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In space, your heart becomes smaller.
In a study published Monday in the journal Circulation, scientists reported that the largest chamber of the heart of Scott Kelly, who spent nearly a year on the International Space Station in 2015 and 2016, has shrunk en masse by more than ‘a quarter for the hour of his return to Earth.
This only adds to the litany of transformations that the human body undergoes without the constant pull of gravity downward. Astronauts also tend to have swollen heads, crushed eyeballs, shriveled legs, and bones that become more fragile.
But a smaller heart didn’t seem to have any ill effects on Mr. Kelly.
“He did remarkably well for a year,” said Dr. Benjamin D. Levine, lead author of Circulation and professor of internal medicine at the University of Texas Southwestern Medical Center and Texas Health Presbyterian Dallas.
“Her heart has adapted to the reduced gravity,” Dr. Levine said. “It did not become dysfunctional, the excess capacity was not reduced to a critical level. He has remained reasonably fit. His heart shrunk and atrophied as one would expect on going into space.
Without the pull of gravity, the heart doesn’t have to pump as hard, and like any other muscle, it loses its physical shape with less intense use. For Mr Kelly, the shrinkage happened while he exercised almost every day on the space station, a diet that has been shown to be effective in limiting weakening of bones and loss of muscle in general. .
But a smaller heart could be a concern for future missions to Mars.
Based on the experience of Mr. Kelly and other astronauts on the space station, “they’ll probably be fine,” Dr. Levine said. But problems could arise if an astronaut was injured or fell ill and couldn’t exercise. Or if the exercise equipment has broken down. With weaker hearts, they could become dizzy and passed out while walking the Red Planet after months of weightless travel.
In the article, Dr. Levine and his colleagues also compared Mr. Kelly’s heart to that of Benoît Lecomte, a long-distance endurance swimmer, when he attempted to cross the Pacific in 2018. Buoyancy in water has many of the same effects on the body in zero gravity. Mr Lecomte was horizontal most of the time – up to eight hours of swimming and eight hours of sleep on a support boat.
Scientists believed that the hours of swimming would be exhausting enough to maintain Mr Lecomte’s heart, which was observed by periodic echocardiograms. Instead, it shrunk, almost as quickly as Mr. Kelly’s in space.
Over 159 days – Mr Lecomte had to give up swimming less than a third of the way on a planned 5,650 mile trip after the boat was damaged by a storm – his heart’s left ventricle lightened d ‘about six ounces to five ounces. The left ventricle is the largest and strongest chamber in the heart, pumping blood into the aorta and through the body.
“I was just shocked,” Dr. Levine said. “I really thought his heart was going to get bigger. It was a lot of exercise he was doing.
In an interview, Mr Lecomte estimated his heart rate was “maybe in the low hundreds” while swimming and described the intensity of long-distance swimming as “more like a brisk walk, maybe , or a very slow run ”.
NASA could now design better exercise programs for astronauts. “There is a big question as to the appropriate intensity and duration of exercise,” said Dr. James MacNamara, cardiology researcher at the University of Texas Southwestern Medical Center and another author of the article. . “Sir. The Lecomte swim gave us the opportunity to watch someone doing a lot” of low intensity exercise.
On the space station, Mr. Kelly exercised six days a week, jogging on a treadmill for about 30 to 40 minutes or exercising on a stationary bike. Plus, he used a resistance machine that mimicked lifting weights.
“It’s pretty tiring,” Kelly, now retired from NASA, said in an interview. “You’re pushing hard enough, more weight than I would be lifting at home here certainly.”
And yet, during his 340 days in space, Mr. Kelly’s heart mass dropped from 6.7 ounces to 4.9 ounces, a drop of about 27%.
Mr. Kelly and Mr. Lecomte’s hearts thinned at a rate of about 1 / 40th of an ounce per week.
Mr Kelly joked that he found the study interesting because it revealed that “my heart acts like an elite athlete”.
Dr Levine said another study examined the hearts of 13 astronauts before and after a six-month stay at the space station. This unpublished study provides a wider range of data that seems reassuring.
“What’s really interesting,” Dr Levine said, “is that it kind of depended on what they were doing before they flew.”
For the more athletic astronauts, their hearts have lost mass in space, as has Mr. Kelly’s. But for those who were couch potatoes on Earth but then had to exercise regularly on the space station, their hearts, like the Grinch’s in Dr. Seuss’ story, grew bigger.
It was not because they experienced a new kindness and generosity, but simply an increased effort.
“The heart is like any other muscle, and it responds to the load placed on it,” Dr. Levine said.
NASA has funded the study of the heart health of the next 10 astronauts who will spend a year in space.
Mr Kelly said his body, which had undergone other changes including bone loss, was almost back to normal.
“I have no symptoms of being in space, at least no physical symptoms,” he said. “Today, if you leave me, I will do it again.”
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