Page 411 - Handbook of Biomechatronics
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406                                                    Graham Brooker


          degradation following which it is cleared from the blood stream, primarily
          by the kidneys. The glucose and insulin systems interact using feedback con-
          trol signals. For example, if a glucose perturbation occurs after eating, beta-
          cells secrete more insulin in response to increased glucose concentration in
          the blood. In turn insulin signaling promotes glucose utilization and inhibits
          glucose production so as to return blood glucose to normal levels. These
          control interactions are usually referred to as insulin sensitivity and beta-cell
          responsivity, respectively.
             In type 2 diabetes, this degradation starts as prediabetes which is charac-
          terized by a slow deterioration of both insulin sensitivity and beta-cell res-
          ponsivity. In contrast, in type 1 diabetes, beta-cells rapidly become virtually
          silent and insulin must be administered by the patient in an attempt to avoid
          hyperglycemia. However, insulin treatment risks potentially fatal hypogly-
          cemia and thus people with type 1 diabetes face a life-long optimization
          problem: to maintain strict glycemic control and reduce hyperglycemia,
          without increasing their risk of hypoglycemia.
             Blood glucose level is both the measurable result of this optimization and
          the principal feedback signal to the patient or an AP for the control of dia-
          betes (Cobelli et al., 2009).
             The ultimate objective of an AP is to replace that function of the natural
          pancreas, which is lost in diabetics. It combines the accurate measurement of
          blood glucose levels with a smart insulin dispenser to maintain the correct
          glucose balance irrespective of external disturbances.



               2 HISTORICAL BACKGROUND

               The diabetes epidemic of the late 20th and early 21st century would
          presuppose that diseases related to pancreatic function were a modern phe-
          nomenon. However that is not the case, and since the dawn of civilization
          documents have referred to people with diabetic-like symptoms and medic-
          inal remedies for the problem. The earliest known record is found in the Ebers
          Papyrus, a collection of medical texts from Egypt, dated to about 1550 BCE
          now kept in the library of the University of Leipzig. This papyrus preserved an
          extensive record of Egyptian medical history including references to anatomy,
          physiology, and toxicology along with treatments and prescriptions for myriad
          common ailments (Crystalinks). A single reference to the symptoms of diabe-
          tes stated “…to eliminate urine which is too plentiful.” Unfortunately this ref-
          erence is ambiguous with the crucial word, asha meaning either plentiful
          or often, and so could relate to cystitis rather than diabetes (Loriaux, 2006).
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