Physiological Challenges of Space Travel and Ground-Based Simulation Possibilities for Monitoring Brain Circulatory Changes: A Rheoencephalography Study

The functional integrity of brain perfusion and oxygen transport profoundly determines mental performance during military flight missions and spaceflight. Presently, at the selection phase of pilot candidates, there are no screening methods to evaluate cerebral circulation and its autonomous regulation (AR), meanwhile the pilot information processing capacity could be insufficient in dangerous flight situations with high mental workload or during high “head-to-foot” G loads. On-board ISS (International Space Station) and during deep-space missions circulatory changes can be evolved in the opposite direction due to the microgravity: blood shift toward the head-neck region can increase ICP (Intracranial Pressure) and tenfold increase of carbon-dioxide concentration can provoke complaints and disturbances in eye and brain blood circulation (Space Associated Neuro-Ocular Syndrome – SANS). The alteration of brain perfusion dynamics and oxygen utilisation was investigated on the head-down tilting table (HDT) test and in the hypobaric (low-pressure) chamber. We registered the brain regional pulse wave changes by the bioimpedance (Rheoencephalography – REG) on 19 volunteers in rest and after the breath-holding manoeuvre. We found that during the head-down tilt (HDT) position, the amplitude of the second peak of the REG pulse wave increased, like the ICP pulse wave, being an unfavourable sign for intracranial pressure increase in clinical cases. Manual readings resulted in significant differences during HDT between the female (P = 0.0007) and male (P < 0.0001) groups. With automated analysis, the increase in REG P2 wave was significant, and the ratio was 4/5 (80%) for women and 10/14 (71%) for men. The newly written automatic program script was able to detect this in 92% of the cases. The calculated values detected the state of cerebral circulatory autoregulation and the identity between the male and female groups. Based on this result and previous REG correlation studies, it can be concluded that REG could be used to monitor fighter pilots, astronauts, and neurocritical care patients in real-time as emergency alert in the transitory cessation of brain perfusion.