Publications
477 results found
Malaweera ASN, Davies JE, Hadjiloizou N, et al., 2008, Peripheral pulsatile arterial pressure is determined by the central reservoir, which is similar across different arterial sites, Annual Scientific Conference of the British-Cardiovascular-Society/British-Society-for-Cardiovascular-Research, Publisher: B M J PUBLISHING GROUP, Pages: A114-A115, ISSN: 1355-6037
Davies JE, Whinnett ZI, Hadjiloizou N, et al., 2008, Microcirculatory-originating pressure predominantly determines coronary blood flow in humans: Evaluation using wave intensity analysis, Annual Scientific Conference of the British-Cardiovascular-Society/British-Society-for-Cardiovascular-Research, Publisher: B M J PUBLISHING GROUP, Pages: A121-+, ISSN: 1355-6037
Hughes AD, Davies JE, Francis D, et al., 2008, Peripheral augmentation index and wave reflection in the radial artery, HYPERTENSION, Vol: 51, Pages: E45-E46, ISSN: 0194-911X
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- Citations: 9
Evans J, Gratzer W, Mohandas N, et al., 2008, Fluctuations of the red blood cell membrane: Relation to mechanical properties and lack of ATP dependence, BIOPHYSICAL JOURNAL, Vol: 94, Pages: 4134-4144, ISSN: 0006-3495
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- Citations: 115
Aguado-Sierra J, Alastruey J, Wang J-J, et al., 2008, Separation of the reservoir and wave pressure and velocity from measurements at an arbitrary location in arteries, PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART H-JOURNAL OF ENGINEERING IN MEDICINE, Vol: 222, Pages: 403-416, ISSN: 0954-4119
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- Citations: 46
Downie SP, Raynor SM, Firmin DN, et al., 2008, Effects of elastic compression stockings on wall shear stress in deep and superficial veins of the calf, AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY, Vol: 294, Pages: H2112-H2120, ISSN: 0363-6135
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- Citations: 36
Davies JE, Hadjiloizou N, Manisty CH, et al., 2008, Evidence to support the role of the aortic reservoir via a direct mechanism in determination of the pressure waveform with ageing, 57th Annual Scientific Session of the American-College-of-Cardiology, Publisher: ELSEVIER SCIENCE INC, Pages: A339-A339, ISSN: 0735-1097
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- Citations: 3
Wang J-J, Shrive NG, Parker KH, et al., 2008, Effects of vasoconstriction and vasodilatation on LV and segmental circulatory energetics, AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY, Vol: 294, Pages: H1216-H1225, ISSN: 0363-6135
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- Citations: 13
Aguado-Sierra J, Davies JE, Hadjiloizou N, et al., 2008, Reservoir-wave separation and wave intensity analysis applied to carotid arteries: A hybrid 1D model to understand haemodynamics, Pages: 1381-1384
Pressure waveforms measured at different locations in the cardiovascular system present a very similar diastolic decay. Previous work has shown the cardiovascular system can be modelled as a Windkessel and wave system. This concept has been extended to any arbitrary location in the cardiovascular system. We suggest that it is possible to calculate a time-varying reservoir pressure P̄(t) and a distance- and time-varying wave pressure p(x, t) by fitting an exponential function to the diastolic decay of the measured pressure P; defining that the measured pressure P(x, i) = P̄(t)+p(x, t). Velocity waveforms U can also be separated into its reservoir, Ū, and wave, u, components as U(x, t) = Ū(x, t) +u(x, t). In this study we explore the implications of applying a reservoir-wave separation and wave intensity analysis techniques to understand the haemodynamics of in-vivo, noninvasive measurements of P and U in the carotid arteries of normal human subjects. Wave intensity analysis reveals a particular wave pattern where reflections can be estimated easily, but foremost, it shows that reflections are a lot smaller than previously thought. We suggest through the use of this model that the heart is the main wave generator of the cardiovascular system. The arterial system instead of impeding the flow, it stores it and distributes it throughout the arteries towards the tissue during diastole. There are some wave reflections, mainly during systole, that contribute to the changes in the pressure and velocity waveforms, however, they are small and are more evident as the measurements get further away from the ascending aorta. The application of wave intensity analysis to non-invasively measured data can provide a good insight on the physiology and the local and global properties of the cardiovascular system in health and disease in the clinical setting. This study shows preliminary results and the potential of the technique for analysing non-invasive measures, and could be particul
Alastruey J, Parker KH, Peiro J, et al., 2008, Lumped parameter outflow models for 1-D blood flow simulations: Effect on pulse waves and parameter estimation, Commun. Comput. Phys., Vol: 4, Pages: 317-336
Several lumped parameter, or zero-dimensional (0-D), models of the micro-circulation are coupled in the time domain to the nonlinear, one-dimensional (1-D) equations of blood flow in large arteries. A linear analysis of the coupled system, together with in-vivo observations, shows that: (i) an inflow resistance that matches the characteristic impedance of the terminal arteries is required to avoid non-physiological wave reflections; (ii) periodic mean pressures and flow distributions in large arteries depend on arterial and peripheral resistances, but not on the compliances and inertias of the system, which only affect instantaneous pressure and flow waveforms; (iii) peripheral inertias have a minor effect on pulse waveforms under normal conditions; and (iv) the time constant of the diastolic pressure decay is the same in any 1-D model artery, if viscous dissipation can be neglected in these arteries, and it depends on all the peripheral compliances and resistances of the system. Following this analysis, we propose an algorithm to accurately estimate peripheral resistances and compliances from in-vivo data. This algorithm is verified against numerical data simulated using a 1-D model network of the 55 largest human arteries, in which the parameters of the peripheral windkessel outflow models are known a-priori. Pressure and flow waveforms in the aorta and the first generation of bifurcations are reproduced with relative root-mean-square errors smaller than 3%.
Byrd-Raynor S, Alastruey J, Hughes A, et al., 2008, The relationship between velocity and cerebral resistance during vasomotor reactivity testing: Should we report a different measurement?, J. Vascular Ultrasound, Vol: 32, Pages: 67-74
Eftekhar A, Vohra F, Toumazou C, et al., 2008, Hilbert-Huang Transform: Preliminary studies in Epilepsy and Cardiac Arrhythmias, IEEE Biomedical Circuits and Systems Conference (BioCAS), Publisher: IEEE, Pages: 373-376
Alastruey J, Moore SM, Parker KH, et al., 2008, Reduced modelling of blood flow in the cerebral circulation: Coupling 1-D, 0-D and cerebral auto-regulation models, Int. J. Numer. Meth. Fluids, Vol: 56, Pages: 1061-1067
Harvey SLR, Coxon P, Bates D, et al., 2008, Metallic ring-disc microelectrode fabrication using inverted hollow cylindrical sputter coater., Sensors and Actuators B: Chemical, Vol: 129, Pages: 659-665
Hughes AD, Parker K, Davies J, 2008, Waves in arteries: A review of wave intensity analysis in the systemic and coronary circulations, Artery Research, Vol: 2, Pages: 51-59
The intermittent ejection of blood by the ventricle results in pulsatile pressure and flow waveforms in the circulation. Understanding and characterizing this pulsatile behaviour is attracting increasing clinical interest, as it may have important implications for risk prediction and the mechanisms of action of therapeutic agents. This review focuses on the theory and use of wave intensity analysis to analyse pulsatile waveforms in the arterial circulation with particular reference to the coronary circulation.
Aguado-Sierra J, Davies JE, Hadjiloizou N, et al., 2008, Reservoir-wave separation and wave intensity analysis applied to carotid arteries: a hybrid 1D model to understand haemodynamics., Annu Int Conf IEEE Eng Med Biol Soc, Vol: 2008, Pages: 1381-1384, ISSN: 2375-7477
Pressure waveforms measured at different locations in the cardiovascular system present a very similar diastolic decay. Previous work has shown the cardiovascular system can be modelled as a Windkessel and wave system. This concept has been extended to any arbitrary location in the cardiovascular system. We suggest that it is possible to calculate a time-varying reservoir pressure P(t) and a distance- and time-varying wave pressure p(x, t) by fitting an exponential function to the diastolic decay of the measured pressure P; defining that the measured pressure P(x, t) = P(t)+p(x, t). Velocity waveforms U can also be separated into its reservoir, U , and wave, u,components as U(x, t) = U (x, t) + u(x, t).In this study we explore the implications of applying are servoir-wave separation and wave intensity analysis techniques to understand the haemodynamics of in-vivo, noninvasive measurements of P and U in the carotid arteries of normal human subjects. Wave intensity analysis reveals a particular wave pattern where reflections can be estimated easily, but foremost, it shows that reflections are a lot smaller than previously thought.We suggest through the use of this model that the heart is the main wave generator of the cardiovascular system. The arterial system instead of impeding the flow, it stores it and distributes it throughout the arteries towards the tissue during diastole. There are some wave reflections, mainly during systole,that contribute to the changes in the pressure and velocity waveforms, however, they are small and are more evident as the measurements get further away from the ascending aorta.The application of wave intensity analysis to non-invasively measured data can provide a good insight on the physiology and the local and global properties of the cardiovascular system in health and disease in the clinical setting. This study shows preliminary results and the potential of the technique for analysing non-invasive measures, and could be particularly
Aguado-Sierra J, Davies JE, Hadjiloizou N, et al., 2008, Reservoir-wave separation and wave intensity analysis applied to carotid arteries: A hybrid 1D model to understand haemodynamics, 30th Annual International Conference of the IEEE-Engineering-in-Medicine-and-Biology-Society, Publisher: IEEE, Pages: 1381-+, ISSN: 1557-170X
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- Citations: 12
Khir AW, Swalen MJP, Feng J, et al., 2007, Simultaneous determination of wave speed and arrival time of reflected waves using the pressure-velocity loop, MEDICAL & BIOLOGICAL ENGINEERING & COMPUTING, Vol: 45, Pages: 1201-1210, ISSN: 0140-0118
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- Citations: 30
Malaweera ASN, Davies JE, Hadjiloizou N, et al., 2007, Pulsatile arterial pressure is predominantly determined by the aortic reservoir, which can be determined non-invasively from peripheral measurement sites, JOURNAL OF HUMAN HYPERTENSION, Vol: 21, Pages: 849-850, ISSN: 0950-9240
Davies JE, Francis DP, Hadjiloizou N, et al., 2007, Changes in arterial reservoir function, not wave reflection, account for the effect of ageing on pressure augmentation in the proximal aorta, JOURNAL OF HUMAN HYPERTENSION, Vol: 21, Pages: 848-848, ISSN: 0950-9240
Hadjiloizou N, Davies JE, Manisty CH, et al., 2007, Physiological mechansims underlying the differences in flow velocity in the left and right coronary arteries, EUROPEAN HEART JOURNAL, Vol: 28, Pages: 753-753, ISSN: 0195-668X
Curtis SL, Zambanini A, Mayet J, et al., 2007, Reduced systolic wave generation and increased peripheral wave reflection in chronic heart failure, AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY, Vol: 293, Pages: H557-H562, ISSN: 0363-6135
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- Citations: 66
Bowles CT, Van Loon R, Dreger SA, et al., 2007, Hydrodynamic evaluation of a bioreactor for tissueengineering heart valves, Conference of the Tissue-Engineering-and-Regenerative-Medicine-International-Society (TERMIS-EU), Publisher: MARY ANN LIEBERT INC, Pages: 1708-1708, ISSN: 1076-3279
Wang J-J, Parker KH, Shrive NG, et al., 2007, Predicting a reflection site from impedance analysis: Implications of the time-domain windkessel, Experimental Biology 2007 Annual Meeting, Publisher: FEDERATION AMER SOC EXP BIOL, Pages: A826-A827, ISSN: 0892-6638
Davies JE, Francis DP, Manisty CH, et al., 2007, A unifying explanation of the aortic pulse waveform in humans, 56th Annual Scientific Session of the American-College-of-Cardiology, Publisher: ELSEVIER SCIENCE INC, Pages: 397A-398A, ISSN: 0735-1097
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- Citations: 5
August E, Parker KH, Barahona M, 2007, A dynamical model of lipoprotein metabolism, BULLETIN OF MATHEMATICAL BIOLOGY, Vol: 69, Pages: {1233-1254}-{1233-1254}, ISSN: 0092-8240
We present a dynamical model of lipoprotein metabolism derived by combining a cascading process in the blood stream and cellular level regulatory dynamics. We analyse the existence and stability of equilibria and show that this low-dimensional, nonlinear model exhibits bistability between a low and a high cholesterol state. A sensitivity analysis indicates that the intracellular concentration of cholesterol is robust to parametric variations while the plasma cholesterol can vary widely. We show how the dynamical response to time-dependent inputs can be used to diagnose the state of the system. We also establish the connection between parameters in the system and medical and genetic conditions.
Martinez-Perez ME, Hughes AD, Thom SA, et al., 2007, Segmentation of blood vessels from red-free and fluorescein retinal images, MEDICAL IMAGE ANALYSIS, Vol: 11, Pages: 47-61, ISSN: 1361-8415
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- Citations: 319
Martinez-Perez ME, Hughes AD, Thom SA, et al., 2007, Improvement of a retinal blood vessel segmentation method using the Insight Segmentation and Registration Toolkit (ITK)., 29th Annual International Conference of the IEEE Engineering in Medicine and Biology Society., Pages: 892-895
Lee KE, Parker KH, Sherwin SJ, et al., 2007, The effects of geometrical configurations on steady flow in non-planar double bends, World Congress on Medical Physics and Biomedical Engineering, Publisher: SPRINGER-VERLAG BERLIN, Pages: 3461-+, ISSN: 1680-0737
Harvey SLR, Parker KH, O'Hare D, 2007, Developing a tissue perfusion sensor, 2007 ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY, VOLS 1-16, Pages: 2689-2692, ISSN: 1094-687X
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