Astronauts' Hearts Take on Spherical Shape in Zero Gravity

To counter the effects of zero gravity, astronauts in orbit must exercise regularly to keep their bodies from suffering deleterious effects, including atrophy. But a new study has revealed the weightlessness has a surprising effect on the human heart: it makes it more spherical.

When exposed to long periods of microgravity in space, the heart becomes more spherical, a change that could lead to cardiovascular problems, according a study of 12 astronauts presented at the American College of Cardiology's 63rd Annual Scientific Session.

The find has implications for both long-distance space travel, such as a manned mission to Mars, a journey that would take about 18 months.

"The heart doesn't work as hard in space, which can cause a loss of muscle mass," senior study author Dr. James Thomas of NASA said in a statement released by the American College of Cardiology. "That can have serious consequences after the return to Earth, so we're looking into whether there are measures that can be taken to prevent or counteract that loss."

The research was conducted by astronauts who were trained to take images of their hearts with a portable ultrasound scanner before, during and after spaceflight. Computer models predicted the effects of microgravity would lead to a more spherical heart shape, and the field test proved the model correct.

Astronauts' hearts became more spherical in shape by a factor of 9.4 percent.

"The models predicted the changes we observed in the astronauts almost exactly. It 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 said.

Changes in the astronauts' hearts appeared to be temporary. Hearts returned to a normal, more elongated, shape shortly after the subjects returned to Earth.

Knowing that the heart's shape can change while in a zero-gravity environment will allow mission designers and trainers to assign more effective exercise techniques to astronauts on long space missions.

The research could also become relevant to people with no intentions of setting food off Earth. Thomas said exercise regimens developed for astronauts could be used to help maintain heart health in people on Earth who have severe physical limitations such as mandatory bed rest or a heart failure regime.