Validation of a Wireless Bluetooth Photoplethysmography Sensor Used on the Earlobe for Monitoring Heart Rate Variability Features during a Stress-Inducing Mental Task in Healthy Individuals

Figure A1. Bland–Altman plots for the pairs of time-domain metrics obtained at rest. The blue line and the green area represent the mean of the differences between measurements and the associated confidence interval. The red lines and the associated area represent the upper and lower LoAs and the associated confidence intervals.

Figure A2. Bland–Altman plots for the pairs of frequency-domain and non-linear metrics obtained at rest. The blue line and the green area represent the mean of the differences between measurements and the associated confidence interval. The red lines and the associated area represent the upper and lower LoAs and the associated confidence intervals.

Figure A3. Bland–Altman plots for the pairs of time-domain metrics obtained during the SCWT. The blue line and area represent the mean of the differences between measurements and the associated confidence interval. The red lines and the associated area represent the upper and lower LoA and the associated confidence intervals.

Figure A4. Bland–Altman plots for the pairs of frequency-domain and non-linear metrics obtained during the SCWT. The blue line and area represent the mean of the differences between measurements and the associated confidence interval. The red lines and the associated area represent the upper and lower LoA and the associated confidence intervals.

Figure 1. Representation of the experimental setup that was used for data acquisition. The experiment entailed two tasks with a duration of five minutes, separated by a one-minute break. Data was acquired and transmitted to a computer via Bluetooth low energy (BLE) using the Polar H10 and James One heart rate sensors, simultaneously.

Figure 2. (a) James One held in place with a magnet on an earlobe. (b) Representation of the main components of the James One PPG sensor.

Figure 3. The interface of the software developed for the detection and correction of abnormal intervals.

Figure 4. Histograms with a fitted kernel density estimation of the intervals obtained from the devices at rest and during the SCWT.

Figure 5. Pairs of HRV metrics obtained at rest plotted against a 45° line (that would represent a perfect agreement). The HRV metrics obtained from the James One are represented on the x-axis and the ones from the Polar H10 on the y-axis.

Figure 6. Pairs of HRV metrics obtained during the SCWT plotted against a 45º line (that would represent a perfect agreement). The HRV metrics obtained from the James One are represented on the x-axis and the ones from the Polar H10 on the y-axis.

Figure 7. Box plots of the comparison between the HRV metrics obtained during the rest task and the SCWT. Each boxplot is divided by a bar that represents the median (50th percentile). The spaces between the middle bar and the top and the bottom of the box indicate the 75th and 25th percentiles, respectively. The IQR is the distance between the 75th and 25th percentiles. The whiskers that extend from the boxes represent the maximum (75th + 1.5 × IQR) and the minimum (25th − 1.5 × IQR) limits, in which a value is not regarded as an outlier. Values plotted outside these whiskers are considered outliers and are shown as ♦.