Aortic frequency response determination via bioimpedance plethysmography

Objective: Arterial stiffness is an important marker to predict cardio vascular events. Common measurement techniques to determine the condition of the aorta are limited to the acquisition of the arterial pulse wave at the extremities. The goal of this work is to enable non-invasive measurements of the aortic pulse wave velocity, instead. An additional aim is to extract further information, related to the conditions of the aorta, from the pulse wave signal instead of only its velocity. Methods: After discussing the problems of common pulse wave analysis procedures, an approach to determine the frequency response of the aorta is presented. Therefore, the aorta is modelled as an electrical equivalent circuit. To determine the specific numeric values of this system, a measurement approach is presented, which is based on non-invasive bioimpedance plethysmography measurements above the aortic arch and at the inguinal region. The conversion of the measurement results to the system parameters is realized by a digital algorithm, which is proposed in this work as well. To evaluate the approach, a study on three subjects is performed. Results: The measurement results demonstrate that the proposed approach yields realistic frequency responses. For better approximation of the aortic system function, more complex models are recommended to investigate in the future. Since this study is limited to three subjects without a ground truth, further measurements will be necessary. Significance: The proposed approach could solve problems of current methods to determine the condition of the aorta. Its application is non-invasive, harmless and easy to execute

Consistency of aortic distensibility and pulse wave velocity estimates with respect to the Bramwell-Hill theoretical model: a cardiovascular magnetic resonance study

<p>Abstract</p> <p>Background</p> <p>Arterial stiffness is considered as an independent predictor of cardiovascular mortality, and is increasingly used in clinical practice. This study aimed at evaluating the consistency of the automated estimation of regional and local aortic stiffness indices from cardiovascular magnetic resonance (CMR) data.</p> <p>Results</p> <p>Forty-six healthy subjects underwent carotid-femoral pulse wave velocity measurements (<it>CF_PWV</it>) by applanation tonometry and CMR with steady-state free-precession and phase contrast acquisitions at the level of the aortic arch. These data were used for the automated evaluation of the aortic arch pulse wave velocity (<it>Arch_PWV</it>), and the ascending aorta distensibility (<it>AA_Distc, AA_Distb)</it>, which were estimated from ascending aorta strain (<it>AA_Strain</it>) combined with either carotid or brachial pulse pressure. The local ascending aorta pulse wave velocity <it>AA_PWVc </it>and <it>AA_PWVb </it>were estimated respectively from these carotid and brachial derived distensibility indices according to the Bramwell-Hill theoretical model, and were compared with the <it>Arch_PWV</it>. In addition, a reproducibility analysis of <it>AA_PWV </it>measurement and its comparison with the standard <it>CF_PWV </it>was performed. Characterization according to the Bramwell-Hill equation resulted in good correlations between <it>Arch_PWV </it>and both local distensibility indices <it>AA_Distc </it>(r = 0.71, p < 0.001) and <it>AA_Distb </it>(r = 0.60, p < 0.001); and between <it>Arch_PWV </it>and both theoretical local indices <it>AA_PWVc </it>(r = 0.78, p < 0.001) and <it>AA_PWVb </it>(r = 0.78, p < 0.001). Furthermore, the <it>Arch_PWV </it>was well related to <it>CF_PWV </it>(r = 0.69, p < 0.001) and its estimation was highly reproducible (inter-operator variability: 7.1%).</p> <p>Conclusions</p> <p>The present work confirmed the consistency and robustness of the regional index <it>Arch_PWV </it>and the local indices <it>AA_Distc and AA_Distb </it>according to the theoretical model, as well as to the well established measurement of <it>CF_PWV</it>, demonstrating the relevance of the regional and local CMR indices.</p

Stiffening and ventricular-arterial interaction in the ascending aorta using Magnetic Resonance Imaging: Ageing effects in healthy humans

2018 The Author(s). Objectives: The aim of this study was to investigate the effect of age and sex on nPWV and ndI in the ascending aorta of healthy humans. Background: Local pulse wave velocity (nPWV) and wave intensity (ndI) in the human ascending aorta have not been studied adequately, due to the need for invasive pressure measurements. However, a recently developed technique made the non-invasive determination of nPWV and ndI possible using measurements of flow velocity and arterial diameter. Methods: Diameter and flow velocity were measured at the level of the ascending aorta in 144 healthy subjects (aged 20-77 years, 66 male), using magnetic resonance imaging. nPWV, ndI parameters; forward (FCW); backward (BCW) compression waves, forward decompression wave (FDW), local aortic distensibility (nDs) and reflection index (nRI) were calculated. Results: nPWV increased significantly with age from 4.7±0.3 m/s for those 20-30 years to 6.4±0.2 m/s for those 70-80 years (P<0.001) and did not differ between sexes. nDs decreased with age (5.3±0.5 vs. 2.6±0.2 10-5 1/Pa, P<0.001) and nRI increased with age (0.17±0.03 vs. 0.39±0.06, P<0.01) for those 20-30 and 70-80 years, respectively. FCW, BCW and FDW decreased significantly with age by 86.3%, 71.3% and 74.2%, respectively (P<0.001), all compared to the lowest age-band. Conclusions: In healthy humans, ageing results in stiffer ascending aorta, with increase in nPWV and decrease in nDs. A decrease in FCW and FDW indicates decline in left ventricular early and late systolic functions with age in healthy humans with no differences between sexes. nRI is more sensitive than BCW in establishing the effects of ageing on reflected waves measured in the ascending aorta

A Systematic Review and Discussion of the Clinical Potential

Funding Information: Funding by Portuguese Foundation for Science and Technology (FCT-MCTES) under the following projects: PTDC/EMD-EMD/1230/2021—Fluid-structure interaction for functional assessment of ascending aortic aneurysms: a biomechanical-based approach toward clinical practice ; UNIDEMI UIDB/00667/2020; A. Mourato PhD grant UI/BD/151212/2021; R. Valente PhD grant 2022.12223.BD. Publisher Copyright: © 2022 by the authors.Aortic aneurysm is a cardiovascular disease related to the alteration of the aortic tissue. It is an important cause of death in developed countries, especially for older patients. The diagnosis and treatment of such pathology is performed according to guidelines, which suggest surgical or interventional (stenting) procedures for aneurysms with a maximum diameter above a critical threshold. Although conservative, this clinical approach is also not able to predict the risk of acute complications for every patient. In the last decade, there has been growing interest towards the development of advanced in silico aortic models, which may assist in clinical diagnosis, surgical procedure planning or the design and validation of medical devices. This paper details a comprehensive review of computational modelling and simulations of blood vessel interaction in aortic aneurysms and dissection, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). In particular, the following questions are addressed: “What mathematical models were applied to simulate the biomechanical behaviour of healthy and diseased aortas?” and “Why are these models not clinically implemented?”. Contemporary evidence proves that computational models are able to provide clinicians with additional, otherwise unavailable in vivo data and potentially identify patients who may benefit from earlier treatment. Notwithstanding the above, these tools are still not widely implemented, primarily due to low accuracy, an extensive reporting time and lack of numerical validation.publishersversionpublishe

On the quantification of arterial wall mechanical properties using invasive and non-invasive experimental investigations and analytical techniques

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University LondonCardiovascular 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.Addenbrooke’s hospita

Magnetic Resonance Imaging of the Neonatal Cardiovascular System : Impact of Patent Ductus Arteriosus

The incidence of premature birth is increasing in absolute number and as a proportion of all births around the world. Many pathologies seen in this cohort are related to abnormal blood supply. Fetal and premature cardiovascular systems differ greatly as to maintain adequate blood flow to the developing organs in the uterine and extra-uterine environments require very different circulations. Subsequently following preterm birth the immature cardiovascular system undergoes abrupt adaptations, often resulting in the prolonged patency of the fetal shunt, ductus arteriosus. The impact of a patent ductus arteriosus (PDA) is poorly understood. However it is thought that large ductal shunt volumes may result in congestive cardiac failure and systemic hypo-­‐perfusion. Cardiac MRI has contributed greatly to the understanding of many cardiovascular diseases and congenital defects in paediatric and adult patients. Translating these imaging techniques to assess the preterm cardiovascular system requires careful optimization due to their condition, size and significantly increased heart rate. The work presented in this thesis employs multiple functional CMR techniques to investigate the preterm cardiovascular system in the presence and absence of PDA and the resultant cardiac function. A novel technique utilizing PC MRI to quantify PDA shunt volume and its impact on flow distribution is presented. Despite large shunt volumes, systemic circulation remained within normal range, although slight reduction is detectable when assessed at group level. Subsequently the impact of PDA and associated increased work load on left ventricular dimensions and function was then investigated using SSFP imaging. Results indicated that cardiac function was maintained even in the presence of large shunt volumes. Finally 4D PC sequences were employed to evaluate pulse wave velocity and flow regime within the preterm aorta, demonstrating the feasibility of hemodynamic assessment in this cohort. The findings of these studies provide insight into the impact of PDA. The reliable measurement and assessment of preterm cardiovascular system provides the potential to improve the understanding of the development and effects of certain pathologies seen in this cohort.Open Acces

Unraveling Bicuspid Aortic Valve Enigmas by Multimodality Imaging: Clinical Implications

Aortic aneurysm; Bicuspid aortic valve; Computed tomographyAneurisma aòrtic; Vàlvula aòrtica bicúspide; Tomografia computadaAneurisma aórtico; Válvula aórtica bicúspide; Tomografía computadaMultimodality imaging is the basis of the diagnosis, follow-up, and surgical management of bicuspid aortic valve (BAV) patients. Transthoracic echocardiography (TTE) is used in our clinical routine practice as a first line imaging for BAV diagnosis, valvular phenotyping and function, measurement of thoracic aorta, exclusion of other aortic malformations, and for the assessment of complications such are infective endocarditis and aortic. Nevertheless, TTE is less useful if we want to assess accurately other aortic segments such as mid-distal ascending aorta, where computed tomography (CT) and magnetic resonance (CMR) could improve the precision of aorta size measurement by multiplanar reconstructions. A major advantage of CT is its superior spatial resolution, which affords a better definition of valve morphology and calcification, accuracy, and reproducibility of ascending aorta size, and allows for coronary artery assessment. Moreover, CMR offers the opportunity of being able to evaluate aortic functional properties and blood flow patterns. In this setting, new developed sequences such as 4D-flow may provide new parameters to predict events during follow up. The integration of all multimodality information facilitates a comprehensive evaluation of morphologic and dynamic features, stratification of the risk, and therapy guidance of this cohort of patients