Abstract for: Biomedical Applications of System Dynamics

The absorption kinetics of subcutaneously injected soluble insulin is unusual in that clinical experiments show that a slow initial absorption after a couple of hours is replaced by a significantly faster absorption. Moreover, experiments with different injection volumes and insulin concentrations demonstrate that there is both a volume and a concentration effect. The slow initial phase disappears if either the injected volume or the concentration of the injected insulin is reduced. On the other hand, in the limits of very low concentrations or small volumes, a tail develops on the absorption curve, representing a new type of slow process. A System Dynamics model of this absorption scenario was original developed in collaboration with the Steno Memorial Hospital. In spite of the fact that the insulin concentrations have increased by an order of magnitude, the model continues to correctly predict the absorption curves, and we are presently using variants of the model to explain the absorption curves for other insulin forms, some of which are bound to protein as they are injected or bind to protein as they enter the blood vessels while yet others are injected in crystalline form or precipitate immediately after the injection.