Computer generated diagram of the Integrated Cardiovascular investigation onboard the ISS. Image Credit: NASA/JSC When humans venture into space for long periods, their muscles tend to weaken. The heart of the matter is that muscles don't have to work as hard without gravity.

Of course, the most important muscle in the body is the heart.

While doctors are well aware of this weakening of the heart in space -- known as cardiac atrophy -- a new study aboard the International Space Station seeks to find out exactly how much the heart muscle decreases in size over a standard six-month station tour and how quickly it occurs.

In addition to evaluating cardiac health in space, the Integrated Cardiovascular investigation also will determine how effective the astronauts' current exercise program is at protecting the heart from getting smaller or weaker.

"This study also will help us determine if there is a risk of abnormal heart rhythms and how significant the risk is in order to develop appropriate countermeasures," said Dr. Deborah Harm, international project scientist for the International Space Station Medical Program at NASA's Johnson Space Center in Houston.

According to Harm, many crew members experience a brief period of lightheadedness and a drop in blood pressure when standing still after coming home to Earth from long-duration missions. Fainting can occur when the heart cannot generate enough force to pump the necessary blood to the brain and the rest of body -- either because the muscle is too small or weak, or because there is an abnormal heart rhythm.

"At this time it is unknown if heart muscle weakening continues throughout a mission or if it levels off at some point. That's what we want to find out," Harm said.

Crew members on Expedition 20, which began in May and will continue through October, are the first to participate. Before, during and after flight, they are measuring their heart rates, heart rhythms and blood pressure for 24- to 48-hours before and after exercise sessions. They're also performing on-orbit cardiac ultrasound scans on each other before and after exercise to look at how effectively the heart fills with blood and pumps it to the rest of the body.

"MRI scans will be done on crewmembers' hearts before and after flight to measure exactly how much heart muscle is present and will be compared to the cardiac ultrasound information to better understand how changes in heart muscle are related to cardiac function," said Dr. Michael Bungo of the investigator team.

"Such an extensive and sophisticated study of the cardiovascular system was virtually impossible before we had six crewmembers onboard the station," Harm added. "There simply was not enough crew time available to complete all the procedures required for this experiment."

Catherine (Cady) Coleman is performing a remotely guided echocardiogram on a test subject utilizing the Integrated Cardiovascular protocols, while Betty Chen, a training coordinator observes. Image Credit: NASA/JSC While in space, crewmembers will wear four devices: a portable Holter monitor that measures heart rate continuously for extended periods; a Cardiopres that measures blood pressure with every heart beat; and two Actiwatches -- one on an ankle and one on a wrist -- to monitor and record body movements.

The data collected is being beamed down to the Payload Operations Center at NASA's Marshall Space Flight Center in Huntsville, Ala., and delivered to the investigator’s team for analysis.

This study shows the breadth of international cooperation and collaboration that occurs on the space station. Three international partner agencies are working together to get the best science for everyone. The European Space Agency (ESA) is providing the Cardiopres device for monitoring blood pressure, and the investigators will be sharing the Holter data with teams for two Canadian-sponsored experiments. One of these experiments also includes ESA investigators.

All of these investigator teams are studying different aspects of the cardiovascular system. Sharing this data among scientists greatly enhances the overall science return. That, in turn, allows us to more efficiently and quickly understand the full range of cardiovascular changes than any one investigation could, Harm said.

"As we move toward exploration missions where astronauts could be in space for longer periods of time, it is very important that we know to what degree they could experience cardiovascular risks, and prepare countermeasures to protect them," said Dr. Julie Robinson, International Space Station program scientist at the Johnson Space Center. "We are eager to see the results from this study."

Knowledge gained in the Integrated Cardiovascular study may help doctors treat patients on Earth who have been confined or on bed rest for long periods. Patients with heart diseases that change their normal cardiac function may also benefit.

For more information, visit:

http://www.nasa.gov/mission_pages/station/science

or

http://www.nasa.gov/mission_pages/station/science/experiments/Integrated_Cardiovascular.html by Lori Meggs, AI Signal Research, Inc.
NASA's Marshall Space Flight Center