Washington, Oct 26 (IANS): When astronauts land on earth, their blood pressure (BP), along with the altitude, drops in a condition known as orthostatic hypotension, according to a research.

The condition occurs in up to half of those astronauts on short-term missions (two weeks or less) and in nearly all astronauts after long-term missions (four to six months).

A new research solves the biological mystery of how this happens by showing that low gravity compromises the ability of arteries and veins to constrict normally, inhibiting the proper flow of blood, the FASEB Journal reported.

"I take great satisfaction with helping in the discovery of how microgravity alters the human body and how we can minimize these effects, so humans can safely explore the bounds of our universe," said study author Michael D. Delp, researcher in applied physiology and kinesiology from the University of Florida.

Prevention and treatment strategies developed for astronauts may also hold promise for elderly populations on Earth who experience orthostatic hypotension more than any other age group, according to a Florida statement.

Delp and colleagues examined arteries and veins from mice housed at Kennedy Space Centre in Florida with blood vessels from groups of mice flown on three of the last five space shuttle missions-STS-131, STS-133 and STS-135.

Mice flown on the STS-131 and STS-135 missions were tested immediately after returning to Earth, whereas mice from STS-133 were tested one, five and seven days after landing.

Not only did they find that these mice experienced the equivalent of orthostatic hypotension in humans, they also discovered that it takes as many as four days in normal gravity before the condition is reversed.