Implanted sensor continuously transmits blood glucose levels for
2 August 2010
A glucose sensor implanted under the skin that transmits
glucose measurements continuously to an external device has been
successfully tested for over 500 days, but only in a pig so far.
The external device shows current blood glucose level, a historical
chart and adjustable warnings of high and low blood glucose
The ultimate goal is to limit the dangerous ups and downs of blood
glucose levels in diabetics, known as 'glucose excursions'. It is these prolonged
glucose excursions that cause the long-term problems associated with
diabetes. The implant used in the pig study is about 1.5" diameter and 5/8"
thick, and could be implanted in a simple outpatient procedure.
The device was developed by engineers at the University of
California, San Diego and GlySens Incorporated and the study of the
device implanted in a pig was published in the July 28, 2010 issue
of the journal Science Translational Medicine .
How the sensor works
Glucose and oxygen from the surrounding tissue diffuse to the
sensor, where the enzyme glucose oxidase carries out a chemical
reaction in which oxygen is consumed in proportion to how much
glucose is present.
The remaining oxygen is measured and compared to the baseline
oxygen recorded by a nearly identical oxygen reference sensor. The
reduced oxygen signal compared to background oxygen signal reflects
the glucose concentration.
The effects of exercise and changes in local blood flow to the
tissues are also largely subtracted out by the differential oxygen
sensing system, which includes the pair of sensors side by side in
the same device. The implanted sensor sends the glucose information
to a data recorder the size of a cell phone.
After human clinical trials and FDA approval, the device may be
useful to people with diabetes as an alternative to finger sticking,
and to short-term needle-like glucose sensors that have to be
replaced every three to seven days.
David Gough, Professor of Bioengineering and the UC San Diego
Jacobs School of Engineering, said, "The Science Translational
Medicine paper shows our implanted sensors to be successful in
animals. You can run the device for a year or more with it
constantly working, and recording glucose quite satisfactorily. Now,
we are focused on getting the human clinical trials going. We hope
to begin the first human trial within in a few months. If all goes
well with the human clinical trials we anticipate that in several
years this device could be purchased under prescription from a
"There are parents with diabetic children who spend their nights
worrying that their child in a nearby bedroom may go into nocturnal
hypoglycemia," said Gough, who explained that the glucose sensors
could be used to send information to a phone that would alert
parents if the child's glucose levels drop to a dangerous level
during the night.
"Four finger sticks per day to measure glucose levels is the
current standard of care, but blood glucose can go on significant
excursions between sticks," said Gough. In contrast, the long-term
implanted glucose monitor would provide continuous monitoring day
and night. "We are moving toward something that will be automatic
and quite unobtrusive. Others wouldn't even know if someone is using
a glucose sensor. Our goal is to get people off the finger stick
cycle," said Gough.
Suitable for Type 1 or Type 2 Diabetes
The long-term glucose sensor could be used by people with either
Type 1 or Type 2 diabetes. People with Type 1 diabetes do not make
enough insulin of their own. The long-term glucose sensors could be
used to adjust the insulin dose and timing of the injection, and
reduce the risk of taking too much insulin and becoming
hypoglycaemic, which can be immediately life threatening.
Hypoglycaemia happens when you get too much insulin for the
available glucose, or when insulin absorbs too rapidly.
People with Type 2 diabetes could use the long-term glucose
sensors to help them adjust their diet and exercise schedule. Also,
some people with Type 2 diabetes take insulin and have the same
hypoglycaemia worries as people with Type 1 diabetes.
Today, there are approximately 800,000 people
using external insulin pumps in the US alone. Currently, these insulin pumps are
open loop — meaning they are not connected to a glucose sensor
directly, and they have to be programmed by a physician. "You can
manually adjust the pump schedule to some extent, but patients must
keep rigid schedules to live with an insulin pump," said Gough.
The bioengineers’ goal is to enable the pumps to automatically
adjust the rate of insulin being administered based on glucose
readings from the implanted sensors, that is, to function like an
artificial pancreatic beta cell. "If insulin pumps were programmed
based on near-real-time readings from implanted glucose sensors, the
pumps would adjust insulin dosing based on what your glucose number
is after a meal. You wouldn't have to be so rigorous about your
schedule," said Gough.
"With an insulin pump, there is always the concern that it will
pump too much insulin, leading to dangerously low blood glucose
levels. The sensor could serve as a safety mechanism against low
blood glucose levels," said Gough, who noted that major research
efforts to use readings from glucose sensors to program insulin
pumps are well underway. Researchers are primarily using needle-type
glucose sensors, but these needle sensors could be replaced with the
new implanted sensors if and when they are approved for human use.
1. David A. Gough, Lucas S. Kumosa, Timothy L. Routh, Joe T Lin and
Joseph Y. Lucisano. Function of an Implanted Tissue Glucose Sensor for More than 1 Year
in Animals. Sci Transl Med 28 July 2010:
Vol. 2, Issue
42, p. 42ra53. DOI: 10.1126/scitranslmed.3001148