# Blood Pressure Estimation Algorithm Based on Photoplethysmography Pulse Analyses
## 4 Discussion  
Medical institutions measure BP using the air pressure measurement method. Many healthcare products have recently been developed for the measurement of BP, but the data obtained using PPG sensors are inaccurate compared with those obtained via the air pressurization method. Thus, the measurement values and the validity of the algorithm are not reliable. The largest errors in these measurements obtained when PPG sensors are used are attributed to the estimation of specific biomarker values [26]. When BP is measured using the PPG, BP values close to those obtained via the air pressure method can be obtained only by inputting body information such as the individual's height and weight, or by entering a blood vessel's cross-sectional area, cardiac output, etc. [27]. However, it is cumbersome to enter these values prior to PPG measurement. The PPG measurement method is an essential condition because it facilitates the reduction of errors in the measured value by utilizing the prior history of the individual-specific value [28]. Photoplethysmography is a measurement method used to analyze blood flow in the blood vessel. It employs PPGs that measure or estimate various biomarkers, such as PWV and PTT, that are highly useful for BP measurements [29; 30]. Among the factors that directly reflect individual vascular conditions, this study emphasizes MAP and helps to utilize the information about the blood transfer by the heart and its relationship with blood vessels. It was hypothesized, as mentioned in Section 1, that if a method were used to obtain specific values to analyze the conditions of blood vessels of an individual based on the absolute value of a specific biomarker pertaining to the blood vessels, this would constitute an alternative method to reduce the errors of the measured values using PPG, and would thereby allow for successful implementation of the algorithm. In this process, the cross-sectional area of the blood vessel (V), specific gravity of blood (\(\rho\)), SVR, and SV were defined as specific values that could express the condition of the blood vessels [31]. We implemented an algorithm that could deduce biomarker values based on the use of the MAP. Algorithms developed in previous studies used the Moens-Korteweg model and the PWV. However, these used the same input values, such as the elasticity of blood vessels, vascular diameter, and vascular thickness as constants [32]. To improve BP measurement accuracy in this study, BP was obtained using an equation that combined specific values from individuals with real-time PPG measurements. This equation yielded BP measurements with the use of the MAP presented in this study with an error rate of 5%, as proposed by the SBP and DBP estimation algorithms. In addition, certain values \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{3}{*}{**Variable**} & \multicolumn{2}{c}{**PPG Estimation**} & \multicolumn{2}{c}{**Electronic Blood**} & \multirow{3}{*}{\begin{tabular}{c} **DBP** \\ **Error** \\ **(\%)** \\ \end{tabular} } \\  & \multicolumn{2}{c}{**Algorithm**} & \multicolumn{2}{c}{**Pressure Measurement**} & \multirow{2}{*}{\
\begin{tabular}{c} **SBP** \\ **Error** \\ **(\%)** \\ \end{tabular} } \\  & \multicolumn{2}{c}{**BP (mmHg)**} & \multicolumn{2}{c}{**BP (mmHg)**} & \multirow{2}{*}{
\begin{tabular}{c} **SBP** \\ **Error** \\ **(\%)** \\ \end{tabular} } \\  & \multicolumn{2}{c}{**SBP**} & \multicolumn{2}{c}{**DBP**} & \multicolumn{2}{c}{**DBP**} \\  & 118.91 & 79.40 & 115.01 & 75.00 & 3.391 & 5.866 \\ Standard & 5.23 & 5.16 & 5.17 & 5.26 & 0.867 & 2.273 \\ deviation & \multicolumn{2}{c}{} & \multicolumn{2}{c}{} & \multicolumn{2}{c}{} & \multicolumn{2}{c}{} \\ SBP (DBP) Error (\%) = (PPG Estimation Algorithm BP - Electronic Blood Pressure Measurement BP)/Electronic Blood Pressure Measurement BP \(\times\) 100. & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Difference between estimated and measured blood pressure mean values (N = 21).