First-time imaging of effects of inspired oxygen concentration on regional lung volumes and breathing pattern during hypergravity.

Borges, João; Hedenstierna, Göran; Bergman, Jakob; Amato, Marcelo; Avenel, Jacques; Montmerle-Borgdorff, Stéphanie

Purpose: Aeroatelectasis can develop in aircrew flying the latest generation high-performance aircraft. Causes alleged are relative hyperoxia, increased gravity in the head-to-foot direction (+G), and compression of legs and stomach by anti-G trousers (AGT). We aimed to assess, in real time, the effects of hyperoxia, +G accelerations and AGT inflation on changes in regional lung volumes and breathing pattern evaluated in an axial plane by electrical impedance tomography (EIT). Methods: The protocol mimicked a routine peacetime flight in combat aircraft. Eight subjects wearing AGT were studied in a human centrifuge during 1 h 15 min exposure of +1 to +3.5G. They performed this sequence three times, breathing AIR, 44.5 % O or 100 % O. Continuous recording of functional EIT enabled uninterrupted assessment of regional lung volumes at the 5th intercostal level. Breathing pattern was also monitored. Results: EIT data showed that +3.5G, compared with any moment without hypergravity, caused an abrupt decrease in regional tidal volume (V) and regional end-expiratory lung volume (EELV) measured in the EIT slice, independently of inspired oxygen concentration. Breathing AIR or 44.5 % O, sub-regional EELV measured in the EIT slice decreased similarly in dorsal and ventral regions, but sub-regional V measured in the EIT slice decreased significantly more dorsally than ventrally. Breathing 100 % O, EELV and V decreased similarly in both regions. Inspired tidal volume increased in hyperoxia, whereas breathing frequency increased in hypergravity and hyperoxia. Conclusions: Our findings suggest that hypergravity and AGT inflation cause airway closure and air trapping in gravity-dependent lung regions, facilitating absorption atelectasis formation, in particular during hyperoxia.

PHYSIOLOGICAL effects of gravity; RESPIRATION; ATELECTASIS; ELECTRICAL impedance tomography; HYPEROXIA; AIRWAY (Anatomy)

European Journal of Applied Physiology, 2015, Vol 115, Issue 2, p353

1439-6319

Academic Journal

10.1007/s00421-014-3020-9