Exercise helps astronauts’ hearts handle months in space, boosting prospects for Mars

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Exercise helps astronauts' hearts handle months in space, boosting prospects for Mars

Study of astronauts found their hearts withstood simulated Martian gravity after six months in space

• Study tracked heart function in 13 astronauts before, during and after space missions
• Astronauts exercised up to two hours a day in space to counter the effects of weightlessness
• Cardiac function dipped at the start of missions but then gradually returned to preflight levels
• Scientists simulated Mars' gravity by tilting astronauts 22 degrees after they returned to Earth
  

CHICAGO - A trip to Mars may be more feasible than previously thought, suggests a new study led by Northwestern Medicine that tracked the heart function of 13 astronauts during roughly six-month missions aboard the International Space Station.

A major question facing NASA in its plan to send astronauts to the Red Planet has been whether their cardiovascular systems could handle the transition from weightlessness in spaceflight (known as microgravity) to arrival on a planet where gravity is about one-third as strong as on Earth.

The new study found that the astronauts adapted well to microgravity during spaceflight - thanks to intense daily workouts - and showed no major signs of cardiovascular strain under simulated Martian gravity upon their return from space.

"With our findings, there is now reason to think that we would be able to traverse to Mars, get there and actually work on the surface of Mars," said study senior author Dr. James Thomas, professor of medicine in the division of cardiology at Northwestern University Feinberg School of Medicine.

The study, published last month in the journal Circulation, is the first to examine how the heart responds to simulated Martian gravity after prolonged exposure to microgravity.

Exercising in space

Many astronauts returning from previous space missions struggled with dizziness and lightheadedness upon standing up when re-entering a gravitational environment. That transition can cause a sudden drop in blood pressure, a phenomenon known as orthostatic hypotension. (If you've seen Sandra Bullock crawling after returning to Earth in "Gravity," you get the idea.)

But the astronauts in this study largely tolerated the transition thanks to their daily exercise regimen. Following a NASA program called Exercise Countermeasures, they worked out for up to about two hours a day, including 30 to 45 minutes of endurance exercise and 60 to 75 minutes of resistance training.

"You lose muscle mass and cardiac mass when you're in a weightless environment because you are working less up there," explained Thomas, who also is a Northwestern Medicine cardiologist. "You're floating around in the air, and you give a little tap with your foot, and you can sail over to say hello to your buddy."

"To counter that, exercise is crucial when you're in space," Thomas added.

Heart scans during spaceflight

For each astronaut, Thomas and his team analyzed echocardiograms - ultrasound scans of the heart - before, during and after the mission. During spaceflight, the astronauts were trained to perform the scans on one another every few weeks so that Thomas and his team, back on Earth, could track their heart function and structure over time. Thomas' team included Dr. Benjamin Levine of UT Southwestern Medical Center and Dr. Michael Bungo of the McGovern Medical School at UTHealth Houston.

"It would be typically about 3 a.m. for me because the space station runs on Greenwich Mean Time," Thomas said. "I would watch the recordings come in live and coach the astronauts in real time to improve the images."

During the first two weeks of spaceflight, the astronauts experienced reductions in cardiac filling, stroke volume and other measures of cardiac performance. In other words, their hearts were initially filling with less blood between beats and pumping less blood with each contraction.

But this adaptation period turned out to be temporary. And as the mission progressed, cardiac filling and stroke volume gradually moved back toward preflight levels.

Mars gravity

To simulate arriving on Mars, the study team tilted the astronauts 22 degrees upward from their lying down position after they returned to Earth. This was meant to shift their blood toward their lower body to mimic Mars' gravity. The scientists found that the astronauts' hearts handled the simulated Martian environment as well as they had handled standing upright on Earth before launch.

The study is titled, "Impact of Prolonged Spaceflight on Cardiac Structure and Function: An Exploratory Longitudinal Observational Study." It was funded by the National Space Biomedical Research Institute (grant NCC9-58), NASA (grant NNJ04HH01A), the IDP Foundation, Sandra Helton and the National Heart Foundation of Australia.