## 3 Results
As a result, this component scores a better Pearson's correlation factor of 0.51, upon analyzing all the data points, than the predecessor tidal peak of 0.39. For the isolated SD values, the \(r\) parameter increased from 0.47 in TDW_PK to 0.70 in TDW_LV. Upon evaluating the TDW_COMP parameter, the obtained data points have a broad overlapping region over the LVET identity line. Also, this composed fiducial point scores a better Pearson's correlation factor of 0.58 upon analyzing all the data points. The performance of this parameter reached the maximum \(r\) factor of 0.75 for the isolated SD data points. The rank of the afore-mentioned parameters is also supported by the linear regression coefficient. The compensated point of the tidal wave again obtained the maximum \(R^{2}\) factor of 0.66. For the PPG waveform, the consistency of the tidal wave components is inverted, as discussed in the interim results. Due to the waveform propagation effect, from the central aortic tree to the peripheral site, TDW_FV underestimates the reference LVET, as depicted in Figure 5b. On the other hand, TDW_PK overestimates readings in the same manner as the TDW_LV component but from the ABP case. Again, the linear compensation parameter, TDW_COMP, reduces the gap between the data points and the identity line by obtaining the largest overlapping region. This finding is reinforced by the maximum Pearson's correlation factor of 0.53 compared to the previous parameters of 0.49 and 0.50 upon analyzing all data points. For the isolated SD data points, the rank of the fiducial points' relevance is maintained, with a maximum \(r\) factor of 0.70 for TDW_COMP. Following the evaluation via simple linear regression, the difference between TDW_PK and TDW_COMP is negligible as the R\({}^{2}\) factor increased slightly from 0.47 to 0.49. Upon comparing the ejection time estimation between ABP and PPG, the compensation parameter is better in the first case, since the signal is recorded from the central part of the arterial network. Therefore, for PPG assessment, more attention is required during the signal processing step to improve LVET accuracy. Figure 4: (**a**) Histogram for selected SYS values; (**b**) histogram for selected DIA values. The overestimation and underestimation effects of the reference LVET alongside the entire spectrum underline the strong influence of the hemodynamic state among individuals. It is known that a shorter ejection time involves higher cardiac contractility due to an increased preload. In Tables 1 and 2, the defined tidal wave parameters together with the dicrotic notch are compared alongside the ABP spectrum, with a granularity of 10 mmHg. Figure 5: Scatter plot of fiducial point values against LVET reference. On the left side, subfigures (**a**,**c**,**e**) show LVET estimation in ABP signal. On the right side, subfigures (**b**,**d**,**f**) show LVET estimation in PPG signal. Note: in the ABP case, TDW_FV is the first component, while in the PPG case, TDW_PK is the first one according to the terminology section. For the ABP case (Table 1), the time difference and standard deviation between the reference LVET and TDW_PK are almost constant. The negative results indicate that the peak appearance happens before the true ending phase of ET. The last tidal wave component, TDW_LV, has a variation between \(-3\) ms and \(42\) ms, thus indicating that the ET phase has just passed. The compensation point, TDW_COMP, is the most fitted parameter as it shows a maximum absolute error of \(29\) ms at lower ABP and a minimum absolute error of \(3\) ms in a higher blood pressure state. The classical NOTCH point shows a strong overestimation between \(61\) ms and \(103\) ms; therefore, it is a weak LVET estimator. For the PPG case (Table 2), the same parametric trend is present as before. The compensation parameter scores a lower absolute error of \(25\) ms within the lower ABP interval and \(4\) ms within the higher blood pressure state.