July 9, 2012 (National Harbor, Maryland) — Astronauts traveling into space undergo changes in the shape, size, and function of their hearts, new preliminary research suggests [1]. The heart becomes more spherical as a result of weightlessness in space, and there are changes detected on the echocardiogram suggestive of a reduction in myocardial contractility.

"The hypothesis of our study is that over time there are potentially deleterious things that can occur, mainly due to the reduced loading conditions on the heart," investigator Dr James Thomas (Cleveland Clinic, OH) told heartwire . "The heart is doing less work since is it not fighting against gravity. So with the heart doing less work, there is a concern that it might atrophy, might lose myocardial mass over time. The real manifestation of all of this is what we're trying to work our way around--orthostatic intolerance when the astronauts come back to ground."

The results of the study were presented last week at the "Hearts in Space" symposium here at the American Society of Echocardiography (ASE) 2012 Scientific Sessions. Thomas noted that when astronauts return to earth, they might be unable to stand up or walk off the shuttle. While there are many possible reasons for this, including dehydration or other neurohormonal changes that might occur with space travel, the researchers wanted to determine whether cardiac atrophy or reduced cardiac function plays a role in orthostatic intolerance.

As part of their experiment, six astronauts underwent preflight testing, including an ambulatory electrocardiogram, blood-pressure measurements, rest and exercise echocardiograms, and tilt-testing echocardiograms to mimic gravitational forces of the moon and Mars. In-flight, the ambulatory electrocardiograms and blood-pressure monitoring were repeated, as well as resting echocardiograms after two to four weeks (and then repeated every 30 to 60 days). The measurements were again conducted upon their return to earth.

The shape of the heart changes in space compared with full gravity, with the heart becoming more spherical, report the investigators. In fact, the group observed an approximate 10% change in the length-to-width ratio. In a second analysis examining heart function using echocardiography, the group performed speckle tracking to assess myocardial strain. The echocardiographic technique showed there was a reduction of the in-flight myocardial longitudinal strain values compared with preflight testing. The change was reversible, however, returning to normal in postflight testing.

To heartwire , Thomas said the changes in myocardial strain suggest a reduction in myocardial contractility, or possibly a side effect of the change in the heart's loading conditions that result from weightlessness. In addition, it's possible the reduction in myocardial strain might result from the change in the heart's geometry during space travel. "It might be that this induces some changes that might have an impact on how efficiently the heart can pump the blood out," said Thomas.

The researchers believe that the earliest expected change in the shape and function of heart is about two weeks in space. Their next steps will include testing more astronauts, up to as many as 13 subjects, as well as testing whether or not the changes can be counteracted with rigorous daily exercise that would help maintain the loading conditions on the heart. From a technological point of view, Thomas said the research is exciting as he is able to log onto the NASA science station and observe the echocardiograms being conducted in real time. In this way, he is able to guide the astronauts in their acquisition of images, directing them for better angles and pictures of the weightless heart in space. Last week, during the ASE meeting, retired astronaut Leroy Chiao also presented his experiences as an "ultrasound-savvy" astronaut for NASA.


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