Analysis of the reaction of cosmonaut's body microcirculatory-tissue systems to postural effects at tilt-table

This study evaluates the peripheral microcirculatory-tissue system (MTS) response of professional cosmonauts to specific postural test, simulating the haemodynamic effects of microgravity. Nineteen Roscosmos cosmonauts underwent a passive tilt-table protocol (-15°, -30°, +70°) at the Yuri A. Gagarin Cosmonaut Training Center while wearing a distributed system of portable multimodal optical analyzers combining laser Doppler flowmetry and fluorescence spectroscopy. Continuous monitoring before, during, and after tilt phases captured changes in average perfusion, oscillatory amplitudes (endothelial, neurogenic, myogenic, respiratory, cardiac), nutritive and shunt blood flow, and normalized NADH fluorescence. Results demonstrate individual adaptation mechanisms: trained cosmonauts maintained metabolic stability (unchanged NADH fluorescence) despite marked microcirculatory rearrangements, with region-specific shifts in perfusion and regulatory oscillations. Cluster analysis of relative parameter changes identified distinct response phenotypes, underscoring intra-and inter-subject variability in microvascular regulation. These findings confirm the high sensitivity of wearable multimodal diagnostics for detecting MTS shifts under orthostatic load and support their use as markers of training efficacy. Personalized information of microhaemodynamic reserves may enhance cosmonaut selection, optimize pre-flight conditioning, and inform countermeasure development for long-duration space missions.