Continuous Blood Pressure Estimation From Electrocardiogram and Photoplethysmogram During Arrhythmias

FIGURE 1. (A) Experimental scene of simultaneous acquisition of ECG, PPG, and IBP signals. (B) Typical ECG, PPG, and IBP waveforms recorded in arrhythmias. The type of each beat is labeled in the ECG waveforms. The two adjacent beats in the IBP waveforms with the largest changes in SBP are marked in the red font. ECG, electrocardiogram; IBP, invasive blood pressure; PVC, premature ventricular contraction; PPG, photoplethysmogram; SR, sinus rhythm; SBP, systolic blood pressure.

FIGURE 2. Extracted physiological features from ECG, PPG, and 1st dPPG in a cardiac cycle. First dPPG indicates the first derivative of PPG. (A) PTT values extraction. (B) PPG features extraction. R represent the R-wave peak of ECG; F/F′ and P represent the foot and peak of the PPG waveform, respectively, and letter M (and its corresponding point M′) represents the peak of the first derivative of PPG. Abbreviations and detailed definitions show in Table 1.

FIGURE 3. Dataset partition for each patient (A) and flowchart of blood pressure estimation model construction and evaluation (B). RMSEDTR, RMSESVR, RMSEAdaboostR, and RMSERFR represents the root mean square error between the reference and the estimated blood pressure values by the DTR, SVR, AdaboostR, and RFR, respectively. RMSE, root-mean-square error; DTR, decision tree regression; SVR, support vector machine regression; AdaboostR, adaptive boosting regression; RFR, random forest regression.

FIGURE 4. (A) Performance (mean value ± standard deviation of RMSEs) of different regression algorithms to estimate SBP and DBP in the validation set of all patients. Triple asterisks “*,” “**,” and “ns” indicate statistical significance at p < 0.05, p < 0.01, and p > 0.05, respectively. (B) Estimated beat-to-beat SBP and DBP comparisons in a representative patient, with the proposed method indicated in red and the reference shown in black. Abbreviations show in Figure 3.

FIGURE 5. Correlation and Bland–Altman plots for estimated SBP (A,B) and DBP (C,D) values from the proposed model (by using the random forest regression model) versus the references in a representative patient. In (B) and (D), the black dotted and solid red lines represent the ME ± 1.96 × STD. DBP, diastolic blood pressure; ME, mean error; STD, standard deviation of error; SBP, systolic blood pressure.

FIGURE 6. Group average absolute correlations (mean value ± standard deviation) between three PTTs and the PPG features that most relevant to blood pressure versus (A) SBP and (B) DBP. DBP, diastolic blood pressure; SBP, systolic blood pressure; other abbreviations and detailed definitions show in Table 1.