IEEE Spectrum June, 2015 - 38

sensors

starts flowing through the vessels in
the arm again; that gives the systolic
reading, a measure of the pressure
during the contraction of the heart.
The cuff continues to deflate until the
doctor can no longer detect the sound
of the blood flowing. This produces
the diastolic reading, the pressure
when the heart muscle is relaxed,
between beats.
A tiny Biostamp can't cut off blood
flow. It can, however, measure the
pulse at two points, just a centimeter
or so apart. With this information, a
smartphone can calculate a physiological indicator called pulse-wave
velocity, which varies as blood pressure changes. So researchers Tony
Banks, SeungMin lee, and Matt Pharr
in Rogers's group are developing two
types of Biostamp pulse detectors.
by the numbers

56 percent
Visits to primary care physicians, as
a percentage of all doctors' visits

38

|

jun 2015

|

north american

|

One uses light; it alternately flashes
a red and an infrared lED and uses
a photodetector to pick up the light
reflected from the skin beneath the
Biostamp. Because deoxygenated
blood absorbs more red light and
oxygenated blood absorbs more of
the infrared, f luctuations in those
levels create a waveform that represents the heartbeat. That's basically
how the newest fitness bands detect
a pulse, though the Biostamp version
can get a more stable signal because
the skin doesn't shift under it. The
other type of pulse detector under
development uses piezoelectric strain
sensors to monitor the stretching and
relaxing of the patch as it reacts to
the blood coursing through the vessels under it. In this scheme, greater
stretch translates to higher pressure.
In either case, these measurements
of pulse converted to pulse-wave
velocity tell the wearer only how blood
pressure is changing-they don't give
the baseline blood pressure reading.
But for patients whose blood pressure
needs to be monitored closely, simply keeping track of variations is vital.

SPectrum.ieee.orG

bioSTaMP brigaDe: These stamps include
a variety of ultrathin unpackaged electronics,
flexible circuits, and sensitive dyes. They
harvest energy and communicate wirelessly
and can support a variety of sensors to allow
the monitoring of different bodily functions.

Instead of seeing a nurse daily for a
blood pressure check or using bulky
home monitoring equipment, the
patient would put on a new Biostamp
every week or two, get it calibrated,
and just scan the stamp with a phone
to take a reading that could be sent
automatically to the doctor.
Another promising Biostamp version will monitor sweat. Daeshik Kang
and Aheyon Koh, postdocs in Rogers's
group who are working with research
staff member Banks, have built a Biostamp with microfluidic channels that
wick sweat along a calibrated path.
Chemically sensitive dye on the path
changes color as the sweat hits it,
while other dyes on the patch change
color in response to glucose, lactic
acid, chloride, and sodium. When
scanned with a smartphone, circuitry
on the patch activates a phone app that
analyzes the color changes and offers

StatiStic Source: 2010 NatioNal ambulatory medical care Survey, cdc

Part 1: Reading the Code
http://SPectrum.ieee.orG
Table of Contents for the Digital Edition of IEEE Spectrum June, 2015
