Atherosclerosis is a form of cardiovascular disease that is a major contributing factor to death and disability worldwide. This study uses computational fluid dynamics (CFD) models as a cost effective and non-invasive method to determine the location and condition of atherosclerosis segments on the arterial wall. It also investigates changes in the abdominal aorta geometry including the inner and outer diameters, the length of the disease segments and the thickness of the arterial wall on the development of disease. Three groups of unhealthy conditions are assumed with each group having eight cases, which are compared to the control case of healthy condition. An invasive catheter pulsatile blood flow is imposed at the ascending aorta and pressure waveforms data is imposed at the four outlets of the aorta and also used to validate the present models. The results show that the stress phase angle at the brachial artery could be correlated to the early stages of atherosclerosis development at the abdominal aorta. This can be detected by measured values of the systolic wall shear stress and elastic strain intensity which increases due to the forward pulse wave resulting from atherosclerosis, while the diastolic values of stresses decreases due to the delay of the backward waves which reach the brachial artery. The three scenarios of atherosclerosis show that the forward and backward waves, which can be attributed to changes in the diameter, length and thickness of the abdominal aorta, can be non-invasively used to diagnose cardiovascular diseases.

Central arterial pressure is a better predictor of adverse cardiovascular outcomes than brachial blood pressure, but noninvasive measurement by applanation tonometry is technically demanding. Pulsecor R6.5 is a novel device adapted from a standard sphygmomanometer which estimates the central aortic pressure from analysis of low-frequency suprasystolic waveforms at the occluded brachial artery. A physics-based model, which simulates the arterial system using elastic, thin-walled tube elements and Navier-Stokes equations, is used to calculate arterial pressure and flow propagation. To determine the reliability of the device, we compared 94 central systolic pressures estimated by Pulsecor to the simultaneous directly measured central aortic pressures at the time of coronary angiography in 37 individuals. There was good correlation in central SBP between catheter measurements and Pulsecor estimates by either invasive or noninvasive calibration methods (r = 0.99, P < 0.0001 and r = 0.95, P < 0.0001, respectively). The mean difference in central systolic pressure was 2.78 (SD 3.90) mmHg and coefficient of variation was 0.03 when the invasive calibration method was used.When the noninvasive calibration method was used, the mean difference in central systolic pressure was 0.25 (SD 6.31) mmHg and coefficient of variation was 0.05. We concluded that Pulsecor R6.5 provides a simple and easy method to noninvasively estimate central SBP, which has highly acceptable accuracy.

This paper investigates the effect of the various terms in the one-dimensional acoustic wave equation on the pulse characteristics within the aorta. To mimic the physiological nature of the systemic arteries, the aorta is modelled as an elastic conical tube. The frequency spectrum is used to study the effect of different terms in this equation on the pressure ratio between the aortic root at the heart exit and the iliac bifurcation. For validation, the effective reflection distance calculated using this model is within 7% error of clinical observations, suggesting that the model is able to mimic physiological pressure propagation with a high degree of accuracy and can therefore be used to generate and test hypotheses. This work demonstrates that: (i) tapering in the aorta lumen radius causes supplementary amplification of the pressure pulses in the system and increases the propagation velocity; however, tapering in the aorta wall thickness generates opposite effects, (ii) increasing the wall stiffness causes a change in the natural frequency of the system and increases the propagation velocity, and (iii) inclusion of either the advective momentum correction term or the viscosity term insignificantly affects the pressure ratio. The last observation suggests that the flow pattern does not influence the pressure propagation characteristics.

This paper presents a 3D finite element upper arm model, validated by experiments as well as clinical data, used to study the error introduced in blood pressure measurements due to variability of arm tissue mechanical properties. The model consists of three separate cylindrical parts: soft tissue, bone and brachial artery. The artery volume changes under the cuff are used to represent the cuff pressure oscillations for analyzing blood pressure measurements. These oscillation trends are identical to observed clinical data. Also an upper arm simulator is designed and built for model validation. The model shows that the variation of soft tissue compressibility introduces an error up to 5% in blood pressure measurements. It is also revealed that the variation of the brachial artery and arm tissue stiffness has an insignificant effect on oscillometric blood pressure measurement method.

Aneurysm is a major contributing factor to death and disability worldwide. This research explores the concept of using computational fluid dynamics (CFD) as a cost effective and non-invasive method to detect the location and condition of diseased segments of blood vessels. In this study, 12 different abdominal aortic aneurysms cases and a controlled case of 3D coupled fluid–structure interaction scheme (FSI) are modeled. Pulse waves travelling through these segments are analyzed with a focus on the reflected waves at diseased region and the brachial artery. A commercial software ANSYS 12.1® is used to solve FSI models. An invasive catheter pulsatile pressure waveforms data is imposed at the inlet and the four outlets of the aorta and also used to validate the presented models. The results show that an increase in the diameter of aneurysmal artery will have an effect on the systolic and diastolic pressure at the brachial artery. The systolic pressure increases due to the forward pulse wave resulting from aneurysm. However, diastolic pressure decreases due to the delay of the backward waves which reach at the brachial artery. These models show that the forward and backward waves, which can be attributed to changes in the diameter of the abdominal aorta, may be useful in diagnosing cardiovascular diseases non-invasively.

This study investigates whether individualized transfer functions for estimating central pressures can be derived based on statistical information on the physical properties of the forearm vasculature. Physical parameters of the uniform thin walled artery model are assigned based on clinical measurements and invasive pressure measurements (n = 20) are used to calculate the effective peripheral load. The calculated load is parameterized by a Windkessel model and the variation of the Windkessel parameters is analyzed with gender, age and height. Whilst there is high spread and poor correlation of the data with age and height, there is clear clustering of data with gender. This suggests that model parameters are significantly different in either gender, and gender-specific transfer functions might be more appropriate for accurate reconstruction of central pressure.

Objective:To assess the effect of age and gender on suprasystolic acquired indices of vascular stiffness using a novel device – Pulsecor® R6.5.Design:Suprasystolic blood pressure measurements were taken in 294 subjects from primary care facilities in Auckland, New Zealand. Three measurements were ta

Different characteristic points used for the evaluation of pulse wave velocity (PWV) give significantly different results. Hence, the accuracy of using these points is questionable. There is need for quantitative comparison of different techniques to determine PWV. Previous studies aimed at comparing different PWV measurement techniques have been noted, however, on a limited number of smaller animals (mice, dogs, etc.). This simulation-based study aims to compare different techniques for PWV measurement in a large representative human population. A computer model is developed for simulating the pressure wave propagation between the carotid and femoral arteries. Using relationships observed in clinical trials, the model input parameters for a statistically representative population are expressed in terms of a person's age, gender and height. The model is used to calculate the carotid-femoral pressure ratio for different individuals, which is then parameterised into a number of features, and the equivalent propagation time is calculated using the phase-slope method. Using this time, the apparent phase velocity is determined and compared with PWV determined by the foot-to-foot technique. The two velocities compare well with a difference of 0.0059±0.0904 m/s. An averaging criterion for the calculation of apparent phase velocity has been tested and shown to give good estimates compared to the foot-to-foot technique. As it does not involve the identification of characteristic points on the measured pressure waves, the phase-slope method is more suitable for implementation in PWV monitors.