## 3 Results
As a result, the waveform propagation effect is reflected as reduced correlation coefficients compared to the first case. If in ABP waveform, the TDW_PK data points formed an overestimated result, and in the PPG case, the opposite effect is present. Therefore, in the peripheral site, the true moment of the ejection ending phase occurs before the appearance of the tidal peak component. By evaluating TDW_FV, the obtained data points form a shorter time duration. So, the beginning of the aortic valve closure occurs around this fiducial point location. Again, the same compensation point, TDW_COMP, is computed as the average of the neighborhood signal markers. This parameter scored a maximum [PERSON]'s correlation factor of 0.24. As in the ABP case, the simple linear compensation forms closer data points to the identity line that have a broad intersection region. On an individual basis, the comparison between ABP and PPG reveals a few findings. First, the measurement site is far away with respect to the heart location, and there is a significant propagation time delay effect. Secondly, the vasomotor state, reflected by arterial blood pressure, changes the compliance factor by affecting Windkessel's effect. An elastic system introduces greater propagation delay time due to mechanical energy absorption. Contrarily, a stiffer network reduces this undesired effect and thus improves the accuracy. This involves an accurate LVET estimation for hypertensive cases, in the absence of any type of result compensation. Each interim result from the patients' recordings was centralized into the final dataset. The post-processing data from 75 individual recordings amounted to up to 30,000 cardiac cycles. Outliers in the final merged dataset were removed by using the statistic method described in the previous section. After this step, the total beats decreased to 27,000 unique data points. The paired ABP data with the LVET reference value are represented by 15,000 distinctive points and 12,000, respectively, for the PPG case. The remaining data pairs sufficiently cover the ABP spectrum by having a uniform value distribution between 90 and 150 mmHg SYS, as depicted in Figure 4. Since each patient was subject to the anesthesia procedure, the provided ABP readings more frequently show normotensive values rather than hypertensive ones. During intermediate results evaluation, the selection procedure also considered the avoidance of unbalance data points for the afore-mentioned blood pressure classes. At a first glance, balanced data across the entire ABP spectrum reduces the results bias and improves the subsequent interpretation. The final merged results are presented visually on scatter plots (Figure 5) and also supported by numerical values. The NOTCH point is discarded from this step as it is a weak predictor. The results of each individual fiducial point are plotted against the reference LVET for both signals, ABP and PPG. With the blue cross symbol, all the values are shown, while with the red cross symbol, only the values under one standard deviation are highlighted. The last type of data point was computed using a granularity of 20 ms LVET as non-overlapped intervals. Therefore, eight regions are defined in a spectrum of 200 ms to 360 ms. Both types of data points are supported by [PERSON]'s coefficient, \(r\), highlighted with the associated color. Additionally, simple linear regression was performed to track the fiducial points values against the reference LVET, as described in the above section. The resulting correlation coefficient is depicted with the \(R^{2}\) symbol. For the ABP waveform, the trend of the selected fiducial points is similar to that of the individual case. The first component, TDW_PK, underestimates the true ET, as shown by the isolated SD values. The last tidal wave component, TDW_LV, forms an overestimated result, meaning that the true ET phase has just passed.