Background
We recently demonstrated that continuous positive airway pressure (CPAP) therapy rapidly improves insulin sensitivity within 2 days in non-diabetic patients with obstructive sleep apnea syndrome. In these very patients we investigated whether this improvement of insulin sensitivity is maintained during long-term CPAP therapy.
Material and Method
After a mean of 2.9 years (963+/-98 days) of CPAP treatment, these patients were reevaluated and hyperinsulinemic euglycemic clamp studies were performed in those with regular and effective CPAP treatment.
Results
From the initial 31 patients 16 could be reevaluated. 4 patients did not use their devices regularly (CPAP usage <2.5 h/night), 2 patients had insufficient CPAP treatment (AHI > or =10/h). One patient had developed type 2 diabetes mellitus. In the remaining 9 patients who used their devices regularly and effective (mean CPAP usage 5.2+/-1.6 h/night, mean AHI 3.3+/-2.6/h), mean insulin sensitivity index (ISI) was significantly higher than the baseline ISI established 2.9 years before (10.6+/-7.0 vs. 6.3+/-5.6 micromol/kg x min; p=0.008). At baseline 7 out of 9 patients had an impaired fasting glucose, after 2.9 years of treatment 3 out of 9 patients still had an impaired fasting glucose. The mean body mass index (BMI) had remained unchanged (31.4+/-7.8 vs. 31.4+/-7.6 kg/m2; mean individual difference -0.02+/-1.9 kg/m2).
Conclusions
OSA is a risk factor for impaired insulin sensitivity. CPAP treatment, when used regularly and with effective pressure, may improve insulin sensitivity over long time.

Keywords: Sleep Apnea, Obstructive - therapy, Insulin Resistance - physiology, Continuous Positive Airway Pressure - methods, Body Mass Index, Blood Glucose - analysis