CHANGES IN BLOOD AND PLASMA COMPOSITION WITH LOWER-BODY NEGATIVE-PRESSURE ON THE GROUND AND IN-SPACE IN ONE SUBJECT

In one cosmonaut, we investigated lower body negative pressure (LBNP) induced capillary fluid shifts which we hypothesized would be changed by microgravity (mu g) adaptation. Sound pulse velocity (SV) wets dete rmined in whole blood and plasma samples using a new method that could detect 0.1% protein concentration changes. Experiments were performed 3 months preflight (supine), during space flight (6th day in orbit), and postflight (supine; 4th day after landing). Antecubital blood was taken at the beginning (3 min: time a) and after shut down (+2 min: ti me b) of 40 min LBNP (-15/-30/-35 mm Hg for 15/15/10 min, respectively ), since in control experiments with multiple sampling on Earth, the l argest difference (increase) between blood and plasma SV wets observed between a and b. Our cosmonaut had a 1.6 m/s increase in blood sound pulse velocity (BSV) preflight and a 4.0 mis increase postflight, wher eas BSV stayed unchanged in flight. plasma sound pulse velocity (PSV) increased 1.2 m/s preflight and 1.7 m/s postflight, whereas PSV did no t rise (-0.4 m/s) in flight. This would indicate profoundly altered LB NP-induced fluid dynamics in flight, compared to control (1 g) conditi ons. On the 4th day postflight, blood and plasma sound velocity increa sed more with LBNP than preflight, indicating greater hemoconcentratio n than under control conditions. In summary, the data suggest: I)alter ed fluid shifts between blood and interstitial compartments during LBN P with 6 d adaptation to microgravity: and 2) increased hemoconcentrat ion during LBNP early after a 10-d spaceflight. investigations of bloo d and plasma SV time courses during and after LBNP in future spaceflig ht missions could validate our results, and clarify the mechanism of a ltered fluid shifts during acute cardiovascular stress due to cardiova scular and interstitial adaptation to microgravity.