Regional cutaneous blood flow in healthy subjects under conditions of 21-day head-down bed rest

Introduction . Research into the microvasculature as an integral component of the cardiovascular system is particularly relevant in space medicine for identifying adaptive changes to weightlessness and developing new diagnostic criteria for assessing the functional state of an astronaut’s body in long-duration space flights. Objective . To study the process of microcirculation and its regulation in various skin areas in healthy volunteers under conditions of 21-day head-down (–6°) bed rest (HDBR). Materials and methods . The experiment involved six male volunteers aged 26–34 years. To simulate translocation of liquid media and physical inactivity, the subjects remained in an antiorthostatic position for 21 days. Microcirculation was studied by laser Doppler flowmetry using LAZMA PF portable laser analyzers (SPE “LAZMA” Ltd, Russia). Participant examination was conducted two days prior the onset of the study, on the 3rd, 7th, 15th, 18th, and 20th day of experimental exposure, as well as two days after the completion of HDBR. Statistical data analysis was performed using the Statistica 13.0 software (IBM, USA). Results . On day 3 of HDBR exposure, a statistically significant decrease in basal perfusion and the amplitude of myogenic oscillations in the skin of the forehead and shin was observed. The analysis of functional tests on the forearm showed a decrease in the respiratory test index by 10.87% throughout the experimental period. On day 3 of hypomobility, a decrease in the venuloarteriolar response by an average of 10.64% and an increase by 91.82% in the capillary blood flow reserve were noted, with the latter persisting throughout the entire exposure. Conclusions. The effect of HDBR is expressed in a decrease in skin perfusion against the background of increased tone of terminal arterioles and precapillary sphincters in the forehead and lower legs, which may indicate microcirculation shift toward larger vessels. Despite the skin perfusion stability in the forearm area at rest, the conducted functional tests showed the probability of changes in vasomotor function under the action of HDBR.