The gravity we experience on Earth is what helps the heart maintain its size and function as it keeps the blood pump through our veins. Even something as simple as standing up and walking helps to draw blood to our legs.
When the element of gravity is replaced by weightlessness, the heart shrinks in response.
Kelly lived in the absence of gravity aboard the International Space Station from March 27, 2015 to March 1, 2016. He worked on a stationary bicycle and a treadmill and incorporated endurance activities into his routine six days a week for two hours each day.
Lecomte swam from June 5 to November 11, 2018, covering 1,753 miles and averaging about six hours a day swimming. This sustained activity may seem extreme, but every day of swimming was considered a low-intensity activity.
Although Lecomte was on Earth, he spent hours a day in the water, which makes up for the effects of gravity. Long-distance swimmers use the prone technique, a horizontal downward position, for these endurance swims.
The researchers hoped that the activities performed by both men would prevent their heart from experiencing any contractions or weakening. Data collected from tests of his heart before, during and after these extreme events proved otherwise.
Kelly and Lecomte experienced a loss of mass and an initial drop in diameter in the left ventricles of the heart during their experiments.
Both long-term spaceflight and prolonged immersion in water led to a very specific adaptation of the heart, said the author of the senior study, Dr. Benjamin Levine, Professor of Internal Medicine / Cardiology at Southwestern Medical Center at the University of Texas.
Although the authors point out that they only studied two men who were both doing extraordinary things, more study is needed to understand how the human body reacts in extreme situations.
No negative impact
In this case, the researchers saw that the heart was adapting, but the contraction did not cause any negative, present, or long-term effects.
“The heart gets smaller, shrinks and atrophies, but it doesn’t get weaker, it’s okay,” said Levine, who is also director of the Institute of Exercise and Environmental Medicine, a collaboration between UT Southwestern and Texas Health Presbyterian Hospital Dallas. “Function is normal, but because the body is used to pumping blood up against gravity in an upright position, when you remove the gravitational stimulus, especially in someone who is quite active and fit before, the heart adapts to this new load “.
Levine noted the plasticity and adaptability of the heart muscle mass, nearly three-quarters of which is sensitive to physical activity.
“If there’s one thing I’ve learned for over 25 years studying how the heart adapts to space flight, exercise training and high altitude, it’s that it’s a very adaptive organ and it responds to demands that are posed to him “.
The greater the load placed on the heart, the greater it becomes; the same goes the other way around.
Currently, the astronauts are left with the same exercise regiment that Kelly used at the station. In the face of missions to the Moon and Mars, you may need to change your exercise countermeasures to prevent muscle and bone loss.
Levine believes the current countermeasures work, but limits will be set due to the space allowed for exercise equipment in future vehicles.
Rowers have the biggest heart of all athletes, Levine said, so a combination of rowing and strength training may be the best strategy for astronauts to move forward. Rowing is a dynamic exercise because it loads the heart in a way that feels like strength and endurance training simultaneously, Levine said.
The effects of space radiation
Future long-term spaceflight missions will return humans to the moon and send them to Mars, so it’s crucial to understand how spaceflight affects all aspects of the heart.
Astronauts are mostly middle-aged men and women, so the main concern is that they may experience a heart attack. These space explorers are highly selected before selection, but they treat the same things everyone else does, including hypertension and high cholesterol. While NASA and medical experts can work with these known parameters as they quantify the risk and choose the healthiest people, there is one big unknown: radiation exposure.
What happens to the heart arteries after prolonged exposure to weightlessness and radiation? This is a question Levine and his research colleagues want to answer in the future. They will analyze the coronary arteries of the astronauts before and after the flight using a computed tomography angiogram, an X-ray test that can reveal the overall structure and lining of the arteries in the heart.
Atrial fibrillation, or a rapid, irregular heartbeat, is the most common form of arrhythmia, and astronauts receive 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, dilate in space.
Levine is concerned that astronauts may be at risk of developing it during a long space flight. While not life-threatening, atrial fibrillation can cause discomfort, reduce exercise tolerance and increase the risk of stroke in people who are otherwise healthy, he said.
Having access to astronauts ’cardiac MRI before and after their flight in the future could provide researchers with a better and more detailed understanding of what’s going on in the right and left ventricles of the heart, Dr. James MacNamara, author of the first study. echocardiography fellow with UT Southwestern working with Levine.
Levine and colleagues will study ten more astronauts who plan to spend a year in space over the next decade, focusing on the more intense gaze on the cardiac arteries and the muscle itself. The study will also include astronauts who spend six months on the space station, as well as shorter flights.
“So we’ll be ready when we go to Mars,” Levine said.