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Updated March 30th, 2021 at 19:46 IST

Human heart gets 'smaller and shrinks' in long space travel, finds study

A recent study published in the journal Circulation found that spending long periods of time in space can alter the structure of the heart, causing shrinkage.

Reported by: Bhavya Sukheja
human heart
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A recent study published in the journal Circulation found that spending long periods of time in space can alter the structure of the heart, causing shrinkage and atrophy. The researchers compared the cardiac effect of extreme duration swimming and space light to determine whether low intensity, long-duration exercise counteracts the effects of repeated weightlessness. They compared the effects of astronaut Scott Kelly’s year in space with a marathon swim by athlete Benoît Lecomte.

The research was led by Dr Benjamin Levine, who is a professor of internal medicine at the University of Texas Southwestern Medical Centre in Dallas. The study found that when Kelly spent nearly a year in space, his heart shrank despite the fact that he worked out six days a week over his 340-day stay. The researchers also observed the same changes in Lecomte after he completed his 159-day swim across the Pacific Ocean in 2018. 

The study said that exercise wasn’t enough in either case to counteract the changes to the heart. It suggested that long-term weightlessness alters the structure of the heart and low-intensity exercise is not enough to keep that from happening. The researchers said that the gravity one experiences on Earth is what helps the heart to maintain both size and function as it keeps blood pumping through veins. 

They said that when the element of gravity is replaced with weightlessness, the heart shrinks in response. According to the study, Kelly lived in the absence of gravity aboard the International Space Station from March 2015 to March 2016. He worked out on a stationary bike and treadmill and incorporated resistance activities into his routine six days a week for two hours each day. Lecomte, on the other hand, swam from June 5 to November 1, 2018, covering 1,753 miles and average about six hours a day swimming. 

‘Heart gets smaller, but doesn’t become weaker’ 

The researchers noted that even though Lecomte was on Earth, he was spending hours a day in the water, which offsets the effects of gravity. They even expected that the activities performed by both men would keep their hearts from experiencing any shrinkage or weakening. However, Kelly and Lecomte both experienced a loss of mass and an initial drop in diameter in the left ventricles of the heart during their experiences. 

But senior study author Dr Benjamin Levine said, “The heart gets smaller and shrinks and atrophies, but it doesn't become weaker -- it's just fine. The function is normal, but because the body is used to pumping blood uphill against gravity in the upright position, when you remove that gravitational stimulus, particularly in someone who is pretty active and fit beforehand, the heart adapts to that new load”. 

(Image: Twitter/Unsplash) 

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Published March 30th, 2021 at 19:46 IST

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