[The interstitial organ in weightlessness: a clinico-physiologic model].

We performed an experiment within the 1991 Austromir mission, 3 months preflight, on the 6th inflight and 4th postflight days, respectively. Primary goal was to measure changes in venous blood and plasma sound velocity (BSV, PSV) with lower body suction (LBNP). Contrasting earth-based findings, there was no increase in BSV nor PSV with LBNP inflight. Postflight, the elevation in both values was greater than expected. Taken together with LBNP data from the German 1992 Mir cosmonaut, we propose the hypothesis that the dynamics of tissue fluid exchange is profoundly influenced by m-g adaptation. A further goal of the experiment was to determine volume- and stress-sensitive hormones. The results need validation by additional flight data and might be considered as an important contribution to our understanding of the normal functioning and pathophysiology of the interstitial organ.