Publications
477 results found
Knoops PG, Biglino G, Hughes AD, et al., 2016, A Mock Circulatory System Incorporating a Compliant 3D-Printed Anatomical Model to Investigate Pulmonary Hemodynamics., Artif Organs
A realistic mock circulatory system (MCS) could be a valuable in vitro testbed to study human circulatory hemodynamics. The objective of this study was to design a MCS replicating the pulmonary arterial circulation, incorporating an anatomically representative arterial model suitable for testing clinically relevant scenarios. A second objective of the study was to ensure the system's compatibility with magnetic resonance imaging (MRI) for additional measurements. A latex pulmonary arterial model with two generations of bifurcations was manufactured starting from a 3D-printed mold reconstructed from patient data. The model was incorporated into a MCS for in vitro hydrodynamic measurements. The setup was tested under physiological pulsatile flow conditions and results were evaluated using wave intensity analysis (WIA) to investigate waves traveling in the arterial system. Increased pulmonary vascular resistance (IPVR) was simulated as an example of one pathological scenario. Flow split between right and left pulmonary artery was found to be realistic (54 and 46%, respectively). No substantial difference in pressure waveform was observed throughout the various generations of bifurcations. Based on WIA, three main waves were identified in the main pulmonary artery (MPA), that is, forward compression wave, backward compression wave, and forward expansion wave. For IPVR, a rise in mean pressure was recorded in the MPA, within the clinical range of pulmonary arterial hypertension. The feasibility of using the MCS in the MRI scanner was demonstrated with the MCS running 2 h consecutively while acquiring preliminary MRI data. This study shows the development and verification of a pulmonary MCS, including an anatomically correct, compliant latex phantom. The setup can be useful to explore a wide range of hemodynamic questions, including the development of patient- and pathology-specific models, considering the ease and low cost of producing rapid prototyping molds, and the ve
Raphael CE, Cooper R, Parker KH, et al., 2016, Mechanisms of myocardial ischemia in hypertrophic cardiomyopathy: insights from wave intensity analysis and magnetic resonance, Journal of the American College of Cardiology, Vol: 68, Pages: 1651-1660, ISSN: 1558-3597
BACKGROUND: Angina is common in hypertrophic cardiomyopathy (HCM) and is associated with abnormal myocardial perfusion. Wave intensity analysis improves the understanding of the mechanics of myocardial ischemia. OBJECTIVES: Wave intensity analysis was used to describe the mechanisms underlying perfusion abnormalities in patients with HCM. METHODS: Simultaneous pressure and flow were measured in the proximal left anterior descending artery in 33 patients with HCM and 20 control patients at rest and during hyperemia, allowing calculation of wave intensity. Patients also underwent quantitative first-pass perfusion cardiac magnetic resonance to measure myocardial perfusion reserve. RESULTS: Patients with HCM had a lower coronary flow reserve than control subjects (1.9 ± 0.8 vs. 2.7 ± 0.9; p = 0.01). Coronary hemodynamics in HCM were characterized by a very large backward compression wave during systole (38 ± 11% vs. 21 ± 6%; p < 0.001) and a proportionately smaller backward expansion wave (27% ± 8% vs. 33 ± 6%; p = 0.006) compared with control subjects. Patients with severe left ventricular outflow tract obstruction had a bisferiens pressure waveform resulting in an additional proximally originating deceleration wave during systole. The proportion of waves acting to accelerate coronary flow increased with hyperemia, and the magnitude of change was proportional to the myocardial perfusion reserve (rho = 0.53; p < 0.01). CONCLUSIONS: Coronary flow in patients with HCM is deranged. Distally, compressive deformation of intramyocardial blood vessels during systole results in an abnormally large backward compression wave, whereas proximally, severe left ventricular outflow tract obstruction is associated with an additional deceleration wave. Perfusion abnormalities in HCM are not simply a consequence of supply/demand mismatch or remodeling of the intramyocardial blood vessels; th
Su J, Manisty C, Parker KH, et al., 2016, Wave intensity analysis in pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension, JOURNAL OF HUMAN HYPERTENSION, Vol: 30, Pages: 647-648, ISSN: 0950-9240
Sluyter JD, Hughes AD, Lowe A, et al., 2016, Different associations between beta-blockers and other antihypertensive medication combinations with brachial blood pressure and aortic waveform parameters, International Journal of Cardiology, Vol: 219, Pages: 257-263, ISSN: 1874-1754
BackgroundComparing the relationships of antihypertensive medications with brachial blood pressure (BP) and aortic waveform parameters may help clinicians to predict the effect on the latter in brachial BP-based antihypertensive therapy. We aimed to make such comparisons with new waveform measures and a wider range of antihypertensive regimens than examined previously.MethodsCross-sectional analysis of 2933 adults (61% male; aged 50–84 years): 1637 on antihypertensive treatment and 1296 untreated hypertensives. Sixteen medicine regimens of up to 4 combinations of drugs from 6 antihypertensive classes were analysed. Aortic systolic BP, augmentation index (AIx), excess pressure integral (EPI), backward pressure amplitude (Pb), reflection index (RI) and pulse wave velocity (PWV) were calculated from aortic pressure waveforms derived from suprasystolic brachial measurement.ResultsForest plots of single-drug class comparisons across regimens with the same number of drugs (for between 1- and 3-drug regimens) revealed that AIx, Pb, RI and/or loge(EPI) were higher (maximum difference = 5.6%, 2.2 mm Hg, 0.0192 and 0.13 loge(mm Hg ⋅ s), respectively) with the use of a beta-blocker compared with vasodilators and diuretics, despite no brachial systolic and diastolic BP differences. These differences were reduced (by 34–57%) or eliminated after adjustment for heart rate, and similar effects occurred when controlling for systolic ejection period or diastolic duration.ConclusionsBeta-blocker effects on brachial BP may overestimate effects on aortic waveform parameters. Compared to other antihypertensives, beta-blockers have weaker associations with wave reflection measures and EPI; this is predominantly due to influences on heart rate.
Aizawa K, Casanova F, Mawson D, et al., 2016, RESERVOIR-PRESSURE ANALYSIS IN TYPE 2 DIABETES INDIVIDUALS WITH CARDIOVASCULAR DISEASE, [PP.11.05] RESERVOIR-PRESSURE ANALYSIS IN TYPE 2 DIABETES INDIVIDUALS WITH CARDIOVASCULAR DISEASE, Publisher: LIPPINCOTT WILLIAMS & WILKINS, Pages: E178-E178, ISSN: 0263-6352
Gray RDM, Parker KH, Quail MA, et al., 2016, A method to implement the reservoir-wave hypothesis using phase-contrast magnetic resonance imaging, MethodsX, Vol: 3, Pages: 508-512, ISSN: 2215-0161
The reservoir-wave hypothesis states that the blood pressure waveform can be usefully divided into a “reservoir pressure” related to the global compliance and resistance of the arterial system, and an “excess pressure” that depends on local conditions. The formulation of the reservoir-wave hypothesis applied to the area waveform is shown, and the analysis is applied to area and velocity data from high-resolution phase-contrast cardiovascular magnetic resonance (CMR) imaging. A validation study shows the success of the principle, with the method producing largely robust and physically reasonable parameters, and the linear relationship between flow and wave pressure seen in the traditional pressure formulation is retained. The method was successfully tested on a cohort of 20 subjects (age range: 20–74 years; 17 males).This paper:•Demonstrates the feasibility of deriving reservoir data non-invasively from CMR.•Includes a validation cohort (CMR data).•Suggests clinical applications of the method.
Li Y, Parker KH, Khir AW, 2016, Using wave intensity analysis to determine local reflection coefficient in flexible tubes, Journal of Biomechanics, Vol: 49, Pages: 2709-2717, ISSN: 1873-2380
It has been shown that reflected waves affect the shape and magnitude of the arterial pressure waveform, and that reflected waves have physiological and clinical prognostic values. In general the reflection coefficient is defined as the ratio of the energy of the reflected to the incident wave. Since pressure has the units of energy per unit volume, arterial reflection coefficient are traditionally defined as the ratio of reflected to the incident pressure. We demonstrate that this approach maybe prone to inaccuracies when applied locally. One of the main objectives of this work is to examine the possibility of using wave intensity, which has units of energy flux per unit area, to determine the reflection coefficient. We used an in vitro experimental setting with a single inlet tube joined to a second tube with different properties to form a single reflection site. The second tube was long enough to ensure that reflections from its outlet did not obscure the interactions of the initial wave. We generated an approximately half sinusoidal wave at the inlet of the tube and took measurements of pressure and flow along the tube. We calculated the reflection coefficient using wave intensity (RdI and RdI(0.5)) and wave energy (RI and RI(0.5)) as well as the measured pressure (RdP) and compared these results with the reflection coefficient calculated theoretically based on the mechanical properties of the tubes. The experimental results show that the reflection coefficients determined by all the techniques we studied increased or decreased with distance from the reflection site, depending on the type of reflection. In our experiments, RdP, RdI(0.5) and RI(0.5) are the most reliable parameters to measure the mean reflection coefficient, whilst RdI and RI provide the best measure of the local reflection coefficient, closest to the reflection site. Additional work with bifurcations, tapered tubes and in vivo experiments are needed to further understand, validate the method and
Torii R, Parker KH, Yacoub MH, 2016, Importance of Stress Mapping of Aortic Wall in Aortic Valve Disease., Journal of the American College of Cardiology, Vol: 67, Pages: 1755-1756, ISSN: 1558-3597
Broyd CJ, Nijjer S, Sen S, et al., 2016, Estimation of coronary wave intensity analysis using noninvasive techniques and its application to exercise physiology, AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY, Vol: 310, Pages: H619-H627, ISSN: 0363-6135
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- Citations: 11
Narayan O, Davies JE, Hughes AD, et al., 2015, Central aortic reservoir-wave analysis improves prediction of cardio-vascular events in elderly hypertensives (vol 65, pg 629, 2015), HYPERTENSION, Vol: 66, Pages: E28-E28, ISSN: 0194-911X
Noor MR, Ho CH, Parker KH, et al., 2015, Investigation of the Characteristics of HeartWare HVAD and Thoratec HeartMate II Under Steady and Pulsatile Flow Conditions, Artificial Organs, Vol: 40, Pages: 549-560, ISSN: 1525-1594
Keegan J, Raphael CE, Parker K, et al., 2015, Validation of high temporal resolution spiral phase velocity mapping of temporal patterns of left and right coronary artery blood flow against Doppler guidewire, Journal of Cardiovascular Magnetic Resonance, Vol: 17, ISSN: 1532-429X
Background: Temporal patterns of coronary blood flow velocity can provide important information on disease state and are currently assessed invasively using a Doppler guidewire. A non-invasive alternative would be beneficial as it would allow study of a wider patient population and serial scanning. Methods: A retrospectively-gated breath-hold spiral phase velocity mapping sequence (TR 19 ms) was developed at 3 Tesla. Velocity maps were acquired in 8 proximal right and 15 proximal left coronary arteries of 18 subjects who had previously had a Doppler guidewire study at the time of coronary angiography. Cardiovascular magnetic resonance (CMR) velocity-time curves were processed semi-automatically and compared with corresponding invasive Doppler data. Results: When corrected for differences in heart rate between the two studies, CMR mean velocity through the cardiac cycle, peak systolic velocity (PSV) and peak diastolic velocity (PDV) were approximately 40 % of the peak Doppler values with a moderate - good linear relationship between the two techniques (R<sup>2</sup>: 0.57, 0.64 and 0.79 respectively). CMR values of PDV/PSV showed a strong linear relationship with Doppler values with a slope close to unity (0.89 and 0.90 for right and left arteries respectively). In individual vessels, plots of CMR velocities at all cardiac phases against corresponding Doppler velocities showed a consistent linear relationship between the two with high R<sup>2</sup> values (mean +/-SD: 0.79 +/-.13). Conclusions: High temporal resolution breath-hold spiral phase velocity mapping underestimates absolute values of coronary flow velocity but allows accurate assessment of the temporal patterns of blood flow.
Broyd CJ, Davies JE, Escaned JE, et al., 2015, Wave intensity analysis and its application to the coronary circulation, Global Cardiology Science and Practice, Vol: 2015
Wave intensity analysis (WIA) is a technique developed from the field of gas dynamics that is now being applied to assess cardiovascular physiology. It allows quantification of the forces acting to alter flow and pressure within a fluid system, and as such it is highly insightful in ascribing cause to dynamic blood pressure or velocity changes. When co-incident waves arrive at the same spatial location they exert either counteracting or summative effects on flow and pressure. WIA however allows waves of different origins to be measured uninfluenced by other simultaneously arriving waves. It therefore has found particular applicability within the coronary circulation where both proximal (aortic) and distal (myocardial) ends of the coronary artery can markedly influence blood flow. Using these concepts, a repeating pattern of 6 waves has been consistently identified within the coronary arteries, 3 originating proximally and 3 distally. Each has been associated with a particular part of the cardiac cycle. The most clinically relevant wave to date is the backward decompression wave, which causes the marked increase in coronary flow velocity observed at the start of the diastole. It has been proposed that this wave is generated by the elastic re-expansion of the intra-myocardial blood vessels that are compressed during systolic contraction. Particularly by quantifying this wave, WIA has been used to provide mechanistic and prognostic insight into a number of conditions including aortic stenosis, left ventricular hypertrophy, coronary artery disease and heart failure. It has proven itself to be highly sensitive and as such a number of novel research directions are encouraged where further insights would be beneficial.
Davies JE, Hughes AD, Parker KH, 2015, Errors of Fact in the Recent Article by Westerhof, Segers, and Westerhof, HYPERTENSION, Vol: 66, Pages: E26-E26, ISSN: 0194-911X
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- Citations: 2
Baksi AJ, Davies JE, Hadjiloizou N, et al., 2015, Attenuation of reflected waves in man during retrograde propagation from femoral artery to proximal aorta, International Journal of Cardiology, Vol: 202, Pages: 441-445, ISSN: 1874-1754
BackgroundWave reflection may be an important influence on blood pressure, but the extent to which reflections undergo attenuation during retrograde propagation has not been studied. We quantified retrograde transmission of a reflected wave created by occlusion of the left femoral artery in man.Methods20 subjects (age 31–83 years; 14 male) underwent invasive measurement of pressure and flow velocity with a sensor-tipped intra-arterial wire at multiple locations distal to the proximal aorta before, during and following occlusion of the left femoral artery by thigh cuff inflation. A numerical model of the circulation was also used to predict reflected wave transmission. Wave reflection was measured as the ratio of backward to forward wave energy (WRI) and the ratio of peak backward to forward pressure (Pb/Pf).ResultsCuff inflation caused a marked reflection which was largest at 5–10 cm from the cuff (change (Δ) in WRI = 0.50 (95% CI 0.38, 0.62); p < 0.001, ΔPb/Pf = 0.23 (0.18–0.29); p < 0.001). The magnitude of the cuff-induced reflection decreased progressively at more proximal locations and was barely discernible at sites > 40 cm from the cuff including in the proximal aorta. Numerical modelling gave similar predictions to those observed experimentally.ConclusionsReflections due to femoral artery occlusion are markedly attenuated by the time they reach the proximal aorta. This is due to impedance mismatches of bifurcations traversed in the backward direction. This degree of attenuation is inconsistent with the idea of a large discrete reflected wave arising from the lower limb and propagating back into the aorta.
Narayan O, Davies JE, Hughes AD, et al., 2015, An increase in peak excess pressure accounts for the rise in systolic blood pressure along the aorta, Congress of the European-Society-of-Cardiology (ESC), Publisher: OXFORD UNIV PRESS, Pages: 845-845, ISSN: 0195-668X
Gavriel C, Parker K, Faisal A, 2015, Smartphone as an ultra-low cost medical tricorder for real-time cardiological measurements via ballistocardiography, IEEE Body Sensor Network Conference 2015
In this preliminary study, we investigate the potential use of smartphones as portable heart-monitoring devices that can capture and analyse heart activity in real time. We have developed a smartphone application called "Medical Tricorder" that can exploit smartphone's inertial sensors and when placed on a subject's chest, it can efficiently capture the motion patterns caused by the mechanical activity of the heart. Using the measured ballistocardiograph signal (BCG), the application can efficiently extract the heart rate in real time while matching the performance of clinical-grade electrocardiographs (ECG). Although the BCG signal can provide much richer information regarding the mechanical aspects of the human heart, we have developed a method of mapping the chest BCG signal into an ECG signal, which can be made directly available to clinicians for diagnostics. Comparing the estimated ECG signal to empirical data from cardiovascular diseases, may allow detection of heart abnormalities at a very early stage without any medical staff involvement. Our method opens up the potential of turning smartphones into portable healthcare systems which can provide patients and general public an easy access to continuous healthcare monitoring. Additionally, given that our solution is mainly software based, it can be deployed on smartphones around the world with minimal costs.
Tyberg JV, Bouwmeester JC, Burrowes LM, et al., 2015, A new teaching model of the systemic circulation that incorporates reservoir characteristics, ARTERY RESEARCH, Vol: 10, Pages: 38-41, ISSN: 1872-9312
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- Citations: 2
Narayan O, Davies J, Hughes A, et al., 2015, THE SYSTOLIC RATE CONSTANT (KS) IS PREDICTIVE OF CARDIOVASCULAR OUTCOMES IN THE ANBP2 AORTIC MECHANICS STUDY, Scientific Session of the American-College-of-Cardiology (ACC), Publisher: ELSEVIER SCIENCE INC, Pages: A1430-A1430, ISSN: 0735-1097
Raphael CE, Cooper R, Keegan J, et al., 2015, IMPACT OF LEFT VENTRICULAR OUTFLOW TRACT OBSTRUCTION AND MICROCIRCULATORY DYSFUNCTION ON CORONARY HAEMODYNAMICS IN HYPERTROPHIC CARDIOMYOPATHY, Scientific Session of the American-College-of-Cardiology (ACC), Publisher: ELSEVIER SCIENCE INC, Pages: A952-A952, ISSN: 0735-1097
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- Citations: 3
Borlotti A, Park C, Parker KH, et al., 2015, Reservoir and reservoir-less pressure effects on arterial waves in the canine aorta, JOURNAL OF HYPERTENSION, Vol: 33, Pages: 564-574, ISSN: 0263-6352
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- Citations: 7
Narayan O, Davies JE, Hughes AD, et al., 2015, Central Aortic Reservoir-Wave Analysis Improves Prediction of Cardiovascular Events in Elderly Hypertensives, HYPERTENSION, Vol: 65, Pages: 629-U287, ISSN: 0194-911X
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- Citations: 38
Clavica F, Parker KH, Khir AW, 2015, Wave intensity analysis in air-filled flexible vessels, JOURNAL OF BIOMECHANICS, Vol: 48, Pages: 687-694, ISSN: 0021-9290
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- Citations: 1
Raphael CE, Hsu LY, Greve AM, et al., 2015, Wave intensity analysis and assessment of myocardial perfusion abnormalities in patients with hypertrophic cardiomyopathy, Journal of Cardiovascular Magnetic Resonance, Vol: 17, ISSN: 1097-6647
Keegan J, Raphael CE, Simpson R, et al., 2015, Validation of high temporal resolution spiral phase velocity mapping of coronary artery blood flow against Doppler flow wire, Journal of Cardiovascular Magnetic Resonance, Pages: 1-3, ISSN: 1097-6647
Morad S, Ulbricht C, Harkin P, et al., 2015, Modelling and control of a water jet cutting probe for flexible surgical robot, IEEE International Conference on Automation Science and Engineering (CASE), Publisher: IEEE, Pages: 1159-1164, ISSN: 2161-8070
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- Citations: 3
Biglino G, Ntsinjana H, Plymen C, et al., 2014, Ventriculovascular interactions late after atrial and arterial repair of transposition of the great arteries, JOURNAL OF THORACIC AND CARDIOVASCULAR SURGERY, Vol: 148, Pages: 2627-2633, ISSN: 0022-5223
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- Citations: 9
Dhutia NM, Cole GD, Zolgharni M, et al., 2014, Automated speckle tracking algorithm to aid on-axis imaging in echocardiography, Journal of Medical Imaging, Vol: 1, ISSN: 2329-4310
Obtaining a "correct" view in echocardiography is a subjective process in which an operator attempts to obtain images conforming to consensus standard views. Real-time objective quantification of image alignment may assist less experienced operators, but no reliable index yet exists. We present a fully automated algorithm for detecting incorrect medial/lateral translation of an ultrasound probe by image analysis. The ability of the algorithm to distinguish optimal from sub-optimal four-chamber images was compared to that of specialists-the current "gold-standard." The orientation assessments produced by the automated algorithm correlated well with consensus visual assessments of the specialists ([Formula: see text]) and compared favourably with the correlation between individual specialists and the consensus, [Formula: see text]. Each individual specialist's assessments were within the consensus of other specialists, [Formula: see text] of the time, and the algorithm's assessments were within the consensus of specialists 85% of the time. The mean discrepancy in probe translation values between individual specialists and their consensus was [Formula: see text], and between the automated algorithm and specialists' consensus was [Formula: see text]. This technology could be incorporated into hardware to provide real-time guidance for image optimisation-a potentially valuable tool both for training and quality control.
Tyberg JV, Bouwmeester JC, Parker KH, et al., 2014, Clinical characteristics, treatment and survival in patients with systolic heart failure - Comparative assessment of a Chinese and a German cohort Response, INTERNATIONAL JOURNAL OF CARDIOLOGY, Vol: 176, Pages: 1391-1391, ISSN: 0167-5273
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- Citations: 4
Davies JE, Lacy P, Tillin T, et al., 2014, Excess Pressure Integral Predicts Cardiovascular Events Independent of Other Risk Factors in the Conduit Artery Functional Evaluation Substudy of Anglo-Scandinavian Cardiac Outcomes Trial, HYPERTENSION, Vol: 64, Pages: 60-68, ISSN: 0194-911X
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- Citations: 73
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