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Designing an insulin pump

Posted: 21 May 2013     Print Version  Bookmark and Share

Keywords:Insulin pump  blood glucose level  analogue front-end 

Insulin is a hormone central to regulating carbohydrate and fat metabolism in the body. It is secreted regularly within the body and aids in converting incoming glucose into energy. When a normal human being's body cannot secrete enough insulin, his/her blood glucose level rises, resulting in many adverse medical conditions.

To treat this problem, certain medicines are used to trigger more insulin secretion within the body. However, this doesn't suit many diabetic patients. Therefore, many of those suffering from diabetes take regular doses of insulin injections. The disadvantage of this approach is that the insulin is injected only in bulk at repetitive intervals and is not continuously mixed with blood as it when secreted during a body's normal functioning. Today, many physicians recommend the use of insulin pumps, which are portable devices attached to the body permanently and deliver constant amounts of insulin to the body via a catheter placed under the skin. The functioning of an insulin pump closely resembles the way in which insulin is secreted normally.

Figure 1 shows how an insulin pump is interfaced with a human body.

Figure 1: Interfacing Insulin pump with the human body.

As per today's statistics, 366 million people around the world suffer from diabetes, yet only around 0.1 per cent of them wear insulin pumps to treat it.

Measurement of insulin dosage
Insulin is measured in "units" where 100 units of insulin is equivalent to 1 ml. In other words, one unit is 10µl.

The insulin pump usually feeds insulin to the body in two formats. They are known as a bolus dose and a basal dose.

A bolus dose is one that is pumped to cover food eaten or to correct a high blood glucose level. The amount of insulin fed to the body would be high at this dose.

A basal dose is one that is pumped continuously at an adjustable basal rate to deliver insulin needed between meals and at night.

Figure 2 indicates the profile of insulin units pumped into the body during bolus dosage and basal dosage during a 24-hour window.

Figure 2: Insulin dosage concentration vs. time.

The duration of bolus dosage shown here is just an example. The duration of bolus and basal doses varies from person to person and should be given as per the physician's recommendations. This means the insulin pump user must have the ability to modify the profile of the rapid-acting insulin by shaping the bolus accordingly. Users can experiment with different bolus shapes to determine which is best for any given food so that they can improve control of blood sugar by adapting the bolus shape to their needs.

Overall working of an insulin pump
An insulin pump or any electronic device used in a critical medical application like this must meet FDA standards, and hence this article takes all these standards into consideration.2

A block diagram of an insulin pump is shown in figure 3.

Figure 3: Block diagram of an insulin pump.


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