ABSTRACT
A major breakthrough in the understanding of the distribution of ventilation was achieved in 1966 with the publication of three papers using radioactive gas techniques to measure regional pulmonary ventilation (1-3). Not only were the measurements more reliable than lobar spirometry, but quantitative data could also be obtained on a topographical basis, corresponding to, for example, the vertical distance from the top to the bottom of the lung. Since then, most of the information on regional ventilation distribution has been obtained with radioactive gases. However, these techniques have never been used in space, and most of the experiments used to study microgravity effects on the lung are indirect techniques such as single-and multiple-breath inert gas washouts (4,5). Predictions were made of the results of the experiments performed in microgravity (obtained in space or in aircraft during parabolic trajectories), and from the differences between predictions and observations we gained insight into the behavior of inhaled gas in the human lung. In this chapter we present a number of examples where studies in microgravity have provided insight into the basic physiology.
