Astronauts' Shrinking Hearts Cause Wooziness Back on Earth

  It takes a lot of heart to become an astronaut, leave Earth,
  and hang out in a dangerous and weightless environment for
  two weeks. More than anyone knew, in fact.

  Upon returning to Earth, some two-thirds of astronauts report
  lightheadedness, dizziness and difficulty concentrating when
  standing up. New research done during a 1998 Space Shuttle
  flight has found the cause: Astronauts hearts grow stiff,
  shrink, and pump less blood.

  The new study involved six male astronauts aboard a
  Neurolab shuttle mission, designed specifically to study the
  human nervous system and to test what's called sympathetic
  nerve activity, which researchers had thought was behind the
  wooziness.

  The researchers examined the astronauts before, during and
  after the 16-day spaceflight, monitoring the astronauts' blood
  pressure and how the cardiovascular system is stressed by
  gravity.

  The research will be published in the January issue of the
  Journal of Physiology.

  By Robert Roy Britt
  Senior Science Writer
  posted: 09:09 am ET
  16 January 2002

http://www.space.com/scienceastronomy/generalscience/astronaut_heart_020116.html

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