## 5 Conclusions  
An advanced signal processing procedure, especially on the PPG waveform, could extract important cardiovascular markers such LVET. This step considers physical phenomena that occur in the arterial network. The compliance property of blood vessels is characterized by [PERSON]'s effect, mainly involving a waveform propagation finite time delay alongside an arterial branch. Therefore, the true ending of ET, marked by the ceasing of blood flow disturbance, will be masked both in ABP and PPG signals, as long as physical distance exists between aortic valve location and the measurement site. Since the last waveform type is recorded from the peripheral site, [PERSON]'s effect will be significant. A good estimator of LVET in both waveform types is the tidal wave feature, characterized in the first derivative domain by two distinctive points linked to blood pressure disturbance: onset and ending. While this feature is affected by the compliance property of the arterial tree, a linear compensation parameter was computed as the average value between tidal wave components. Even if this new parameter reduces the overestimation and underestimation effects of the true LVET value, the current findings suggest the need for an advanced compensation technique for accuracy improvement. The dicrotic notch feature has become an obsolete estimator of ET according to both newer findings in the literature and the presented results. Its time location alongside the cardiac cycle is far from the true ET point, with an overestimation over 100 ms. But its amplitude location alongside the ABP or PPG contour reveals information about vasomotor state, as observed in related research [41, 42]. This hemodynamic marker could be part of advanced compensation techniques since LVET estimation is strongly dependent on central blood pressure value. The detection of tidal wave components using the gradient method is critical, mainly for the performance of electronic devices. The ability to record high-quality waveforms is derisible in synergy with advanced signal processing procedures. This need would involve the development of the next generation of wearable devices with improved performance of the PPG technique. Thus, cardiovascular disorders characterized by LVET variation could benefit from remote monitoring with a high confidence level. Also, users or patients would benefit from personalized medicine accessibility. The assessment of extracting valuable cardiovascular information exclusively using PPG technology is a challenging task since waveform morphologies influenced by hemodynamic states are yet to be properly understood. Another aspect implies a universally agreed measurement protocol for LVET, not only to define a clear prerequisite for assessment but also to develop compensation techniques for an acceptable error range. During a day, a user or patient is subject to uncontrolled settings that render them ineligible for cardiovascular assessment. By defining a clear measurement protocol, ejection time estimation based on non-invasive technology could reach clinical-grade use. The potential applications of this assessment would involve the tracking and monitoring over time of cardiovascular disorders, which are linked to LVET changes such heart failure, hypertension or valvular disease. Further research will focus on developing advanced compensation techniques in order to improve accuracy. Also, a feasibility study will be conducted to find eligible disorders that could be efficiently tracked via remote LVET measurement. Conceptualization, L.E., D.D., S.S. and L.D. ; methodology, L.E. and S.S.; software, L.E. ; validation, L.E., L.D., S.S. and S.H. ; formal analysis, L.E. and S.S.; investigation, L.E. ; resources L.E. ; data curation, L.E. ; writing--original draft preparation, L.E. ; writing--review and editing, L.E. and L.D. ; visualization. L.E., D.D. and L.D. supervision, L.D. and D.D. ; project administration, L.D. ; funding acquisition, L.D. All authors have read and agreed to the published version of the manuscript.