Ex vivo experimental investigations and modelling of the layer-dependent, anisotropic, visco-hyperelastic behaviour of the human oesophagus

As a mechanical organ, the material properties of the oesophagus are integral to its function. The quantification of these properties is necessary to investigate the organ’s pathophysiology and is required for a range of applications including medical device design, surgical simula-tions and tissue engineering. However, according to a systematic review of mechanical exper-imentation conducted on the gastrointestinal organs, the discrete layer-dependent properties of the oesophagus have not been investigated using human tissue, especially regarding its vis-coelastic and stress-softening behaviour. Therefore, extensive experimentation was conducted to determine the time, layer and direction-dependent material response of the oesophagus us-ing cadaveric human tissue. The residual strains of the organ were also considered via opening angle experiments. Overall, the results showed distinct properties in each layer, highlighting the importance of treating the oesophagus as a multi-layered composite material. Furthermore, a strong anisotropy was exhibited across both layers, where the longitudinal directions were much stiffer than the circumferential directions. Due to the COVID-19 pandemic, fresh human cadavers were not available from the anatomy laboratory for a considerable amount of time. Therefore, mechanical testing was first completed on embalmed human tissue and then, once available, on fresh human tissue. This unforeseen circumstance, through comparison of the two preservation states, allowed for an interesting discussion on the role of the tissue’s con-stituents on its complex material behaviour. In addition, histological analysis was carried out to determine the density of the oesophagus’ most mechanically relevant fibres: collagen and elastin. This knowledge was then used to inform constitutive modelling of the soft tissue’s behaviour, the outcome of which was able to capture the anisotropy, visco-hyperelasticity and stress-softening observed in the experimental data

Association of Aerobic Fitness and Metabolic Syndrome in Male Firefighters

Association of Aerobic Fitness and Metabolic Syndrome in Male Firefighters. Durcan, C.M.*, S.E. Martin‡, B.S. Lambert†, N.P. Greene†, J.M. Markos†, A.F. Carbuhn†, J.S. Green‡, FACSM and S.F. Crouse‡, FACSM. Department of Health and Kinesiology, Texas A&M University, College Station, TX. Metabolic syndrome has been shown in numerous studies to be related to a higher incidence of coronary artery disease. A study by R. Jurca et.al., in Med. Sci. Sports Exerc 36(38), found a relationship between aerobic fitness and the prevalence of metabolic syndrome in a group of men enrolled in the Aerobics Center Longitudinal Study. Information on this relationship in male firefighters is currently lacking. Purpose: To determine the association of metabolic syndrome and aerobic fitness in male fire fighters. Methods: As part of an annual physical exam, 213 male fire fighters (average age = 37) underwent evaluation of risk factors associated with metabolic syndrome as defined by NCEP III. These include the presence of three or more of the following: Waist circumference \u3e 40 , HDL Cholesterol \u3c 40 mg/dL, Triglycerides \u3e 150 mg/dL, Blood Glucose \u3e 110 mg/dL, and resting blood pressure \u3e 130/85 mm Hg. Aerobic Fitness was determined by estimating VO2max from time on treadmill during a Bruce protocol. Results: The subjects were ranked and divided into quartiles based on VO2max. All data were analyzed using a Chi Square test (p \u3c .05). Prevalence of metabolic syndrome increased significantly across quartiles as aerobic fitness declined. Conclusion: The data suggest that as aerobic fitness improves, the likelihood of male firefighters having metabolic syndrome decreases. These data are similar to the results found by R. Jurca et.al

The Cell and Molecular Biology of Neurodegenerative Diseases: An Overview

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Characterization of the layer, direction and time-dependent mechanical behaviour of the human oesophagus and the effects of formalin preservation

The mechanical characterization of the oesophagus is essential for applications such as medical device design, surgical simulations and tissue engineering, as well as for investigating the organ’s pathophysiology. However, the material response of the oesophagus has not been established ex vivo in regard to the more complex aspects of its mechanical behaviour using fresh, human tissue: as of yet, in the literature, only the hyperelastic response of the intact wall has been studied. Therefore, in this study, the layer-dependent, anisotropic, visco-hyperelastic behaviour of the human oesophagus was investigated through various mechanical tests. For this, cyclic tests, with increasing stretch levels, were conducted on the layers of the human oesophagus in the longitudinal and circumferential directions and at two different strain rates. Additionally, stress-relaxation tests on the oesophageal layers were carried out in both directions. Overall, the results show discrete properties in each layer and direction, highlighting the importance of treating the oesophagus as a multi-layered composite material with direction-dependent behaviour. Previously, the authors conducted layer-dependent cyclic experimentation on formalin-embalmed human oesophagi. A comparison between the fresh and embalmed tissue response was carried out and revealed surprising similarities in terms of anisotropy, strain-rate dependency, stress-softening and hysteresis, with the main difference between the two preservation states being the magnitude of these properties. As formalin fixation is known to notably affect the formation of cross-links between the collagen of biological materials, the differences may reveal the influence of cross-links on the mechanical behaviour of soft tissues

Investigating soil carbon dynamic along land use change gradients in subtropicaland tropical grazing lands

Tropical and subtropical forests play an important role in the carbon cycle. Being situated in warmer climates, these forests have the potential to sequester large amounts of soil carbon and mitigate against climate change. Despite this, due to increased demand for livestock and other agricultural products, deforestation followed by grazing in these climates have led to the emission of large amounts of greenhouse gas emissions, and degradation of soils. In order to understand how soil carbon sequestration can be maximized in these environments in the future, it is imperative to understand the impacts of land use change on soil carbon dynamics and the complex interactions between soil characteristics and vegetation, something which is understudied in particular for the tropics and sub-tropics. This thesis aimed to investigate the impacts of land use conversion for grazing on soil carbon dynamics and soil quality through the analysis of existing data, and further detailed research into a subtropical dry forest ecosystem. A meta-analysis gathered existing data to investigate the impacts of grazing and land management practices on soil organic carbon and other soil properties in subtropical and tropical climates, identifying that low intensity grazing (into grazing lands through a chronosequence design over a land use transition in the Chaco, Argentina (Forest – Young Pasture (0-5 years) – Intermediate Pasture (10-15 years) – Old Pasture (>20 years), showed that deforestation decreases soil carbon stocks (0-50 cm)in the topsoil by 16 – 53%, alongside decreases in soil nitrogen (5 – 55%), total phosphorus (6 – 68%), and root biomass (68 – 82%). Whilst age of pasture did not impact soil C or N, total P was observed to increase by 46% between intermediate and old pastures. Deforestation in this region has increased pH and decreased electrical conductivity (by 8 – 13%, and 28 – 69% respectively), and increased the salinity and sodicity of these soils, with changes in the dominance of cations in sites with the loss of native vegetation. The analysis of phospholipid-derived fatty acids (PLFAs) in soil samples – a proxy of microbial community composition showed that intermediate pastures had decreased total fungal and total gram-negative bacteria than forest soils in the topsoil, whereas in the subsoil total fungal PLFAs decreased in comparison to young pastures

An Investigation Of The Factors Associated With Community Ambulation In Chronic Stroke

Loss of independent community ambulation is one of the most disabling consequences of stroke. While the relationship between gait speed and community ambulation has been well established, other underlying factors that may influence return to independent community ambulation post stroke are not clearly understood. Aims and Objectives: The aim of this research was to investigate the factors associated with community ambulation in patients between one and three years post stroke. More specifically, it examined the association of multiple personal and post stroke factors with community ambulation and which factors were independently associated with community ambulation. Methods: A cross-sectional study design was used. Forty community-dwelling stroke patients, between one and three years post stroke were recruited into the study. Each participant attended Baggot Street Hospital for one assessment. The primary outcome measure was a Community Ambulation Questionnaire. Other outcome measures included: 10 Metre Walk Test, Timed-Up and Go Test, Activities-Specific Balance Confidence Scale, Fatigue Severity Scale, Hospital Anxiety and Depression Scale, Trail-Making Test-Part B and Single Letter Cancellation Test. Demographic information was also recorded ii Results: Age, number of medications and use of a walking aid were found to be significantly associated with community ambulation (p ≤ 0.05). Gait speed, walking balance and balance self-efficacy were also found to be significantly associated with community ambulation (p ≤ 0.05). Balance self-efficacy was the only factor independently associated with community ambulation post stroke. Conclusion: Balance self-efficacy may be a significant determinant in the attainment of independent community ambulation post stroke. This suggests that physical aspects such as gait speed and walking balance should not be considered in isolation when addressing community ambulation post stroke. Implication of Findings: Clinically, the results support the need for assessment and treatment of balance self-efficacy when addressing community ambulation post stroke. Also, the role of balance self-efficacy should be considered when developing future outcome measures and interventions for community ambulation post stroke

DRAC:Dose Rate and Age Calculator for trapped charge dating

Accurate calculation of the environmental radiation dose rate (Ḋ) is an essential part of trapped charge dating methods, such as luminescence and electron spin resonance dating. Although the calculation of Ḋ is not mathematically complex, the incorporation of multiple variables and the propagation of uncertainties can be challenging. The Dose Rate and Age Calculator (DRAC) is an open access, web-based program which enables rapid Ḋ calculation for trapped charge dating applications. Users can select from recently published attenuation and conversion factors to make mathematically robust, reproducible Ḋ calculations. Comparison of DRAC calculated Ḋ values against the published Ḋ determinations of 422 samples from 32 studies results in a reproducibility ratio of 1.01 ± 0.05. It is anticipated that DRAC will facilitate easier inter-laboratory comparisons and will provide greater transparency for Ḋ calculations. DRAC will be updated to reflect the latest advances in Ḋ calculation and is freely accessible at www.aber.ac.uk/alrl/drac. The code for DRAC is available from github at https://github.com/DRAC-calculator/DRAC-calculator