THE EVOLUTION OF INSULIN PUMPS

by Donna Blake

Photo:� portrait.� Caption: �Donna Blake

Believe it or not, insulin pumps have been in existence for over 20 years.� In the seventies, the first insulin pump was approximately the size of a microwave oven.� That first pump performed exactly the same functions that the beta cells did in a non-diabetic pancreas.� The Biostater measured blood glucose levels and dispensed insulin into the blood stream every five minutes.� Because of it�s size it was used to treat diabetic ketoacidosis (DKA), and in diabetes related research studies.� As the concept of daily blood glucose monitoring developed and came into being, researchers at Yale University had an idea:� why not allow a person with diabetes to monitor their blood glucose levels and regulate the pump based on their own judgement.� Thus, the concept of a portable insulin pump began.

The first portable insulin pump was in fact a chemotherapy pump, and the idea taken from the way cancer patients were given their medicines.� Patients undergoing treatment for cancer wore small portable pumps on their belts, which either delivered their chemotherapy medicines or morphine to help control the pain.� The first pump weighed over a pound (not by much) and used a large syringe placed on the outside of the pump.

The early pump was about the size of an aerosol can, only a bit wider and rectangular.� Besides the dials being located on the outside (two round half-inch projections) there were also blinking red LED lights.� The pump delivered diluted regular insulin at a constant rate and the user pumped in extra insulin based upon meal times and blood glucose levels.�

In order to become a pump user, people were required to undergo psychological testing, and required at least a one-week stay in a hospital.� Dedication to blood glucose monitoring was an essential condition to using an insulin pump.

The first "real" insulin pumps were also fashioned by the manufacturers of the chemotherapy pumps.� The pumps were somewhat smaller and lighter than the chemotherapy pumps, with the syringe mechanisms hidden in a covered compartment.� These pumps were much thinner and sturdier, which gave them distinct advantages over the converted chemotherapy pumps.� First, the pump was more cosmetic for the user.� Second, it allowed for the user to be more active, with a bit less caution, to avoid damaging the pump during activities.

However, the pump had a major design flaw.� The pump user still had to dilute U-100 insulin into concentrations like U-18 or U-36 with saline (sterile salty water) and eventually the same fluid that insulin is dissolved in.� The reason why this had to be done was the fact that the pump design was based upon how chemotherapy drugs were delivered and not how hormones such as insulin were produced and used in the body.� The pumps were designed to deliver a specific amount of fluid at specific intervals, with no variations.� These manufacturers did not consider that insulin must be delivered at different rates throughout the day.� Insulin doses had to be calculated out to achieve the proper amount for each patient.

In the early days, insulin pumps had only one rate of flow over a 24-hour period and this was called the basal rate.� The basal rate is similar to a long acting insulin in that it is the amount of insulin delivered to keep the blood glucose normal if there are no changes in diet or activity.� Boluses (the doses given at meal times and if the blood glucose was elevated) could be any amount the user needed to manually tell the pump to put in.

The popularity of insulin pumps increased based on several �advantages.�� The first advantage of pump use was tighter blood glucose control, one of the most important reasons.� Another advantage of pump use was being able to sleep in the morning and not having to follow such a rigid schedule based upon the peaks of insulin taken with daily injections.� A third popular reason for using a pump was the ability to not be caught without your insulin and the ability to vary the insulin dose based upon activity, meals and other factors.� For most pump users, the stigma of wearing a pump was not a concern, since the main goal of pump therapy was tighter diabetic control.� Activities were not a problem with the pump and in fact, the pump led to a decrease in insulin reactions since the pump could be removed for activities.� The hour by hour changes that could be made with an insulin pump were actually beneficial for active pump wearers--the only exception being that an extended disconnection from the pump was not always beneficial.� Current pumps are worn with all activities including swimming, and it was the early models that led to this advance.

As the population of pump users increased, so did the number of pump manufacturers.� Along with the increase of manufacturers, a variety of insulin pumps appeared, with different features.� Lily (CPI) was one of the first manufacturers to make an advanced pump; this was an insulin pump that used U-100 insulin and had four programmable basal rates.� In addition, its size was substantially smaller than the first generation of insulin pumps (half� of the size of a 6" x 4 �" x 1 �" cassette shipping container from National Library Service), and it had a numeric touch� keyboard exactly like a microwave oven.� This was considered to be the Cadillac of pumps.� Soon the market was flooded with insulin pumps of all types, some good and others, well, not so good.

With the increase in insulin pumps and increase in users, it became apparent there were drawbacks as well as benefits to pump use.� Most pumps required battery charging and changing every few days.� Some pumps used very specialized insulin reservoirs, which were costly.� There were even pumps that used specialized internal pumping mechanisms, which affected the stability of the insulin.� In addition, all pumps delivered insulin under the skin, just like a regular insulin injection--and needed to keep a needle in the site at all times.� Their insertion sites were prone to infection, and frequently were quite sore (especially if the pump user was thin).� The needle had to be changed every three days to prevent irritation and infection; this is still the practice with today�s newer and more comfortable �needles.�

In addition to these inconveniences, it quickly became apparent that insulin pump users were more prone to DKA.� Pump users were more susceptible to this condition because at any given moment there were only minutes of insulin within the body, and when this insulin delivery was interrupted, a rapid rise in blood glucose would occur.� A significant drawback for many pump users was the 15 to 20 pound weight gain generally associated with tight diabetes control.

After approximately five years of popularity, the use of the insulin pump began to decline.� This was for a variety of reasons, but mainly because the pump did not provide better control than multiple daily injections (at least three or more).� Another noteworthy reason for discontinuing pump use was that the pumps were expensive, and prone to damage and breakdown.� Finally, many of the younger pump wearers didn�t want the stigma of wearing a pump and thus making themselves �different� from their friends whom did not have diabetes.

Soon many pump users found their pump company had decided to discontinue the pumps, and in some instances, it became difficult to obtain supplies.� By the late eighties, there were only a few pump companies in existence and few advances were being made.� An implantable pump was created, but that generated difficulties.� The implantable pump was placed just under the skin and was visible to others as a projection from the surgery site.� (It looked like a hockey puck under someone�s skin.)� The two areas the pump could be implanted were in the abdomen (just below the ribs), or located on the wearer�s chest where the hand is placed over the heart in �I Pledge Allegiance to The Flag�.� This pump needed to be refilled with a large-gauge needle, and the wearer was required to carry around a programming unit.� The programming unit was about the size of the current Accu-Chek Voice-Mate talking glucose monitor (3" x 2 �" x 6 �"), and in order to deliver insulin boluses the wearer had to hold the programming unit over the pump to convey to the pump its instructions.� High magnetic or electric fields could disrupt the programming of the pump.� Though it was rare, the pump could break down, requiring surgery to replace it.� Every five years, the battery of this implantable pump needed to be changed.

Despite these drawbacks, two pump companies have continued to create innovations in pump therapy.� These two companies are MiniMed of California and Disetronic Medical Systems of Switzerland, with a United States office in Minnesota.� Today�s pump is much different than its predecessors.� The new-generation pumps are still controlled by the wearer (called an "open loop system") but they offer a much wider variety of features, and a decrease in size.� Often today�s pumps are mistaken for beepers, since they are only slightly larger, and come in a variety of designer colors.� A distinct advantage of today's pumps is they are more durable than their ancestors, and often go unnoticed on the belts (and in other places) of their owners.

Modern pumps use a special small syringe, which resides in the pump and is connected to the wearer via a small cannula (like an IV needle/catheter).� Battery changes are every few months and available right off the shelf in just about any store; one pump uses a four-year lithium battery, so no battery changing is needed.� Although not yet self-adjusting, modern pumps are the closest thing to a healthy pancreas we can get.� Just about any type of insulin delivery can be programmed into them, to fit a variety of lifestyles and requirements.� The newer pumps contain a variety of alarms, which warn the user of clogged tubing and low power supplies.

The newer pumps also have features which make it easier to track trends in lifestyle.� They store huge quantities of data such as when and how much insulin the user has taken or when alarms have gone off and for what reason.� New pumps also use lighted screens (for sighted users in dark locations) or audio cues for those users who have a visual impairment.

The mindset of today�s pump user is also somewhat different.� People who use pumps today really want the pump for its flexibility and tight control, and usually test their blood glucose four to ten times per day.

There are no restrictions on the activities of pump users today.� Watertight cases are available to allow for swimming.� People on pumps have done everything from running or biking across America to hiking up Mt. McKinley.� In addition, many professionals, such as 1999�s Miss America, use pumps without anyone ever knowing.� People using a pump today perform all types of jobs and participate in any activity they desire--the pump never holds the user back!� At night, most people just place the pump on the waistband of the garment they are wearing, or in a pocket.� Other pump wearers place the pump next to them when they sleep, since the tubing on the catheter can range from 24 inches to 42 inches.� Wherever the pump is placed for activities or sleeping, it usually does not get in the way.

Where are pumps heading in the future?� Pumps are heading toward self-adjustment, toward being a closed-loop system.� Such a pump would test the wearer�s blood glucose and deliver an insulin dose accordingly.

Currently, there is a blood glucose sensor, worn at the belt like a pump, which measures the blood sugar at specific short-time intervals, through a catheter, like the pump,� It gives an averaged readout every few minutes.� Eventually, I am sure, this sensor will be incorporated into a pump, making it self-adjusting.� Designs are in the works at this very moment, and the technology is here.� Within a few years such a device should be available to all those who want to become pump users.