateau of +5 Gz while breathing 94 % O₂ during all but one control exposure (21 % O₂). Lung volumes and gas exchange limiation were assessed after each exposure. Regional lung impedance and compliance were measured post Gz exposure using electrical impedance tomography (EIT) and the forced oscillatory technique (FOT), respectively. Results The presence of acceleration atelectasis was confirmed by 10 to 17 % reductions in vital and inspiratory capacity after 60 and 90 s Gz exposures (P < 0.05) and resulted in reduced regional lung impedance and a gas exchange limitation of 8.1 and 12.5 %, respectively (P < 0.05). There was also a small but significant decrease in regional lung impedance after 30 s exposures. Functional residual capacity and lung compliance were unchanged in atelectatic lungs (P > 0.05). Discussion In the majority of individuals > 60 s of Gz exposure while breathing 94 % O₂ causes acceleration atelectasis. EIT and the measurement of gas exchange limitation provide useful indicators of acceleration atelectasis. Acceleration atelectasis exerts its effects primarily through basal lung closure and reflex inspiratory limitation both of which can be reversed by performing three maximal inspiratory breathing manoeuvres. This article is protected by copyright. All rights reserved