Non-invasive assessment of arterial stiffness using applanation tonometry

According to the World Health Organization, cardiovascular diseases are the leading cause of death worldwide, causing a global burden of an estimated 17.9 million deaths. Cardiovascular functionality together with aging are strongly associated to changes in arterial pulse pressure and arterial stiffness. In fact, the latter is considered as a biomarker of cardiovascular risk, and the gold-standard non-invasive technique to assess it is through the pulse wave velocity (PWV), meaning the velocity of propagation of arterial blood pulse within the cardiovascular system. PWV is strongly related to both the biomechanical properties and the local hemodynamics developing within arteries, thus with the pathological mechanisms underlying cardiovascular diseases. The global PWV is estimated based on the measurements of the pressure waveform at two recording sites along the arterial tree, by means of the distance between them and the transit time required for the pulse wave to travel that distance, also known as pulse transit time (PTT). Depending on the assessment technique used to compute PTT, PWV could be estimated exploiting different methods. In this context, this thesis project aims at comparing different methods proposed in the literature for the assessment of PWV starting from pulse pressure waveforms, using a dataset of over 3000 virtual healthy subjects. In addition to that, the effect of age on PWV and other related hemodynamic parameters was investigated in over 4000 virtual healthy adult subjects aged between 25 and 75 years uniformly distributed in ten-year increments. To complete the present study, the PWV changes in patients before and after Endovascular Aneurism Repair (EVAR), recruited from the specialised center IRCCS Policlinico San Donato (Milan, Italy), were measured in vivo and investigated. In this case, the pulse pressure measurements were obtained with applanation tonometry, exploiting the PulsePen commercial device. The analysis of the pulse pressure signals was carried out on MATLAB with specific codes for the implementation of the PWV assessment algorithms and to compute other hemodynamic parameters of interest. Among the main results it emerged that advancing age leads to an increase in systolic blood pressure followed by a reduced diastolic blood pressure, thus to an increase of PWV, as expected. Furthermore, the algorithm used to compute PTT from the pulse pressure waveform analysis has demonstrated to have an impact on the estimated PWV.