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Hyperglycaemia refers to an elevated glucose concentration in the circulating blood. While blood glucose level (BG) is often elevated after a meal, it usually normalises to a range of 3.5–5.6 mmol/l within 3 hours of a meal in a healthy individual. During fasting, BGs are also usually maintained within the normal range of 3.5–5.6 mmol/l [1].

Automatic regulation of a patient’s blood glucose (BG) level requires a minimum of three components, namely, a continuous BG sensor, a controller that matches BG level with an appropriate insulin delivery rate, and an infusion pump to deliver the insulin to the subject.

The role of the control algorithm in a closed-loop insulin delivery system is to regulate the patient’s BG level, replacing the intrinsic glucose regulatory function, which is abnormal in diabetics. To develop an effective algorithm, a knowledge of how glucose is intrinsically regulated in a healthy person is essential.

We have looked at blood glucose measurement, insulin infusion (Chapter 2), and the characteristics of the patient in terms of the blood glucose control (Chapter 3). In this chapter, we look at the control algorithms (or the “smarts”) that, when worked together with the glucose sensor and insulin infusion pump, would ideally re-balance a patient’s blood glucose level.

MiniMed® CGMS is, perhaps, the first commercially-available subcutaneous glucose sensor for use by the masses. CGMS consists of a disposable subcutaneous glucose sensor assembly connected by a cable to a pager-sized glucose monitor. CGMS takes a glucose measurement every 10 seconds and stores a smoothed and filtered average of these values every 5 minutes in the memory bank on-board.

Researches have found that a well-controlled BG greatly reduces the mortality and morbidity associated with diabetes. A closed-loop control system could be used to achieve a tight BG control. It can be seen (in Chapter 4) that designing a closed-loop system for BG control is not an easy task. The design of the closed-loop system needs to consider the characteristics of each components in the system, the design of the control algorithm, and how the combination (of the sensor, infuser and algorithm) can achieve the desired outcome. The design of the control algorithm depends on the selection of the BG measurement method and insulin infusion routes. The selection of the BG measurement method and insulin infusion route depends on the available technology and issue of safety associated with the selected method/routes.