Blood Plasma Proteins Associated With Heart Rate Variability in Cosmonauts Who Have Completed Long-Duration Space Missions.

The study presents the results of evaluating the changes in the concentrations of blood plasma proteins associated with heart rate variability (HRV) in cosmonauts who have completed space missions lasting about 6months. The concentrations of 125 proteins were quantified in biological samples of the cosmonauts' blood plasma. The subgroups of proteins associated with the physiological processes of the HRV autonomic regulation were identified using bioinformatic resources (Immunoglobulin heavy constant mu, Complement C1q subcomponent subunit C, Plasma serine protease inhibitor, Protein-72kDa type IV collagenase, Fibulin-1, Immunoglobulin lambda constant 3). The concentration of these proteins in the blood plasma before the flight, and the dynamics of concentration changes on the 1st and 7th days of the post-flight rehabilitation period differed in the groups of cosmonauts with a predominance of sympathetic or parasympathetic modulating autonomous influences. The dynamics of changes in the concentrations of the identified set of proteins reveal that in cosmonauts with a predominance of sympathetic modulating influences, the mechanisms of autonomic regulation are exposed to significant stress in the recovery period immediately after the completion of the space mission, compared with the cosmonauts with a predominance of parasympathetic modulating influences.

The Effect of Five-Day Dry Immersion on the Nervous and Metabolic Mechanisms of the Circulatory System.

The purpose of the study was to investigate the regulatory and metabolic changes in the circulatory system when simulating microgravity conditions in a five-day dry immersion. These changes reflect the adaptation processes characteristic for the initial stages of a space flight or a short-duration space flight. Studies were conducted with 13 healthy male volunteers aged 21 to 29 years. The assessment of regulatory and metabolic processes in the circulatory system was based on the heart rate variability (HRV) and urine proteomic profile analysis. It was found that the restructuring of hemodynamics during 5 days hypogravity begins with the inclusion of the nervous circuit of regulation, and for manifestations at the body fluids protein composition level and activation of the metabolic regulation, these periods are apparently insufficient. Perhaps this is due to the fact that the metabolic regulation, being evolutionarily ancient and genetically determined, is more stable and requires more time for its pronounced activation when stimulated by extreme life conditions.

NT-ProBNP levels, water and sodium homeostasis in healthy men: effects of 7 days of dry immersion.

Immersion is a useful tool for studying fluid-volume homeostasis. Natriuretic peptides play a vital role in renal, humoral, and cardiovascular regulation under changing environmental conditions. We hypothesized that dry immersion would rapidly induce a new steady state for water and sodium metabolism, and that serum NT-proBNP levels, a proxy measure for brain natriuretic peptide (BNP), would decrease during long-term dry immersion and increase during recovery. Eight healthy young men were studied before, during, and after 7 days of dry immersion. Body weight, water balance, and plasma volume changes were evaluated. Plasma and serum samples were analyzed for active renin, NT-proBNP, aldosterone, electrolytes, osmolality, total protein, and creatinine. Urine samples were analyzed to determine levels of electrolytes, osmolality, creatinine, and free cortisol. A stand test was performed before and after dry immersion to evaluate cardiovascular deconditioning. Long-term dry immersion induced acute changes in water and sodium homeostasis on day 1, followed by a new steady state. Plasma volume decreased significantly during dry immersion. The serum levels of NT-proBNP increased significantly in recovery (10 ± 3 ng/L before dry immersion vs. 26 ± 5 ng/L on the fourth recovery day). Heart rate in the standing position was significantly greater after immersion. Results suggest that chronic dry immersion rapidly induced a new level of water-electrolyte homeostasis. The increase in NT-proBNP levels during the recovery period may be related to greater cardiac work and might reflect the degree of cardiovascular deconditioning.