Overnight metabolic control with pulsed intermittent versus continuous subcutaneous insulin infusion

Subcutaneous insulin pumps deliver insulin both as a premeal bolus and as a continuous basal rate. It has been shown that the effect of the basal component is primarily to maintain normoglycemia overnight, but it is not known whether an intermittent pulsed infusion would achieve similar metabolic control. Six type I diabetic subjects (19-31 yr) were studied for 2 wk. Glycemic control was maintained by premeal injections of regular insulin with subcutaneous infusion overnight. A constant basal flow rate of insulin was delivered either continuously or intermittently as pulses spaced at 30-, 60-, and 120-min intervals. With each type of infusion, given in a randomized order, plasma glucose levels at 0600 h were: 81 +/- 12, 89 +/- 11, 102 +/- 14, and 94 +/- 13 mg/dl (mean +/- SEM), respectively. These values are not significantly different and remained stable until 1000 h. In addition, the hormonal responses (immunoreactive glucagon and "free" insulin levels) and metabolite levels (lactate, pyruvate, 3-hydroxybutyrate, alanine, and glycerol) were the same with continuous and pulsed insulin. These findings are in keeping with the expected kinetics for subcutaneously injected insulin. They may be of considerable interest for the design of smaller and more efficient subcutaneous insulin infusion pumps and demonstrate the wide physiologic limits for subcutaneous basal insulin replacement.