Austin AW, Patterson SM, Ziegler MG, Mills PJ. Plasma volume and flight duration effects on post-spaceflight soluble adhesion molecules. Aviat Space Environ Med 2014; 85:912–8. Background: We examined the effects of plasma volume (PV) changes and flight duration on circulating soluble adhesion markers (sP-selectin, sE-selectin, and sICAM-1). Methods: Study participants were 22 astronauts (2 women). Missions ranged from 5 to 16 d. Astronauts were split into two groups: those who spent less than 8 d in space and those who spent more than 8 d in space. Soluble adhesion markers and PV were assessed 10 d prelaunch, immediately after landing, and 2-4 d postflight. Results: Compared to prelaunch, PV significantly decreased by 4.9% after landing and increased by 9.9% 2-4 d postflight. After landing, sICAM-1 decreased (233.15 vs. 226.78 ng · ml⁻¹) and remained lowered 2-4 d after landing (223.25 ng · ml⁻¹). Adjusting for PV changes, sICAM-1 upon landing was less than prelaunch (218.23 ng · ml⁻¹), but became greater 2-4 d postflight (250.30 ng · ml⁻¹). From prelaunch to landing, sE-selectin decreased significantly (30.25 vs. 28.51 ng · ml⁻¹) and returned to prelaunch levels 2-4 d postflight (30.10 ng · ml⁻¹). Adjusting for PV changes, sE-selectin was significantly greater 2-4 d postflight (33.48 ng · ml⁻¹) compared to prelaunch. In those who spent less than 8 d in space only, sP-selectin increased from prelaunch levels to landing day (31.66 vs. 48.06 ng · ml⁻¹), with and without adjustment for PV changes. Flight duration did not influence PV, sICAM-1, or sE-selectin. Discussion: Spaceflight leads to an internal environment that decreases PV during flight but rebounds after flight, leading to a dilution of sICAM-1 and sE-selectin, but does not appear to affect sP-selectin. Flight duration only affected sP-selectin.