Astronauts in the Apollo program after just a few days in space, felt dizzy when standing. Tests revealed that each beat of their heart pumped less blood than it had before the mission. To better understand and improve astronaut safety, Stanford University student researchers are developing a device to monitor an astronaut's heart function, and have flown in near-zero-gravity to show that it works.

Stanford researchers worked aboard a plane that enabled them to test their device while weightless. (Credit: James Blair, NASA)

When humans go into space, reduced gravity can weaken the heart's ability to pump hard in response to a crisis. With every beat, your heart pumps a third of a cup of blood up into the aorta, and creates a small, but measurable, force that creates a small perturbation, or "wiggle," in your weight. This wiggle can be monitored and analyzed to produce a score of how efficiently a person's heart is pumping, known as a ballistocardiograph.

The signal can also relay information regarding cardiovascular reserve, an indicator of the person's capacity to respond to strenuous demands, such as guiding a spacecraft toward reentry into Earth's atmosphere.

Doctoral students designed a device that could isolate this signal, even in microgravity, using a commercial bathroom scale with some low-cost electronics to increase sensitivity to record the ballistocardiograph signal.

They worked with NASA's Flight Opportunities Program and Reduced Gravity Office to conduct two series of weeklong experimental sessions on a modified Boeing 727, operated by Zero Gravity Corporation, used to produce short periods of weightlessness.

After bolting the scale to the plane's floor, the students took turns as test subjects, and were able to demonstrate a proof of concept that the device could provide a detailed assessment of a subject's heart activity in space-like conditions. They also demonstrated technology that successfully isolated the signal from vibrations of the plane, a critical step for any device to be deployed on a spacecraft or the International Space Station, which vibrates from constantly running fans and motors.

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