# Blood Pressure Estimation Algorithm Based on Photoplethysmography Pulse Analyses
## 3 Results  
The measurement screen, as shown in Figure 3, was obtained through PPG filtering. Figure 3a shows the results of the ECG and PPG measurements in time, confirming that the peak of the R wave and the intersection of the PPG were 80%, as shown in Figure 1, to obtain the PTT. Therefore, as shown in Figure 3b, it was possible to obtain both values necessary for BP measurement via two PPG measurements. Therefore, the sampling was repeated, and the values automatically measured. As shown in Figure 3b, a program was implemented for automatic measurements with repetitions.  
Figure 3: Images showing PPG measurements plotted on the monitor of the device. (**a**) Measurement by changing the PTT standard through electrocardiography (ECG) and PPG, (**b**) Measurement of PT, PT, and pulse rate (PR) through two PPGs.  
Using the two PPGs measurements obtained from the fingers, the MAP algorithm presented in this study yielded the specific values for constants a and b for different individuals (Table 1). These values could be obtained in the same manner by which the values were obtained in the case of SBP and DBP. The correlations between SBP and DBP, and PT and MAP can be analyzed to study the linear relationships between them (Figure 4).  
The higher the SBP, the more the PT appeared, and the more the MAP tended to increase. PTT appeared to decrease as the SBP increased, which was consistent with the tendency of small-time difference between the two PPG peaks. Upon comparison of the graph with Figure 4, it was observed that SBP tended to be more affected by MAP than was the DBP. It can therefore be said that an individual-specific value of blood vessels tends to be affected by SBP. The MAP had the same effect on SBP and DBP, but the R\({}^{2}\) value for DBP was as low as 0.0671, while that for SBP was as high as 0.4219.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Variable**} & \multicolumn{2}{c}{**Electronic BP Measurement (mmHg)**} & \multicolumn{2}{c}{**PPG Estimation Algorithm**} & \multirow{2}{*}{**a**} & \multirow{2}{*}{**b**} \\ \cline{2-2} \cline{5-8}  & **SBP** & **DBP** & **PP** & **PT** & **PR** & **MAP** & \\ \hline Mean & 115.61 & 75.00 & 40.60 & 36.71 & 67.19 & 88.48 & 0.032811 & 55,186.8 \\ Standard & 5.20 & 5.18 & 3.65 & 2.27 & 2.82 & 4.89 & 0.003985 & 11,027.23 \\ deviation & & & & & & & & \\ \hline \hline \end{tabular}  
\end{table}
Table 1: Estimated constants a and b based on the use of PPG (N = 21).  
Figure 4: Systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), and PT correlation analyses. (**a**) Analysis of the correlation of SBP with PT and MAP; (**b**) Analysis of the correlation of DBP with PT and MAP.  
The specific values of constants a and b were estimated for specific individuals for the same target. Then, the error (%) of the estimated BP, calculated via the algorithm using PPG for 10 days, and the absolute value, measured using the automatic BP device, were estimated, as listed in Table 2. The SBP yielded a slightly lower error rate than the DBP, and the value measured using the PPG yielded a stable error value of approximately 5%.