Continuous Monitoring of Vital Signs With Wearable Sensors During Daily Life Activities: Validation Study

Abstract

Background: Continuous telemonitoring of vital signs in a clinical or home setting may lead to improved knowledge of patients' baseline vital signs and earlier detection of patient deterioration, and it may also facilitate the migration of care toward home. Little is known about the performance of available wearable sensors, especially during daily life activities, although accurate technology is critical for clinical decision-making.

Objective: The aim of this study is to assess the data availability, accuracy, and concurrent validity of vital sign data measured with wearable sensors in volunteers during various daily life activities in a simulated free-living environment.

Methods: Volunteers were equipped with 4 wearable sensors (Everion placed on the left and right arms, VitalPatch, and Fitbit Charge 3) and 2 reference devices (Oxycon Mobile and iButton) to obtain continuous measurements of heart rate (HR), respiratory rate (RR), oxygen saturation (SpO₂), and temperature. Participants performed standardized activities, including resting, walking, metronome breathing, chores, stationary cycling, and recovery afterward. Data availability was measured as the percentage of missing data. Accuracy was evaluated by the median absolute percentage error (MAPE) and concurrent validity using the Bland-Altman plot with mean difference and 95% limits of agreement (LoA).

Results: A total of 20 volunteers (median age 64 years, range 20-74 years) were included. Data availability was high for all vital signs measured by VitalPatch and for HR and temperature measured by Everion. Data availability for HR was the lowest for Fitbit (4807/13,680, 35.14% missing data points). For SpO₂ measured by Everion, median percentages of missing data of up to 100% were noted. The overall accuracy of HR was high for all wearable sensors, except during walking. For RR, an overall MAPE of 8.6% was noted for VitalPatch and that of 18.9% for Everion, with a higher MAPE noted during physical activity (up to 27.1%) for both sensors. The accuracy of temperature was high for VitalPatch (MAPE up to 1.7%), and it decreased for Everion (MAPE from 6.3% to 9%). Bland-Altman analyses showed small mean differences of VitalPatch for HR (0.1 beats/min [bpm]), RR (-0.1 breaths/min), and temperature (0.5 °C). Everion and Fitbit underestimated HR up to 5.3 (LoA of -39.0 to 28.3) bpm and 11.4 (LoA of -53.8 to 30.9) bpm, respectively. Everion had a small mean difference with large LoA (-10.8 to 10.4 breaths/min) for RR, underestimated SpO₂ (>1%), and overestimated temperature up to 2.9 °C.

Conclusions: Data availability, accuracy, and concurrent validity of the studied wearable sensors varied and differed according to activity. In this study, the accuracy of all sensors decreased with physical activity. Of the tested sensors, VitalPatch was found to be the most accurate and valid for vital signs monitoring.

Keywords: accuracy; biosensor; continuous monitoring; mHealth; telemonitoring; validity; vital signs; wearable; wearable sensors.

Figure 1

(A) Schematic overview of wearable sensors and reference devices and their placement on the participant’s body (B) during application and (C) during the experiment. Details: (1) Everion placed on the (a) right arm and (b) left arm; (2) VitalPatch; (3) Fitbit Charge 3; (4) Oxycon Mobile (a) 4 electrocardiography electrodes, (b) oxygen saturation probe, and (c) face mask; (5) iButton placed on the (a) right arm, (b) left arm, and (c) chest.

Figure 2

Boxplot (median, IQR, range, and outliers) of the percentages of missing samples per participant per activity cluster and over all tasks for each sensor based on its expected storage frequency per vital sign.

Figure 3

Measured data of all sensors for one study participant, classified by vital sign. White boxes represent the tasks, and the grey boxes the transition periods between tasks.

Figure 4

Bland-Altman plots for the 12 combinations of vital signs measured by the wearable sensors and reference devices for individual samples during the preselected activity cluster, where the x-axis represents the mean of and the y-axis the difference (Δ) between both sensors. Dotted lines represent the mean difference and limits of agreement for repeated measurements. bpm: beats per minute; brpm: breaths per minute; HR: heart rate; RR: respiratory rate; SpO₂: oxygen saturation; T: temperature.

Figure 5

Bland-Altman plots for the 12 combinations of vital signs measured by the wearable sensors and reference devices of median data per minute during the preselected activity cluster, where the x-axis represents the mean of and the y-axis represents the difference (Δ) between both sensors. Dotted lines represent the bias and limits of agreement for the repeated measurements. bpm: beats per minute; brpm: breaths per minute; HR: heart rate; RR: respiratory rate; SpO₂: oxygen saturation; T: temperature.