Salivary stress markers and psychological stress in simulated microgravity: 21 days in 6° head-down tilt.

Spaceflight occurs in an environment of temperature extremes, microgravity, solar and galactic cosmic radiation, lack of atmospheric pressure, and high-speed micrometeorites. Exposure to microgravity and the space environment during space missions of short and long duration has important medical and health implications for astronauts. Psychological well-being is of increasing importance in planned spaceflights and interplanetary missions of long duration. The 6° head-down tilt (HDT) is an established method of mimicking low gravity on earth. The aim of the present study was to determine the effects of 21 days of HDT on psychological stress in 12 healthy male volunteers. Psychological state was assessed by the current stress test, and chromogranin-A (CgA), cortisol, alpha-amylase, and beta-endorphin were measured in saliva. After one week of HDT, all volunteers developed psychological stress, and secretion of CgA, cortisol, alpha-amylase, and beta-endorphin were all significantly higher. Thus, 6° HDT appears to be a valid model to induce psychological stress changes in the immune system, changes that might also be encountered by astronauts and cosmonauts during both a short stay in space, such as that required while orbiting a space station, and in longer spaceflights.