Clinical evaluation of a noninvasive alarm system for nocturnal hypoglycemia

Abstract

Background: The aim of this study was to evaluate the performance of a prototype noninvasive alarm system (HypoMon) for the detection of nocturnal hypoglycemia. A prospective cohort study evaluated an alarm system that included a sensor belt, a radio frequency transmitter for chest belt signals, and a receiver. The receiver incorporated integrated "real-time" algorithms designed to recognize hypoglycemia "signatures" in the physiological parameters monitored by the sensor belt.

Methods: Fifty-two children and young adults with type 1 diabetes mellitus (T1DM) participated in this blinded, prospective, in-clinic, overnight study. Participants had a mean age of 16 years (standard deviation 2.1, range 12-20 years) and were asked to follow their normal meal and insulin routines for the day of the study. Participants had physiological parameters monitored overnight by a single HypoMon system. Their BG levels were also monitored overnight at regular intervals via an intravenous cannula and read on two independent Yellow Springs Instruments analyzers. Hypoglycemia was not induced by any manipulations of diabetes management, rather the subjects were monitored overnight for "natural" occurrences of hypoglycemia. Performance analyses included comparing HypoMon system alarm times with allowed time windows associated with each hypoglycemic event.

Results: The primary recognition algorithm in the prototype alarm system performed at a level consistent with expectations based on prior user surveys. The HypoMon system correctly recognized 8 out of the 11 naturally occurring overnight hypoglycemic events and falsely alarmed on 13 out of the remaining 41 normal nights [sensitivity 73% (8/11), specificity 68% (28/41), positive predictive value 38%,negative predictive value 90%].

Conclusion: The prototype HypoMon shows potential as an adjunct method for noninvasive overnight monitoring for hypoglycemia events in young people with T1DM.

Figure 1.

Example result for a participant night showing a true positive alarm. This alarm was raised when the patient’s BG level was within the “error band.” MDI, multiple daily injections; BMI, body mass index.

Figure 2.

Example of a participant night showing a case of false negative, as the HypoMon^® did not elicit a response, despite the BG level falling to less than 54 mg/dl. MDI, multiple daily injections; BMI, body mass index.

Figure 3.

Example of a participant night where patient’s BG level remains euglycemic and HypoMon^® does not produce an alarm (true negative). BMI, body mass index.

Figure 4.

Example of a participant night where a false alarm is raised when the patient’s BG level is in the euglycemic range. BMI, body mass index.