The human heart was not meant to pump in space.
Early astronauts in the Apollo program performed every conceivable physical test to ensure that they were each at the pinnacle of human fitness. And yet, when they returned to Earth after just a few days in space, they felt dizzy when standing and tests showed that each beat of their heart pumped less blood than it had before the mission.
A lack of gravity, NASA scientists found, caused the astronaut's heart to weaken and become deconditioned compared to the effort it must exert in Earth's gravity. In particular, the muscular pump loses the high-end performance reserve that lets it kick into high gear during a crisis event, when the astronaut's muscles are screaming for more oxygen-rich blood.
In an effort to improve astronaut safety, Gregory Kovacs, a professor of electrical engineering at Stanford; Laurent Giovangrandi, a senior research engineer; and their lab of graduate and undergraduate students have worked to develop a device that could provide high-fidelity measurements of astronauts' cardiovascular performance.
Stanford student researchers have flown in near-zero-gravity to develop a device to monitor an astronaut's heart function. (Video: Kurt Hickman/Gregory Kovacs)
"If you're going to put people on long-term missions in an environment that's going to alter their physiology, it's nice to know that you can measure those changes," said Kovacs, who also has a courtesy appointment in the Stanford School of Medicine.
For the past two years, his group has been testing their diagnostic tool in rarefied air, aboard an airplane that astronauts have affectionately dubbed the "vomit comet."
With every beat, your heart gushes a third of a cup of blood upward and into the aorta, blood's highway to the rest of your body. That pumping action transfers a small amount of energy to your body, causing it to jiggle ever so slightly. (You can actually feel the force if you lie very still in bed or when you're scuba diving.)
As blood pumps, it creates a small, but measurable, force that creates a small perturbation, or "wiggle," in your weight.
This slight wiggle can be monitored and analyzed to produce a score of how efficiently a person's heart is pumping, known as a ballistocardiograph. This 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.
A few years ago, Kovacs suggested to two of his doctoral students, Omer Inan (electrical engineering) and Richard Wiard (bioengineering) that they design a device that could isolate this signal, even in microgravity, and that could also fit in the confined quarters of a spacecraft. The pulse of blood exerts 1 to 3 Newtons of force throughout the body, roughly equivalent to a little less than half a pound — just enough for a digital bathroom scale to register.
Inan and Wiard hacked a commercial bathroom scale and added some low-cost electronics to increase its sensitivity and home in on the ballistocardiograph signal. It worked well: After more than a dozen publications on the technology and its performance in human tests, the researchers found that the ballistocardiograph measured by their modified scale could measure cardiovascular activity in equal or better resolution than other clinical mechanical monitoring devices.
In a single 10-second measurement, the scale can glean enough data from a patient to assess his or her cardiovascular risks. Wiard said that the scale does this with greater accuracy than the standard assessment used today, and also provides a clearer picture of a patient's (or space-faring astronaut's) near-term risk.
"For most people who aren't in the near term at risk of developing cardiovascular disease, the standard cardiovascular assessment is a littler better than a coin flip in terms of predictability," Wiard said. "What we've done is develop a powerful and simple tool that provides indications of both the short- and long-term cardiovascular risks a person may develop. It's a powerful prognostic for the near term without any intrusive instruments."
With a high-fidelity test in hand, the researchers set off for an airstrip in Houston to see if the scale performed as well on reduced-gravity flights.
The researchers 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, that is used to produce short periods of weightlessness.
The so-called vomit comet climbs to an altitude of about 34,000 feet and then nosedives for 10,000 feet. This gives its passengers up to 30 seconds of freefall and allows them to float around as they would in the International Space Station before the plane levels and begins climbing to repeat the maneuver.
The researchers bolted the scale to the plane's floor and, over the course of several days, healthy volunteers and professors, as well as undergraduate and graduate students, took turns as test subjects. There were a few technical glitches, but after some fine-tuning, the scale started providing clean signals 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.
The researchers think that the scale could help mission operators to monitor astronauts' fitness while in space, and to design and test effective exercises that strengthen the heart to restore its natural reserve so that, if necessary, it can pump as it would in Earth's gravity.
For the second round of experiments, after demonstrating proof of concept, Kovacs charged Zach Stuart, a mechanical engineering student, to come up with a better way to keep test subjects in contact with the scale.
Stuart learned about the zero-gravity campaign two winters ago when he was taking Kovacs' freshman seminar, Electronics Rocks, an introductory electrical engineering course designed to open students to the world of hacking devices or building them from scratch. That summer, Stuart worked in Kovacs' lab experimenting with using infrared thermography for seizure detection in epileptic patients along with Corey McCall, a graduate student in Kovacs' lab group.
The following fall, the opportunity arose for Stuart to accompany Kovacs' group on the zero-gravity flights as a test subject in the first campaign. Stuart took about a nanosecond to sign up.
The successful data collection of the first campaign convinced NASA to sponsor a second round of experiments this past fall. As well as the scale performed on the first flights, though, it experienced a few hiccups. For one, some test subjects began to float away — it was very difficult to keep their feet secured to the device; breaking contact with the scale renders it essentially useless.
Kovacs offered Stuart another seat on the vomit comet the following year, this time as part of the research team. All Stuart had to do was design a better, and safe, way to keep people attached to the scale.
Stuart experimented with a variety of solutions, but ultimately settled on modifying snowboard bindings and attaching them to the scale. The bindings provided a snug fit and kept the user's feet in constant contact with the scale while providing a quick release strategy in case of an emergency.
"It worked well, and we got better, more consistent data," Stuart said. "It was incredible to be a part of the scientific team this time, and to contribute to the research."
The scientists presented results from the first test flight last summer at the Annual IEEE Engineering in Medicine and Biology Conference in Japan, and expect to publish the results of their second flight this year. Those results could convince NASA to fund a third flight to refine the technology.
The experience has been meaningful for all involved. Inan is currently an assistant professor of electrical and computer engineering at Georgia Tech, and Wiard has maintained visiting scholar status while working at a medical device startup and mentoring students interested in biomedical engineering. McCall is now a doctoral candidate in Kovacs' lab.
"We as professors can't give ourselves too much credit for the success of our students," Kovacs said. "You can just choose well and give them the best environment to succeed, and they take it from there and they do amazing things."
Stuart, now a junior, has thoroughly enjoyed his taste of being on the frontlines of graduate-level research, which he said will be invaluable when he applies for graduate programs or jobs.
"It's awesome that I was able to ask and receive the opportunity to do this research as an undergrad, and I think that goes for Stanford across the board in terms of being so open to undergraduate research," Stuart said. "I'm two-and-a-half years in, and I've worked on two separate graduate-level research projects in Kovacs' lab, including one that was run twice with NASA. It's pretty unreal, and I'm extremely grateful that I've been able to do that through Stanford."
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