Cerebral Hemodynamics During Exposure to Hypergravity (+G_z) or Microgravity (0 G)

BACKGROUND: Optimal human performance and health is dependent on steady blood supply to the brain. Hypergravity (+G_z) may impair cerebral blood flow (CBF), and several investigators have also reported that microgravity (0 G) may influence cerebral hemodynamics. This has led to concerns for safe performance during acceleration maneuvers in aviation or the impact long-duration spaceflights may have on astronaut health.METHODS: A systematic PEO (Population, Exposure, Outcome) search was done in PubMed and Web of Science, addressing studies on how elevated +G_z forces or absence of such may impact cerebral hemodynamics. All primary research containing anatomical or physiological data on relevant intracranial parameters were included. Quality of the evidence was analyzed using the GRADE tool.RESULTS: The search revealed 92 eligible articles. It is evident that impaired CBF during +G_z acceleration remains an important challenge in aviation, but there are significant variations in individual tolerance. The reports on cerebral hemodynamics during weightlessness are inconsistent, but published data indicate that adaptation to sustained microgravity is also characterized by significant variations among individuals.DISCUSSION: Despite a high number of publications, the quality of evidence is limited due to observational study design, too few included subjects, and methodological challenges. Clinical consequences of high +G_z exposure are well described, but there are significant gaps in knowledge regarding the intracranial pathophysiology and individual hemodynamic tolerance to both hypergravity and microgravity environments.Saehle T.