Predicting Insulin Requirements for a Portable Insulin Pump Using the Biostator: Evidence for Reversible Insulin Resistance in Poorly Controlled Type I Diabetics
- Departments of Medicine and Pediatrics, Medical University of South Carolina Charleston, South Carolina
- Address reprint requests to Ronald K. Mayfield, MD., Medical University of South Carolina, Department of Medicine, 171 Ashley Avenue, Charleston, South Carolina 29425.
Glycemie control was achieved in 14 patients with insulin-dependent diabetes mellitus (IDOM) by 36–48-h treatment with a recently marketed clinical model, Biostator glucose controller (Life Science Instruments, Miles Laboratories, Elkhart, Indiana). Control was maintained by continuous subcutaneous insulin infusion with a portable pump, programmed using infusion profiles from the Biostator. Control of glycemie excursion with the Biostator was variable among patients. This control, reflected by the M-value or a blood glucose index (mean of pre-, peak, and 2-h postmeal levels for four meals) of each patient, correlated directly with their prior glycemie control, as assessed by hemoglobin A1c (HbA1c) level (r = 0.66, P < 0.01 and r = 0.82, P < 0.005, for M-value and blood glucose index, respectively).
Total insulin infused by the Biostator/24 h overpre-dicted the subcutaneous infusion dose required on day 2 of pump treatment (183 ± 11%, P < 0.001). Therefore, these data were not used to program the portable pump. Instead, total insulin dose was estimated using a dietary glucose/insulin (G/l) ratio. This ratio, derived from dietary total available glucose, urine glucose, and insulin dose/24 h during depot insulin treatment, accurately estimated total insulin for pump infusion (97 ± 4%). The basal infusion rate of the Biostator between 2400 and 0600 h also exceeded the subcutaneous infusion requirement and was reduced to 40% for the initial pump basal rate. The remainder of the insulin (total minus basal) was distributed as premeal boluses according to the Biostator infusion profile for meals. This initial distribution (%) of premeal insulin correlated well with that eventually needed for optimal control with infusion pump treatment (r = 0.88, P < 0.001). The insulin regimens derived resulted in average premeal plasma glucose levels of 113 ± 5.9 mg/dl on day 2 of pump treatment.
During 5–10 days of continued infusion pump treatment, the insulin dose needed to maintain blood glucose control decreased in the group as a whole. This decrease was primarily due to the dose reductions seen in patients who were in poor glycemie control before study. The decrease (%) in insulin dose in patients with HbA1c > 11% was 31.3 ± 4.1% (P < 0.001) compared with 8.6 ± 4.9% in patients with HbA1c < 11% (P = NS). In all patients, the change in insulin requirements (%) correlated with their initial HbA1c level (r = 0.72, P < 0.05). Glycemie control did not change significantly during this period.
Our study supports the coordinated use of closed-and open-loop insulin delivery systems. The Biostator infusion profiles are helpful in programming meal insulin distribution for the portable infusion pump. However, with the algorithms we used, the Biostator significantly overestimates total and basal insulin needs for subcutaneous infusion. The correlation between initial HbA1c levels and glycemie control on the Biostator as well as the relationship of HbA1c to the subsequent decrease in insulin requirements during pump treatment suggest that patients with poorly controlled IDDM are insulin resistant, and that this improves with strict glycemie control.
- Received April 12, 1982.
- Revision received March 28, 1983.
- Copyright © 1983 by the American Diabetes Association