Evaluation of a Wearable in-Ear Sensor for Temperature and Heart Rate Monitoring: A Pilot Study

Abstract

In the context of the COVID-19 pandemic, wearable sensors are important for early detection of critical illness especially in COVID-19 outpatients. We sought to determine in this pilot study whether a wearable in-ear sensor for continuous body temperature and heart rate monitoring (Cosinuss company, Munich) is sufficiently accurate for body temperature and heart rate monitoring. Comparing with several anesthesiologic standard of care monitoring devices (urinary bladder and zero-heat flux thermometer and ECG), we evaluated the in-ear sensor during non-cardiac surgery (German Clinical Trials Register Reg.-No: DRKS00012848). Limits of Agreement (LoA) based on Bland-Altman analysis were used to study the agreement between the in-ear sensor and the reference methods. The estimated LoA of the Cosinuss One and bladder temperature monitoring were [-0.79, 0.49] °C (95% confidence intervals [-1.03, -0.65] (lower LoA) and [0.35, 0.73] (upper LoA)), and [-0.78, 0.34] °C (95% confidence intervals [-1.18, -0.59] (lower LoA) and [0.16, 0.74] (upper LoA)) of the Cosinuss One and zero-heat flux temperature monitoring. 89% and 79% of Cosinuss One temperature monitoring were within ± 0.5 °C limit of bladder and zero-heat flux monitoring, respectively. The estimated LoA of Cosinuss One and ECG heart rate monitoring were [-4.81, 4.27] BPM (95% confidence intervals [-5.09, -4.56] (lower LoA) and [4.01, 4.54] (upper LoA)). The proportion of detection differences within ± 2BPM was 84%. Body temperature and heart rate were reliably measured by the wearable in-ear sensor.

Keywords: Body core temperature; Ear-sensor; Heart rate; Postoperative monitoring; Thermometer; Wearable sensors.

Fig. 1

Wearable Cosinuss One in-ear sensor for continuous temperature and heart rate monitoring

Fig. 2

Exemplary presentation of temperatures curves. The Cosinuss One sensor (mean value) is depicted as the cyan line, the Cosinuss One raw data are depicted as the pink line, the bladder temperature monitoring is depicted as the red line and the zero-heat flux temperature monitoring is depicted as the green line. Cosinuss One and zero-heat flux monitoring needed a short equilibration period (vertical dotted black line). Bladder temperature monitoring showed always higher temperatures at the beginning of surgery

Fig. 3

Exemplary presentation of heart rate curves. The Cosinuss One sensor mean value are depicted as the cyan line, the Cosinuss One raw data are depicted as the pink line and the ECG heart rate monitoring is depicted as the red line

Fig. 4

Bland–Altman plots of temperature measurements of A bladder (T_U) and in-ear sensor (T_C), B zero heat flux (T_B) and in-ear sensor (T_C), and C heart rate measurements. Each point depicts one paired measurement of the respective methods. Repeated pairs of measurements of one patient are shown in the same color. The solid line highlights the bias with 95% confidence interval shown as dotted lines. Limits of agreement are shown as dashed lines with respective 95% confidence intervals shown as dash-dotted lines