Effect of gravity and posture on lung mechanics

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 similar to2.7 cmH(2)O going from 1 to 0 vertical acceleration (G(z)), whereas it increased by similar to3.5 cmH(2)O in 30degrees tilted head-up and supine postures. No substantial change was found going from I 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 similar to580 ml at 0 G(z) relative to 1 G(z) and of similar to1,200 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.