increase in urine output during weightlessness, but there may be a relative increase compared
to the intake of fluid because the intake of fluid and food tend to decrease. It is likely that
vasoconstriction is maintained or increased in the lower part of the body inflight. Thus
sympathetic activity may be increased to counteract the increase in blood flow to the brain and
to other organs above the heart level during microgravity. In conclusion, a relative high
sympathoadrenal activity as compared to preflight values seems to be an integrated part of the
regulatory response to microgravity. Furthermore, HDBR cannot be applied to simulate changes
in sympathoadrenal activity in humans during microgravity.
PUBLICATION(S)
Christensen NJ, Heer MA, Ivanova K, Norsk P. Sympathetic nervous activity decreases during
head down bed rest but not during microgravity. Microgravity Science and Technology.
September 2007;19(5-6):95-97. doi: 10.1007/BF02919460.
Christensen NJ, Heer MA, Ivanova K, Norsk P. Sympathetic nervous activity decreases during
head-down bed rest but not during microgravity. Journal of Applied Physiology. June 16, 2005;
99(4):1552-1557. doi: 10.1152/japplphysiol.00017.2005.
This investigation is complete and all results are published.