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The gravity we feel on Earth is what helps the heart maintain its size and function while continuing to circulate blood through our veins. Even something as simple as getting up and going for a walk helps the blood flow to our legs.
When the element of gravity is replaced by weightlessness, the heart shrinks in response.
Kelly lived gravity-free aboard the International Space Station from March 27, 2015 to March 1, 2016. He trained on a stationary bike and treadmill and incorporated resistance activities into his six-day routine. per week for two hours a day.
Lecomte swam from June 5 to November 11, 2018, covering 1,753 miles and averaging about six hours a day of swimming. This sustained activity may seem extreme, but each day of swimming was considered a low intensity activity.
Even though Lecomte was on Earth, he spent hours a day in the water, which compensates for the effects of gravity. Long-distance swimmers use the prone technique, a horizontal, face-down position, for these endurance swims.
The researchers expected that the activities performed by the two men would prevent their hearts from shrinking or weakening. Data collected from testing their hearts before, during and after these extreme events showed the opposite.
Kelly and Lecomte both experienced mass loss and an initial decrease in diameter in the left ventricles of the heart during their experiments.
Long-duration spaceflight and prolonged immersion in water led to a very specific adaptation of the heart, said lead author of the study, Dr Benjamin Levine, professor of internal medicine / cardiology at the University of Texas Southwestern Medical Center.
While the authors stress that they have only studied two men who both accomplished extraordinary things, more studies are needed to understand how the human body reacts in extreme situations.
No negative impact
In this case, the researchers saw that the heart had adapted, but the narrowing caused no ill effects, present or long term.
“The heart gets smaller and shrinks and atrophies, but it doesn’t weaken – that’s fine,” said Levine, who is also director of the Institute for Exercise and Environmental Medicine, a collaboration between the ‘UT Southwestern and Texas Health Presbyterian Hospital Dallas. “The function is normal, but because the body is used to pumping blood against gravity in an upright position, when you remove this gravitational stimulus, especially in someone who is quite active and in good shape beforehand, the heart s adapts to this new load. “
Levine noted the plasticity and adaptability of muscle mass in the heart, nearly three-quarters of which is responsive to physical activity.
“If there’s one thing I’ve learned in 25 years studying how the heart adapts to spaceflight, physical training and high altitude, it’s that it’s a remarkably adaptive organ. and that it meets the requirements imposed on it.
The greater the load placed on the heart, the more it grows; the same thing happens in reverse.
Currently, the astronauts are sticking to the same exercise regiment Kelly used on the station. In the run-up to missions to the Moon and Mars, the countermeasures to exercises aimed at preventing muscle and bone loss may need to change.
Levine believes current countermeasures work, but limits will be imposed due to the space allowed for exercise equipment on future vehicles.
Rowers have the biggest hearts of any athlete, Levine said, so a combination of rowing and weight training may be the best strategy for astronauts in the future. Rowing is dynamic exercise because it loads the heart in a way that resembles strength and endurance training simultaneously, Levine said.
The effects of space radiation
Future long-term spaceflight missions will bring humans back to the Moon and send them to Mars, so understanding how spaceflight affects all aspects of the heart is crucial.
Astronauts are largely middle-aged men and women, so the main concern is that they may have a heart attack. These Space Explorers are heavily screened before screening, but they face the same things everyone else does, including high blood pressure and high cholesterol. While NASA and medical experts can work with these known parameters when quantifying risk and choosing the healthiest people, there is one big unknown: radiation exposure.
What happens to the heart arteries after prolonged exposure to weightlessness and radiation? That’s a question Levine and his fellow researchers want to answer in the future. They will examine astronauts’ coronary arteries before and after flight using a CT angiogram, an x-ray test that can reveal the overall structure and lining of the heart arteries.
Atrial fibrillation, or a fast and irregular heartbeat, is the most common form of arrhythmia – and astronauts get it about a decade earlier than the rest of the population, Levine said. This may be because the atria, the two upper chambers of the heart, expand into space.
Levine is concerned that astronauts run the risk of developing this during long-duration space flights. While not life threatening, atrial fibrillation can cause discomfort, reduce exercise tolerance and increase the risk of stroke in healthy people, he said. .
Having access to cardiac MRIs of astronauts before and after their flight in the future could provide researchers with a better and more detailed understanding of what is happening in the heart’s right and left ventricles, the study’s first author said, Dr. James MacNamara, an echocardiography fellow with UT Southwestern who works with Levine.
Levine and his colleagues will study 10 more astronauts who plan to spend a year in space over the next decade, focusing on the most intensive examination of the heart arteries and the muscles themselves. The study will also include astronauts spending six months on the space station, as well as shorter flights.
“So we’ll be ready when we get to Mars,” Levine said.
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