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- BOSTON--An estimated 16 million people worldwide suffer wildly fluctuating
blood-glucose levels, often resulting in serious medical complications
or even death because their bodies don't produce the hormone insulin, which
helps cells process sugar.
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- University of Delaware research may someday
help Type I diabetes mellitus patients better control their blood-sugar
levels using an implantable insulin pump, scientists said today during
the Association for the Advancement of Medical Instrumention (AAMI) conference.*
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- Prof. Francis J. Doyle III and doctoral
candidate Robert S. Parker say their mathematical commands for controlling
sugar levels are simple enough to fit on a computer chip, making them compatible
with a surgically implanted insulin pump. The UD algorithms-coupled with
glucose sensors now in development by many different research teams around
the world-could significantly improve implantable pumps currently being
tested, according to Doyle.
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- "Our vision is for people with diabetes
to enjoy a healthy lifestyle, unimpeded by a device hanging at their hip,
and without the need for multiple needle pricks to monitor blood-sugar
levels or to inject insulin," says Doyle, an associate professor in
UD's Department of Chemical Engineering, who is collaborating with Prof.
Nicholas A. Peppas of Purdue University.
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- Sponsored by Roche Diagnostics--maker
of Accu-Chek blood-glucose monitoring systems--and by the National Science
Foundation, the UD project was among a dozen presented during an AAMI session
on efforts to mimic normal pancreas function with an implantable insulin
pump. Researchers at the session, chaired by Jeffrey I. Joseph of the Artificial
Pancreas Center at Thomas Jefferson University, described glucose sensors
and insulin-delivery technologies emerging from academic, industrial and
government laboratories.
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- An external insulin pump has been on
the market since the early 1980s, providing patients with an option to
periodic insulin injections, Parker says. In clinical trials, meanwhile,
some 600 diabetic patients worldwide are using MiniMed Technologies' revolutionary
implantable pump, which has not yet been approved by the U.S. Food and
Drug Administration (FDA).
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- Compared to frequent insulin injections,
Doyle says, pumps seem to provide patients with improved control of their
blood-sugar levels, so that they're less vulnerable to diabetes-related
health problems.
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- Smart pumps on the horizon?
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- But, existing implantable designs simply
deliver a low dose of insulin on a continuous basis, Parker notes. Patients
also can self-administer additional insulin before a meal.
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- "By developing glucose sensors and
predictive algorithms for these devices," Parker says, "we hope
to dramatically improve and automate the control of blood-sugar levels."
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- Highly precise control is important because
sugar concentrations above the normal level of 70 to 120 milligrams of
glucose per deciliter of blood (mg/dl) have been associated with liver
damage, blindness and other medical problems. And, cells begin to starve
when blood-sugar levels fall too low.
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- So, UD researchers are working on "a
smarter brain for the next generation of implantable insulin pumps,"
Doyle says. "In the future, our system could fit on a computer chip,
processing glucose sensor information, and then translating that data into
pump action."
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- Predicting the body's insulin needs
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- Traditionally, mathematical commands
or algorithms for controlling blood-sugar levels have been "like a
thermostat-either on or off," Doyle says. "The classic approach
has been a bang-bang type of algorithm," he added. "When sugar
levels are high, these systems deliver a dose of insulin. When sugar is
low, they turn insulin delivery back down."
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- Unfortunately, this approach isn't "meal-proof,"
Doyle says, and it doesn't reflect dramatic variations among individuals.
In other words, "These algorithms can't predict and plan ahead for
the increased blood-sugar levels that can occur after a diabetic patient
eats," he explains.
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- As a result, he says, patients may experience
many hours of very high or low sugar levels before returning to a normal
state.
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- The UD system more precisely controls
blood sugar by constantly predicting the patient's need for insulin. Based
on a mathematical model of the human glucose-insulin system, the algorithms
analyze data from past events to forecast future insulin requirements.
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- And, because the algorithms are "linear,"
or simplified to approximate the function of the gut, the pancreas and
other portions of body systems, they could be maintained on a tiny computer
chip, Doyle says.
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- His approach, based on "model predictive
control with state estimation" (MPCSE) algorithms, effectively reduced
peak glucose levels by 44 percent, in computer simulations, compared to
algorithms published in scholarly literature.
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- The system also reduced by 80 percent
the "overshoot," or degree to which blood-sugar levels rose above
a targeted range of 81 mg/dl, compared to patients with uncontrolled diabetes,
Parker says. Small delays in receiving data from glucose sensors didn't
seem to impair the performance of the UD system, which demonstrated a settling
time of about 4.5 hours.
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- Doyle predicts that "smart"
implantable insulin pumps won't become available to patients for another
three to five years, even with FDA approval. But, he says, research presented
at the AAMI meeting confirms the viability of this promising new technology.
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- Someday, he says: "Automatically
controlled, implantable insulin delivery systems will no longer be science
fiction."
-
-
- Note: This story has been adapted from
a news release issued by University Of Delaware for journalists and other
members of the public. If you wish to quote from any part of this story,
please credit University Of Delaware as the original source. You may
also wish to include the following link in any citation: <http://www.sciencedaily.com/releases/1999/06/990608071652.htmhttp://www.scien
cedaily.com/releases/1999/06/990608071652.htm
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