Effect of gravity and posture on lung mechanics

1 Dipartimento di Medicina Sperimentale, Ambientale e Biotecnologie Mediche, Università di Milano-Bicocca, I-20052 Monza (MI), Italy; 2 Médecine Aerospatiale, Université de Bordeaux, F-33076 Bordeaux; 4 Centre Chirurgical Marie Lannelougue, UPRES EA2397, Université Paris XI, F-92350 Le Plessis Robinson; and 3 Hôpital Lariboisière, F-75010 Paris, France The volume-pressure relationship of the lung was studied in six subjects on changing the gravity vector during parabolic flights and body posture. Lung recoil pressure decreased by ~2.7 cmH 2 O going from 1 to 0 vertical acceleration (G z ), whereas it increased by ~3.5 cmH 2 O in 30° tilted head-up and supine postures. No substantial change was found going from 1 to 1.8 G z . Matching the changes in volume-pressure relationships of the lung and chest wall (previous data), results in a decrease in functional respiratory capacity of ~580 ml at 0 G z relative to 1 G z and of ~1,200 ml going to supine posture. Microgravity causes a decrease in lung and chest wall recoil pressures as it removes most of the distortion of lung parenchyma and thorax induced by changing gravity field and/or posture. Hypergravity does not greatly affect respiratory mechanics, suggesting that mechanical distortion is close to maximum already at 1 G z . The end-expiratory volume during quiet breathing corresponds to the mechanical functional residual capacity in each condition. lung compliance; esophageal pressure; functional residual capacity; interstitial pressure