Analysis of the Effect of the Lowest SpO₂ on Nocturnal Blood Glucose Fluctuation in Type 2 Diabetes Measured by WatchPAT and Continuous Glucose Monitoring

Although sleep apnea syndrome reportedly increases nocturnal blood glucose (BG) variability, few studies have assessed the effect of the lowest oxygen saturation (SpO₂) during sleep on short-term BG levels. Thus, this prospective study of BG fluctuations while sleeping was conducted on subjects fitted with a continuous glucose monitoring (CGM) device and a WatchPAT^®, allowing simple evaluation of sleep-disordered breathing. Ninety-two patients with type 2 diabetes were fitted with the two devices overnight in the hospital when the glycemia was stable (∼7-10 days) in order to avoid the effects of hyperglycemia. The subjects were aged at least 18 years.

Results: The subjects were categorized according to their lowest SpO₂ by WatchPAT (SpO₂ ≥90%, 85%≤ and <90%, or <85%). As SpO₂ decreased, elevated body mass index (BMI) (20.3±3.3 vs. 25.3±3.9 vs. 28.7±5.8 kg/m², mean±standard deviation (SD); p<0.001) and increased endogenous insulin secretion (1.3±0.7 vs. 2.2±1.1 vs. 2.5±1.3 ng/mL; p=0.002) were observed. Using BG level at the time of the lowest SpO₂ as baseline, comparison of the differences in BG values every 30 minutes for 3 hours showed significantly worsened BG levels for SpO₂ <90% (30 min-baseline 4.4±3.2 vs. 180 min-baseline 18.7±22.4 mg/dL; p<0.001). In addition, in the 30 minutes after the lowest SpO₂, the BG level was elevated in the SpO₂ <85% group compared to those in the other groups (SpO₂ ≤90% 4.1±3.2 vs. 85%≤ SpO₂ <90% 4.4±3.2 vs. SpO₂ <85% 7.8±6.9 mg/dL; p=0.03). In contrast, no significant differences were noted in mean BG, mean amplitude of glycemic excursions (MAGE), SD, or coefficient of variation (CV) among the three groups from 00:00 to 06:00.

Conclusions: Even without differences in nocturnal fluctuations of BG levels, because of treatment, hypoxemia during sleep causes short-term worsening of glycemia. Moreover, the greater the degree of hypoxemia, the earlier the worsening is likely.