Jordi Alastruey

King's College London | KCL · School of Biomedical Engineering & Imaging Sciences

Endothelial dysfunction is thought to underpin atherosclerotic cardiovascular disease. The most widely used in vivo test of endothelial function is flow mediated dilation (FMD). However, the results of FMD may be subject to some confounding factors that are not fully understood. We investigated potential biophysical confounding factors that could c...

Mental stress is a major burden for our society. Invasive and non-invasive methods have been proposed to monitor and quantify it using various sensors on and off body. In this study we investigated the use of the arm photoplethysmogram (PPG) to assess mental stress in laboratory conditions. Results were in correspondence with our previous in silico...

The arterial pulse wave (PW) is a rich source of information on cardiovascular (CV) health. It is widely measured by both consumer and clinical devices. However, the physical determinants of the PW are not yet fully understood, and the development of PW analysis algorithms is limited by a lack of PW datasets containing reference CV measurements. Ou...

Alzheimer’s disease (AD) is the most common cause of dementia. Several haemodynamic risk factors for AD have been identified, including ageing, increased arterial stiffness, high systolic blood pressure (BP) and brain hypoperfusion. We propose a novel approach for assessing haemodynamic risk factors by analysing arterial pulse waves (PWs). The aim...

Hæmodynamical simulations using one-dimensional (1D) computational models exhibit many of the features of the systemic circulation under normal and diseased conditions. Recent interest in verifying 1D numerical schemes has led to the development of alternative experimental setups and the use of three-dimensional numerical models to acquire data not...

Vascular ageing (VA) involves structural and functional changes in blood vessels that contribute to cardiovascular disease. Several non-invasive pulse wave (PW) indices have been proposed to assess the arterial stiffness component of VA in the clinic and daily life. This study investigated 19 of these indices, identified in recent review articles o...

Background Arterial stiffening and peripheral wave reflections have been considered the major determinants of raised pulse pressure (PP) and isolated systolic hypertension, but the importance of cardiac contractility and ventricular ejection dynamics is also recognised. Methods We examined the contributions of arterial compliance and ventricular c...

Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): MRC. Background Cardiac catheterisation is the gold standard for assessing cardiac pressures. However, this is an invasive and costly procedure. A minimally invasive alternative may be to use the subharmonic signal of microbubble ultra...

Background and objective: The blood pressure and flow waveforms carry valuable information about the condition of the cardiovascular system and a patient's health. Waveform analysis in health and pathological conditions can be performed in the time or frequency domains; the information to be emphasised defines the use of either domain. However, ph...

Magnetic resonance imaging and computed tomography allow the characterization of arterial state and function with high confidence and thus play a key role in the understanding of arterial aging and its translation into the clinic. Decades of research into the development of innovative imaging sequences and image analysis techniques have led to the...

A novel temporal convolutional network (TCN) model is utilized to reconstruct the central aortic blood pressure (aBP) waveform from the radial blood pressure waveform. The method does not need manual feature extraction as traditional transfer function approaches. The data acquired by the SphygmoCor CVMS device in 1,032 participants as a measured da...

Arterial pulse waves (PWs) such as blood pressure and photoplethysmogram signals contain a wealth of information on the cardiovascular (CV) system that can be exploited to assess vascular age and identify individuals at elevated CV risk. We review the possibilities, limitations, complementarity, and differences of reduced-order, biophysical models...

Prevention of cardiovascular disease (CVD) remains one of the largest public health challenges of our time. Identifying individuals at increased cardiovascular risk at an asymptomatic, subclinical stage is of paramount importance for minimizing disease progression as well as the substantial health and economic burden associated with overt CVD. Vasc...

Background and objective: This paper proposes a novel strategy to localize anomalies in the arterial network based on its response to controlled transient waves. The idea is borrowed from system identification theories in which wave reflections can render significant information about a target system. Cardiovascular system studies often focus on t...

This study investigated the effects of cardiac properties variability on arterial pulse wave morphology using blood flow modelling and pulse wave analysis. A lumpedparameter model of the left part of the heart was coupled to a one‐dimensional model of the arterial network and validated using reference pulse waveforms in turn verified by comparison...

Hypertension arises mainly from an increase in pulse pressure. However, the haemodynamic basis of this increase is still debated. Historically, early wave reflection from peripheral arteries has been considered the main determinant. Recently, the importance of ventricular-aortic coupling has also been highlighted. In this work, the relative role of...

A key factor governing the mechanical performance of the heart is the bidirectional coupling with the vascular system, where alterations in vascular properties modulate the pulsatile load imposed on the heart. Current models of cardiac electromechanics (EM) use simplified 0D representations of the vascular system when coupling to anatomically accur...

This work presents a computational study aimed to infer cardiac properties from vascular blood waveforms. A cardiovascular model, coupling a 0-D cardiac contraction model and a 1-D haemodynamic model of the human arterial tree, is used. Blood waveforms and the most relevant haemodynamics indices are subjected to a univariate sensitivity analysis va...

Smart wearables provide an opportunity to monitor health in daily life and are emerging as potential tools for detecting cardiovascular disease (CVD). Wearables such as fitness bands and smartwatches routinely monitor the photoplethysmogram signal, an optical measure of the arterial pulse wave that is strongly influenced by the heart and blood vess...

The development of methodologies that provide a comprehensive assessment of cardiac function from pulse wave analysis in the systemic circulation could avoid current practice using expensive, invasive and operator-dependent measurement techniques. This work addressed this topic computationally. A cardiovascular model, constituted of a lumped-parame...

Ventricular-vascular interaction is central in the adaptation to cardiovascular disease. However, cardiomyopathy patients are predominantly monitored using cardiac biomarkers. The aim of this study is therefore to explore aortic function in dilated cardiomyopathy (DCM). Fourteen idiopathic DCM patients and 16 controls underwent cardiac magnetic res...

Objective: A novel method was presented to separate the central blood pressure wave (CBPW) into five components with different biophysical and temporal origins. It includes a time-varying emission coefficient () that quantifies pulse wave generation and reflection at the aortic root. Methods: The method was applied to normotensive subjects with...

The impact of increased stiffness and pulsatile load on the circulation and their influence on heart performance have been documented not only for cardiovascular events but also for ventricular dysfunctions. For this reason, computer models of cardiac electromechanics (EM) have to integrate effects of the circulatory system on heart function to be...

Background Black African/African-Caribbean individuals with hypertension (BH) are at greater risk of heart failure than those of white European ethnicity (WH). The mechanisms underlying this dissimilarity remain poorly understood. Purpose To investigate the influence of ethnicity on left ventricular (LV) remodelling using multi-parametric cardiova...

Funding Acknowledgements Type of funding sources: Foundation. Main funding source(s): Dr Georgiopoulos was supported by the Onassis Foundation under the special grant & support program for scholars" association members Introduction – Black Afro-Caribbean hypertensives (BAHs) are exposed to a higher risk of heart failure (HF) than white hypertensive...

One of the European gold standard measurement of vascular ageing, a risk factor for cardiovascular disease, is the carotid-femoral pulse wave velocity (cfPWV), which requires an experienced operator to measure pulse waves at two sites. In this work, two machine learning pipelines were proposed to estimate cfPWV from the peripheral pulse wave measur...

An abdominal aortic aneurysm (AAA) is usually asymptomatic until rupture, which is associated with extremely high mortality. Consequently, the early detection of AAAs is of paramount importance in reducing mortality; however, most AAAs are detected by medical imaging only incidentally. The aim of this study was to investigate the feasibility of mac...

One-dimensional (1-D) arterial blood flow modelling was tested in a series of idealized vascular geometries representing the abdominal aorta, common carotid and iliac arteries with different sizes of stenoses and/or aneurysms. Three-dimensional (3-D) modelling and in vitro measurements were used as ground truth to assess the accuracy of 1-D model p...

An abdominal aortic aneurysm (AAA) is usually asymptomatic until rupture, which is associated with extremely high mortality. Consequently, early detection of AAAs is of paramount importance in reducing mortality; however, most AAAs are detected by medical imaging incidentally. The aim of this study was to investigate the feasibility of machine lear...

Impedance pneumography (ImP) is widely used for respiratory rate (RR) monitoring. However, ImP-derived RRs can be imprecise. The aim of this study was to develop a signal quality index (SQI) for the ImP signal, and couple it with a RR algorithm, to improve RR monitoring. An SQI was designed which identifies candidate breaths and assesses signal qua...

Objective: Central systolic blood pressure (cSBP, the peak of the central waveform) is usually regarded as the determinant of peripheral systolic blood pressure with amplification of peripheral systolic BP (pSBP) measured with reference to cSBP. However, the earlier portion of the central waveform, up to the first systolic shoulder (P1) may be the...

Several studies suggest that central (aortic) blood pressure (cBP) is a better marker of cardiovascular disease risk than peripheral blood pressure (pBP). The morphology of the pBP wave, usually assessed non-invasively in the arm, differs significantly from the cBP wave, whose direct measurement is highly invasive. In particular, pulse pressure, PP...

The European gold standard measurement of vascular ageing, a risk factor for cardiovascular disease, is the carotid-femoral pulse wave velocity (cfPWV), which requires an experienced operator to measure pulse waves at multiple sites. In this work, two machine learning pipelines have been proposed to estimate cfPWV from a peripheral pulse wave measu...

The photoplethysmogram (PPG) signal is widely measured by smart watches and fitness bands for heart rate monitoring. New applications of the PPG are also emerging, such as to detect irregular heart rhythms, track infectious diseases, and monitor blood pressure. Consequently, datasets of PPG signals acquired in daily life are valuable for algorithm...

Objective and Motivation: Pulse wave velocity (PWV) is known to be associated with vascular ageing, a risk factor for cardiovascular disease (CVD) [1]. The European gold standard measurement of PWV requires an experienced operator to measure pulse waveforms at multiple sites, sometimes together with an electrocardiogram [2,3]. This study aims to es...

Background: Abdominal aortic aneurysm (AAA) is usually asymptomatic and has an extremely high mortality if rupture occurs. Therefore, early detection and intervention are important. However, AAA is most often detected as an accidental finding during clinical imaging for other purposes [1]. Considering that AAA has a systemic impact on the biophysic...

Central blood pressure (cBP) is a highly prognostic cardiovascular (CV) risk factor whose accurate, invasive assessment is costly and carries risks to patients. We developed and assessed novel algorithms for estimating cBP from noninvasive aortic hemodynamic data and a peripheral blood pressure measurement. These algorithms were created using three...

In this work we present a one-dimensional (1D) mathematical model of the coronary circulation and use it to study the effects of arrhythmias on coronary blood flow (CBF). Hydrodynamical models are rarely used to study arrhythmias’ effects on CBF. Our model accounts for action potential duration, which updates the length of systole depending on the...

An algorithm for estimating the parameters of 1D blood flow modelling is proposed. The following parameters are identified based on the blood flow velocity measurement at certain points: elasticity of arteries, hydraulic resistances of peripheral regions and cardiac output. The estimation method is based on the algorithm of linear optimization. Thi...

Objective and Motivation: Endothelial dysfunction is thought to underpin atherosclerotic cardiovascular diseases. However, the widely used flow mediated dilation (FMD) in-vivotest of endothelial function relates poorly to clinical outcomes. In this study, we investigated potential confounding factors affecting the FMD test that could prevent FMD fr...

The influence of arterial and ventricular parameters on the main fiducial pressure points and index during systole has been investigated using a mix of in silico and in vivo data. Notably, an index, QIx, based entirely on ventricular ejection patterns has been developed and its potential in describing the augmentation pressure index, AIx, has been...

Aortic tapering is a known characteristic of the arterial tree affecting the development of pressure in the aorta. With tapering, the cross-sectional area of vessels decreases moving towards the periphery causing reflections to travel back to the heart. The reflection waves present in the aorta are an amalgamation of reflections from tapering, bifu...

Purpose: Vascular age may be a better marker of cardiovascular risk than age. It has been proposed that vascular age could be assessed easily and inexpensively from the photoplethysmogram (PPG) pulse wave, which is measured by pulse oximeters and fitness bands. Our aim was to assess the performance of existing PPG-derived indices and provide direct...

We examined the influence of arterial stiffening and ventricular ejection dynamics on the age-related increase in central pulse pressure. A total of 2033 women aged 18 to 91 years from the Twins UK cohort were studied. Aortic flow and central blood pressure were measured by Doppler sonography and carotid tonometry, respectively. Measured values of...

As computational models of the cardiovascular system are applied in modern personalized medicine, maximizing certainty of model input becomes crucial. A model with a high number of arterial segments results in a more realistic description of the system, but also requires a high number of parameters with associated uncertainties. In this paper, we p...

Purpose: Aortic stiffness is predictive of cardiovascular morbidity and mortality. However, the gold standard method for assessing aortic stiffness, carotid-femoral pulse wave velocity, is time-consuming and requires a trained operator. An alternative approach could be to derive an arterial stiffness index (ASI) from the easily measured finger phot...

We examined the ability of a simple reduced model comprising a proximal characteristic impedance linked to a Windkessel element to accurately predict central Pulse Pressure (PP) from aortic blood flow, verified that parameters of the model corresponded to physical properties, and applied the model to examine PP dependence on cardiac and vascular pr...

Supplementary material for optimization of complexity for arterial blood flow models

An individual’s cardiovascular state is a crucial aspect of a healthy life. However, it is not routinely assessed outside the clinical setting. Smart wearables use photoplethysmography (PPG) to monitor the arterial pulse wave (PW) and estimate heart rate. The PPG PW is strongly influenced by the ejection of blood from the heart, providing an opport...

The rate at which an individual recovers from exercise is known to be indicative of cardiovascular risk. It has been widely shown that the reduction in heart rate immediately after exercise is predictive of mortality. However, little research has been conducted into whether the time taken for the blood vessels to return to normal is also indicative...

Objective: A recent numerical study investigated the potential utility of peripheral PWV measurements for assessing aortic stiffness by simulating pulse wave propagation through the arterial tree. Approach: In this Comment we provide additional analysis of the simulations in which arterial compliances were changed. Main results: The analysis i...

Objective: Mental stress is detrimental to cardiovascular health, being a risk factor for coronary heart disease and a trigger for cardiac events. However, it is not currently routinely assessed. The aim of this study was to identify features of the photoplethysmogram (PPG) pulse wave which are indicative of mental stress. Approach: A numerical mo...

Background Pulse wave velocity (PWV) is a biomarker for the intrinsic stiffness of the aortic wall, and has been shown to be predictive for cardiovascular events. It can be assessed using cardiovascular magnetic resonance (CMR) from the delay between phase-contrast flow waveforms at two or more locations in the aorta, and the distance on CMR images...

Accepted abstract submission for the American Heart Association's 2017 Scientific Sessions and Resuscitation Science Symposium. Title: Validation of non-invasive MRI-based assessment of central blood pressure in a population of repaired coarctation patients

Hypertension is a well-documented predictive factor for cardiovascular events. Clinical studies have extensively demonstrated the differential hemodynamic consequences of various anti-hypertensive drugs, but failed to clearly elucidate the underlying mechanisms due to the difficulty in performing a quantitative deterministic analysis based on clini...

We examined the ability of a simple reduced model comprising a proximal characteristic impedance linked to a Windkessel element to accurately predict central pulse pressure (PP) from aortic blood flow, verified that parameters of the model corresponded to physical properties, and applied the model to examine PP dependence on cardiac and vascular pr...

Breathing rate (BR) is a key physiological parameter used in a range of clinical settings. Despite its diagnostic and prognostic value, it is still widely measured by counting breaths manually. A plethora of algorithms have been proposed to estimate BR from the electrocardiogram (ECG) and pulse oximetry (photoplethysmogram, PPG) signals. These BR a...

Objective: Local arterial wave speed, a surrogate of vessel stiffness, can be estimated via the pressure-velocity (PU) and diameter-velocity (ln(D)U) loop methods. These assume negligible early-systolic reflected waves (RWes) and require measurement of cross-sectionally averaged velocity (U_mean), which itself is a valuable quantity rela...

Arterial pressure is an important diagnostic parameter for cardiovascular disease. However relative contributions of individual ventricular and arterial parameters in generating and augmenting pressure are not understood. Using a novel experimental arterial model, our aim was to characterise individual parameter contributions to arterial pressure a...

This paper aims to summarize and map contemporary views on some contentious aspects of arterial hemodynamics that have remained unresolved despite years of research. These were discussed during a workshop entitled Arterial hemodynamics: past, present and future held in London on June 14 and 15, 2016. To do this we formulated a list of potential con...

Objective: Breathing rate (BR) can be estimated by extracting respiratory signals from the electrocardiogram (ECG) or photoplethysmogram (PPG). The extracted respiratory signals may be influenced by several technical and physiological factors. In this study, our aim was to determine how technical and physiological factors influence the quality of...

Non-invasive assessment of haemodynamic data, such as pressure and flow profiles, is helpful in detecting cardiac disease at an early stage. However, current methods lack spatial accuracy and do not take local variations into account. This paper presents a software tool that extracts the arterial geometry and blood inflow profiles from MR images, w...

We tested the hypothesis that increased pulse wave reflection and altered backward waveform morphology contribute to increased pulse pressure in subjects with higher pulse pressure compared with lower pulse pressure and to actions of vasoactive drugs to increase pulse pressure. We examined the relationship of backward to forward wave morphology in...