Microstructural and mechanical insight into atherosclerotic plaques: an ex vivo DTI study to better assess plaque vulnerability

Non-invasive microstructural characterisation has the potential to determine the stability, or lack thereof, of atherosclerotic plaques and ultimately aid in better assessing plaques' risk to rupture. If linked with mechanical characterisation using a clinically relevant imaging technique, mechanically sensitive rupture risk indicators could be possible. This study aims to provide this link-between a clinically relevant imaging technique and mechanical characterisation within human atherosclerotic plaques. Ex vivo diffusion tensor imaging, mechanical testing, and histological analysis were carried out on human carotid atherosclerotic plaques. DTI-derived tractography was found to yield significant mechanical insight into the mechanical properties of more stable and more vulnerable microstructures. Coupled with insights from digital image correlation and histology, specific failure characteristics of different microstructural arrangements furthered this finding. More circumferentially uniform microstructures failed at higher stresses and strains when compared to samples which had multiple microstructures, like those seen in a plaque cap. The novel findings in this study motivate diagnostic measures which use non-invasive characterisation of the underlying microstructure of plaques to determine their vulnerability to rupture.

Development of in silico models to guide the experimental characterisation of penile tissue and inform surgical treatment of erectile dysfunction

This paper presents a computational study to investigate the mechanical properties of human penile tissues. Different experimental testing regimes, namely indentation and plate-compression tests, are compared to establish the most suitable testing regime for establishing the mechanical properties of the different penile tissues. An idealised MRI-based geometry of the penis, containing different tissue layers, is simulated using the finite element (FE) method to enable realistic predictions of the deformation of the penis. Unlike the linear elastic models used in the literature to-date, hyperelastic isotropic/anisotropic material models are used to capture material nonlinearity and anisotropy. The influence of material properties, morphological variations, material nonlinearity and anisotropy are investigated. Moreover, the implantation of an inflatable penile prosthesis (IPP) is simulated to assess the effects of the implantation procedure, material nonlinearity, and anisotropy on tissue stresses. The results indicate that the interior layers of the penis do not affect the overall stiffness of the penis in the indentation test, while the plate-compression test is able to capture the effects of these layers. Tunica Albuginea (TA) is found to have the most significant contribution to the total stiffness of the penis under load. It can also be observed that buckling occurs in the septum of the penis during the compression tests, and different morphologies dictate different compressive behaviours. There is a clear need for future experimental studies on penile tissues given the lack of relevant test data in the literature. Based on this study, plate-compression testing would offer the most insightful experimental data for such tissue characterisation.

Phosphotungstic acid (PTA) preferentially binds to collagen- rich regions of porcine carotid arteries and human atherosclerotic plaques observed using contrast enhanced micro-computed tomography (CE-µCT)

Background and aims: Atherosclerotic plaque rupture in the carotid artery can cause small emboli to travel to cerebral arteries, causing blockages and preventing blood flow leading to stroke. Contrast enhanced micro computed tomography (CEμCT) using a novel stain, phosphotungstic acid (PTA) can provide insights into the microstructure of the vessel wall and atherosclerotic plaque, and hence their likelihood to rupture. Furthermore, it has been suggested that collagen content and orientation can be related to mechanical integrity. This study aims to build on existing literature and establish a robust and reproducible staining and imaging technique to non-destructively quantify the collagen content within arteries and plaques as an alternative to routine histology. Methods: Porcine carotid arteries and human atherosclerotic plaques were stained with a concentration of 1% PTA staining solution and imaged using MicroCT to establish the in situ architecture of the tissue and measure collagen content. A histological assessment of the collagen content was also performed from picrosirius red (PSR) staining. Results: PTA stained arterial samples highlight the reproducibility of the PTA staining and MicroCT imaging technique used with a quantitative analysis showing a positive correlation between the collagen content measured from CEμCT and histology. Furthermore, collagen-rich areas can be clearly visualised in both the vessel wall and atherosclerotic plaque. 3D reconstruction was also performed showing that different layers of the vessel wall and various atherosclerotic plaque components can be differentiated using Hounsfield Unit (HU) values. Conclusion: The work presented here is unique as it offers a quantitative method of segmenting the vessel wall into its individual components and non-destructively quantifying the collagen content within these tissues, whilst also delivering a visual representation of the fibrous structure using a single contrast agent.

Farm animal careers and perception of 'fit' in undergraduate veterinary students: A mixed methods study

BACKGROUND

Recruitment and retention of farm veterinarians have been the focus of recent research. Previous work suggests that a feeling of 'fit' is important for students to consider a farm career. The aim of this study was to identify whether students feel that they 'fit' in farm practice and reasons for their answer.

METHODS

An online survey was distributed to students at all British and Irish veterinary schools. A mixed methods approach was considered, with thematic analysis on free text answers and regression analysis on demographic variables.

RESULTS

Thematic analysis identified six themes: career opportunities, nature of farm veterinary work, relationships and interactions, individual experiences, expectations and perceptions, and no perceived barriers. Females, marginalised ethnic groups and those from an urban/suburban background were all identified as having significantly (p < 0.05) less agreement with the statement 'I feel able to pursue a career in farm practice'.

LIMITATIONS

Survey limitations include those with a clear bias being likely to respond. However, alignment of the qualitative and quantitative results increased confidence in the findings of this mixed methods approach.

CONCLUSION

This study confirms that biases that exist within wider society do have an influence on veterinary undergraduates' intentions to pursue a farm animal career. This is vital to consider both at a university level and when considering students' experiences on placements. Urgent action is required to improve inclusivity in the farm animal veterinary sector.

Native extracellular matrix orientation determines multipotent vascular stem cell proliferation in response to cyclic uniaxial tensile strain and simulated stent indentation

Cardiovascular disease is the leading cause of death worldwide, with multipotent vascular stem cells (MVSC) implicated in contributing to diseased vessels. MVSC are mechanosensitive cells which align perpendicular to cyclic uniaxial tensile strain. Within the blood vessel wall, collagen fibers constrain cells so that they are forced to align circumferentially, in the primary direction of tensile strain. In these experiments, MVSC were seeded onto the medial layer of decellularized porcine carotid arteries, then exposed to 10%, 1 Hz cyclic tensile strain for 10 days with the collagen fiber direction either parallel or perpendicular to the direction of strain. Cells aligned with the direction of the collagen fibers regardless of the orientation to strain. Cells aligned with the direction of strain showed an increased number of proliferative Ki67 positive cells, while those strained perpendicular to the direction of cell alignment showed no change in cell proliferation. A bioreactor system was designed to simulate the indentation of a single, wire stent strut. After 10 days of cyclic loading to 10% strain, MVSC showed regions of densely packed, highly proliferative cells. Therefore, MVSC may play a significant role in in-stent restenosis, and this proliferative response could potentially be controlled by controlling MVSC orientation relative to applied strain.

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ECM constrained MVSC align with collagen fibers when cells are strained parallel to collagen.

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Straining MVSC aligned parallel to the direction of strain increased cell proliferation.

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Simulated stent strut indentation showed increased cell density surrounding the indented wire.

Biomaterials enhancing performance of cell and nucleic-acid therapies: An opportunity in the brain

The brain has limited innate ability to promote repair, regeneration and functional recovery following injury, disease, or developmental disorder. Although cell and gene therapies have significant potential in the brain, no single treatment is likely to succeed in isolation. Here we discuss the current state of the art in cell and nucleic-acid-based neurotherapeutics and argue for the development of combination therapies that use biomaterials to help overcome the current limitations of cell and gene therapies alone.

Understanding the deformation gradient in Abaqus and key guidelines for anisotropic hyperelastic user material subroutines (UMATs)

This tutorial paper provides a step-by-step guide to developing a comprehensive understanding of the different forms of the deformation gradient used in Abaqus, and outlines a number of key issues that must be considered when developing an Abaqus user defined material subroutine (UMAT) in which the Cauchy stress is computed from the deformation gradient. Firstly, we examine the "classical" forms of global and local deformation gradients. We then show that Abaqus/Standard does not use the classical form of the local deformation gradient when continuum elements are used, and we highlight the important implications for UMAT development. We outline the key steps that must be implemented in developing an anisotropic fibre-reinforced hyperelastic UMAT for use with continuum elements and local orientation systems. We also demonstrate that a classical local deformation gradient is provided by Abaqus/Standard if structural (shell and membrane) elements are used, and by Abaqus/Explicit for all element types. We emphasise, however, that the majority of biomechanical simulations rely on the use of continuum elements with a local coordinate system in Abaqus/Standard, and therefore the development of a hyperelastic UMAT requires an in-depth and precise understanding of the form of the non-classical deformation gradient provided as input by Abaqus. Several worked examples and case studies are provided for each section, so that the details and implications of the form of the deformation gradient can be fully understood. For each worked example in this tutorial paper the source files and code (Abaqus input files, UMATs, and Matlab script files) are provided, allowing the reader to efficiently explore the implications of the form of the deformation gradient in the development of a UMAT.

AB0130 QUESTIONING THE USEFULNESS OF CDAI AS A MEASURE OF DISEASE ACTIVITY IN A TREAT TO TARGET PROGRAMME

Background:

Rheumatoid arthritis (RA) is a chronic autoimmune condition which if not treated can lead to joint destruction and long term disability. In RA, the concept of T2T is recommended as the appropriate method to manage early arthritis 1. It has shown promising results to achieve clinical remission (CR) or low disease activity (LDA) 2.

Objectives:

The objective of this study was to investigate the potential to achieve remission or LDA according to the Clinical Disease Activity Index (CDAI) for RA, during treatment with Disease-Modifying Anti-Rheumatic Drugs (DMARDs) and Biologics, and the factors that affect the remission/LDA outcome.

Methods:

We performed an observational prospective study on patients’ data available from our Early Arthritis Cohort. All patients with newly diagnosed RA who met the American College of Rheumatology (ACR) criteria were enrolled. Patients are managed by an Advanced Nurse Practitioner (ANP) with consultant supervision. To assess their response to treatment, we used the Clinical Disease Activity Index3. Analysis was performed using SPSS.

Results:

Out of a total of 459 patients, 353 completed the programme. 217 patients (61.5%) were female and (136) 38.5 % were male. Mean age was 53.98 (SD 14.66). 195 patients were on monotherapy, 40 on combination DMARDs and 115 were on Biologics/Janus Kinase Inhibitors (JAK-Inh). Remission-rates in the monotherapy and combination DMARDs groups were approximately 60%, whilst the remission rate in the Biologics/JAK-Inh group was 41.7%. Amongst female patients 15.9% had erosions on X-ray at the time of diagnosis whilst the equivalent figure for male patients was 29.6%.

Conclusion:

An association between male gender and the likelihood of erosions on X-Ray was observed. In addition an association between final medication and outcome was observed. An increased likelihood of non-remission was noted in patients that required escalation to Biologics/JAKs. A possible explanation for the lower levels of remission seen throughout the groups is the difficulty in achieving remission under the CDAI score as compared to DAS-28.

References:

[1]Smolen JS, Breedveld FC, Burmester GR, Bykerk V, Dougados M, Emery P, et al. Treating rheumatoid arthritis to target: 2014 update of the recommendations of an international task force. Annals of the Rheumatic Diseases. 2016;75(1):3.

[2]Scott IC, Ibrahim F, Panayi G, Cope AP, Garrood T, Vincent A, Scott DL, Kirkham B; TITRATE Programme Investigators. The frequency of remission and low disease activity in patients with rheumatoid arthritis, and their ability to identify people with low disability and normal quality of life. Semin Arthritis Rheum. 2019 Aug;49(1):20-26. doi: 10.1016/j.semarthrit.2018.12.006. Epub 2018 Dec 28. PMID: 30685064.

Disclosure of Interests:

None declared

Diffusion tensor imaging and arterial tissue: establishing the influence of arterial tissue microstructure on fractional anisotropy, mean diffusivity and tractography

This study investigates diffusion tensor imaging (DTI) for providing microstructural insight into changes in arterial tissue by exploring how cell, collagen and elastin content effect fractional anisotropy (FA), mean diffusivity (MD) and tractography. Five ex vivo porcine carotid artery models (n = 6 each) were compared-native, fixed native, collagen degraded, elastin degraded and decellularised. Vessels were imaged at 7 T using a DTI protocol with b = 0 and 800 s/mm2 and 10 isotopically distributed directions. FA and MD were evaluated in the vessel media and compared across models. FA values measured in native (p < 0.0001), fixed native (p < 0.0001) and collagen degraded (p = 0.0018, p = 0.0016, respectively) were significantly higher than those in elastin degraded and decellularised arteries. Native and fixed native had significantly lower MD values than elastin degraded (p < 0.0001) and decellularised tissue (p = 0.0032, p = 0.0003, respectively). Significantly lower MD was measured in collagen degraded compared with the elastin degraded model (p = 0.0001). Tractography yielded helically arranged tracts for native and collagen degraded vessels only. FA, MD and tractography were found to be highly sensitive to changes in the microstructural composition of arterial tissue, specifically pointing to cell, not collagen, content as the dominant source of the measured anisotropy in the vessel wall.

The use of small angle light scattering in assessing strain induced collagen degradation in arterial tissue ex vivo

Collagen is the predominant load bearing component in many soft tissues including arterial tissue and is therefore critical in determining the mechanical integrity of such tissues. Degradation of collagen fibres is hypothesized to be a strain dependent process whereby the rate of degradation is affected by the magnitude of strain applied to the collagen fibres. The aim of this study is to investigate the ability of small angle light scattering (SALS) imaging to identify strain dependent degradation of collagen fibres in arterial tissue ex vivo, and determine whether a strain induced protection mechanism exists in arterial tissue as observed in pure collagen and other collagenous tissues. SALS was used in combination with histological and second harmonic generation (SHG) analysis to determine the collagen fibre architecture in arterial tissue subjected to strain directed degradation. SALS alignment analysis identified statistically significant differences in fibre alignment depending on the strain magnitude applied to the tissue. These results were also observed using histology and SHG. Our findings suggest a strain protection mechanism may exist for arterial collagen at intermediate strain magnitudes between 0% and 25%. These findings may have implications for the onset and progression of arterial disease where changes in the mechanical environment of arterial tissue may lead to changes in the collagen degradation rate.

Strain mediated enzymatic degradation of arterial tissue: Insights into the role of the non-collagenous tissue matrix and collagen crimp

Collagen fibre remodelling is a strain dependent process which is stimulated by the degradation of existing collagen. To date, literature has focussed on strain dependent degradation of pure collagen or structurally simple collagenous tissues, often overlooking degradation within more complex, heterogenous soft tissues. The aim of this study is to identify, for the first time, the strain dependent degradation behaviour and mechanical factors influencing collagen degradation in arterial tissue using a combined experimental and numerical approach. To achieve this, structural analysis was carried out using small angle light scattering to determine the fibre level response due to strain induced degradation. Next, strain dependent degradation rates were determined from stress relaxation experiments in the presence of crude and purified collagenase to determine the tissue level degradation response. Finally, a 1D theoretical model was developed, incorporating matrix stiffness and a gradient of collagen fibre crimp to decouple the mechanism behind strain dependent arterial degradation. SALS structural analysis identified a strain mediated degradation response in arterial tissue at the fibre level not dissimilar to that found in literature for pure collagen. Interestingly, two distinctly different strain mediated degradation responses were identified experimentally at the tissue level, not seen in other collagenous tissues. Our model was able to accurately predict these experimental findings, but only once the load bearing matrix, its degradation response and the gradient of collagen fibre crimp across the arterial wall were incorporated. These findings highlight the critical role that the various tissue constituents play in the degradation response of arterial tissue.

STATEMENT OF SIGNIFICANCE

Collagen fibre architecture is the dominant load bearing component of arterial tissue. Remodelling of this architecture is a strain dependent process stimulated by the degradation of existing collagen. Despite this, degradation of arterial tissue and in particular, arterial collagen, is not fully understood or studied. In the current study, we identified for the first time, the strain dependent degradation response of arterial tissue, which has not been observed in other collagenous tissues in literature. We hypothesised that this unique degradation response was due to the complex structure observed in arterial tissue. Based on this hypothesis, we developed a novel numerical model capable of explaining this unique degradation response which may provide critical insights into disease development and aid in the design of interventional medical devices.

Optimisation of a novel glass-alginate hydrogel for the treatment of intracranial aneurysms

The current gold standard for aneurysm treatment is endovascular coiling. However, recurrence is observed in over 20% of cases. A novel hydrogel has been developed to treat aneurysms. This hydrogel is composed of a polymeric alginate, a novel ion releasing glass and glucono-delta-lactone. This is an internally setting alginate hydrogel, wherein the setting rate can be controlled by both the glass and the alginate chemistry. The aim of this work is to examine the effect of each component of the hydrogel and optimise the composition of the hydrogel, specifically the alginate molecular weight, M/G ratio and concentration. The effects of gamma sterilisation will also be examined. The results show that alginate concentration, chemical composition and molecular weight affect the compressive strength, working time, hardening time and deliverability of the hydrogel. Gamma irradiation of the alginate reduces the molecular weight, which has a negative effect on the usability of this hydrogel.

Antagonisms between Surfactants: The Case of Laundry Detergents

Interaction between surfactants forms micelles that typically lead to a reduction of the irritation potential of the mixture. The objective of this study is to illustrate that such antagonism between surfactants is applicable to actual cases of consumer products e.g. laundry detergent products. The Zein test is an in vitro assay measuring corn protein denaturation by solutions of surfactant(s) and often used to predict their acute irritation potential. The Zein test data for the surfactant mixtures from nine representative laundry detergents demonstrate that the protein denaturation by the mixtures is, in all cases, lower than the cumulative score of protein denaturation by the different surfactants tested separately. The data clearly indicate that antagonism occurs between the actual surfactants present in their exact proportions as found in the consumer laundry detergent products. These data support the view that the hazard classification of detergent products as (irritant) by the dangerous preparation directive should not be based on a simple cumulative score of the irritation properties of the individual components of the products.

New gene variants associated with venous thrombosis: a replication study in White and Black Americans

BACKGROUND

We evaluated 10 single-nucleotide polymorphisms (SNPs) identified in three European case-control studies as risk factors for venous thrombosis.

OBJECTIVES

We sought to replicate the positive findings from this report among Whites and to evaluate the association of these SNPs with venous thrombosis for the first time among Blacks.

PATIENT/METHODS

These SNPs were evaluated in a case-control study of deep vein thrombosis and pulmonary embolism that included 1076 cases and 1239 controls. About 50% of subjects were African Americans. We measured plasma factor (F) XI on a subset of subjects.

RESULTS

Among Whites, positive findings for rs13146272 in the CYP4V2 gene, for rs3087505 in the KLKB1 gene and for rs3756008 and rs2036914 in the F11 gene were found. We did not find significant associations for rs2227589 in the SERPINC1 gene and for rs1613662 in the GP6 gene. Among Blacks, rs2036914 in F11 and rs670659 in RGS7 were related to venous thrombosis, but the study had limited statistical power for many SNPs. Among Blacks, plasma FXI was related to two SNPs and the OR relating to the 90th percentile of the control distribution of plasma FXI was 2.6 (95% CI, 1.4, 5.0).

CONCLUSIONS

Our study supports the finding that genetic variants in the F11 gene are risk factors for venous thrombosis among both Whites and Blacks, although the findings in Blacks require confirmation. A meta-analysis of five case-control studies indicates that rs2227589 in the SERPINC1 gene, rs13146272 in the CYP4V2 gene and rs1613662 in the GP6 gene are risk factors for venous thrombosis among Whites.

Computational simulation methodologies for mechanobiological modelling: a cell-centred approach to neointima development in stents

The design of medical devices could be very much improved if robust tools were available for computational simulation of tissue response to the presence of the implant. Such tools require algorithms to simulate the response of tissues to mechanical and chemical stimuli. Available methodologies include those based on the principle of mechanical homeostasis, those which use continuum models to simulate biological constituents, and the cell-centred approach, which models cells as autonomous agents. In the latter approach, cell behaviour is governed by rules based on the state of the local environment around the cell; and informed by experiment. Tissue growth and differentiation requires simulating many of these cells together. In this paper, the methodology and applications of cell-centred techniques--with particular application to mechanobiology--are reviewed, and a cell-centred model of tissue formation in the lumen of an artery in response to the deployment of a stent is presented. The method is capable of capturing some of the most important aspects of restenosis, including nonlinear lesion growth with time. The approach taken in this paper provides a framework for simulating restenosis; the next step will be to couple it with more patient-specific geometries and quantitative parameter data.

An analysis of the strain field in biaxial Flexcell membranes for different waveforms and frequencies

Mechanical stimuli have been shown to affect cell behaviour in terms of proliferation, apoptosis, and protein expression. In terms of cardiovascular diseases, for example, endothelial and smooth muscle cells exposed to an abnormal strain environment have been associated with atherosclerosis and in-stent restenosis. The FX-4000™ system (Flexercell® Tension Plus System, Flexcell Corporation, McKeesport, Pennsylvania, USA) is an in-vitro system that is widely used to strain cells in order to evaluate their response to strain. The precision, accuracy, and repeatability of the strains controlled by the system are therefore crucial to analyse and interpret the results confidently. The aim of this study was to investigate the mechanical behaviour of the FX-4000™ Flexercell® six-well-plate silicon membranes for static and dynamic cyclic strains by measuring the maximum peak strain and analysing the change in the membrane deformation after cyclic strain for 0 h, 24 h, and 48 h at different strain amplitudes and frequencies. The results of the tests conducted demonstrate notable differences between the measured strains of the membranes in comparison with both the inputs and the outputs of the Flexcell® software. The calibration method used by Flexcell® International assumes that the strain values determined for a given vacuum pressure on the silicone membranes are reliable for different waveforms and frequencies. The data reported here clearly indicate that this is not the case. The results indicate that a unique calibration pressure—strain curve must be determined for each test given the viscoelastic nature of the Flexcell system. A new method to calibrate the machine in house was applied using new pressure—strain equations. This new calibration method has been presented and should enable researchers using the Flexcell® machine to set up their cell experiments more accurately.

Endoscopic ultrasound for preoperative staging of esophageal carcinoma

BACKGROUND

Endoscopic ultrasound (EUS) is potentially the best method for pretreatment staging of esophageal carcinoma once distant metastases have been excluded by other methods. However, its apparent accuracy might be influenced by the use of neoadjuvant therapy. To determine the accuracy of EUS in patients undergoing esophageal resection, the authors reviewed their experience with EUS.

METHODS

A total of 73 patients with esophageal carcinoma who underwent an esophagectomy between April 2000 and February 2005 were examined using preoperative EUS and computed tomography (CT). Of these patients, 39 also underwent preoperative neoadjuvant chemoradiotherapy. Both EUS and CT scan were used to determine the depth of tumor penetration (T-stage) and the presence of lymph node metastases (N-stage). These results then were compared with staging determined after pathologic examination of the resected surgical specimen.

RESULTS

For patients not undergoing neoadjuvant therapy, T-stage was accurately determined by EUS in 79%, N-stage in 74%, and tumor node metastasis (TNM) classification in 65% of the cases. However, when patients who had undergone neoadjuvant chemoradiotherapy were included, the overall accuracy of EUS was 64% for T-stage, 63% for N-stage, and 53% for TNM classification. For the patients who underwent neoadjuvant therapy, EUS indicated a more advanced T-stage in 49%, N-stage in 38%, and TNM classification in 51% of the cases, as compared with pathology. The overall accuracy of EUS for T- and N-stage carcinomas was superior to that of CT scanning.

CONCLUSION

For patients who do not undergo preoperative neoadjuvant chemotherapy and radiotherapy, EUS is a more accurate method for determining T- and N-stage resected esophageal carcinomas. Neoadjuvant therapy, however, results in apparent overstaging, predominantly because of tumor downstaging, and this reduces the apparent accuracy of EUS (and CT scanning) in this patient group. Nevertheless, EUS staging before neoadjuvant therapy could be more accurate than pathologic staging after treatment, thereby providing better initial staging information, which can be used to facilitate treatment.

Cardiovascular stent design and vessel stresses: a finite element analysis

Intravascular stents of various designs are currently in use to restore patency in atherosclerotic coronary arteries and it has been found that different stents have different in-stent restenosis rates. It has been hypothesized that the level of vascular injury caused to a vessel by a stent determines the level of restenosis. Computational studies may be used to investigate the mechanical behaviour of stents and to determine the biomechanical interaction between the stent and the artery in a stenting procedure. In this paper, we test the hypothesis that two different stent designs will provoke different levels of stress within an atherosclerotic artery and hence cause different levels of vascular injury. The stents analysed using the finite-element method were the S7 (Medtronic AVE) and the NIR (Boston Scientific) stent designs. An analysis of the arterial wall stresses in the stented arteries indicates that the modular S7 stent design causes lower stress to an atherosclerotic vessel with a localized stenotic lesion compared to the slotted tube NIR design. These results correlate with observed clinical restenosis rates, which have found higher restenosis rates in the NIR compared with the S7 stent design. Therefore, the testing methodology outlined here is proposed as a pre-clinical testing tool, which could be used to compare and contrast existing stent designs and to develop novel stent designs.

Elastic Behavior of Porcine Coronary Artery Tissue Under Uniaxial and Equibiaxial Tension

The aim of this study was to characterize the nonlinear anisotropic elastic behavior of healthy porcine coronary arteries under uniaxial and equibiaxial tension. Porcine coronary tissue was chosen for its availability and similarity to human arterial tissue. A biaxial test device previously used to test human femoral arterial tissue samples (Prendergast, P. J., C. Lally, S. Daly, A. J. Reid, T. C. Lee, D. Quinn, and F. Dolan. ASME J. Biomech. Eng., Vol. 125, pp. 692-699, 2003) was further developed to test porcine coronary tissue specimens. The device applies an equal force to the four sides of a square specimen and therefore creates a biaxial stretch that demonstrates the anisotropy of arterial tissue. The nonlinear elastic behavior was marked in both uniaxial and biaxial tests. The tissue demonstrated higher stiffness in the circumferential direction in four out of eight cases subjected to biaxial tension. Even though anisotropy is demonstrated it is proposed that an isotropic hyperelastic model may adequately represent the properties of an artery, provided that an axial stretch is applied to the vessel to simulate the in vivo longitudinal tethering on the vessel. Isotropic hyperelastic models based on the Mooney-Rivlin constitutive equation were derived from the test data by averaging the longitudinal and circumferential equibiaxial data. Three different hyperelastic models were established to represent the test specimens that exhibited a high stiffness, an average stiffness, and a low stiffness response; these three models allow the analyst to account for the variability in the arterial tissue mechanical properties. These models, which take account of the nonlinear elastic behavior of coronary tissue, may be implemented in finite element models and used to carry out preclinical tests of intravascular devices. The errors associated with the hyperelastic models when fitting to both the uniaxial and equibiaxial data for the low stiffness, average stiffness, and high stiffness models were found to be 0.836, 5.206, and 2.980, respectively.

Trends in clinical management of women with von Willebrand disease: a survey of 75 women enrolled in haemophilia treatment centres in the United States

OBJECTIVE

To assess the management of women with von Willebrand disease( vWD) in an Heamophilia Treatment Center (HTC) setting.

METHODS

A total of 75 women with vWd who were registered in HTCs in the United States participated in this study. A telephone interview elicited information about symptoms pertaining to bleeding disorders, diagnostic issues, referral patterns, treatment modalities before and after the enrollment in the HTC, HTC services provided, and satisfaction with care in the HTC.

RESULTS

Menorrhagia was the most commonly reported symptom (84%). The average time from the first symptom until clinician recognition was 16 years (range 0-39). In HTC, DDAVP was the most commonly used drug (31%). Of the 75 women, 71 reported a strong positive opinion and satisfaction about their care in the HTCs.

DISCUSSION

Women with VWD were typically diagnosed with the condition well into adulthood, in spite of the fact that majority of them experienced several bleeding symptoms beginning in early childhood. In general an HTC setting is appropriate for management of women with bleeding disorders. Diagnosis, treatment and education provided in the HTCs were viewed positively by those surveyed.

Analysis of Prolapse in Cardiovascular Stents: A Constitutive Equation for Vascular Tissue and Finite-Element Modelling

The effectiveness of a cardiovascular stent depends on many factors, such as its ability to sustain the compression applied by the vessel wall, minimal longitudinal contraction when it is expanded, and its ability to flex when navigating tortuous blood vessels. The long-term reaction of the tissue to the stent is also device dependant; in particular some designs provoke in-stent restenosis (i.e., regrowth of the occlusion around the stent). The mechanism of restenosis is thought to involve injury or damage to the vessel wall due to the high stresses generated around the stent when it expands. Because of this, the deflection of the tissue between the struts of the stent (called prolapse or “draping”) has been used as a measure of the potential of a stent to cause restenosis. In this paper, uniaxial and biaxial experiments on human femoral artery and porcine aortic vascular tissue are used to develop a hyperelastic constitutive model of vascular tissue suitable for implementation in finite-element analysis. To analyze prolapse, four stent designs (BeStent 2, Medtronic AVE; NIROYAL, Boston Scientific; VELOCITY, Cordis; TETRA, Guidant) were expanded in vitro to determine their repeating-unit dimensions. This geometric data was used to generate a finite element model of the vascular tissue supported within a repeating-unit of the stent. Under a pressure of 450 mm Hg (representing the radial compression of the vessel wall), maximum radial deflection of 0.253 mm, 0.279 mm, 0.348 mm and 0.48 mm were calculated for each of the four stents. Stresses in the vascular wall were highest for the VELOCITY stent. The method is proposed as a way to compare stents relative to their potential for restenosis and as a basis for a biomechanical design of a stent repeating-unit that would minimize restenosis.

Medical, reproductive and psychosocial experiences of women diagnosed with von Willebrand's disease receiving care in haemophilia treatment centres: a case-control study

OBJECTIVE

To assess the medical, gynaecological and reproductive experiences of women with von Willebrand's disease (VWD) and to evaluate the impact of VWD on mental health and life activities.

METHODS

A total of 102 women with VWD who were registered in haemophilia treatment Centres (HTCs) in the United States and 88 controls were interviewed regarding medical, gynaecological and reproductive history, life activities and symptoms of depression. Symptoms of depression were measured using the Center for Epidemiological Studies Depression Scale (CES-D).

RESULTS

Excessive bleeding symptoms were reported in 74% of VWD cases compared with 6% of controls. Women with VWD had a higher prevalence of menorrhagia, excessive postpartum bleeding, other gynaecological conditions, arthritis and migraine headaches than did controls. More VWD cases than controls reported that menstruation had a negative impact on overall life activities. No difference in the prevalence of depression was found between cases and controls.

DISCUSSION

Women with VWD experience menorrhagia and other gynaecological conditions at a higher frequency than women without bleeding disorders. Menstruation in women with VWD has a negative impact on life activities. The prevalence of depression was not elevated in this group of women whose VWD is being managed in an HTC.

von Willebrand disease and other inherited bleeding disorders in women with diagnosed menorrhagia

OBJECTIVE

To estimate the prevalence of von Willebrand disease and other bleeding disorders in women with and without diagnosed menorrhagia.

METHODS

Women with menorrhagia were identified among members of a health maintenance organization in the southeastern United States through a computer search for appropriate International Classification of Diseases, 9th Revision codes. A random sample of members with no such code was selected as controls. The study included 121 women with menorrhagia and 123 controls. Subjects were interviewed in person, and blood was drawn for coagulation testing. Laboratory results for menorrhagia patients were compared with those in controls using race and blood type specific ranges developed from the control group. A test was considered abnormal if it exceeded two standard deviations below the control mean.

RESULTS

Bleeding disorders (von Willebrand disease, factor deficiency, or a platelet abnormality) were diagnosed in 10.7% of menorrhagia patients and 3.2% of controls (P =.02). von Willebrand disease was present in eight menorrhagia patients (6.6%) and in one control (0.8%) (P =.02); separate analyses by race revealed a von Willebrand disease prevalence of 15.9% among white and 1.4% among black menorrhagia patients (P =.01). Women with bleeding disorders did not differ significantly from controls in other symptoms of bleeding.

CONCLUSION

The prevalence of inherited bleeding disorders among white women with menorrhagia was substantial, consistent with European data published recently. For unknown reasons, the prevalence of von Willebrand disease was lower among black women. These findings indicate the importance of considering inherited bleeding disorders as a cause of menorrhagia.

Passive smoking exposure and female breast cancer mortality

BACKGROUND

Several studies have reported positive associations between environmental tobacco smoke (ETS) and increased risk of breast cancer. However, studies of active smoking and risk of breast cancer are equivocal and in general do not support a positive association. To try to resolve this paradox, we examined the association between breast cancer mortality and potential ETS exposure from spousal smoking in an American Cancer Society prospective study of U.S. adult women.

METHODS

We assessed breast cancer death rates in a cohort of 146 488 never-smoking, single-marriage women who were cancer free at enrollment in 1982. Breast cancer death rates among women whose husbands smoked were compared with those among women married to men who had never smoked. Cox proportional hazards modeling was used to control for potential risk factors other than ETS exposure.

RESULTS

After 12 years of follow-up, 669 cases of fatal breast cancer were observed in the cohort. Overall, we saw no association between exposure to ETS and death from breast cancer (rate ratio [RR] = 1.0; 95% confidence interval [CI] = 0.8-1.2). We did, however, find a small, not statistically significant increased risk of breast cancer mortality among women who were married before age 20 years to smokers (RR = 1. 2; 95% CI = 0.8-1.8).

CONCLUSIONS

In contrast to the results of previous studies, this study found no association between exposure to ETS and female breast cancer mortality. The results of our study are particularly compelling because of its prospective design as compared with most earlier studies, the relatively large number of exposed women with breast cancer deaths, and the reporting of exposure by the spouse rather than by proxy.

Venous thrombosis in relation to fibrinogen and factor VII genes among African-Americans

We evaluated the relation between venous thrombosis and plasma fibrinogen levels, the HaeIII and BcI polymorphisms of the beta fibrinogen gene, and the MspI polymorphisms of the factor VII gene in a case-control study of African-Americans. The study included 91 venous thrombosis cases and 185 control subjects obtained from a hospital in Atlanta, Georgia. High plasma fibrinogen was associated with increased risk of venous thrombosis, but the finding was not statistically significant. There was little association between the HaeIII polymorphisms and the BclI polymorphisms and the risk of venous thrombosis. The prevalence of the M2/M2 genotype of the factor VII gene was higher among cases than controls, but the difference was not statistically significant. The prevalence of the HaeIII H2 allele and the BclI B2 allele of the beta fibrinogen gene, both of which have been associated with slightly higher levels of plasma fibrinogen in most studies, is considerably lower among African-Americans in this study than it is among Whites in the United States and among Northern Europeans. The study is limited by its small size. However, despite this limitation, it supports the belief that increased plasma fibrinogen levels are associated with increased venous thrombosis risk. The study also indicated that the HaeIII and the BclI polymorphisms of the beta fibrinogen gene and the MspI polymorphisms of the factor VII gene are not strong determinants of venous thrombosis.

The role of the t-PA I/D and PAI-1 4G/5G polymorphisms in African-American adults with a diagnosis of myocardial infarction or venous thromboembolism

To determine whether or not the PAI-1 4G/5G and t-PA I/D polymorphisms in African-Americans were linked to cardiovascular disease, the association of these polymorphisms to disease expression was analyzed in a recently completed case-control study of myocardial infarction or venous thromboembolism among African-Americans. All African-Americans patients with a history of venous thromboembolism attending an anticoagulant clinic, and patients with a history of a MI attending a cardiology clinic at a large local urban public hospital were eligible for inclusion as cases in the study. In this study it was observed that there was a statistically significant association between the D allele of the t-PA I/D polymorphism and venous thromboembolism and a nonsignificant association between the D allele and myocardial infarction among African-Americans. t-PA antigen levels were statistically significantly higher among both myocardial infarction and venous thromboembolism cases compared with control subjects. The genotypes were unrelated to t-PA plasma levels. There was no association between either myocardial infarction or venous thromboembolism and the 4G/5G PAI-1 genotype. It was also found that genotype frequencies for both PAI-1 4G/5G and t-PA I/D polymorphisms in African-American adults were different from those reported for both U.S. Causcians and Europeans.

The relationship between polymorphisms in the endothelial cell nitric oxide synthase gene and the platelet GPIIIa gene with myocardial infarction and venous thromboembolism in African Americans

STUDY OBJECTIVES

To determine whether the polymorphic dinucleotide repeats found in intron 4 of the endothelial cell nitric oxide synthase (ecNOS) gene and the platelet GPIIIa PLA(1)/A(2) polymorphism are associated with myocardial infarction (MI) and venous thromboembolism (VTE) in African Americans. Because these two genes may interact physiologically, the third objective was to determine if there was a relationship between the polymorphisms with respect to MI and VTE.

DESIGN

A hospital-based case-control study. After informed consent was obtained, blood used for DNA extraction was drawn from the subjects.

SETTING

The study was conducted in the Anticoagulant Clinic and the Cardiology Clinic at Grady Memorial Hospital in Atlanta Georgia.

PATIENTS

Subjects were recruited from African-American patients with a reported history of MI (n = 110) or VTE (n = 91). Control subjects (n = 185) without a history of cardiovascular or venous disease were recruited from an outpatient clinic.

MEASUREMENTS AND RESULTS

The 393 ecNOS allele was more common among MI cases (36%; p = 0.01) and VTE cases (35%; p = 0.04) than among control subjects (26%). There was no association between the GPIIIa genotypes and either MI or VTE. However, among the MI subjects, there was a strong association between the ecNOS 393/393 genotype and the Pl(A2) allele. It was also found that the frequency of the 393 allele was higher in African-American persons (0.26) compared with what has been reported for Australian Caucasians (0. 14) and Japanese (0.10).

CONCLUSIONS

The 393 allele but not the Pl(A2) allele was significantly associated with both MI and VTE in African Americans. Homozygosity for the 393 allele was significantly associated to the diagnosis of MI prior to the age of 45. The combination of the 393 allele and a Pl(A2) allele was also highly associated with MI. The frequency of the 393 allele was significantly higher in African Americans than what has been reported for other populations. This study furthers not only extends the association of the 393 allele to VTE but has demonstrated an interaction with the Pl(A2) allele with respect to MI.

Cyclosporine A-induced cell cycle arrest and cell death in renal epithelial cells

We studied the effects of cyclosporine A (CsA) on the proliferation of LLC-PK1 proximal tubule epithelial cells. DNA damage was found to be an early event in CsA nephrotoxicity and could be a sensitive indicator of CsA injury in renal epithelial cells. Cell cycle arrest induced by CsA was coincident with elevated p53 levels. It is possible that trans-activating p21 may mediate the halting of the cell cycle through the CsA-induced accumulation of p53.

Apoptosis and necrosis: mechanisms of cell death induced by cyclosporine A in a renal proximal tubular cell line

BACKGROUND

The mechanisms of cyclosporine (CsA)-induced nephrotoxicity are not fully understood. While hemodynamic changes may be involved in vivo, there is also some evidence for tubular involvement. We previously showed direct toxicity of CsA in the LLC-PK1 renal tubular cell line. In the current study we examined mechanisms (apoptosis or necrosis) of cell death induced by CsA in the LLC-PK1 renal proximal tubular cell line. The possible role of the Fas (APO-1/CD95) antigen-Fas ligand system in the mediation of CsA-induced cell death was also investigated.

METHODS

Cells were treated with CsA (0.42 nM to 83 microM) for 24 hours and alterations in DNA and protein synthesis and membrane integrity were examined. Flow cytometry was used to investigate: (i) alterations in the DNA content and cell cycle; (ii) the forward (FSC) and side (SSC) light scattering properties (indicators of cell size and granularity, respectively); (iii) the externalization of phosphatidylserine (PS) as a marker of early apoptosis using FITC-annexin V binding; and (iv) expression of the apoptotic Fas protein. DNA fragmentation in apoptotic cells was also determined by the TUNEL assay.

RESULTS

CsA (all doses) caused a block in the G0/G1 phase of the cell cycle as indicated by a decrease in DNA synthesis and supported by an increase in the % of cells in the G0/G1 phase with concurrent decreases of those in the S and G2/M phases. The effect on protein synthesis appeared to be much less. Lower doses of CsA (4.2 nM) caused the appearance of a "sub-G0/G1" peak, indicative of reduced DNA content, on the DNA histogram that was paralleled by a reduction in cell size and an increased cell granularity and an increase in FITC-annexin V binding. DNA fragmentation was evident in these cells as assessed using the TUNEL assay. Higher doses of CsA increased cell size and decreased cell granularity and reduced membrane integrity. Expression of Fas, the cell surface molecule that stimulates apoptosis, was increased following low dose CsA exposure.

CONCLUSIONS

These results indicate that CsA is directly toxic to LLC-PK1 cells with reduced DNA synthesis and cell cycle blockade. The mode of cell death, namely apoptosis or necrosis, is dose dependent. Fas may be an important mediator of CsA induced apoptosis in renal proximal tubular cells.

Relation of three genetic traits to venous thrombosis in an African-American population

A mutation in the Factor V gene (Factor V Leiden), a variant in the 5,10-methylenetetrahydrofolate reductase gene (MTHFR), and an insertion/deletion polymorphism of the angiotensin I-converting enzyme gene (ACE) may be related to abnormal blood clotting. The authors examined the associations between these genetic traits and venous thrombosis among African Americans. This study comprised 93 patients with venous thrombosis and 185 control subjects attending clinics at an urban, public hospital in Atlanta, Georgia, in 1995-1996. Subjects' DNA was extracted from blood and assayed for these genetic traits. Odds ratios were obtained from logistic regression and used as a measure of association between each genetic trait and venous thrombosis. Factor V Leiden was unrelated to venous thrombosis, but the mutation ws too rare among our African-American subjects to evaluate adequately its relation to venous thrombosis. The homozygous and heterozygous genotypes for the V allele of the MTHFR gene were unrelated to venous thrombosis (odds ratio = 0.9, 95% confidence interval 0.5-1.8). Subjects with the deletion/deletion ACE polymorphism experienced a moderate increase in venous thrombosis risk compared with persons with the other genotypes (odds ratio = 1.5, 95% confidence interval 0.9-2.6). However, women with this ACE genotype experienced no increased risk (odds ratio = 0.9, 95% confidence interval 0.5-1.9), whereas men with this genotype had nearly three times the risk (odds ratio = 2.8, 95% confidence interval 1.2-6.2; p value for interaction = 0.06). These data indicate that the prevalence of Factor V Leiden and the V allele of the MTHFR gene is low among African Americans. The D allele of the ACE gene is equally prevalent among African Americans and whites and may be related to venous thrombosis among African-American men.

A case-control study of lung cancer at a foundry and two engine plants

A nested case-control study of lung cancer was conducted among workers at an iron foundry and two engine manufacturing plants whose lung cancer mortality rates were slightly higher than expected. The study included 231 lung cancer cases and 408 controls for whom complete work histories were obtained. There was no association between usual plant of employment and lung cancer mortality. The odds ratio for persons employed for 20 or more years in the foundry compared with persons employed in the engine plants was 0.90 (95% confidence interval: 0.55, 1.5). Long-term employment as an engine plant worker was associated with odds ratios slightly, but not statistically significantly, below unity. In the foundry, only usual employment in the material handling departmental group and any employment in the quality control departmental group were statistically significantly directly related to lung cancer risk. However, the number of subjects so employed was small and there was no dose-response relation between length of employment in these departmental groups and lung cancer risk. Cases were less frequently employed than were controls in engine plant machining and assembly jobs and departments. It is concluded that employment in this facility was either unrelated, or only weakly related, to lung cancer risk.

Parity and coronary heart disease among women in the American Cancer Society CPS II population

Four of five cohort studies have shown an increase in cardio-vascular disease with increased parity, after control for a number of cardiovascular risk factors. The effect has been observed primarily in categories of four or more livebirths. To analyze this issue further, we conducted an analysis of 585,445 women from the American Cancer Society Cancer Prevention Survey II (CPS II). There were 4,787 deaths from coronary heart disease (International Classification of Diseases Codes 410-414) among these women during the follow-up period from 1981 to 1989. After controlling for a number of cardiovascular risk factors, we found no increased trend in heart disease with increased parity. Rare ratios for women with no live births or 1, 2, 3, 4, 5, and 6 or more livebirths were 1.00, 0.95, 0.89, 0.82, 0.94, 0.98, 0.94, respectively. Without control over confounders, however, we observed an increased risk for the highest party category (rate ratio = 1.18; 95% confidence interval = 1.04-1.34). Positive findings for parity to date have been found primarily in cohort studies representative of the general population, whereas our own data and another earlier negative study among nurses came from more select populations likely to be relatively homogeneous for socioeconomic variables. Positive findings in the literature may be due, at least in part, to confounding by unmeasured variables related to socioeconomic status.

Environmental tobacco smoke and coronary heart disease in the American Cancer Society CPS-II cohort

BACKGROUND

Thirteen of 14 epidemiological studies have shown an increased risk of approximately 20% for coronary heart disease (CHD) for never-smokers exposed to environmental tobacco smoke (ETS), but this association remains controversial. If true, ETS might account for an estimated 35,000 to 40,000 heart disease deaths per year in the United States.

METHODS AND RESULTS

We have conducted the largest study to date, a prospective study of 353,180 female and 126,500 male never-smokers enrolled in 1982 in the American Cancer Society's Cancer Prevention Study II and followed through 1989. Analyses focused on subcohorts of 309,599 married pairs and of 135,237 subjects concordant for self-reported exposure and exposure reported by each one's spouse. More than 2800 CHD deaths (ICD 410-414) occurred among married pairs; 10% of married men and 28% of married women were married to currently smoking spouses, while 10% and 32%, respectively, were married to former smokers. After controlling for many cardiovascular risk factors, we found 22% higher CHD mortality (rate ratio, 1.22; 95% CI, 1.07 to 1.40) among never-smoking men married to currently smoking wives compared with those married to wives who had never smoked. The corresponding rate ratio for women was 1.10 (0.96 to 1.27). Never-smokers living with former smokers showed no increased risk. When analyses were restricted to subjects whose ETS exposure was classified via both their own self-report and a spouse's report, the rate ratio was 1.23 (1.03 to 1.47) for currently exposed men and 1.19 (0.97 to 1.45) for women.

CONCLUSIONS

Results are consistent with prior reports that never-smokers currently exposed to ETS have about 20% higher CHD death rates. However, our data do not show consistent dose-response trends and are possibly subject to confounding by unmeasured risk factors.

Nickel, cobalt and chromium in consumer products: a role in allergic contact dermatitis?

In spite of the improved awareness of the potential for nickel, cobalt and chromium to cause skin allergy, the incidence of sensitization to them is generally on the increase, especially for nickel. We review data from the literature and industry on transition metal contamination of consumer products and assess the hazard to man. Consumer products are defined as personal care items and detergent/cleaning products used regularly in domestic work. The analytical data demonstrate that consumer products are a relatively minor source of contact with nickel, cobalt or chromium. The traces found in consumer products will not be the primary cause of sensitization to these metals: levels will be too low and exposure too brief. A person sensitized to these metals has many other more significant sources of daily contact such as earrings, jewelry and metal objects. It is therefore necessary to focus on decreasing the high exposure to these transition metals from other sources rather than on possible trace amounts found in consumer products. Current good manufacturing practice ensures that trace nickel, cobalt and chromium concentrations in consumer products are less than 5 ppm of each metal. It is recommended that this be accepted as a standard for maximum concentrations and that the target should be to achieve concentrations as low as 1 ppm.

Correlates of sociometric status in school children in Buenos Aires

Teacher ratings on Spanish translations of the Comprehensive Behavior Rating Scale for Children and peer nominations were obtained for 110 school children (42 boys and 68 girls) in grades 2-5 at a public elementary school in Buenos Aires. Nominations of "likes best" were negatively correlated with language processing deficits, attention problems, and sluggish tempo as rated by both teachers and peers, and positively correlated with teacher ratings of social competence, for both boys and girls. The reverse pattern was found for nominations of "likes least." Children were assigned to sociometric status groups of popular (n = 27), rejected (n = 28), neglected (n = 7) controversial (n = 11), and average (n = 37) based on number of LL and LB nominations. Rejected and popular children could be differentiated by teacher and peer ratings of linguistic information processing deficits, inattention, and sluggish tempo. Behavioral characteristics of motor hyperactivity, impulsivity, and aggression were significantly associated with being male but did not differ by sociometric status group.

A size analysis of the adenovirus replicon

The linear double-stranded genome of adenovirus DNA replicates semiconservatively from two origins of replication at either of the two molecular ends. Using an in vitro replication system which is able to initiate de novo DNA synthesis we have mapped the origin of DNA replication within the terminal 19 bp of the viral genome. Our conclusions are based on the use of different natural DNA templates, i.e., adenovirus type 2 and mouse adenovirus Fl DNA. In addition, we have employed linearized plasmid DNA templates which contain cloned terminal restriction enzyme fragments as well as chemically synthesized adenovirus termini of different length.