USE OF A SUBCUTANEOUS GLUCOSE SENSOR TO DETECT DECREASES IN GLUCOSE-CONCENTRATION PRIOR TO OBSERVATION IN BLOOD

The development of a hypoglycemic alarm system using a subcutaneous gl ucose sensor implies that a decrease in blood glucose is rapidly follo wed by a decrease in the signal generated by the sensor, In a first se t of experiments, the linearity and the kinetics of the response of se nsors implanted in the subcutaneous tissue of normal rats were investi gated during a progressive increase in plasma glucose concentration: t he sensitivities determined between 5 and 10 mM and between 10 and 15 mM were not significantly different, and a 5-10 min delay in the senso r's response was observed. In a second set of experiments, performed i n diabetic rats, the kinetics of the decrease in subcutaneous glucose concentration following insulin administration was monitored during a decrease in plasma glucose level, from 15 to 3 mmol/L. During the 20 f irst min following insulin-administration, the sensor monitored glucos e concentration in subcutaneous tissue with no lag time, Subsequently, the decrease in the estimation of subcutaneous glucose concentration preceded that of plasma glucose, This phenomenon was not observed when the same sensors were investigated in vitro during a similar decrease in glucose concentration and may be due to a mechanism occurring in v ivo, such as the effect of insulin on glucose transfer from the inters titial space to the cells surrounding the sensor, It reinforces the in terest of the use of implantable glucose sensors as a part of a hypogl ycemic alarm.