IEEE Spectrum November, 2014 - 21

HEArt-FAilurE HElpEr:
A microwave transceiver [center]
can do what other sensors can't:
measure the accumulation of water
in a patient's lungs.

even weighing the patient over
time to quantify the decrease.
The most hands-off method
requires measuring the impeda nce of elec t r ic it y pa ssi ng
through the patient's body with
a bulky vest, but this method can
fail if the patient shifts position.
Now a team of researchers
at the University of Hawaii, at
Manoa, have a new way to measure lung water, along with many
other vital signs. As their coin-size
sensor rests on a patient's chest, it
emits microwaves and measures
how they reflect. The list of what
the researchers can decode from
these patterns of reflected microwaves is only growing.
"Because of the ability for microwaves
to penetrate the body, we can extract a
wide variety of things, depending on what
you are trying to monitor," says Magdy
Iskander, director of the Hawaii Center
for Advanced Communications at the University of Hawaii's College of Engineering. But the ability to measure fluid in a
patient's lungs might be what really sets
the microwave stethoscope apart. The
level of water in the lungs can be an indicator of a patient's reaction to medication,
the effectiveness of treatment for critically
burned patients, and, most important, the
extent of heart failure, he says.
To get a clear signal, Iskander's team
had to develop a compact microwave
transmitter that beams tightly focused
waves, something that ordinary antennas won't do. "You can't use microwave
antennas-the signal is all over the place,"
says Iskander. "What you receive next to
it is coming from the transmitter and not
from inside the body." Instead, the device
focuses the beams using waveguides.
Upon capturing the reflected waves, the
engineers apply advanced signal process-

ing algorithms to pull out as much information as possible. The signals can then
be sent to a smartphone or another display.
The group first tested the sensor solely
for measuring lung water, but they soon
realized that the data also revealed
other vital signs-heart rate, breathing,
and volume of blood pumped per beat.
They've rigorously measured the lung
water content of model systems and of
animals and are just beginning human
tests. In the meantime, the team has
ensured that the stethoscope can accurately measure vital signs by using it side
by side with a commercial set of medical sensors.
Ruthsenne Perron, a Ph.D. student
who's worked on developing the stethoscope's different incarnations with
Iskander, says that there are several
devices for reading vital signs noninvasively. But their microwave stethoscope
has a key difference-mobility. "We used
some of the devices that they use in the
hospital to benchmark our results," she
says. "But when the person is moving
around, they just start beeping because
they can't handle the movement. That's
one of the advantages to what we have-
it doesn't hinder mobility for the patient."
"It's a huge challenge manag ing
patients whose cardiac status varies
a lot," says John Spertus, a cardiologist at Saint Luke's Mid America Heart
Institute, in Kansas City, Mo. Spertus
learned about the device in April and
has helped Iskander's group improve
protocols for tests on humans. "The

stiCk-oN sENsor: The microwave stethoscope
consists of a transmitter, a focusing antenna, and
a receiver.

holy grail is to be able to detect early
that somebody's accumulating fluid,"
Spertus says. Although there are other
ways to approximate changes in lung
water levels, he says, "none of them
are either accurate enough or accessible enough in routine clinical care to
reach the vast majority of heart failure
patients. This is a really creative and
novel solution for addressing that." Still,
Spertus acknowledges that the device
needs more testing before it's ready for
hospital or home use.
According to Kenneth Foster, a professor of bioengineering at the University of
Pennsylvania, in Philadelphia, it's also
challenging to ensure that new sensors
will work with any kind of patient: "The
device would need to give reliable and
medically useful information for every
patient who walks through the door-
300-pound Sumo wrestlers to 95-pound
cancer patients. It is premature at this
point to speculate how the device will
work in the real world of medicine."
Brian Rosenfeld, the chief medical
officer for telehealth at Philips, says
that a microwave stethoscope may be
more practical for one-off uses than for
full-time monitoring, which could add
unnecessary expense to an intensive
care unit. For continuous monitoring,
as in a remote ICU, Rosenfeld thinks that
physicians should instead use improved
algorithms to collect and analyze the
measurements already available, which
would allow them to predict patient outcomes without extra equipment.
Besides beginning a human lung
water-measurement trial at the Queen's
Medical Center, in Honolulu, Iskander's
group is considering other uses for the
stethoscope-like sewing it into a shirt
or a bra to monitor the medical condition of a soldier over time. The sensor
could even watch for signs of dehydration, which earlier research has connected to lung water content.
"We're just beginning to find out more
about what our device can do," says
Perron. -sa r a h lewin

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Table of Contents for the Digital Edition of IEEE Spectrum November, 2014