IEEE Spectrum June, 2015 - 42

Part 1: Reading the Code

monitoring

parking. Finally, at the end of the rainbow, the Google self-driving car. The
first step toward a robotic pancreas
came in 1964, when a hospital-based
experiment proved, in principle, that
it was possible to achieve near-normal
blood-sugar control. In the 1970s, Dean
Kamen invented the insulin pump,
making it possible for patients to
administer insulin to themselves in a
continuous fashion, rather than
through frequent injections. Soon after,
a hospital system called Bio stator
GCIIS was released in Germany; it com-

bined a pump with a large, complex
continuous glucose monitor.
In recent years, pumps have become
smaller, more reliable, more programmable, and more comfortable, using
ever-finer pipettes, which the patient
inserts through a slightly larger needle.
Continuous glucose monitors were
first approved a decade ago, and they
are beginning to replace the fingerprick method, now that improved
coatings and other engineering details
have allowed patients to keep their
superthin electrochemical sensors

How it workS

Blood
vessel
Glucose

The pump administers
the insulin via a pipette
under the skin.

Transmitter
Insulin
pump

The sensor continuously
samples the glucose
concentration under the skin
and sends the data stream to
be analyzed.

Copying
the Pancreas

The computer algorithm
applies to the data the rules
it has derived from past behavior
to determine the insulin dosage.

S o o n a f t e r a r i S e i n g l u c o S e in the bloodstream, a parallel
rise in the intercellular fluid of the skin occurs. Sensors inserted into the
skin detect that rise and beam the data to a computer, which directs
a pump to send pulses of insulin under the skin. From there the insulin
moves on to the bloodstream and throughout the body, lowering the
glucose to safe levels.

jun 2015

north american

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under the skin for seven days. "I've
had this one in for eight," says Herrick.
The first machine worthy of the
name of ar tif icial pancreas was
Medtronic's Minimed 530G, which
went on sale in the United States in
2014. It stops the flow of insulin when
the patient's blood glucose falls below a
set point. Then, in January, Medtronic
began selling the 640T; like the system
Herrick tested, this system stops the
insulin when its algorithm merely predicts that the patient's blood sugar will
drop. It's on the market in Australia
and is set to sell in Europe later this
year. In the United States, the clinical
trials are just getting under way.
Medtronic's first clinical tests
of what became the 640T began
about a decade ago, says Francine R.
Kaufmann, the company's chief medical officer and a practicing endocrinologist. Why the long delay between
the proof of concept and routine use?
"There's a big difference when you take
someone who goes out and lives daily
life, exercises, gets drunk, and other
stuff," Kaufmann says.
Much can go wrong. Pumps clog,
algorithms misfire, sensors get walled
off by scar tissue. Some of the recent
technical advances are proprietary
and still under wraps, but it's known
that Medtronic and Dexcom have
developed biocompatible coatings as
well as sensors with multiple electrochemical sites that can be polled to see
which ones no longer work properly.
One of the biggest challenges is lag.
In a feedback-control system with too
much lag, your efforts to lower the
upswings and raise the downswings
can make those variations worse. Glucose sensors typically show you where
your blood sugar was 10 minutes ago,
but because they also track changes
over time, they can give you a pretty
good idea of where you stand now. The
real problem is the insulin. Today's
illustRation by

James Provost

http://SPectrum.ieee.orG

Table of Contents for the Digital Edition of IEEE Spectrum June, 2015