Speckleplethysmographic (SPG) Estimation of Heart Rate Variability During an Orthostatic Challenge

Figure 1. An in vivo comparison of ECG (black), SPG (blue), and PPG (red) waveforms measured from a single subject. Because of the pulse transit time from the chest (ECG) to the finger (SPG/PPG), the ECG has its R peak before the SPG peak. SPG peaks before PPG.

Figure 2. A box plot comparison of the percentage of artifacts corrected for ECG (green), SPG (blue), and PPG (black) during the orthostatic challenge (n = 17). The circles represent outliers. Motion artifact and noise negatively impacted the peak detection algorithm accuracy, especially for PPG.

Figure 3. A comparison of SPG, PPG, and ECG HRV time domain parameters (SDNN; ms and RMSSD; ms) for the 17 subjects during both sitting and standing conditions. SPG and PPG are compared to ECG on scatter plots with a line of best fit and the line of best fit equation, the Pearson’s correlation coefficient, and significance in the upper left corner of the plot. Each Bland-Altman plot corresponds to the scatter plot directly above it, with the mean difference (black line), the 95% upper and lower limits of agreement (blue dashed lines), and the acceptable upper and lower limits of agreement (red dashed lines) also plotted. It should be noted that the Bland-Altman plots for SPG and PPG have different y-axis scales.

Figure 4. A comparison of SPG, PPG, and ECG HRV frequency domain parameters (LF; ms2 and HF; ms2) for the 17 subjects during both sitting and standing conditions. SPG and PPG are compared to ECG on scatter plots with a line of best fit and the line of best fit equation, the Pearson’s correlation coefficient, and significance in the upper left corner of the plot. Each Bland-Altman plot corresponds to the scatter plot directly above it, with the mean difference (black line), the 95% upper and lower limits of agreement (blue dashed lines), and the acceptable upper and lower limits of agreement (red dashed lines) also plotted. It should be noted that some of the Bland-Altman plots for SPG and PPG have different y-axis scales.

Figure 5. A comparison of additional SPG, PPG, and ECG HRV frequency domain parameters (normalized HF; normalized units (n.u.) and LF/HF; ratio) for the 17 subjects during both sitting and standing conditions. SPG and PPG are compared to ECG on scatter plots with a line of best fit and the line of best fit equation, the Pearson’s correlation coefficient, and significance in the upper left corner of the plot. Each Bland-Altman plot corresponds to the scatter plot directly above it, with the mean difference (black line), the 95% upper and lower limits of agreement (blue dashed lines), and the acceptable upper and lower limits of agreement (red dashed lines) also plotted.

Figure 6. Subjects remained seated for 5 minutes while a finger-clip device simultaneously collected SPG and PPG data and a wireless system collected ECG data. After a 30 second transition period for the subject to go from sitting to standing, 5 minutes of SPG, PPG, and ECG data were collected while the subject remained standing.

Figure 7. SPG (blue) and PPG (red) data taken from a subject while seated. For consistency in SPG peak detection, the first peak after a major trough for each period was used for SPG N-N interval analysis. The first PPG peak after the nearest detected SPG peak was used for PPG N-N interval analysis.