Preprogrammed intravenous insulin infusion in diabetic humans: metabolic consequences of altering meal size

Abstract

New implantable, variable-rate, intravenous insulin infusion systems offer the possibility of increased dietary flexibility in the treatment of diabetes mellitus. However, the development of insulin infusion algorithms required to maintain near-normal glycemia inthe presence of a nonconstant diet first requires information concerning the metabolic response to meals of varying size when the insulin dose is fixed. With this goal in mind, we studied five type I diabetics aged 16–40 yr who were treated for 3 wk with a portable intravenous insulin infusion system. Initially, the patient's usual prescribed diabetic diet was provided, and an individual waveform of insulin infusion resulting in diurnalnormoglycemia was defined for each meal. Subsequently, small (12% of total daily calories) and large (36% of total daily calories) versions of the regular breakfast (24% of totaldaily calories) were provided without change in the insulin infusion waveforms, and the resulting metabolic profiles were studied. The overall mean fasting plasma glucose levels before the meals of varying size were not significantly different, but the incremental rises in plasma glucose with the small (31 ± 5 mg/dl), regular (48 ± 7 mg/dl), and large (64 ± 5 mg/dl) breakfasts varied directly with the meal size. The subsequent mean plasma glucose levels before the regular lunch were significantlydifferent (P < .05) after the small (50 ± 4 mg/dl) and large breakfasts (131 ± 9 mg/dl), compared with the regular breakfast (81 ± 7 mg/dl). Despite these differences, the plasma glucose levels before dinner were virtually identical. We conclude that large variations in meal size produce glycemic changes in keeping with the caloric content of the meal. These changes are associated only with the meal in question and do not result in sustained adverse glycemic consequences. Nevertheless, these results suggest the necessity of developing guidelines for changing mealtime insulin infusion profiles to maintain normoglycemia, despite variations in caloric intake. Only in this way will the unique capabilities of implantable intravenous insulin delivery devices be fully exploited.