Physical Activity Sensors Are Superior to Heart Rate Monitoring for Real-Time Activity Detection: Implications for Closed-Loop Diabetes Control

Objective: We have recently shown that mild/moderate-grade physical activity (PA) influences glucose status in healthy individuals and age/gender matched type 1 diabetes mellitus (T1DM) using continuous subcutaneous insulin infusion. Currently in closed-loop studies, instantaneous heart rate and accelerometers are being evaluated to measure PA. We compared PA measured by accelerometers to instantaneous heart rate output. Methods: A total of 23 subjects (11 controls and 12 T1DM) underwent a carefully planned and supervised PA protocol. Where continuous glucose data were captured using Dexcom SEVEN PLUS\uae continuous glucose sensor, PA data were collected using MSR accelerometers (MSR Electronics GmbH, Seuzach, Switzerland) attached to a participant\u2019s body using an elastic belt. The heart rate data were captured on IntelliVue patient monitors (Philips Healthcare, Andover, MA) using finger clip pulse oximeters. The data were compared for two inactive (premeal and meal) bouts and two active bouts to test repeatability. Heart rate and accelerometer data were scaled to a 0% to 100% range based on the participant-specific minimum and maximum values, and intraclass coefficient (ICC) was computed for concordance measures. Results: Heart rate profiles by patient were highly variable, whereas accelerometers tracked the study protocol more closely. While the concordance, by ICC, varied considerably by patient, it did not differ statistically between T1DM and controls (p = .44). For both controls and T1DM, during active periods, both heart rate and accelerometery output varied appropriately, but during the two sedentary periods, the heart rate data showed more variability (p = .02 and p = .04, respectively). Conclusion: Highly accurate accelerometery shows more accuracy compared with instantaneous heart rate and has more potential for incorporation into closed-loop systems for T1D