Human lung mechanics during water immersion.

We measured lung volumes, static deflation pressure-volume curves of the lung, maximum expiratory flow-volume curves, and closing capacities in five men standing immersed to the neck in water. FRC was decreased 27%, while other lung volumes did not change significantly. At high lung volumes immersion tended to increase lung elastic recoil while recoil was decreased at low lung volumes, changes compatible with vascular congestion. Maximum expiratory flow was increased at high lung volumes, probably because of hydrostatic pressure. At low lung volumes maximum expiratory flow was decreased. This was probably due to decreased recoil since the relationship between elastic recoil and maximum flow was unchanged. Closing capacities by the N2 technique were unchanged but the slope of the alveolar plateau and the amplitude of cardiogenic oscillations were decreased in some individuals. Static and dynamic lung properties were unchanged by 5 min of immersion with tidal volume restricted to 0.5 liter. Though immersion produced volume restriction comparable with that reported with chest strapping, it did not produce similar changes in lung mechanics.