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The hearts of 13 astronauts adjusted to six months in space and coped with simulated Mars gravity
Without gravity pulling blood toward the feet, the heart fills differently. Scanning 13 astronauts before, during and after long missions showed the early changes settled down in flight.
- This small observational study followed 13 astronauts on missions to the International Space Station.
- In the first two weeks in space, heart filling and pumping volume dropped, much as when standing on Earth.
- Over the rest of the mission, those measures drifted back toward values seen lying down before flight.
- After landing, simulated Mars gravity put no more strain on the heart than standing upright had before launch.
- The authors call it a small exploratory study and tie the results to exercise done in flight.
Stand up quickly after lying on the couch and you may feel a brief wobble. Gravity pulls blood toward your legs, and your heart and blood vessels have to adjust. Now imagine taking gravity away almost entirely for six months. A study that scanned the hearts of 13 astronauts before, during and after long missions to the International Space Station shows how the heart copes.
The short version is reassuring. The heart changed quickly when it reached space, then settled. After landing, a simulation of the weaker gravity on Mars put no more strain on astronauts’ hearts than simply standing up on Earth.
What happens to the heart without gravity?
On Earth, the heart’s workload shifts every time you change position. Lying flat, blood returns easily and the heart fills well. Standing, gravity pools blood lower in the body, so the heart fills a little less with each beat.
The authors point out that gravity, from Earth’s full pull to the near-zero of orbit and the partial gravity of Mars in between, directly affects how blood moves through the heart and vessels. A trip to Mars would mean months of weightlessness followed by landing in gravity about 38% as strong as Earth’s. Knowing how the heart handles those shifts matters for crew safety.
How were the astronauts’ hearts measured?
Writing in Circulation, the researchers followed 13 astronauts, 9 of them men, with an average age of 49. Their median time in space was 164 days.
The main tool was echocardiography, an ultrasound scan of the heart that shows how much blood the chambers hold and how the muscle squeezes and relaxes. Scans were taken before flight while lying down and while tilted at set angles, on board the space station, on landing, and again after landing.
The clever part was the Mars test. Lying on a table tilted to 22 degrees means only part of Earth’s gravity acts along the body, roughly 0.38 of normal, which is about what astronauts would feel on Mars. That let the team compare the heart’s response to Mars-like gravity before launch and after months in orbit.
How did the heart change during spaceflight?
Within the first 14 days in space, the heart’s main pumping chamber, the left ventricle, held less blood at the end of each filling phase, and it pushed out less blood per beat. Measures of how the muscle stretched and squeezed also shifted.
Those early in-flight values looked a lot like the same astronauts standing upright on Earth before launch, with small differences in two measures of how the heart muscle deformed. In other words, the heart in space was not doing anything wildly unusual. It resembled a heart adjusting to posture.
Over the rest of the mission, filling volume and the amount pumped per beat drifted back up toward the values measured while lying down before flight. In the authors’ words, the early changes were transient and stabilized during flight.
Would a Mars landing strain the heart?
After roughly six months in space, the astronauts were tested again at the Mars-like tilt. No measure showed more load or stress on the heart than standing upright had before flight. The authors conclude that trouble standing up after landing, a problem called orthostatic intolerance, may be unlikely on Mars after a six-month journey, provided crews keep up appropriate exercise.
That last condition is important. Astronauts on the space station use exercise as a countermeasure against the effects of weightlessness. The results reflect hearts that were being actively looked after, not hearts left to adapt on their own.
What can a study of 13 astronauts not tell us?
The authors call this a small exploratory study, and that is the honest framing. With 13 people, subtle but real changes could easily be missed, and the findings may not apply to crews who are older, less fit, or in space for longer.
Mars gravity was also simulated with a tilt table on Earth after landing, not experienced after a real journey to Mars. And the study describes what happened to one group over time, without a comparison group, so it cannot separate the effects of weightlessness from everything else that comes with a mission.
What do astronaut hearts tell the rest of us?
Mostly, they show how adaptable the heart is. The changes seen in space largely mirrored what happens every day when people move between lying down and standing up, and they returned to baseline after return to Earth.
For people on the ground, the study offers no new advice, but it is a reminder of what matters. MedlinePlus notes that heart disease is the leading cause of death in the United States, but there are ways to prevent and manage many types. Keeping the heart active and challenged, whether in orbit or at home, is part of that.
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What did the study find?
The volume of the left ventricle, the heart's main pumping chamber, at the end of filling, along with stroke volume and heart muscle deformation measures, fell from preflight lying-down values early in flight, to levels similar to standing upright on Earth. Over the rest of the flight, volumes rose back toward preflight lying-down values. After about 6 months in space, simulated Martian gravity produced no greater load or stress on the heart than upright posture on Earth before flight.
How do you simulate Mars gravity on Earth?
By tilting a person on a table. Lying at a 22 degree angle means only part of Earth's gravity pulls along the body, about 0.38 of normal, which matches the pull on Mars.
Did astronauts' hearts shrink in space?
Filling volumes fell early in flight, then recovered toward normal over the mission. The authors found no large changes in heart structure or function after flights of up to about six months.
What is an echocardiogram?
An ultrasound scan of the heart. It shows the size of the heart's chambers and how well the muscle squeezes and relaxes.
Does this mean a trip to Mars is safe for the heart?
It is encouraging but not proof. The study was small, covered missions of about six months, and relied on astronauts doing their usual exercise in flight.
What does this mean for people on Earth?
Mostly it shows how responsive the heart is to posture and gravity. It does not offer health advice, but it underlines the role of exercise in keeping the heart adaptable.