Postprandial blood glucose response to exercise in type I diabetes: comparison between pump and injection therapy

The effect of 40 min ergometer exercise on glucose homeostasis was studied 90 min after morning insulin and a breakfast meal in 11 insulin-dependent diabetic subjects treated with conventional injection therapy or with continuous subcutaneous insulin infusion with a portable pump. During conventional therapy plasma free insulin levels rose slowly (7 +/- 2 microU/ml) after the morning injection, allowing an excessive postprandial rise in blood glucose levels (6.4 +/- 0.4 mmol/L). Physical exercise was able to reverse this increase of blood glucose. With insulin infusion therapy, the initial rise in plasma free insulin after a preprandial bolus was 3.5-fold higher (25 +/- 4 microU/ml, P less than 0.01) and postprandial hyperglycemia was reduced by 70% as compared with conventional therapy (P less than 0.02). During exercise blood glucose fell 60% more in pump than in conventionally treated patients (P less than 0.02). However, the decline continued during the recovery period in conventionally treated but not in pump patients, resulting in a comparable total fall in blood glucose in both groups. Fluctuations in blood glucose were avoided when exercise was performed in the fasting state with basal insulin infusion. In conclusion, when exercise was performed after breakfast, the total fall in blood glucose was similar during pump and conventional therapy, although the fall was faster on the pump. This can be explained, at least in part, by greater peak insulin levels obtained by the pump. Since postprandial glucose levels are lower in pump than in conventionally treated patients, a risk for hypoglycemia induced by postmeal exercise may be greater in pump than in conventionally treated patients.