Publications
476 results found
Francis N, Hosny M, Yacoub MH, et al., 2023, Asymmetry of flow in aortic root and its application in hypertrophic obstructive cardiomyopathy., J Appl Physiol (1985), Vol: 135, Pages: 840-848
The aortic root (AR) performs sophisticated functions regulating the blood dynamics during the cardiac cycle. Such complex function depends on the nature of flow in the AR. Here, we investigate the potential of new quantitative parameters of flow asymmetry that could have clinical implications. We developed a MATLAB program to study the AR hemodynamics in each sinus of Valsalva using two-dimensional (2-D) cardiac magnetic resonance imaging during systole and particularly at peak systolic flow in 13 healthy volunteers and compared with 10 patients with hypertrophic obstructive cardiomyopathy (HOCM). We show that the effective area of the aortic jet in healthy volunteers is significantly higher at peak systolic flow and on average during systole. The flow asymmetry index, indicating how the jet is skewed away from the left coronary sinus (LCS), is small in healthy volunteers and much larger in HOCM at peak systole. The average of this index over systole is significantly more different between cohorts. Looking in more detail at the flow in the sinuses during systole, we show that the AR jet in healthy volunteers is more symmetrical, affecting the three sinuses almost equally, unlike the asymmetric AR jet in patients with HOCM that has decreased flow rate in the LCS and increased fractional area of backward flow in the LCS. The percentage of backward flow in the sinuses of Valsalva calculated over systole is a potential indicator of perturbed AR hemodynamics and the distribution of vortical flow and could be used as a measure of flow asymmetry.NEW & NOTEWORTHY The aortic root is a vital organ responsible for performing sophisticated functions to regulate the blood flow dynamics during the cardiac cycle. Such synchronized complex performance affects and is affected by the flow symmetry and type of flow reaching the aorta. Here, we report flow asymmetry in the aortic root which could have clinical implications, and we investigate the potential of various quantitative
El-Nashar H, Sabry M, Tseng Y-T, et al., 2023, Multiscale Structure and Function of the Aortic Valve Apparatus., Physiol Rev
While studying the aortic valve in isolation has facilitated the development of life-saving procedures and technologies, the dynamic interplay of the aortic valve and its surrounding structures is vital to preserving their function across the wide range of conditions encountered in an active lifestyle. Our view is that these structures should be viewed as an integrated functional unit, herein referred to as the aortic valve apparatus (AVA). The coupling of the aortic valve and root, left ventricular outflow tract, and blood circulation is crucial for AVA's functions: unidirectional flow out of the left ventricle, coronary perfusion, reservoir function, and supporting left ventricular function. In this review, we explore the multiscale biological and physical phenomena that underly the simultaneous fulfilment of these functions. A brief overview of the tools used to investigate the AVA is included, such as: medical imaging modalities, experimental methods, and computational modelling, specifically fluid-structure interaction (FSI) simulations, is included. Some pathologies affecting the AVA are explored, and insights are provided on treatments and interventions that aim to maintain quality of life. The concepts explained in this paper support the idea of AVA being an integrated functional unit and help identify unanswered research questions. Incorporating phenomena through the molecular, micro, meso and whole tissue scales is crucial for understanding the sophisticated normal functions and diseases of the AVA.
Martinez-Perez ME, Hughes AD, Thom SAM, et al., 2023, Evaluation of a portable retinal imaging device: towards a comparative quantitative analysis for morphological measurements of retinal blood vessels, ROYAL SOCIETY OPEN SCIENCE, Vol: 10, ISSN: 2054-5703
Aizawa K, Thompson C, Hughes AD, et al., 2023, EFFECTS OF 2-WEEK DIETARY NITRATE SUPPLEMENTATION AND ANTIBACTERIAL MOUTHWASH TREATMENT ON RESERVOIR-EXCESS PRESSURE PARAMETERS IN HEALTHY OLDER ADULTS, Publisher: LIPPINCOTT WILLIAMS & WILKINS, Pages: E60-E60, ISSN: 0263-6352
Aizawa K, Hughes AD, Casanova F, et al., 2022, Reservoir Pressure Integral Is Independently Associated With the Reduction in Renal Function in Older Adults, HYPERTENSION, Vol: 79, Pages: 2364-2372, ISSN: 0194-911X
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Weinberg PDD, Schroter RCC, Parker KHH, et al., 2022, In Memoriam: Colin Caro 1925-2022, JOURNAL OF BIOMECHANICAL ENGINEERING-TRANSACTIONS OF THE ASME, Vol: 144, ISSN: 0148-0731
Parker KH, de Tombe P, van der Velden J, et al., 2022, The nature of waves in the arteries in memoriam: Nico Westerhof and John Tyberg, JOURNAL OF PHYSIOLOGY-LONDON, Vol: 600, Pages: 4045-4050, ISSN: 0022-3751
Palombo C, Kozakova M, Morizzo C, et al., 2022, Carotid reservoir pressure decrease after prolonged head down tilt bed rest in young healthy subjects is associated with reduction in left ventricular ejection time and diastolic length (vol 13, 866045, 2022), FRONTIERS IN PHYSIOLOGY, Vol: 13
Jordan AN, Aizawa K, Gooding KM, et al., 2022, ARTERIAL HAEMODYNAMIC PARAMETERS LINKED TO ARTERIAL PULSATILITY, EXCESS WAVE PROPAGATION AND COGNITIVE FUNCTION, Journal of hypertension, Vol: 40
OBJECTIVE: Hypertension is associated with the development of cognitive impairment and dementia in an ageing population. Aortic stiffness and alterations in central artery haemodynamics could intensify the penetration of excess wave energy into the cerebral circulation, damaging the microvasculature in addition to age-associated vascular changes. We aimed to determine whether haemodynamic parameters linked to arterial pulsatility and excess wave propagation was associated with cognitive function in a sample of normotensive and hypertensive individuals. DESIGN AND METHOD: We studied 35 treatment-naïve patients with stage II/III hypertension (HT: 63.8 ± 7.4yrs, 19F, SBP 175.6 ± 16.8 mmHg) and 35 age-, sex- and body mass index-matched normotensive individuals (NT: SBP 127.2 ± 8.2 mmHg). Indices of excess pressure including excess pressure integral (INTXSP) and peak excess pressure (MAXXSP) were obtained by radial artery tonometry. Aortic forward compression wave intensity (FCWI) and aortic pulse wave velocity (aPWV) were estimated as proposed by Hughes et al (Front Physiol. 2020). A battery of cognitive examination tests was administered including Addenbrooke's Cognitive Examination-III (ACE), Mini-Mental State Examination (MMSE), Trail making test part A (TMT-A) and B (TMT-B). RESULTS: Both INTXSP (9.2 ± 2.7 vs 5.4 ± 1.2 mmHg s) and MAXXSP (54.1 ± 12.8 vs 33.4 ± 5.9 mmHg) were significantly higher in HT compared to NT (p < 0.001). Additionally, FCWI [14.9 (12.0-20.0) vs 8.0 (6.8-9.3) x105 W/m2] and aPWV (7.2 ± 1.7 vs 4.5 ± 0.8 m/s) were significantly greater in HT compared with NT (p < 0.001). Higher INTXSP was associated with poorer ACE (rs = -0.310, p = 0.009), longer TMT-A (r = 0.409, p < 0.001) and TMT-B (r = 0.380, p = 0.001). Similarly, higher MAXXSP was associated with poorer ACE (rs = -0.343, p = 0.004), longer TMT-A (r = 0.397, p = 0.001) and TMT-B (r = 0.330, p = 0.006), and greater
To C, Aizawa K, Gates PE, et al., 2022, SHORT-TERM HIGH SALT INTAKE ADVERSELY AFFECTS PARAMETERS DERIVED FROM RESERVOIR-EXCESS PRESSURE ANALYSIS AND CENTRAL ARTERY HAEMODYNAMICS IN OVERWEIGHT/OBESE ADULTS, Journal of hypertension, Vol: 40
OBJECTIVE: The association between high salt intake and blood pressure is well-recognised. In overweight/obese individuals, obesity-associated hyperinsulinaemia augments renal sodium reabsorption and in combination with high salt intake this may alter blood pressure and arterial haemodynamics. We determined whether short-term high salt intake altered reservoir-excess pressure and central artery haemodynamic parameters in overweight/obese individuals. DESIGN AND METHOD: We studied 15 middle-aged and older adults (59.3 ± 6.4 yrs, 5F) who were overweight/obese with elevated systolic blood pressure (130 < SBP < 159 mmHg). In a double-blind cross-over design, they were randomly assigned to seven days of low salt diet (LSD: 50 mmol/day) or high salt intake (HIS: LSD with 200 mmol/day of sodium tablets) separated by a two-week washout period. The parameters derived from reservoir-excess pressure analysis including reservoir pressure integral, peak reservoir pressure (MAXPR), excess pressure integral (INTXSP), peak excess pressure (MAXXSP), systolic rate constant and diastolic rate constant (DRC) were obtained by radial artery tonometry. Additionally central artery haemodynamic parameters including aortic systolic pressure (aSBP), diastolic pressure (aDBP), pulse pressure (aPP) and subendocardial viability index (SVI) were derived from ensemble-averaged radial pulse waveform using generalised transfer function. Aortic pulse wave velocity (aPWV) was estimated as proposed by Hughes et al (Front Physiol. 2020). RESULTS: MAXPR (111.0 ± 10.9 vs 105.4 ± 10.4 mmHg), MAXXSP (41.7 ± 12.0 vs 36.6 ± 5.7 mmHg) and DRC (2.0 ± 0.4 vs 1.8 ± 0.3 s-1) were higher following HIS compared to LSD (p < 0.05). There was no convincing evidence that INTXSP was greater following HIS than LSD (6.9 ± 3.2 vs 5.8 ± 1.6 mmHg s, p = 0.055). aSBP (126.3 ± 15.4 vs 117.6 ± 10.1 mmHg), aDBP (76.3 ± 6.2 vs 73.1 ±
To C, Aizawa K, Gates PE, et al., 2022, SHORT-TERM HIGH SALT INTAKE ADVERSELY AFFECTS PARAMETERS DERIVED FROM RESERVOIR-EXCESS PRESSURE ANALYSIS AND CENTRAL ARTERY HAEMODYNAMICS IN OVERWEIGHT/OBESE ADULTS, 31st Annual Scientific Meeting of the European-Society-of-Hypertension (ESH) on Hypertension and Cardiovascular Protection, Publisher: LIPPINCOTT WILLIAMS & WILKINS, Pages: E259-E259, ISSN: 0263-6352
To C, Aizawa K, Gates PE, et al., 2022, SHORT-TERM HIGH SALT INTAKE ADVERSELY AFFECTS PARAMETERS DERIVED FROM RESERVOIR-EXCESS PRESSURE ANALYSIS AND CENTRAL ARTERY HAEMODYNAMICS IN OVERWEIGHT/OBESE ADULTS, 31st Annual Scientific Meeting of the European-Society-of-Hypertension (ESH) on Hypertension and Cardiovascular Protection, Publisher: LIPPINCOTT WILLIAMS & WILKINS, Pages: E259-E259, ISSN: 0263-6352
Jordan AN, Aizawa K, Gooding KM, et al., 2022, ARTERIAL HAEMODYNAMIC PARAMETERS LINKED TO ARTERIAL PULSATILITY, EXCESS WAVE PROPAGATION AND COGNITIVE FUNCTION, 31st Annual Scientific Meeting of the European-Society-of-Hypertension (ESH) on Hypertension and Cardiovascular Protection, Publisher: LIPPINCOTT WILLIAMS & WILKINS, Pages: E259-E259, ISSN: 0263-6352
Jordan AN, Aizawa K, Gooding KM, et al., 2022, ARTERIAL HAEMODYNAMIC PARAMETERS LINKED TO ARTERIAL PULSATILITY, EXCESS WAVE PROPAGATION AND COGNITIVE FUNCTION, 31st Annual Scientific Meeting of the European-Society-of-Hypertension (ESH) on Hypertension and Cardiovascular Protection, Publisher: LIPPINCOTT WILLIAMS & WILKINS, Pages: E259-E259, ISSN: 0263-6352
Palombo C, Kozakova M, Morizzo C, et al., 2022, Carotid Reservoir Pressure Decrease After Prolonged Head Down Tilt Bed Rest in Young Healthy Subjects Is Associated With Reduction in Left Ventricular Ejection Time and Diastolic Length, FRONTIERS IN PHYSIOLOGY, Vol: 13
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- Citations: 2
Ratneswaren A, Hadjiloizou N, Ahmad Y, et al., 2021, Coronary haemodynamics associated with left ventricular hypertrophy in aortic stenosis and hypertension, Publisher: OXFORD UNIV PRESS, Pages: 1728-1728, ISSN: 0195-668X
Francis N, Selwanos PP, Yacoub MH, et al., 2021, The Use of Maximum Entropy to Enhance Wave Intensity Analysis: An Application to Coronary Arteries in Hypertrophic Obstructive Cardiomyopathy, FRONTIERS IN CARDIOVASCULAR MEDICINE, Vol: 8, ISSN: 2297-055X
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- Citations: 1
Aizawa K, Casanova F, Gates PE, et al., 2021, Reservoir-Excess Pressure Parameters Independently Predict Cardiovascular Events in Individuals With Type 2 Diabetes, HYPERTENSION, Vol: 78, Pages: 40-50, ISSN: 0194-911X
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- Citations: 2
Ramakrishnan A, Hadjiloizou N, Ahmad Y, et al., 2021, DIFFERENTIAL EFFECTS OF LEFT VENTRICULAR HYPERTROPHY ON CORONARY HAEMODYNAMICS IN AORTIC STENOSIS AND HYPERTENSION, Virtual Annual Conference of the British-Cardiovascular-Society - Cardiology and the Environment, Publisher: BMJ PUBLISHING GROUP, Pages: A1-A2, ISSN: 1355-6037
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- Citations: 1
Aizawa K, Casanova F, Mawson DM, et al., 2021, ELEVATED EXCESS PRESSURE INTEGRAL IS ASSOCIATED WITH VASCULAR BIOMARKERS OF SUBCLINICAL ATHEROSCLEROSIS IN OLDER ADULTS, Publisher: LIPPINCOTT WILLIAMS & WILKINS, Pages: E314-E314, ISSN: 0263-6352
Hughes AD, Parker KH, 2020, The modified arterial reservoir: An update with consideration of asymptotic pressure (<i>P<sub>∞</sub></i>) and zero-flow pressure (<i>P<sub>zf</sub></i>), PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART H-JOURNAL OF ENGINEERING IN MEDICINE, Vol: 234, Pages: 1288-1299, ISSN: 0954-4119
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- Citations: 12
Abou Gamrah M, Xu J, El Sawy A, et al., 2020, Mechanics of the dicrotic notch: An acceleration hypothesis, PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART H-JOURNAL OF ENGINEERING IN MEDICINE, Vol: 234, Pages: 1253-1259, ISSN: 0954-4119
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- Citations: 6
Morad S, Ulbricht C, Harkin P, et al., 2020, Surgical Robot Platform with a Novel Concentric Joint for Minimally Invasive Procedures, Journal of Medical Robotics Research, Vol: 5, ISSN: 2424-9068
In this paper, a surgical robot platform with a novel concentric connector joint (CCJ) is presented. The surgical robot is a parallel robot platform comprised of multiple struts, arranged in a geometrically stable array, connected at their end points via the CCJ. The CCJ joints have near-perfect concentricity of rotation around the node point, which enables the tension and compression forces of the struts to be resolved in a structurally-efficient manner. The preliminary feasibility tests, modeling and simulations were introduced.
Bowles AJ, Fowler GD, O'Sullivan C, et al., 2020, Sustainable rubber recycling from waste tyres by waterjet: A novel mechanistic and practical analysis, Sustainable Materials and Technologies, Vol: 25, Pages: 1-15, ISSN: 2214-9937
Production and disposal of car tyres are major contributors to environmental damage. The first stage in tyre rubber recycling is granulation to smaller particle sizes. The sub-optimal physical, mechanical and chemical properties of mechanically ground tyre rubber (GTR) when incorporated into recycled blends are major obstacles to wider use of this potentially sustainable, recovered resource. Consequently, newly manufactured tyres contain less than 5% recycled material. This study compares two types of GTR product: mechanically ground crumb (MGC) and ultrahigh pressure waterjet-produced rubber crumb (WJC). A novel image analysis method showed that when the two particle types were compared, MGC was associated with both greater convexity and sphericity: the geometric mean ratio of MGC/WJC sphericity was 1.67. When part-recycled rubber blends comprising 30% crumb of particle size < 300 μm were compared to virgin polymer, the WJC blend exhibited superior mechanical properties to the MGC blend. These results can be explained by the higher surface area to volume ratio of WJC when compared to MGC which results in strong bonding in new blends using WJC. Further analysis by scanning electron microscopy (SEM) elucidated significant shape and textural variation within the WJC sample, allowing grouping into two sub-categories: “W1” which comprises particles with complex geometries, and “W2” particles which have a relatively simple topology that is similar to MGC. Maximising the W1:W2 particle ratio is likely to be crucial to the optimisation of output quality in the WJC process, and so a composite model is proposed that unifies three well-established fluid effects: brittle fracturing, impact cratering and cavitation. Impact cratering and cavitation effects should be maximised by altering process parameters with the aim of producing a higher proportion of crumb with a more irregular surface morphology to achieve better bonding properties in recycled
Bhuva AN, D'Silva A, Torlasco C, et al., 2020, Non-invasive assessment of ventriculo-arterial coupling using aortic wave intensity analysis combining central blood pressure and phase-contrast cardiovascular magnetic resonance, EUROPEAN HEART JOURNAL-CARDIOVASCULAR IMAGING, Vol: 21, Pages: 805-813, ISSN: 2047-2404
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- Citations: 10
Michail M, Hughes AD, Comella A, et al., 2020, Acute Effects of Transcatheter Aortic Valve Replacement on Central Aortic Hemodynamics in Patients With Severe Aortic Stenosis, HYPERTENSION, Vol: 75, Pages: 1557-1564, ISSN: 0194-911X
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- Citations: 9
Hughes AD, Park C, Ramakrishnan A, et al., 2020, Feasibility of estimation of aortic wave intensity using non-invasive pressure recordings in the absence of flow velocity in man, Frontiers in Physiology, Vol: 11, Pages: 1-9, ISSN: 1664-042X
Background: Wave intensity analysis provides valuable information on ventriculo-arterial function, hemodynamics, and energy transfer in the arterial circulation. Widespread use of wave intensity analysis is limited by the need for concurrent measurement of pressure and flow waveforms. We describe a method that can estimate wave intensity patterns using only non-invasive pressure waveforms (pWIA).Methods: Radial artery pressure and left ventricular outflow tract (LVOT) flow velocity waveforms were recorded in 12 participants in the Southall and Brent Revisited (SABRE) study. Pressure waveforms were analyzed using custom-written software to derive the excess pressure (Pxs) which was scaled to peak LVOT velocity and used to calculate wave intensity. These data were compared with wave intensity calculated using the measured LVOT flow velocity waveform. In a separate study, repeat measures of pWIA were performed on 34 individuals who attended two clinic visits at an interval of ≈1 month to assess reproducibility and reliability of the method.Results: Pxs waveforms were similar in shape to aortic flow velocity waveforms and the time of peak Pxs and peak aortic velocity agreed closely. Wave intensity estimated using pWIA showed acceptable agreement with estimates using LVOT velocity tracings and estimates of wave intensity were similar to values reported previously in the literature. The method showed fair to good reproducibility for most parameters.Conclusion: The Pxs is a surrogate of LVOT flow velocity which, when appropriately scaled, allows estimation of aortic wave intensity with acceptable reproducibility. This may enable wider application of wave intensity analysis to large studies.
Martinez-Perez ME, Parker KH, Witt N, et al., 2020, Automatic artery/vein classification in colour retinal images, 12th International Conference on Machine Vision (ICMV), Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X
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- Citations: 2
Sherwood JM, Boazak EM, Feola AJ, et al., 2019, Measurement of ocular compliance using iPerfusion, Frontiers in Bioengineering and Biotechnology, Vol: 7, Pages: 1-15, ISSN: 2296-4185
The pressure-volume relationship of the eye is determined by the biomechanical properties of the corneoscleral shell and is classically characterised by Friedenwald's coefficient of ocular rigidity or, alternatively, by the ocular compliance (OC), defined as dV/dP. OC is important in any situation where the volume (V) or pressure (P) of the eye is perturbed, as occurs during several physiological and pathological processes. However, accurately measuring OC is challenging, particularly in rodents. We measured OC in 24 untreated enucleated eyes from 12 C57BL/6 mice using the iPerfusion system to apply controlled pressure steps, whilst measuring the time-varying flow rate into the eye. Pressure and flow data were analysed by a “Discrete Volume” (integrating the flow trace) and “Step Response” method (fitting an analytical solution to the pressure trace). OC evaluated at 13 mmHg was similar between the two methods (Step Response, 41 [37, 46] vs. Discrete Volume, 42 [37, 48] nl/mmHg; mean [95% CI]), although the Step Response Method yielded tighter confidence bounds on individual eyes. OC was tightly correlated between contralateral eyes (R2 = 0.75, p = 0.0003). Following treatment with the cross-linking agent genipin, OC decreased by 40 [33, 47]% (p = 0.0001; N = 6, Step Response Method). Measuring OC provides a powerful tool to assess corneoscleral biomechanics in mice and other species.
Michail M, Comella A, McCormick L, et al., 2019, The Immediate Physiological Impact of Transcatheter Aortic Valve Replacement on Central Aortic Pressure in Patients With Severe Aortic Stenosis, 31st Annual Symposium on Transcatheter Cardiovascular Therapeutics (TCT), Publisher: ELSEVIER SCIENCE INC, Pages: B137-B137, ISSN: 0735-1097
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