Publications by authors named "Chris Bradley"

40 Publications

Glow in the dark: Using a heat-sensitive camera for blind individuals with prosthetic vision.

Vision Res 2021 Mar 26;184:23-29. Epub 2021 Mar 26.

Department of Ophthalmology, Johns Hopkins School of Medicine, Baltimore, MD, USA.

To date, retinal implants are the only available treatment for blind individuals with retinal degenerations such as retinitis pigmentosa. Argus II is the only visual implant with FDA approval, with more than 300 users worldwide. Argus II stimulation is based on a grayscale image coming from a head-mounted visible-light camera. Normally, the 11×19 field of view of the Argus II user is full of objects that may elicit similar phosphenes. The prosthesis cannot meaningfully convey so much visual information, and the percept is reduced to an ambiguous impression of light. This study is aimed at investigating the efficacy of simplifying the video input in real-time using a heat-sensitive camera. Data were acquired from four Argus II users in 5 stationary tasks with either hot objects or human targets as stimuli. All tasks were of m-alternative forced choice design where precisely one of the m≥2 response alternatives was defined to be "correct" by the experimenter. To compare performance with heat-sensitive and normal cameras across all tasks, regardless of m, we used an extension of signal detection theory to latent variables, estimating person ability and item difficulty in d' units. Results demonstrate that subject performance was significantly better across all tasks with the thermal camera compared to the regular Argus II camera. The future addition of thermal imaging to devices with very poor spatial resolution may have significant real-life benefits for orientation, personal safety, and social interactions, thereby improving quality of life.
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http://dx.doi.org/10.1016/j.visres.2021.02.009DOI Listing
March 2021

The middle cerebral artery blood velocity response to acute normobaric hypoxia occurs independently of changes in ventilation in humans.

Exp Physiol 2021 Apr 11;106(4):861-867. Epub 2021 Feb 11.

Department of Physiology, Faculty of Medical & Health Sciences, University of Auckland, Auckland, New Zealand.

New Findings: What is the central question of this study? Does the ventilatory response to moderate acute hypoxia increase cerebral perfusion independently of changes in arterial oxygen tension in humans? What is the main finding and its importance? The ventilatory response does not increase middle cerebral artery mean blood velocity during moderate isocapnic acute hypoxia beyond that elicited by reduced oxygen saturation.

Abstract: Hypoxia induces ventilatory, cardiovascular and cerebrovascular adjustments to defend against reductions in systemic oxygen delivery. We aimed to determine whether the ventilatory response to moderate acute hypoxia increases cerebral perfusion independently of changes in arterial oxygenation. Eleven young healthy individuals were exposed to four 15 min experimental conditions: (1) normoxia (partial pressure of end-tidal oxygen,  = 100 mmHg), (2) hypoxia (  = 50 mmHg), (3) normoxia with breathing volitionally matched to levels observed during hypoxia (hyperpnoea;  = 100 mmHg) and (4) hypoxia ( = 50 mmHg) with respiratory frequency and tidal volume volitionally matched to levels observed during normoxia (i.e., restricted breathing (RB)). Isocapnia was maintained in all conditions. Middle cerebral artery mean blood velocity (MCA V ), assessed by transcranial Doppler ultrasound, was increased during hypoxia (58 ± 12 cm/s, P = 0.04) and hypoxia + RB (61 ± 14 cm/s, P < 0.001) compared to normoxia (55 ± 11 cm/s), while it was unchanged during hyperpnoea (52 ± 13 cm/s, P = 0.08). MCA V was not different between hypoxia and hypoxia + RB (P > 0.05). These findings suggest that the hypoxic ventilatory response does not increase cerebral perfusion, indexed using MCA V , during moderate isocapnic acute hypoxia beyond that elicited by reduced oxygen saturation.
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http://dx.doi.org/10.1113/EP089127DOI Listing
April 2021

Sedimentary microplastic concentrations from the Romanian Danube River to the Black Sea.

Sci Rep 2021 Jan 21;11(1):2000. Epub 2021 Jan 21.

School of Geography, Earth and Environmental Sciences, The University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK.

A multitude of recent studies have detailed microplastic concentrations in aquatic and terrestrial environments, although questions remain over their ultimate fate. At present, few studies have detailed microplastic characteristics and abundance along a freshwater-marine interface, and considerable uncertainties remain over the modelled contribution of terrestrial and riverine microplastic to the world's oceans. In this article, for the first time, we detail sedimentary microplastic concentrations along a River-Sea transect from the lower reaches of a major continental river, the River Danube, through the Danube Delta, the Black Sea coast to the Romanian and Bulgarian inner shelf of the Black Sea. Our results indicate that isolated areas of the Danube Delta are still relatively pristine, with few microplastic particles in some of the sediments sampled.
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http://dx.doi.org/10.1038/s41598-021-81724-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7820245PMC
January 2021

Prosthetic Visual Performance Using a Disparity-Based Distance-Filtering System.

Transl Vis Sci Technol 2020 11 20;9(12):27. Epub 2020 Nov 20.

Department of Ophthalmology, Johns Hopkins School of Medicine, Baltimore, MD, USA.

Purpose: At present, Argus II is the only retinal prosthesis approved by the US Food and Drug Administration that induces visual percepts in people who are blind from end-stage outer retinal degenerations such as retinitis pigmentosa. It has been shown to work well in sparse, high-contrast settings, but in daily practice visual performance with the device is likely to be hampered by the cognitive load presented by a cluttered real-world environment. In this study, we investigated the effect of a stereo-disparity-based distance-filtering system on four experienced Argus II users for a range of tasks: object localization, depth discrimination, orientation and size discrimination, and people detection and direction of motion.

Methods: Functional vision was assessed in a semicontrolled setup using unfiltered (normal camera) and distance-filtered (stereo camera) imagery. All tasks were forced choice designs and an extension of signal detection theory to latent (unobservable) variables was used to analyze the data, allowing estimation of person ability (person measures) and task difficulty (item measures) on the same axis.

Results: All subjects performed better with the distance filter compared with the unfiltered image (  < 0.001 on all tasks except localization).

Conclusions: Our results show that depth filtering using a disparity-based algorithm has significant benefits for people with Argus II implants.

Translational Relevance: The improvement in functional vision with the distance filter found in this study may have an important impact on vision rehabilitation and quality of life for people with visual prostheses and ultra low vision.
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http://dx.doi.org/10.1167/tvst.9.12.27DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7683856PMC
November 2020

Combining in-situ fluorometry and distributed rainfall data provides new insights into natural organic matter transport dynamics in an urban river.

Sci Total Environ 2021 Feb 6;755(Pt 1):142731. Epub 2020 Oct 6.

School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, United Kingdom of Great Britain and Northern Ireland.

Urbanization alters the quality and quantity of Dissolved Organic Matter (DOM) fluxes to rivers potentially leading to water quality problems and impaired ecosystem function. Traditional synoptic and point sampling approaches are generally inadequate for monitoring DOM source dynamics. To identify links between spatial heterogeneity in precipitation and DOM dynamics, we used a unique approach combining high spatial and temporal resolution precipitation datasets featuring point, catchment, and land-cover weighted precipitation to characterise catchment transport dynamics. These datasets were linked to fluorescence records from an urban stream (Bourn Brook, Birmingham, UK). Humic-like fluorescence (HLF: Ex. 365 nm, Em. 490 nm) and Tryptophan-like fluorescence (TLF: Ex. 285 nm, Em. 340 nm) were measured, (plus river flow and turbidity) at 5 min intervals for 10 weeks during Autumn 2017. The relationship between discharge (Q) and concentration (C) for TLF and HLF were strongly chemodynamic at low Q (
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http://dx.doi.org/10.1016/j.scitotenv.2020.142731DOI Listing
February 2021

The haemodynamics of the human placenta in utero.

PLoS Biol 2020 05 28;18(5):e3000676. Epub 2020 May 28.

Sir Peter Mansfield Imaging Centre, School of Physics and Astronomy, University of Nottingham, Nottingham, United Kingdom.

We have used magnetic resonance imaging (MRI) to provide important new insights into the function of the human placenta in utero. We have measured slow net flow and high net oxygenation in the placenta in vivo, which are consistent with efficient delivery of oxygen from mother to fetus. Our experimental evidence substantiates previous hypotheses on the effects of spiral artery remodelling in utero and also indicates rapid venous drainage from the placenta, which is important because this outflow has been largely neglected in the past. Furthermore, beyond Braxton Hicks contractions, which involve the entire uterus, we have identified a new physiological phenomenon, the 'utero-placental pump', by which the placenta and underlying uterine wall contract independently of the rest of the uterus, expelling maternal blood from the intervillous space.
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http://dx.doi.org/10.1371/journal.pbio.3000676DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7255609PMC
May 2020

Efficient estimation of load-free left ventricular geometry and passive myocardial properties using principal component analysis.

Int J Numer Method Biomed Eng 2020 03 14;36(3):e3313. Epub 2020 Feb 14.

Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand.

Models of cardiac mechanics require a well-defined reference geometry from which deformations and hence myocardial strain and stress can be calculated. In the in vivo beating heart, the load-free (LF) geometry generally cannot be measured directly, since, in many cases, there is no stage at which the lumen pressures and contractile state are all zero. Therefore, there is a need for an efficient method to estimate the LF geometry, which is essential for an accurate mechanical simulation of left ventricular (LV) mechanics, and for estimations of passive and contractile constitutive parameters of the heart muscle. In this paper, we present a novel method for estimating both the LF geometry and the passive stiffness of the myocardium. A linear combination of principal components from a population of diastolic displacements is used to construct the LF geometry. For each estimate of the LF geometry and tissue stiffness, LV inflation is simulated, and the model predictions are compared with surface data at multiple stages during passive diastolic filling. The feasibility of this method was demonstrated using synthetically deformation data that were generated using LV models derived from clinical magnetic resonance image data, and the identifiability of the LF geometry and passive stiffness parameters were analysed using Hessian metrics. Applications of this method to clinical data would improve the accuracy of constitutive parameter estimation and allow a better simulation of LV wall strains and stresses.
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http://dx.doi.org/10.1002/cnm.3313DOI Listing
March 2020

Estimating measures of latent variables from m-alternative forced choice responses.

PLoS One 2019 22;14(11):e0225581. Epub 2019 Nov 22.

Department of Ophthalmology, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.

Signal Detection Theory is the standard method used in psychophysics to estimate person ability in m-alternative forced choice tasks where stimuli are typically generated with known physical properties (e.g., size, frequency, contrast, etc …) and lie at known locations on a physical measurement axis. In contrast, variants of Item Response Theory are preferred in fields such as medical research and educational testing where the axis locations of items on questionnaires or multiple choice tests are not defined by any observable physical property and are instead defined by a latent (or unobservable) variable. We provide an extension of Signal Detection Theory to latent variables that employs the same strategy used in Item Response Theory and demonstrate the practical utility of our method by applying it to a set of clinically relevant face perception tasks with visually impaired individuals as subjects. A key advantage of our approach is that Signal Detection Theory explicitly models the m-alternative forced choice task while Item Response Theory does not. We show that Item Response Theory is inconsistent with key assumptions of the m-alternative forced choice task and is not a valid model for this paradigm. However, the simplest Item Response Theory model-the dichotomous Rasch model-is found to be a special case of SDT and provides a good approximation as long as the number of response alternatives m is small and remains fixed for all items.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0225581PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6874343PMC
March 2020

Unilateral Exertional Compartment Syndrome in a Pediatric Competitive Figure Skater.

Cureus 2019 Sep 9;11(9):e5611. Epub 2019 Sep 9.

Physical Therapy, Beaumont Health, Royal Oak, USA.

Chronic exertional compartment syndrome (CECS) occurs when there is an increase in interstitial pressure within a non-compliant fascial compartment during exercise. The hallmark sign of CECS is a consistent onset of symptoms at a specific time, distance or intensity of activity followed by resolution of symptoms when the activity is stopped. Chronic exertional compartment syndrome commonly occurs in the lower legs, is bilateral 85% to 95% of the time and occurs most often in running athletes. The purpose of this case report is to describe the clinical presentation of unilateral chronic exertional compartment syndrome in a pediatric athlete that did not present with the hallmark signs for CECS and additionally participates in a sport where CECS is not common. The subject is a 13 year old female competitive figure skater who presented to physical therapy with right calf pain when figure skating and performing functional tasks. During the initial evaluation the patient had pain at rest as well as with objective testing of the right lower leg. The patient did not progress as expected in physical therapy and therefore the differential diagnosis was re-visited and additional measures were performed. The patient was re-diagnosed with unilateral chronic exertional compartment syndrome. The diagnosis was first clinical and later confirmed by intracompartmental testing. This case report illustrates a patient diagnosed with CECS by intra-compartmental pressure testing that did not present with the standard signs and symptoms; she did not participate in a sport where CECS is typically seen and her symptoms were unilateral. This report represents the importance of consistently including CECS in the differential diagnosis of lower leg pain in athletes regardless of the initial presentation and the sport in which they participate. Additionally, it highlights the importance of a detailed subjective history and the significance of aggravating and alleviating factors in relation to training.
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http://dx.doi.org/10.7759/cureus.5611DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6822883PMC
September 2019

Preliminary Evaluation of Two Digital Image Processing Strategies for Head-Mounted Magnification for Low Vision Patients.

Transl Vis Sci Technol 2019 Jan 28;8(1):23. Epub 2019 Feb 28.

Lions Vision Research and Rehabilitation Center, Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, MD, USA.

Purpose: In an observational clinical outcome study, we tested the effectiveness and use of the combination of two innovative approaches to magnification: a virtual bioptic telescope and a virtual projection screen, implemented with digital image processing in a head-mounted display (HMD) equipped with a high-resolution video camera and head trackers.

Methods: We recruited 30 participants with best-corrected visual acuity <20/100 in the better-seeing eye and bilateral central scotomas. Participants were trained on the HMD system, then completed a 7- to 10-day in-home trial. The Activity Inventory was administered before and after the home trial to measure the effect of system use on self-reported visual function. A simulator sickness questionnaire (SSQ) and a system-use survey were administered. Rasch analysis was used to assess outcomes.

Results: Significant improvements were seen in functional ability measures estimated from goal difficulty ratings (Cohen's = 0.79, < 0.001), and reading ( = 1.28, < 0.001) and visual information ( = 1.11, < 0.001) tasks. There was no improvement in patient-reported visual motor function or mobility. One participant had moderately severe discomfort symptoms after SSQ item calibration. The average patient rating of the system's use was 7.14/10.

Conclusions: Use of the system resulted in functional vision improvements in reading and visual information processing. Lack of improvement in mobility and visual motor function is most likely due to limited field of view, poor depth perception, and lack of binocular disparity.

Translational Relevance: We determine if these new image processing approaches to magnification are beneficial to low vision patients performing everyday activities.
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http://dx.doi.org/10.1167/tvst.8.1.23DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6396685PMC
January 2019

Method of successive dichotomizations: An improved method for estimating measures of latent variables from rating scale data.

PLoS One 2018 18;13(10):e0206106. Epub 2018 Oct 18.

Department of Ophthalmology, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America.

The most commonly used models for estimating measures of latent variables from polytomous rating scale data are the Andrich rating scale model and the Samejima graded response model. The Andrich model has the undesirable property of estimating disordered rating category thresholds, and users of the model are advised to manipulate data to force thresholds to come out ordered. The Samejima model estimates ordered thresholds, but has the undesirable property of estimating person measures on a non-invariant scale-the scale depends on which items a person rates and makes comparisons across people difficult. We derive the rating scale model logically implied by the generally agreed upon definition of rating scale-a real line partitioned by ordered thresholds into ordered intervals called rating categories-and show that it estimates ordered thresholds as well as person and item measures on an invariant scale. The derived model turns out to be a special case of the Samejima model, but with no item discrimination parameter and with common thresholds across items. All parameters in our model are estimated using a fast and efficient method called the Method of Successive Dichotomizations, which applies the dichotomous Rasch model as many times as there are thresholds and demonstrates that the derived model is a polytomous Rasch model that estimates ordered thresholds. We tested both the Method of Successive Dichotomizations and the Andrich model against simulated rating scale data and found that the estimated parameters of our model were nearly perfectly correlated with the true values, while estimated thresholds of the Andrich model became negatively correlated with the true values as the number of rating categories increased. Our method also estimates parameters on a scale that remains invariant to the number of rating categories, in contrast to the Andrich model.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0206106PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6193733PMC
March 2019

Promoting hygienic weaning food handling practices through a community-based programme: intervention implementation and baseline characteristics for a cluster randomised controlled trial in rural Gambia.

BMJ Open 2018 08 5;8(8):e017573. Epub 2018 Aug 5.

Institute of Applied Health Research, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK.

Objective: Contamination of weaning food leads to diarrhoea in children under 5 years. Public health interventions to improve practices in low-income and middle-income countries are rare and often not evaluated using a randomised method. We describe an intervention implementation and provide baseline data for such a trial.

Design: Clustered randomised controlled trial.

Setting: Rural Gambia.

Participants: 15 villages/clusters each with 20 randomly selected mothers with children aged 6-24 months per arm.

Intervention: To develop the public health intervention, we used: (A) formative research findings to determine theoretically based critical control point corrective measures and motivational drives for behaviour change of mothers; (B) lessons from a community-based weaning food hygiene programme in Nepal and a handwashing intervention programme in India; and (C) culturally based performing arts, competitions and environmental clues. Four intensive intervention days per village involved the existing health systems and village/cultural structures that enabled per-protocol implementation and engagement of whole villager communities.

Results: Baseline village and mother's characteristics were balanced between the arms after randomisation. Most villages were farming villages accessing health centres within 10 miles, with no schools but numerous village committees and representing all Gambia's three main ethnic groups. Mothers were mainly illiterate (60%) and farmers (92%); 24% and 10% of children under 5 years were reported to have diarrhoea and respiratory symptoms, respectively, in the last 7 days (dry season). Intervention process engaged whole village members and provided lessons for future implementation; culturally adapted performing arts were an important element.

Conclusion: This research has potential as a new low-cost and broadly available public health programme to reduce infection through weaning food. The theory-based intervention was widely consulted in the Gambia and with experts and was well accepted by the communities. Baseline analysis provides socioeconomic data and confirmation of Unicefs Multiple Indicator Cluster Survey (MICS) data on the prevalence of diarrhoea and respiratory symptoms in the dry season in the poorest region of Gambia.

Trial Registration Number: PACTR201410000859336; Pre-results.
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http://dx.doi.org/10.1136/bmjopen-2017-017573DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6078275PMC
August 2018

Enabling Detailed, Biophysics-Based Skeletal Muscle Models on HPC Systems.

Front Physiol 2018 12;9:816. Epub 2018 Jul 12.

Stuttgart Centre for Simulation Sciences, University of Stuttgart, Stuttgart, Germany.

Realistic simulations of detailed, biophysics-based, multi-scale models often require very high resolution and, thus, large-scale compute facilities. Existing simulation environments, especially for biomedical applications, are typically designed to allow for high flexibility and generality in model development. Flexibility and model development, however, are often a limiting factor for large-scale simulations. Therefore, new models are typically tested and run on small-scale compute facilities. By using a detailed biophysics-based, chemo-electromechanical skeletal muscle model and the international open-source software library OpenCMISS as an example, we present an approach to upgrade an existing muscle simulation framework from a moderately parallel version toward a massively parallel one that scales both in terms of problem size and in terms of the number of parallel processes. For this purpose, we investigate different modeling, algorithmic and implementational aspects. We present improvements addressing both numerical and parallel scalability. In addition, our approach includes a novel visualization environment which is based on the MegaMol framework and is capable of handling large amounts of simulated data. We present the results of a number of scaling studies at the Tier-1 supercomputer HazelHen at the High Performance Computing Center Stuttgart (HLRS). We improve the overall runtime by a factor of up to 2.6 and achieve good scalability on up to 768 cores.
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http://dx.doi.org/10.3389/fphys.2018.00816DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6052132PMC
July 2018

Left Ventricular Diastolic Myocardial Stiffness and End-Diastolic Myofibre Stress in Human Heart Failure Using Personalised Biomechanical Analysis.

J Cardiovasc Transl Res 2018 08 11;11(4):346-356. Epub 2018 Jul 11.

The Heart Center, St Francis Hospital, Roslyn, NY, USA.

Understanding the aetiology of heart failure with preserved (HFpEF) and reduced (HFrEF) ejection fraction requires knowledge of biomechanical factors such as diastolic myocardial stiffness and stress. Cine CMR images and intra-ventricular pressure recordings were acquired in 8 HFrEF, 11 HFpEF and 5 control subjects. Diastolic myocardial stiffness was estimated using biomechanical models and found to be greater in HFrEF (6.4 ± 1.2 kPa) than HFpEF (2.7 ± 0.6 kPa, p < 0.05) and also greater than control (1.2 ± 0.4 kPa, p < 0.005). End-diastolic mid-ventricular myofibre stress derived from the personalised biomechanics model was higher in HFrEF (2.9 ± 0.3 kPa) than control (0.9 ± 0.3 kPa, p < 0.01). Chamber stiffness, measured from the slope of the diastolic pressure-volume relationship, is determined by the intrinsic tissue properties as well as the size and shape of the heart, and was unable to distinguish between any of the three groups (p > 0.05). Personalised biomechanical analysis may provide more specific information about myocardial mechanical behaviour than global chamber indices, which are confounded by variations in ventricular geometry.
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http://dx.doi.org/10.1007/s12265-018-9816-yDOI Listing
August 2018

Spatio-temporal Organization During Ventricular Fibrillation in the Human Heart.

Ann Biomed Eng 2018 Jun 15;46(6):864-876. Epub 2018 Mar 15.

Department of Automatic Control and Systems Engineering, University of Sheffield, Sheffield, UK.

In this paper, we present a novel approach to quantify the spatio-temporal organization of electrical activation during human ventricular fibrillation (VF). We propose three different methods based on correlation analysis, graph theoretical measures and hierarchical clustering. Using the proposed approach, we quantified the level of spatio-temporal organization during three episodes of VF in ten patients, recorded using multi-electrode epicardial recordings with 30 s coronary perfusion, 150 s global myocardial ischaemia and 30 s reflow. Our findings show a steady decline in spatio-temporal organization from the onset of VF with coronary perfusion. We observed transient increases in spatio-temporal organization during global myocardial ischaemia. However, the decline in spatio-temporal organization continued during reflow. Our results were consistent across all patients, and were consistent with the numbers of phase singularities. Our findings show that the complex spatio-temporal patterns can be studied using complex network analysis.
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http://dx.doi.org/10.1007/s10439-018-2007-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5934463PMC
June 2018

Estimates of Incidence and Prevalence of Visual Impairment, Low Vision, and Blindness in the United States.

JAMA Ophthalmol 2018 01;136(1):12-19

The Lions Vision Research and Rehabilitation Center at the Johns Hopkins University School of Medicine, Baltimore, Maryland.

Importance: Updated estimates of the prevalence and incidence rates of low vision and blindness are needed to inform policy makers and develop plans to meet the future demands for low vision rehabilitation services.

Objective: To provide updated estimates of the incidence and prevalence of low vision and blindness in the United States.

Design, Setting, And Participants: Visual acuity measurements as a function of age from the 2007-2008 National Health and Nutrition Examination Survey, with representation of racial and ethnic groups, were used to estimate the prevalence and incidence of visual impairments. Data from 6016 survey participants, ranging in age from younger than 18 years to older than 45 years, were obtained to estimate prevalence rates for different age groups. Incidence and prevalence rates of low vision (best-corrected visual acuity [BCVA] in the better-seeing eye of <20/40 and <20/60) and blindness (BCVA of ≤20/200) in older adults were estimated from exponential models, fit to prevalence rates as a function of age (specified in 5-year age bins). The prevalence and annual incidence of low vision and blindness in the United States were estimated, using the 2010 US census data by age, from the rate models applied to the census projections for 2017, 2030, and 2050. Data were collected from November 1, 2007, to October 31, 2008. Data analysis took place from March 31, 2016, to March 19, 2017.

Main Outcomes And Measures: Prevalence and incidence rates of low vision and blindness in the United States.

Results: Of the 6016 people in the study, 1714 (28.4%) were younger than 18 years of age, 2358 (39.1%) were 18 to 44 years of age, and 1944 (32.3%) were 45 years of age or older. There were 2888 male (48%) and 3128 female (52%) participants. The prevalence of low vision and blindness for older adults (≥45 years) in the United States in 2017 is estimated to be 3 894 406 persons (95% CI, 3 034 442-4 862 549 persons) with a BCVA less than 20/40, 1 483 703 persons (95% CI, 968 656-2 370 513 persons) with a BCVA less than 20/60, and 1 082 790 persons (95% CI, 637 771-1 741 864 persons) with a BCVA of 20/200 or less. The estimated 2017 annual incidence (projected from 2010 census data) of low vision and blindness among older adults (≥45 years) in the United States is 481 970 persons (95% CI, 375 541-601 787 persons) with a BCVA less than 20/40, 183 618 persons (95% CI, 119 878-293 367 persons) with a BCVA less than 20/60, and 134 002 persons (95% CI, 83 383-215 567 persons) with a BCVA of 20/200 or less. The total annual incidence for each BCVA criterion is 12.4% of the total prevalence.

Conclusions And Relevance: Low vision and blindness affect a substantial portion of the older population in the United States. Estimates of the prevalence and annual incidence of visual impairment assist policy planners in allocating and developing resources for this life-changing loss of function.
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http://dx.doi.org/10.1001/jamaophthalmol.2017.4655DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5833607PMC
January 2018

Validating Translations of Rating Scale Questionnaires Using Rasch Analysis.

Ophthalmic Epidemiol 2017 02;24(1):1-2

a Wilmer Eye Institute, Johns Hopkins University School of Medicine , Baltimore , MD , USA.

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http://dx.doi.org/10.1080/09286586.2016.1246667DOI Listing
February 2017

Real-time monitoring of nutrients and dissolved organic matter in rivers: Capturing event dynamics, technological opportunities and future directions.

Sci Total Environ 2016 Nov 2;569-570:647-660. Epub 2016 Jul 2.

School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.

Excessive riverine nutrient concentrations threaten aquatic ecosystem structure and functioning and can pose substantial risks to human health. Robust monitoring strategies are therefore required to generate reliable estimates of river nutrient loads and to improve understanding of the catchment processes that drive nutrient fluxes. Furthermore, these data are vital for prediction of future trends under changing environmental conditions and thus the development of appropriate mitigation measures. In recent years, technological developments have led to an increase in the use of in-situ nutrient analysers, which enable measurements at far higher temporal resolutions than can be achieved with discrete sampling and subsequent laboratory analysis. In this paper, we review the principles underlying the key techniques used for in-situ nutrient monitoring and highlight both the advantages, opportunities and challenges associated with high-resolution sampling programs. We then suggest how adaptive monitoring strategies, comprising several different temporal sample frequencies, controlled by one or more 'trigger variables' (e.g. river stage, turbidity, or nutrient concentration), can advance our understanding of catchment nutrient dynamics while simultaneously overcoming many of the practical and economic challenges encountered in typical in-situ river nutrient monitoring applications. We present examples of short-term variability in river nutrient dynamics, driven by complex catchment behaviour, which support our case for the development of monitoring systems that can adapt in real-time to rapid changes in environmental conditions. Finally, we suggest future research directions based on emerging technologies in this field.
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http://dx.doi.org/10.1016/j.scitotenv.2016.06.116DOI Listing
November 2016

Verification of cardiac mechanics software: benchmark problems and solutions for testing active and passive material behaviour.

Proc Math Phys Eng Sci 2015 Dec;471(2184):20150641

Auckland Bioengineering Institute, University of Auckland , Auckland, New Zealand.

Models of cardiac mechanics are increasingly used to investigate cardiac physiology. These models are characterized by a high level of complexity, including the particular anisotropic material properties of biological tissue and the actively contracting material. A large number of independent simulation codes have been developed, but a consistent way of verifying the accuracy and replicability of simulations is lacking. To aid in the verification of current and future cardiac mechanics solvers, this study provides three benchmark problems for cardiac mechanics. These benchmark problems test the ability to accurately simulate pressure-type forces that depend on the deformed objects geometry, anisotropic and spatially varying material properties similar to those seen in the left ventricle and active contractile forces. The benchmark was solved by 11 different groups to generate consensus solutions, with typical differences in higher-resolution solutions at approximately 0.5%, and consistent results between linear, quadratic and cubic finite elements as well as different approaches to simulating incompressible materials. Online tools and solutions are made available to allow these tests to be effectively used in verification of future cardiac mechanics software.
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http://dx.doi.org/10.1098/rspa.2015.0641DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4707707PMC
December 2015

Spatial and seasonal variations in the composition of dissolved organic matter in a tropical catchment: the Lower Kinabatangan River, Sabah, Malaysia.

Environ Sci Process Impacts 2016 Jan;18(1):137-50

ECOBIO, OSUR, University of Rennes 1, campus de Beaulieu, 35042 Rennes Cedex, France.

Dissolved organic matter (DOM) was characterised in water samples sampled in the Lower Kinabatangan River Catchment, Sabah, Malaysia between October 2009 and May 2010. This study aims at: (i) distinguishing between the quality of DOM in waters draining palm oil plantations (OP), secondary forests (SF) and coastal swamps (CS) and, (ii) identifying the seasonal variability of DOM quantity and quality. Surface waters were sampled during fieldwork campaigns that spanned the wet and dry seasons. DOM was characterised optically by using the fluorescence Excitation Emission Matrix (EEM), the absorption coefficient at 340 nm and the spectral slope coefficient (S). Parallel Factor Analysis (PARAFAC) was undertaken to assess the DOM composition from EEM spectra and five terrestrial derived components were identified: (C1, C2, C3, C4 and C5). Components C1 and C4 contributed the most to DOM fluorescence in all study areas during both the wet and dry seasons. The results suggest that component C4 could be a significant (and common) PARAFAC signal found in similar catchments. Peak M (C2 and C3) was dominant in all samples collected during wet and dry seasons, which could be anthropogenic in origin given the active land use change in the study area. In conclusion, there were significant seasonal and spatial variations in DOM which demonstrated the effects of land use cover and precipitation amounts in the Kinabatangan catchment.
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http://dx.doi.org/10.1039/c5em00462dDOI Listing
January 2016

Challenges of river basin management: Current status of, and prospects for, the River Danube from a river engineering perspective.

Sci Total Environ 2016 Feb 14;543(Pt A):828-845. Epub 2015 Nov 14.

School of Geography, Earth and Environmental Sciences, the University of Birmingham, Birmingham, UK.

In the Danube River Basin multiple pressures affect the river system as a consequence of river engineering works, altering both the river hydrodynamics and morphodynamics. The main objective of this paper is to identify the effects of hydropower development, flood protection and engineering works for navigation on the Danube and to examine specific impacts of these developments on sediment transport and river morphology. Whereas impoundments are characterised by deposition and an excess of sediment with remobilisation of fine sediments during severe floods, the remaining five free flowing sections of the Danube are experiencing river bed erosion of the order of several centimetres per year. Besides the effect of interruption of the sediment continuum, river bed degradation is caused by an increase in the sediment transport capacity following an increase in slope, a reduction of river bed width due to canalisation, prohibition of bank erosion by riprap or regressive erosion following base level lowering by flood protection measures and sediment dredging. As a consequence, the groundwater table is lowered, side-arms are disconnected, instream structures are lost and habitat quality deteriorates affecting the ecological status of valuable floodplains. The lack of sediments, together with cutting off meanders, leads also to erosion of the bed of main arms in the Danube Delta and coastal erosion. This paper details the causes and effects of river engineering measures and hydromorphological changes for the Danube. It highlights the importance of adopting a basin-wide holistic approach to river management and demonstrates that past management in the basin has been characterised by a lack of integration. To-date insufficient attention has been paid to the wide-ranging impacts of river engineering works throughout the basin: from the basin headwaters to the Danube Delta, on the Black Sea coast. This highlights the importance of new initiatives that seek to advance knowledge exchange and knowledge transfer within the basin to reach the goal of integrated basin management.
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http://dx.doi.org/10.1016/j.scitotenv.2015.10.123DOI Listing
February 2016

ISO 55000: Creating an asset management system.

Health Estate 2015 Feb;69(2):64-6

In the October 2014 issue of HEJ, Keith Hamer, group vice-president, Asset Management & Engineering at Sodexo, and marketing director at Asset Wisdom, Kevin Main, argued that the new ISO 55000 standards present facilities managers with an opportunity to create 'a joined-up, whole lifecycle approach' to managing and delivering value from assets. In this article, Kevin Main and Chris Bradley, who runs various asset management projects, examine the process of creating an asset management system.
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February 2015

To what extent can portable fluorescence spectroscopy be used in the real-time assessment of microbial water quality?

Sci Total Environ 2015 Nov 5;532:14-9. Epub 2015 Jun 5.

School of Civil Engineering, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.

The intrinsic fluorescence of aquatic organic matter emitted at 350 nm when excited at 280 nm correlates widely with water quality parameters such as biochemical oxygen demand. Hence, in sewage-impacted rivers and groundwater, it might be expected that fluorescence at these wavelengths will also correlate with the microbial water quality. In this paper we use a portable fluorimeter to assess the relationship between fluorescence intensity at this wavelength pair and Escherichia coli enumeration in contrasting river catchments of poor water quality: in KwaZulu-Natal, S. Africa and the West Midlands, UK. Across all catchments we demonstrate a log correlation (r = 0.74) between fluorescence intensity and E. coli over a seven-log range in E. coli enumerations on non-perturbed (unfiltered) samples. Within specific catchments, the relationship between fluorescence intensity and E. coli is more variable, demonstrating the importance of catchment-specific interference. Our research demonstrates the potential of using a portable fluorimeter as an initial screening tool for indicative microbial water quality, and one that is ideally suited to simple pollution scenarios such as assessing the impact of faecal contamination in river or groundwater at specific sites.
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http://dx.doi.org/10.1016/j.scitotenv.2015.05.114DOI Listing
November 2015

Effect of global cardiac ischemia on human ventricular fibrillation: insights from a multi-scale mechanistic model of the human heart.

PLoS Comput Biol 2014 Nov 6;10(11):e1003891. Epub 2014 Nov 6.

Department of Physics and Astronomy, Ghent University, Ghent, Belgium; Moscow Institute of Physics and Technology (State University), Dolgoprudny, Moscow Region, Russia.

Acute regional ischemia in the heart can lead to cardiac arrhythmias such as ventricular fibrillation (VF), which in turn compromise cardiac output and result in secondary global cardiac ischemia. The secondary ischemia may influence the underlying arrhythmia mechanism. A recent clinical study documents the effect of global cardiac ischaemia on the mechanisms of VF. During 150 seconds of global ischemia the dominant frequency of activation decreased, while after reperfusion it increased rapidly. At the same time the complexity of epicardial excitation, measured as the number of epicardical phase singularity points, remained approximately constant during ischemia. Here we perform numerical studies based on these clinical data and propose explanations for the observed dynamics of the period and complexity of activation patterns. In particular, we study the effects on ischemia in pseudo-1D and 2D cardiac tissue models as well as in an anatomically accurate model of human heart ventricles. We demonstrate that the fall of dominant frequency in VF during secondary ischemia can be explained by an increase in extracellular potassium, while the increase during reperfusion is consistent with washout of potassium and continued activation of the ATP-dependent potassium channels. We also suggest that memory effects are responsible for the observed complexity dynamics. In addition, we present unpublished clinical results of individual patient recordings and propose a way of estimating extracellular potassium and activation of ATP-dependent potassium channels from these measurements.
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http://dx.doi.org/10.1371/journal.pcbi.1003891DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4222598PMC
November 2014

Novel benzoxazines as inhibitors of angiogenesis.

Invest New Drugs 2015 Feb 23;33(1):45-52. Epub 2014 Oct 23.

School of Pharmacy and Applied Sciences, La Trobe University, Bendigo, VIC, Australia.

Dysregulation of angiogenesis has been associated with many pathological disorders, including cancer; where angiogenesis has been found to be critical for the maintenance and metastasis of tumours. One of the pathways involved in the regulation of angiogenesis is the phosphatidylinositol3-kinase (PI3K) signalling pathway. The PI3K family consists of enzymes that phosphorylate the 3-OH of the inositol ring of phosphatidyl inositol. There are four isoforms, PI3Kα, PI3Kβ, PI3Kγ and PI3Kδ, that are signalling intermediaries involved in numerous pathways that sustain and maintain the tumours. In this study, we screened eight novel benzoxazine inhibitors of both PI3K isoforms and the related DNA-PK, for their anti-angiogenic effects. Our findings identified the novel benzoxazine (7, 8 (substituted)-2-morpholino-benz (1,3) oxazine: LTUSI122) to be non-toxic at concentrations up to 5 μM, while exhibiting significant inhibition of various aspects of angiogenesis including endothelial proliferation, migration and tube formation. The molecular mechanisms were examined using an angiogenesis array, revealing inhibition of several proliferative and migratory angiogenic factors, including VEGFR, MMP, IL-8, uPAR and MCP; and stimulation of the endogenous inhibitor, endostatin. We hypothesize that these anti-angiogenic effects are mediated by targeting an important signaling intermediary, PI3Kα, and subsequently its action on vascular endothelial growth factor (VEGF, a key growth factor in the process of angiogenesis). If used in combination with more targeted therapies, LTUSI122 could reduce tumour growth and increase the efficacy of these treatments.
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http://dx.doi.org/10.1007/s10637-014-0172-8DOI Listing
February 2015

Retina-V1 model of detectability across the visual field.

J Vis 2014 Oct 21;14(12). Epub 2014 Oct 21.

University of Texas at Austin, Austin, TX, USA.

A practical model is proposed for predicting the detectability of targets at arbitrary locations in the visual field, in arbitrary gray scale backgrounds, and under photopic viewing conditions. The major factors incorporated into the model include (a) the optical point spread function of the eye, (b) local luminance gain control (Weber's law), (c) the sampling array of retinal ganglion cells, (d) orientation and spatial frequency-dependent contrast masking, (e) broadband contrast masking, and (f) efficient response pooling. The model is tested against previously reported threshold measurements on uniform backgrounds (the ModelFest data set and data from Foley, Varadharajan, Koh, & Farias, 2007) and against new measurements reported here for several ModelFest targets presented on uniform, 1/f noise, and natural backgrounds at retinal eccentricities ranging from 0° to 10°. Although the model has few free parameters, it is able to account quite well for all the threshold measurements.
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http://dx.doi.org/10.1167/14.12.22DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4204678PMC
October 2014

FieldML, a proposed open standard for the Physiome project for mathematical model representation.

Med Biol Eng Comput 2013 Nov 31;51(11):1191-207. Epub 2013 Jul 31.

University of Auckland, Auckland, New Zealand,

The FieldML project has made significant progress towards the goal of addressing the need to have open standards and open source software for representing finite element method (FEM) models and, more generally, multivariate field models, such as many of the models that are core to the euHeart project and the Physiome project. FieldML version 0.5 is the most recently released format from the FieldML project. It is an XML format that already has sufficient capability to represent the majority of euHeart's explicit models such as the anatomical FEM models and simulation solution fields. The details of FieldML version 0.5 are presented, as well as its limitations and some discussion of the progress being made to address these limitations.
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http://dx.doi.org/10.1007/s11517-013-1097-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3825639PMC
November 2013

A finite-element approach to the direct computation of relative cardiovascular pressure from time-resolved MR velocity data.

Med Image Anal 2012 Jul 3;16(5):1029-37. Epub 2012 May 3.

Oxford University Computing Laboratory, University of Oxford, UK.

The evaluation of cardiovascular velocities, their changes through the cardiac cycle and the consequent pressure gradients has the capacity to improve understanding of subject-specific blood flow in relation to adjacent soft tissue movements. Magnetic resonance time-resolved 3D phase contrast velocity acquisitions (4D flow) represent an emerging technology capable of measuring the cyclic changes of large scale, multi-directional, subject-specific blood flow. A subsequent evaluation of pressure differences in enclosed vascular compartments is a further step which is currently not directly available from such data. The focus of this work is to address this deficiency through the development of a novel simulation workflow for the direct computation of relative cardiovascular pressure fields. Input information is provided by enhanced 4D flow data and derived MR domain masking. The underlying methodology shows numerical advantages in terms of robustness, global domain composition, the isolation of local fluid compartments and a treatment of boundary conditions. This approach is demonstrated across a range of validation examples which are compared with analytic solutions. Four subject-specific test cases are subsequently run, showing good agreement with previously published calculations of intra-vascular pressure differences. The computational engine presented in this work contributes to non-invasive access to relative pressure fields, incorporates the effects of both blood flow acceleration and viscous dissipation, and enables enhanced evaluation of cardiovascular blood flow.
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http://dx.doi.org/10.1016/j.media.2012.04.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3387378PMC
July 2012

Verification of cardiac tissue electrophysiology simulators using an N-version benchmark.

Philos Trans A Math Phys Eng Sci 2011 Nov;369(1954):4331-51

Department of Biomedical Engineering, Division of Imaging Sciences and Biomedical Engineering, King's College London, UK.

Ongoing developments in cardiac modelling have resulted, in particular, in the development of advanced and increasingly complex computational frameworks for simulating cardiac tissue electrophysiology. The goal of these simulations is often to represent the detailed physiology and pathologies of the heart using codes that exploit the computational potential of high-performance computing architectures. These developments have rapidly progressed the simulation capacity of cardiac virtual physiological human style models; however, they have also made it increasingly challenging to verify that a given code provides a faithful representation of the purported governing equations and corresponding solution techniques. This study provides the first cardiac tissue electrophysiology simulation benchmark to allow these codes to be verified. The benchmark was successfully evaluated on 11 simulation platforms to generate a consensus gold-standard converged solution. The benchmark definition in combination with the gold-standard solution can now be used to verify new simulation codes and numerical methods in the future.
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http://dx.doi.org/10.1098/rsta.2011.0139DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3263775PMC
November 2011

The social difficulties of cancer patients of South Asian Indian and Pakistani origin: a cross-sectional questionnaire and interview study.

BMJ Support Palliat Care 2011 Sep 2;1(2):154-61. Epub 2011 Aug 2.

King's College London, Division of Health and Social Care Research, UK.

Objectives: To evaluate, in a sample of patients of South Asian (SA) origin, the acceptability of introducing assessment of social difficulties in everyday practice, examine the range and severity of reported social difficulties and inquire about their management.

Design: A cross-sectional study in which participants completed the Social Difficulties Inventory (SDI-21) in English, Urdu, Punjabi or Hindi followed by a semi-structured interview.

Participants: Participants comprised 26 men and 29 women of SA origin ranging between 18 and 80 years of age. The commonest primary languages were Urdu (n=17) and Punjabi (n=17). English was the primary language of three participants. A range of cancer diagnoses and stages of disease were represented.

Setting: Patients were recruited from outpatient haematology and oncology clinics in Bradford, Airedale and Leeds hospitals.

Results: SA cancer patients welcomed routine assessment of social difficulties as part of their cancer care. They reported higher levels of social distress than found in earlier studies of white British patients. The majority managed their social difficulties themselves with little discussion with the clinical team, although, at times, this would have been welcomed. SA patients lacked information and were unaware of the support available to them, especially when language was a barrier.

Conclusions: Introduction of routine assessment of social difficulties into cancer care will require not only relevant and accessible screening tools such as the SDI-21, but also staff trained to respond to the difficulties disclosed, with knowledge of information sources and supportive care services when patients request these.
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http://dx.doi.org/10.1136/bmjspcare-2011-000013DOI Listing
September 2011