http://bura.brunel.ac.uk/handle/2438/154 Brunel Institute for Bioengineering (BIB) is a multidisciplinary innovative research and development organisation where ideas turn into reality within industrial timescales. Founded in 1983 by Professor Heinz Wolff, it is a financially self-supporting organisation specialising in science and engineering for space, health care and contract work for industry. 2026-04-19T02:46:30Z http://bura.brunel.ac.uk/handle/2438/26159 Title: Tri-layered constitutive modelling unveils functional differences between the pig ascending and lower thoracic aorta Authors: Giudici, A; Spronck, B; Wilkinson, IB; Khir, AW Abstract: Copyright © 2023 The Authors. The arterial wall's tri-layered macroscopic and layer-specific microscopic structure determine its mechanical properties, which vary at different arterial locations. Combining layer-specific mechanical data and tri-layered modelling, this study aimed to characterise functional differences between the pig ascending (AA) and lower thoracic aorta (LTA). AA and LTA segments were obtained for n=9 pigs. For each location, circumferentially and axially oriented intact wall and isolated layer strips were tested uniaxially and the layer-specific mechanical response modelled using a hyperelastic strain energy function. Then, layer-specific constitutive relations and intact wall mechanical data were combined to develop a tri-layered model of an AA and LTA cylindrical vessel, accounting for the layer-specific residual stresses. AA and LTA behaviours were then characterised for in vivo pressure ranges while stretched axially to in vivo length. The media dominated the AA response, bearing>2/3 of the circumferential load both at physiological (100 mmHg) and hypertensive pressures (160 mmHg). The LTA media bore most of the circumferential load at physiological pressure only (57± 7% at 100 mmHg), while adventitia and media load bearings were comparable at 160 mmHg. Furthermore, increased axial elongation affected the media/adventitia load-bearing only at the LTA. The pig AA and LTA presented strong functional differences, likely reflecting their different roles in the circulation. The media-dominated compliant and anisotropic AA stores large amounts of elastic energy in response to both circumferential and axial deformations, which maximises diastolic recoiling function. This function is reduced at the LTA, where the adventitia shields the artery against supra-physiological circumferential and axial loads. Description: Data availability: Data will be made available on request.; Supplementary data to this article available online at: https://www.sciencedirect.com/science/article/pii/S1751616123001054#appsec1 2023-03-02T00:00:00Z http://bura.brunel.ac.uk/handle/2438/23343 Title: Transfer-function free technique for the non-invasive determination of the human arterial pressure waveform Authors: Giudici, A; Palombo, C; Morizzo, C; Kozakova, M; Cruickshank, JK; Wilkinson, IB; Khir, AW Abstract: © 2021 The Authors. The estimation of central aortic blood pressure is a cardinal measurement, carrying effective physiological, and prognostic data beyond routine peripheral blood pressure. Transfer function-based devices effectively estimate aortic systolic and diastolic blood pressure from peripheral pressure waveforms, but the reconstructed pressure waveform seems to preserve features of the peripheral waveform. We sought to develop a new method for converting the local diameter distension waveform into a pressure waveform, through an exponential function whose parameters depend on the local wave speed. The proposed method was then tested at the common carotid artery. Diameter and blood velocity waveforms were acquired via ultrasound at the right common carotid artery while simultaneously recording pressure at the left common carotid artery via tonometer in 203 people (122 men, 50 ± 18 years). The wave speed was noninvasively estimated via the lnDU-loop method and then used to define the exponential function to convert the diameter into pressure. Noninvasive systolic and mean pressures estimated by the new technique were 3.8 ± 21.8 (p = 0.015) and 2.3 ± 9.6 mmHg (p = 0.011) higher than those obtained using tonometery. However, differences were much reduced and not significant in people >35 years (0.6 ± 18.7 and 0.8 ± 8.3 mmHg, respectively). This proof of concept study demonstrated that local wave speed, estimated from noninvasive local measurement of diameter and flow velocity, can be used to determine an exponential function that describes the relationship between local pressure and diameter. This pressure-diameter function can then be used for the noninvasive estimation of local arterial pressure. 2021-09-22T00:00:00Z http://bura.brunel.ac.uk/handle/2438/23289 Title: On the quantification of arterial wall mechanical properties using invasive and non-invasive experimental investigations and analytical techniques Authors: Giudici, Alessandro Abstract: Cardiovascular diseases are the leading cause of death worldwide. Therefore, understanding their aetiology and development is a fundamental goal for biomedical research. Large arteries play a pivotal role in cardiovascular physiology; their elastic properties allow transforming the intermittent heart pulsation into a relatively steady flow. However, age-related microstructural changes of the arterial wall impair their compliant function, with negative consequences on the heart and other organs, including the brain. For this reason, arterial stiffness, assessed clinically by pulse wave velocity (PWV), has gained a central role in the prediction of cardiovascular risk. This thesis aimed to advance our understanding of the performance of the arterial wall, devising effective methods for the characterisation of its complex mechanical behaviour and, more specifically, stiffness both in vivo and ex vivo. The first part of this work comprises invasive ex vivo studies on arterial mechanics. The formulation of a novel tri-layered model of the arterial wall allowed investigating the layer-specific contribution to the macroscopic behaviour of arteries, providing a structural explanation to the pressure-dependence of arterial stiffness. Furthermore, the effects of the age-related remodelling of the wall microstructure on its non-linear behaviour were directly assessed via analysis of mechanical data of human donors’ aortae. The second part of this work consisted of the development and application of non-invasive techniques for the clinical assessment of arterial mechanics. First, the hysteresis area and the different slopes of the systolic and diastolic arms of the carotid pressure-diameter loops were used to quantify arterial viscoelasticity in a cohort of healthy people and hypertensive and diabetic patients. Second, exponential modelling of the carotid pressure-area relationship was used to define the relationship between local PWV, exponential parameters and blood pressure. This allowed assessing arterial stiffness independently of acute inter-subject differences in blood pressure. Furthermore, the viability of a new technique using ultrasound-based PWV to operate an exponential conversion of local diameter distension waveform into non-invasive pressure has been evaluated. Description: This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University London 2021-01-01T00:00:00Z http://bura.brunel.ac.uk/handle/2438/22733 Title: Simulation of 3D solid tumour angiogenesis including arteriole, capillary and venule Authors: Wu, J; Long, Q; Xu, S; Padhani, AR; Jiang, Y Abstract: Copyright © 2008 The Author(s). In this paper, a 3D mathematical model of tumour angiogenesis is developed, to generate a functional tumour vasculature for blood microcirculation. The model follows that of Anderson and Chaplain (1998) with three exceptions: (a) extending the model from 2D to 3D, one arteriole and one venule is induced as two parent vessels to form an intact circulation network for blood flow; (b) generating networks able to penetrate into the tumour interior rather than the exterior only; (c) considering branching generations with different diameters, based on which three groups of vessels, such as arterioles, venules and capillaries are classified. The present study contains four steps: 1. Generation of 3D angiogenic vasculature induced from one arteriole and one venule, with branching generations considered. 2. Examination of vessel connectivity among each other to construct a functional network for blood circulation, investigation of sensitivity of network architectures to changes in some model parameters. 3. Simulation of blood flow in the developed vasculatures. 4. Comparisons of blood flow calculated on the networks induced from an arteriole-venule system and from a single parent vessel. The networks from simulations could present basic geometric and morphological features of tumour vasculatures. The sensitivity analysis indicates the controllability of the created networks, which could construct architectures of some specific geometric features to suit different types of tumours. The comparisons of blood flow mentioned above demonstrate the validity of the present vasculature, which could be served as a more realistic network structure for research of microcirculation, drug delivery in solid tumors. 2008-12-01T00:00:00Z