Washington, March 30 (IANS): In an alarming revelation, a new study finds that astronauts' hearts become more spherical when exposed to long periods of microgravity in space -- a change that could lead to cardiac problems when they are back on earth.

With implications for an eventual manned mission to Mars, the findings represent an important step toward understanding how a spaceflight of 18 months or more could affect astronauts' heart health.

"The heart does not work as hard in space which can cause a loss of muscle mass," said James Thomas, Moore Chair of cardiovascular imaging and lead scientist for ultrasound at NASA.

That can have serious consequences after the return to earth so we are looking into whether there are measures that can be taken to prevent or counteract that loss, he added.

The researchers say that knowing the amount and type of exercise astronauts need to perform to keep the heart healthy is going to be very important to guarantee their safety on a long flight like a mission to Mars.

The exercise regimens developed for astronauts could also be used to help maintain heart health in people on earth who have severe physical limitations, such as people on extended bed rest or those with heart failure regime.

During their research, the team trained astronauts to take images of their hearts using ultrasound machines installed on the International Space Station (ISS).

Twelve astronauts participated, providing data on heart shape before, during and after spaceflight.

The results show the heart in space becomes more spherical by a factor of 9.4 percent, a transformation similar to what scientists had predicted with sophisticated mathematical models developed for the project.

By validating those models, the study could also lead to a better understanding of common cardiovascular conditions in patients on earth.

"This gives us confidence that we can move ahead and start using these models for more clinically important applications on earth, such as to predict what happens to the heart under different stresses," Thomas noted.

The team is now working to generalise the models to analyze such conditions as ischemic heart disease, hypertrophic cardiomyopathy and valvular heart disease.

The more spherical shape experienced in space may mean the heart is performing less efficiently.

Upon return to earth, astronauts commonly become lightheaded or pass out in a condition known as orthostatic hypotension, in which the body experiences a sudden drop in blood pressure when standing up, the study concluded.