Study Finds Astronaut's Heart Shrank After A Year In Space Despite Exercise
NASA is gearing up to send astronauts to Mars in the coming decades, and part of the gear-up is studying the effects of long-term space travel on humans. A new study was published by scientists at UT Southwestern that found the heart of an astronaut who spent nearly a year in space aboard the ISS shrank despite regular exercise. The study found that while the astronaut's heart shrank, it continued to function well.The study was conducted on astronaut Scott Kelly, who is now retired, and found that his heart lost an average of about 0.74 grams per week in mass from its left ventricle during the 340 days he spent in space between March 27, 2015, and March 1, 2016. The heart shrinkage was observed despite Kelly's weekly exercise regime of at least six days of cycling, treadmill, or resistance work.
According to the study, despite the heart's shrinkage, which was accompanied by an initial drop in the left ventricle diameter when relaxed to fill with blood (known as diastolic diameter), the astronaut's heart adapted relatively well to space. The senior author of the study is Doctor Benjamin Levine, MD, a professor of internal medicine at UT Southwestern. Levine says that Kelly's heart did shrink a little bit and atrophy, but function remained good.
The researcher says he believes this is encouraging for long-duration spaceflight. The study results show that even after a year in space, the heart adapted "relatively well." Levine notes that similar reductions in heart size are seen in patients undergoing strict bed rest and will stabilize over time. The most recent study conducted by Levine looked at the heart structure and function in 13 astronauts who spent six months on the ISS.
The study found cardiac adaptation to space varied from astronaut to astronaut, with the fittest astronauts losing heart muscle mass during their stay in space. Interestingly, some of the least fit astronauts gained muscle mass. Levine says it depended on how much work the astronaut's heart did in space compared to how much it regularly did on the ground.