Blood glucose regulation using an open-loop insulin delivery system in pancreatectomized dogs given glucose infusions. I. Portal square waves

Continuous subcutaneous insulin infusions: Closing the loop

CONTEXT

Continuous subcutaneous insulin infusions (CSIIs) and continuous glucose monitors (CGMs) have revolutionized the management of diabetes mellitus (DM). Over the last two decades the development of advanced, small, and user-friendly technology has progressed substantially, essentially closing the loop in the fasting and post-absorptive state, nearing the promise of an artificial pancreas. The momentum was mostly driven by the diabetes community itself, to improve its health and quality of life.

EVIDENCE ACQUISITION

Literature regarding CSII and CGM was reviewed.

EVIDENCE SYNTHESIS

Management of DM aims to regulate blood glucose to prevent long term micro and macrovascular complications. CSIIs combined with CGMs provide an integrated system to maintain tight glycemic control in a safe and uninterrupted fashion, while minimizing hypoglycemic events. Recent advances have allowed to 'close the loop' by better mimicking endogenous insulin secretion and glucose level regulation. Evidence supports sustained improvement in glycemic control with reduced episodes of hypoglycemia using these systems, while improving quality of life. Ongoing work in delivery algorithms with or without counterregulatory hormones will allow for further layers of regulation of the artificial pancreas.

CONCLUSION

Ongoing efforts to develop an artificial pancreas have created effective tools to improve the management of DM. CSIIs and CGMs are useful in diverse populations ranging from children to the elderly, as well as in various clinical contexts. Individually and more so together, these have had a tremendous impact in the management of DM, while avoiding treatment fatigue. However, cost and accessibility are still a hindrance to its wider application.

24-hour blood glucose profiles in insulin-dependent diabetics treated with intravenous insulin infusion systems. A comparison between closed- and open-loop systems

The aim of this study was to compare the 24-hour blood glucose profiles of insulin-dependent diabetics during treatment with preprogramed insulin delivery systems with those of patients on treatment with the artificial beta cell (Biostator). Mean blood glucose (MGB) was 4.4 +/- 0.5 mmol/l for 15 controls, 5.8 +/- 1.0 for 53 patients on open-loop and 6.0 +/- 0.6 for 20 patients on closed-loop treatment. MBG was significantly higher in diabetics than in non-diabetic, but the difference between the two diabetic populations was not significant. Mean amplitude of blood glucose excursion was 1.8 +/- 0.6, 4.3 +/- 1.3 and 3.5 +/- 0.8 mmol/l respectively, the difference between the diabetic groups being significant. No hypoglycemia was seen in patients during closed-loop treatment, whereas this was the case in 10 of 53 patients on treatment with open-loop systems. Physical exercise resulted in small but normal decreases in blood glucose without hypoglycemia. Plasma insulin was within the normal range during both regimes. It is concluded that blood glucose control during treatment with closed-loop system is superior to that during treatment with open-loop systems. However, under standard conditions i.v. insulin infusion with preprogramed pump devices resulted in blood glucose fluctuations comparable with those during Biostator treatment.

Significance of hyperinsulinemia in ventromedial hypothalamus-lesioned rats

The significance of the hyperinsulinemia on the altered metabolism in ventromedial hypothalamus (VMH)-lesioned rats was tested. VMH lesions induced increases in fatty acid synthesis, lipoprotein lipase (LPL) activity, and plasma urea levels, and a decrease in plasma triglyceride concentrations. Similarly, in normal rats treated with pharmacological doses of insulin (14 U X rat-1 X day-1), fatty acid synthesis and LPL activity in fat tissue and the plasma urea were considerably elevated and plasma triglyceride was lowered compared with untreated controls. When endogenous insulin production was abolished by streptozotocin treatment, the four metabolic variables in the VMH-lesioned rats did not differ from those in diabetic controls. Substitution with 2 U of insulin X rat-1 X day-1, however, restored the differences in metabolism between VMH-lesioned diabetic and control diabetic rats. Substitution with 3 or 4 U insulin X rat-1 X day-1 showed the same differences. In VMH-lesioned rats the insulin level increased significantly from the 10th to the 70th day postoperatively; however, the rate of fatty acid synthesis, LPL activity, and plasma urea levels decreased, whereas plasma triglyceride concentrations increased. The results strongly suggest that the metabolic changes occurring after VMH lesions are only in part explained by the hyperinsulinemia associated with the VMH syndrome and indicate that other hormonal and/or nervous factors are involved.

Intraperitoneal delivery of insulin by a portable microinfusion pump

The feasibility of intraperitoneal insulin delivery in six healthy, insulin-dependent diabetic men utilizing a preprogrammed, portable insulin pump was examined. Blood glucose concentration was well controlled throughout breakfast, lunch, and supper during the intraperitoneal insulin infusion as assessed by both the mean glucose concentration and the integrated "glucose exposure.# Plasma free insulin concentration demonstrated a meal-related rise and fall similar to that observed in normal, nondiabetic persons. These short-term infusion studies suggest that intraperitoneal insulin may control meal-induced hyperglycemia in diabetic man. More prolonged intraperitoneal infusion studies will be necessary to confirm the feasibility of the peritoneum as an insulin delivery route by an artificial pancreas.

Insulin, glucagon, and amino acids during glycemic control by the artificial pancreas in diabetic man

The artificial endocrine pancreas (AEP) can normalize glycemia at rest and with meals. To determine whether insulin, glucagon, and amino acid profiles are also normalized, nine diabetics on subcutaneous insulin (S/C) and AEP control were compared to ten normal controls (NC). Glycemia was monitored continuously over 10 hr during which meals were consumed. Insulin infusion rate, and the levels of immunoreactive insulin (IRI) (in NC), free insulin (in S/C and AEP), C-peptide, glucagon, and amino acids are reported. Glycemia in AEP started at somewhat higher levels than in NC, but with breakfast and thereafter, it was identical. In S/C, hyperglycemia prevailed throughout, with no systematic change in free IRI. In AEP, both basal and peak free insulin levels, measured in four patients, were significantly higher than in NC. C-peptide values were significantly lower in diabetics and did not change with meals. Basal glucagon values were not different in the three groups and changes with meals were of small magnitude. Branched chain amino acids were higher in S/C and did not increase as in NC. In AEP, levels were lower than NC after the first two meals. Similarly, lysine and threonine were lower in AEP than in NC at the same times. Alanine, though similar at the onset, was lower 2 hr postbreakfast and higher 2 hrs postsupper in AEP and S/C compared to NC. These studies demonstrate that glycemic control with AEP is accompanied by hyperinsulinemia, which could account for the amino acid responses and the small alterations in immunoreactive glucagon (IRG) patterns. Further refinement is needed to obtain full normalization of metabolic profiles.

Blood glucose regulation using closed- and open-loop insulin delivery systems. II. Peripheral primed square wave infusions

Glucose was infused into anaesthetized dogs before and after pancreatectomy. In the diabetics blood glucose was regulated first by closed-loop and then by open-loop insulin delivery schemes. Insulin requirements for the latter were determined by resolving the former into a sequence of 3 different infusion rates: during the baseline and recovery periods, basal insulin was delivered at 0.37 +/- 0.02 mU/kg/min, while during the 60 min glucose infusion (10 mg/kg/min) there was an 8 min infusion at 4.96 +/- 0.37 mU/kg/min and a 52 min component at 1.85 +/- 0.08 mU/kg/min. With the open-loop method under these highly standardized conditions glycaemia was similar to normal controls but IRI levels were significantly higher, 13.5 vs 8.0 microU/ml (p less than 0.05) in the baseline and recovery periods and 74 vs 25 microU/ml (p less than 0.05) during the glucose infusion. It was concluded that: constant normoglycaemia can be maintained in the basal state by a constant rate of peripheral insulin delivery but at rates resulting in peripheral hyperinsulinaemia; the glycaemic response to glucose infusion can be normalized by a two component waveform of insulin delivery; and the closed-loop method can serve as a useful guide in determining insulin requirements.