Non-invasive Evaluation Methods Of Large Artery Function Based On Pulse Wave Velocity And Central Arterial Pressure

Arterial stiffness is the common pathophysiology basis of various cardiovascular disease. Arterial dysfunction is an early sign of atherosclerosis lesions. Early screening and active intervention of arterial dysfunction is an important measures for prevention and treatment of cardiovascular diseases. Carotid-femoral pulse wave velocity (CFPWV) and central arterial pressure (CAP) is the main indicators for noninvasive assessment of large artery elastic function. The measurement of CFPWV is dependent on an accurate estimation of pulse transit time (PTT). However, the existing "foot-to-foot" methods may have the problem of insufficient precision when used to estimate PTT, and different "foot-to-foot" methods may yield substantially different CFPWV values. Therefore, a new method for PTT estimation is needed for advancing the accuracy of aortic stiffness assessment by CFPWV. Carotid tonometry is a common method for noninvasive assessment of CAP, but carotid artery buried deep in the neck and relatively mobile, it is difficult to obtain reproducible signals, and oppression of carotid artery bring discomfort to patients. The carotid pressure waveform can be obtained from the radial artery which is easily measured, by a generalized transfer function. (GTF), however, GTF are mainly constructed and validated in foreign population. Constructing GTF in Chinese population and developing the appropriate testing equipment will be of great significance for noninvasive assessment of CAP. Based on the above demands, this thesis carried out studies from the aspects of PTT estimation methods and GTF-based CAP methods. The contents of the thesis are as follows:1. Studies on region-matching based method for PTT estimationThrough the analysis of the rise upstroke of pulse waveform, we proposed a waveform matching (WFMA) method to estimate PTT. The WFMA method selected a region between the diastole minimum point and the maximum systolic upstroke of the carotid and femoral pressure waveforms as the two matching segments, and determined PTT by a temporal shift technique. Carotid and femoral pulse data were recorded from 81 subjects, PTT were estimated by the reference method, "foot-to-foot" and WFMA methods and subsequently used to calculate CFPWV. The results showed that the WFMA method yielded CFPWV with a better accuracy and repeatability than the "foot-to-foot" methods. The WFMA method improves the reliability of CFPWV measurement and has the potential clinical value.2. The factors affecting CFPWV measurement by the WFMA methodThe effects of calibration of pulse waveform, selection of the matching region, and age on the proposed method were further investigated. By comparing the differences in CFPWV measurement generated by the WFMA method before and after calibrating the pulse wave, we found that the WFMA method yielded CFPWV with smaller bias in calibrated pressure waveforms, leading to more accurate assessment of CFPWV. We selected the part and whole of the upstroke of the pulse wave to estimate PTT respectively. The results showed that the accuracy of CFPWV measurement by the WFMA method reduced significantly when the whole upstroke of the waveform was matched. According to the age, the study subjects were divided into younger, middle, and elderly groups. The WFMA method performed well in all the three age categories, with a higher agreement and accuracy found in young subjects. This finding suggested that the WFMA method has good age applicability, establishing the foundation for its application in clinical practice.3. The method for constructing GTF based on an autoregressive exogenous modelThe radial-to-carotid individual transfer function (ITF) and GTF were constructed in Chinese population based on autoregressive exogenous (ARX) model in system identification. The 65 subjects were studied and divided into the construction and validation groups. In the construction group, we used cross-validation technique and Akaike’s information criterion to determine the optimal model order (10), and constructed radial-to-carotid GTF. In the validation group, the accuracy of the GTF was tested and compared with ITF. Central systolic blood pressure (SBP) can be well predicted by GTF from radial pressure waveform, but the exact shape of the central arterial pressure waveform was less well reproduced. GTF performed unfavorably at estimating parameters depended on the high-frequency content. Compared with GTF, ITF improved the accuracy for the estimation of central arterial pressure and waveform. The results provided the theory and technology support for developing noninvasive CAP analyzer.4. The effects of central pressure waveform morphology on GTF-derived central arterial waveform characteristicsOne hundred and nine subjects were included and divided into two groups (Group A and C) on the basis of the type of central waveform morphology (Type A and C). The mean transfer function (MTFA and MTFC) of the group A and C and the GTF of the whole subjects were constructed respectively. The results showed that a morphology-appropriate transfer function slightly but not significantly improved the estimation of some parameters, including central SBP, systolic and diastolic pressure time integrals. However, it significantly improved the parameters that depended on the pressure waveform contour, such as augmentation index (AIx). This finding preliminarily suggested that the use of a morphology-specific transfer function may be more suitable for deriving central hemodynamic characteristics.5. Development and demonstration application of the arterial stiffness and central arterial pressure testing instrumentBased on the methods and techniques established in the study, we developed arterial stiffness detector (BX-CFTI-200) and noninvasive central arterial pressure analyzer (BX-CAP-100), and demonstrated them in the exercise intervention clinic of Chinese PLA hospital. BX-CFTI-200 evaluates large arterial stiffness by using CFPWV measured by the WFMA method. BX-CAP-100 records radial pulse waveform using applanation tonometry and obtain central arterial pressure waveform by the transformation of GTF. Pulse wave analysis was then applied to extract a number of hemodynamic index, including central SBP, AIx and SEVR. These two equipment have cheap cost and easy to operate, satisfying the requirement of the early screening of the atherosclerosis.