The Order of Inclusion of Circulatory System Regulation Circuits in Adaptation Mechanisms during Simulation of Microgravity Effects via 5-Day Dry Immersion

Complex interactions between circuits regulating blood circulation are determined by multidirectional effects of a variety of factors in a system maintaining homeostasis at an optimal level. An important methodological approach used in the study opens up new opportunities for analyzing the patterns in intersystem interactions of regulatory circuits and processes that are nonlinear and are in a stable non-equilibrium state. An experiment with 5-day dry immersion (DI) was carried out to determine the degree of synchronization and the timing of involvement in adaptation process for regulatory circuits of the circulatory system. The circuits were evaluated by analyzing the heart rate variability (HRV) (nervous regulatory circuit), blood chemistry (humoral regulatory circuit), and the urinary proteomic profile (metabolic regulatory circuit). DI is commonly used in gravitational physiology to study the effect of microgravity on physiological systems of the body. The study involved 11 healthy male volunteers aged 28 ± 4 years. A principal component analysis was used to study the regulatory interactions at all DI stages. The functionality of each circuit was analyzed as a whole, which made it possible to reveal hidden patterns that remain undetectable when individual variables are analyzed. The direction and time of response were estimated for various circuits of the regulation of blood circulation to characterize their reactivity, which reflects the adaptive capabilities of the body. Concerted estimates were obtained for different regulatory circuits.