Double-pole in closed-loop minimal model of insulin kinetics

In the simplest version of minimal model the glucose and insulin levels are provided in the form of lookup tables. When insulin accumulation is presented as a differential equation, the insulin production rate appears increasing linearly with time. This has a limited physiological basis and could be unstable in some conditions. It is shown here that the insulin compartment can be modelled as having a double-pole which naturally produces the time term, accompanied by a decaying exponential for insulin accumulation rate. In a closed-loop configuration this model produces the `shoulder´ often seen in insulin concentration- time profiles.