Hearts in Space

Dr. Michael Bungo, a cardiologist at UT Health Houston, works with NASA astronauts to learn what spaceflight does to their hearts

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By Kathryn Lundstrom
Population Health Scholar
University of Texas System
MA Student in Journalism
UT Austin Moody College of Communication


Almost 50 years after the moon landing, and 41 years after the premiere of the first Star Wars, it’s easy to forget that we’re still just taking baby steps into outer space.

“We’re in the exploration phase of space right now­­,” said Dr. Michael W. Bungo. “We’re not in the colonization phase.”


Bungo is a professor of cardiovascular medicine with McGovern Medical  School at The University of Texas Health Science Center at Houston (UTHealth).  In collaboration with NASA, he studies what happens to astronauts’ hearts in space. Though humans have been venturing into space since the 1960s, there are still a lot of questions about what the physical and psychological effects are.

For example, how much weaker does the heart get during a long-term space flight? Is it possible to exercise enough without gravity to keep up an Earthlike level of cardiac fitness?

Those questions – and the difficulty of answering them – means we’re very far away from being able to safely send regular folks off into the final frontier, according to Bungo. There’s still a lot of research to be done first.

“We’re not loading up the Conestoga wagons right now and settling the prairie,” he said. “We are in the Lewis and Clark phase, or the Columbus or Magellan phase.”

In 1980, Bungo finished his residency and fellowship at Harvard. “I looked at traditional jobs in academia, industry, and private practice,” said Bungo.

In the midst of his job hunt, Bungo visited the Kennedy Space Center. The excitement of the work there brought him back to his youth, reminding him of the unique thrill that space exploration held for him. There was a time the country hung on every mission of the Mercury, Gemini, and Apollo flights. The world literally stopped during the moon landing missions.

“I just said, gee, I wonder if NASA needs any cardiologists,” he said. “So I wrote a blind letter to NASA seeing if there was any interest or what have you. As fate may have it, there was, and the rest is kind of history.”

NASA’s first shuttle, the Space Shuttle Columbia, launched in April of 1981 –– just nine months after Bungo started. “It seemed like both NASA’s resurgent program and my career were starting off at the same time.”

Though many people go into research positions at NASA with the goal of transitioning into the astronaut corps, Bungo wasn’t ever one of those. “I never really wanted to commit the time to be an astronaut because I thought it would take away from being a cardiologist,” he said.

After 11 years full time at the Johnson Space Center, he transitioned into academia, spending seven years teaching at UTMB Galveston before joining the faculty at UT Houston. From there he’s been able to continue working with NASA on research.

Since the International Space Station launched into orbit in 1998, Bungo’s team has been able to do longer studies assessing the effects of spaceflight on cardiac functioning. But even with the more frequent trips, data collection takes years.

“As the space program transitioned from the shuttle flights to the longer space station missions and people were up there for three, four, and finally six and in some cases even 12 months at a time, there were two major cardiac concerns,” said Bungo.

First was whether the heart muscle would atrophy in space. Second was whether there’d be increased cardiac rhythm abnormalities –– something researchers had anecdotally noticed in shorter flights.

In their most recent study, Bungo’s team of researchers  (in conjunction with Ben Levine, a colleague at UT Southwestern) did extensive pre-flight testing on astronauts’  hearts, taught the astronauts to use the equipment necessary to continue regular testing while in flight, and then continued with more extensive testing upon the astronauts’ return.

They learned that the current prescription of exercise per day, while in space, was enough to prevent “deleterious effects” on the heart muscle.

“These crewmembers participate in a pretty vigorous exercise program,” said Bungo. “And the good news is that to the level of exercise they did, which was substantial, two hours a day every day, we saw no significant cardiac atrophy.”

But the astronauts’ hearts did change shape a bit. “On Earth, your heart kind of hangs in your chest a little bit –– it’s suspended, really, in your chest by a number of ligaments,” Bungo explained. “But in space flight, you’re weightless, and the heart actually becomes more spherical.”

After about a month after their return to Earth, the astronauts’ hearts were back to their normal shape. But Bungo remains concerned that hearts’ tendency to become spherical in zero-gravity could remodel with even longer times in space.

And heart shape is only one of many concerns. “You literally need to study everything,” he said, from radiation exposure to the physical effects of low gravity to the isolation of long flights. “For humans to function in space, there isn’t this single issue. There’s this whole multitude of issues and effects on different systems.”

All those issues –– and the research it’ll take to work through them –– will keep this team busy for quite a while. And sending humans into space with so many unknowns still involves a lot of risk. “But that’s what makes it exciting, too,” said Bungo.