Abstract: INTRODUCTION. Headward fluid shift and hypodynamia during microgravity exposure can lead to morphological and functional alterations in vessels of lower extremities. This leads to excessive blood pooling in legs in upright posture after spaceflight. Periodic exposure to artificial gravity (AG), whether in real or simulated microgravity, might slow down the development of these changes and prevent orthostatic intolerance. AIM of the study is to evaluate the influence of periodic short-arm centrifugation sessions during head-down bed rest (HDBR) on the dynamics of blood redistribution to the lower extremities in tilt test. METHODS. 12 healthy volunteers were confined in 6 degrees HDBR for 21 days. Starting from day 8, five out of the 12 participants were subjected to intermittent, ~1.25 G and 2 G 3-min bouts (33 min total per session) on a short-arm centrifuge every three days (AG group). Both control and AG group undergone 15-min passive tilt tests before and on 19th day of HDBR. Near-infrared spectroscopy (NIRO-200, Hamamatsu, Japan) was used to continuously measure changes in total (tHb), oxygenated (OHb), and deoxygenated (HHb) hemoglobin levels in the lower leg muscles during tilt test. Tilt table was equipped with saddle to mitigate the influence of lower leg contractions on recorded parameters. Continuous recordings of ECG and arterial pressure were obtained to control central hemodynamic parameters. RESULTS. In control group, an increase in OHb, HHb, and tHb accumulation during tilt test is observed after exposure to HDBR compared to tests before HDBR (Figure 1, A,C, p<0.05), which reflects an increase in blood filling of small vessels during standing. The absence of a decrease in OHb after the initial rapid increase after verticalization may be associated with an alteration of compensatory vasoconstriction in lower leg muscles. In the AG group, there were little to no difference in the accumulation of tHb, OHb, and HHb between pre- and post-HDBR tests (Figure 1 B,C). Moreover, there was a stark difference in the dynamics of OHb between the two groups after HDBR. This may be due to the preservation of the ability of small vessels in the lower extremities to constrict during orthostatic challenge. CONCLUSION. Periodic AG during HDBR counteracts excessive blood filling of lower leg microvasculature during orthostatic challenge possibly due to preserved compensatory vasoconstriction. FUNDING. The study was supported by the program of basic scientific research at the Institute of Biomedical Problems of the Russian Academy of Sciences (topic FMFR-2024-0032).

Cite: Zhedyaev R.Y. , Vinogradova O.L. , Tarasova O.S. , Yashina V.A. , Puchkova A.A. , Salʹnikov A.V. , Koloteva M.I. , Borovik A.S.
Short-arm centrifuge sessions during head-down bed rest reduce excessive blood redistribution to the lower extremities in tilt test
44 Annual the International Society of Gravitational Physiology Meeting (ISGP), Sapporo, 2025 18-23 May 2025