Among the adolescents , the mean plasma glucose level was also lower during the bionic-pancreas period than during the control period ( 13818 vs. 15727 mg per deciliter [ 7.71.0 vs. 8.71.5 mmol per liter ] , P = 0.004 ) , but the percentage of time with a low plasma glucose reading was similar during the two periods ( 6.1 % and 7.6 % , respectively ; P = 0.23 ) .