ABSTRACT
Changing G causes great modifications in the regional blood distribution and therefore is expected to affect fluid balance in the interstitial spaces. For example, it is well known that increasing G causes a marked accumulation of blood into the caudal part of the body, the reverse being true in 0 G where the general appearance of a subject is described as having' 'spider legs and puffy face." In the latter condition, leg volume decreases by about 2 L (1) and tissue thickness of the forehead increases by approximately 7% with respect to normal (2). Although changes in interstitial fluid volume do occur in various organs depending on functional conditions, they certainly ought to be prevented in the lung tissue to assure optimal gas diffusion. This chapter deals with the pulmonary interstitial fluid balance in physiological conditions at 1 G and discusses the possible perturbations induced by 0 G exposure. Data obtained during space missions and parabolic flights indicate that 0 G exposure caused an increase in pulmonary blood volume and perfusion (3), conditions potentially leading to an increase in interstitial fluid volume; it will therefore be useful to discuss the series of events leading to interstitial fluid accumulation in the transition toward development of pulmonary edema. In parallel, we also present fluid dynamics in the pleural cavity,
which is exquisitely sensitive to gravity and whose fate is closely associated with pulmonary fluid balance.
