Cardiovascular System Under Simulated Weightlessness: Head-Down Bed Rest vs. Dry Immersion.

Background: The most applicable human models of weightlessness are -6° head-down bed rest (HDBR) and head-out dry immersion (DI). A detailed experimental comparison of cardiovascular responses in both models has not yet been carried out, in spite of numerous studies having been performed in each of the models separately.

Objectives: We compared changes in central hemodynamics, autonomic regulation, plasma volume, and water balance induced by -6° HDBR and DI.