A Finite Element Model for Describing the Effect of Muscle Shortening on Surface EMG

A finite-element model for the generation of single fiber action potentials in a muscle undergoing various degrees of fiber shortening is developed. The muscle is assumed fusiform with muscle fibers following a curvilinear path described by a Gaussian function. Different degrees of fiber shortening are simulated by changing the parameters of the fiber path and maintaining the volume of the muscle constant. The conductivity tensor is adapted to the muscle fiber orientation. In each point of the volume conductor, the conductivity of the muscle tissue in the direction of the fiber is larger than that in the transversal direction. Thus, the conductivity tensor changes point-by-point with fiber shortening, adapting to the fiber paths. An analytical derivation of the conductivity tensor is provided. The volume conductor is then studied with a finite-element approach using the analytically derived conductivity tensor. Representative simulations of single fiber action potentials with the muscle at different degrees of shortening are presented. It is shown that the geometrical changes in the muscle, which imply changes in the conductivity tensor, determine important variations in action potential shape, thus affecting its amplitude and frequency content. The model provides a new tool for interpreting surface EMG signal features with changes in muscle geometry, as it happens during dynamic contractions

Inverse method for static load reconstruction with sensitivity filtering and optimal sensor placement

Thesis (MEng)--Stellenbosch University, 2021.ENGLISH ABSTRACT: Static load reconstruction is a technique that uses the surface strain response of a prototype structure, in conjunction with a numerical model, to determine the magnitude of the applied loads with a least-squares estimate. A unit-load finite element (FE) model describes the relationship between every input load and the elemental output strain where each finite-element represents a potential location for mounting a strain gauge. The candidate set contains every desired potential gauge location-orientation combination (or candidate point). It is impossible to mount gauges at every candidate point, but with a D-optimal design, the optimal sensor placement can be determined. The response is assumed linear in order for the superposition principle to hold. The D-optimal design selects elements that span the maximum volume of the candidate set, but makes no consideration for the practical aspects associated with mounting strain gauges. For example, during pilot studies, the design chose locations which were either inaccessible or where gauges measured incorrect strain values. A variety of filters have been designed to exclude specific elements from the candidate set to prevent any practical difficulties in mounting strain gauges. These filters are not limited to load reconstruction and can also be used in other strain gauge operations. The structural filters remove elements at open and sharp edges as well as triangular finite-elements. Next, incorrect values will be measured if the strain output is below the measuring capability of the sensor; thus, another filter excludes elements whose numerically computed strain values are below this threshold. Experience has taught that a strain gauge should be mounted in an area of high strain, but of low strain gradient. The final alter is a statistical algorithm that considers high strain gradients to be outliers and utilises an adjusted boxplot method to remove candidate points that are associated with a high strain gradient. Numerical experiments investigated the optimisation of various versions of the candidate set, as well as how the number of candidate points in the design matrix affects the reconstructed loads. All methods worked adequately, and more points in the design (proportionality) matrix improved the accuracy with which loads were calculated. During a physical experiment, it was found that a weighted average proportionality matrix should be used to reconstruct the applied loads if a strain gauge is glued over more than one finite-element. Furthermore, the most signifcant source of error between the calculated and actual loads originates from the differences between the FE and the actual model.AFRIKAANSE OPSOMMING: Statiese lasrekonstruksie is 'n tegniek wat die oppervlakterespons van 'n prototipe-struktuur gebruik om die grootte van die insetlaste te bepaal. As `n prototipe van die struktuur bestaan, kan die vervorming op die oppervlak gebruik word, met behulp van `n numeriese model, om die grootte van die insetlaste te bereken, mits die struktuur se respons linieêr is, sodat die beginsel van superposisie toegepas kan word. Die verhouding tussen die insetlaste en oppervlakvervorming kan bepaal word met behulp van `n eenheidslas-eindige elementmodel, waar elke element in die eindige elementmodel `n posisie voorstel waar `n rekstrokie geplak kan word teen `n sekere oriëntasie. Alle moontlike posisie-oriëntasie kombinasies word saamgestel in `n enkele struktuur, wat die kandidaatstel genoem word. Dit is ontmoontlik om `n rekstrokie by elke moontlik posisie-oriëntasie kombinasie (d.w.s kandidaatpunt) te plak, dus is 'n D-optimale ontwerp gebruik om optimale sensor plasings te bepaal. Die D-optimale ontwerp kies kandidaatspunte wat strek oor die volume van die kandidaatstel, maar maak geen voorsiening vir die praktiese aanhegtig van rekstrokies nie. Dit veroorsaak dat die algoritme elemente kies wat ontoeganklik is, of die rekstrokie verkeerde lesings meet. Filters is ontwerp om sekere elemente van die kandidaatstel te verwyder. Hierdie filters is nie beperk tot lasrekonstruksie nie en kan vir ander rekstrokie verwante toetse ook gebruik word. Die strukturele filters verwyder alle driehoekige elemente, asook elemente wat teen oop en skerp rande gevind word vanuit die numeriese model. `n Rekstrokie sal 'n verkeerde lesing meet indien dit geplak word waar die vervorming kleiner is as die minimum meetvermoë van die rekstrokie, dus moet elemente wat geassosieer word met `n klein vervormingswaarde verwyder word van die kandidaatstel. Verder het ervaring geleer dat 'n rekstrokie ideaal in `n area met hoë vervorming geplak moet word, maar waar die vervormingsgradiënt laag is. `n Statistiese filter is ontwerp wat hoë spanningsgradiënte as uitskieters sien en 'n aangepaste `boksplot' metode is gebruik om elemente, wat geassosieer word met hierdie uitskieters, vanuit die kandidaatstel te verwyder. Numeriese eksperimente is uitgevoer om te ondersoek hoe verskillende variasies van die kandidaatstel die D-optimale ontwerp beïnvloed, asook hoe die aantal kandidaatspunte in die ontwerpsmatriks die rekonstruksie van insetlaste verander. Dit is bevestig dat alle variasies van die kandidaatstel bevredigend werk en dat hoe meer punte daar in die ontwerpsmatriks is, hoe meer akkuraat word die laste gerekonstrueer. Nadat al die bogenoemde oorwegings in ag geneem is, is 'n siese eksperiment uitgevoer. Daar is gevind dat indien 'n rekstrokie oor meer as een eindige-element geplak word, dat `n geweegde gemiddelde ontwerpsmatriks gebruik moet word om die insetlaste te bereken. Verder is dit bevestig dat die grootste oorsaak van foute ontstaan uit verskille tussen die numeriese en die werklike model.Master

A Finite Element Model for Describing the Effect of Muscle Shortening on Surface EMG

A finite-element model for the generation of single fiber action potentials in a muscle undergoing various degrees of fiber shortening is developed. The muscle is assumed fusiform with muscle fibers following a curvilinear path described by a Gaussian function. Different degrees of fiber shortening are simulated by changing the parameters of the fiber path and maintaining the volume of the muscle constant. The conductivity tensor is adapted to the muscle fiber orientation. In each point of the volume conductor, the conductivity of the muscle tissue in the direction of the fiber is larger than that in the transversal direction. Thus, the conductivity tensor changes point-by-point with fiber shortening, adapting to the fiber paths. An analytical derivation of the conductivity tensor is provided. The volume conductor is then studied with a finite-element approach using the analytically derived conductivity tensor. Representative simulations of single fiber action potentials with the muscle at different degrees of shortening are presented. It is shown that the geometrical changes in the muscle, which imply changes in the conductivity tensor, determine important variations in action potential shape, thus affecting its amplitude and frequency content. The model provides a new tool for interpreting surface EMG signal features with changes in muscle geometry, as it happens during dynamic contractions

Risk factors of poor anthropometric status in children under five years of age living in rural districts of the Eastern Cape and KwaZulu-Natal provinces, South Africa

Objectives: Factors associated with children’s anthropometric status were determined.Design: Secondary analysis was done using data from a cross-sectional survey including children under five years of age (n = 2 485) and their mothers in rural districts of the Eastern Cape and KwaZulu-Natal provinces, South Africa.Methods: Data generated by questionnaire and anthropometric indices were used to construct a logistic regression model, taking into account hierarchical relationships of risk factors to determine the odds of a child being stunted, underweight or overweight. Statistical significance was set at p < 0.05.Results: Factors associated with stunting were child of male gender (odds ratio (OR) = 1.233), the mother’s perception that child was not growing well (OR = 1.346), household receiving no food handouts (OR = 0.719) and mother not making important household decisions (OR = 0.760). Underweight was associated with child of male gender (OR = 1.432), low maternal education (OR = 1.720), mother’s perception that child was not growing well (OR = 2.526), any current breastfeeding (children < 24 months: OR = 2.022), and prior gastrointestinal symptoms (OR = 1.527). Factors associated with child overweight were the household not having a regular source of income (OR = 1.473), low maternal education (OR = 0.595) and mother’s perception that child is not growing well (OR = 0.361).Conclusion: Boys were more likely to be stunted and/or underweight.  children of mothers with less than five years schooling were more likely to be underweight. A regular source of household income was associated with child overweight/obesity.Keywords: child malnutrition; risk factors; stunting; underweight; overweight; rural; South Afric

Analysis of time to regulatory and ethical approval of SATVI TB vaccine trials in South Africa

Background. Tuberculosis (TB) vaccine trials in South Africa must be approved by the Medicines Control Council (MCC) and by a human research ethics committee (HREC). Delays in regulatory and ethical approval may affect operational and budget planning and clinical development of the product. Aim. Our aim was to analyse the time to regulatory and ethical approval for TB vaccine trials conducted by the South African Tuberculosis Vaccine Initiative (SATVI) and to evaluate factors that influence time to final approval. Method. Sixteen new TB vaccine clinical trials conducted by SATVI between 2004 and 2012 on infants, children, and adults were included. The period between submission and final approval was determined for protocols submitted to the MCC and the University of Cape Town HREC. Results. Median approval time following first submission to the MCC was 122 days (IQR 112 - 168; range 71 - 350), and for protocol amendments 103 days (interquartile range (IQR) 76 - 141; range 23 - 191; n=30). Median time following first submission for HREC approval was 60 days (IQR 33 - 81; range 18 - 125), and for amendments 6 days (IQR 4 - 13; range 1 - 37; n=30). There was no significant difference in approval time by trial phase, year of submission, revisions required, study population, sample size, or whether a clinical research organisation (CRO) was used. Conclusion. The time needed for regulatory and ethics approval was highly variable, but MCC approval for first submissions took twice as long as HREC approval and was the primary determinant of time to final approval. National regulatory capacity should be strengthened to facilitate the conduct of new TB vaccine trials in this country with its high burden of TB

Risky behaviour and psychosocial correlates in adolescents – is there a link with tuberculosis?

Objective: Reasons for the increase in incidence of Tuberculosis (TB) in late adolescence are poorly understood. One hypothesis is that psychological and behavioural variables associated with adolescence may increase risk of developing TB. The study aimed to determine whether psychosocial and behavioural variables affect incidence of TB disease in adolescents. Methods: A casecontrol study design was used in adolescents who were participants in a TB epidemiological study. Cases were adolescents diagnosed with TB disease. Approximately half of the controls had no TB disease but a positive TST indicative of latent TB. Half had neither TB disease nor latent TB. A self-administered questionnaire was completed by participants. The questionnaire consisted of a combination of standardised psychosocial instruments. Results: Of 292 participants, 62 were cases, 112 had latent TB and 118 neither TB disease nor latent TB. There were no significant differences in instrument scores between cases and controls. There was a trend for certain adverse life events to be more common in the TB-disease group. Conclusion: In adolescents, a trend for association between TB incidence and psychosocial and behavioural variables was not statistically significant. Given the trend, research with larger samples, and more comprehensive assessment of the relationship between stressors and TB, is warranted.Keywords: Tuberculosis; Adolescents; Self-injurious behaviour; Psychosocial factor

Induction of Granulysin and Perforin Cytolytic Mediator Expression in 10-Week-Old Infants Vaccinated with BCG at Birth

Background. While vaccination at birth with Mycobacterium bovis Bacilli Calmette-Guérin (BCG) protects against severe childhood tuberculosis, there is no consensus as to which components of the BCG-induced immune response mediate this protection. However, granulysin and perforin, found in the granules of cytotoxic T lymphocytes and Natural Killer (NK) cells, can kill intracellular mycobacteria and are implicated in protection against Mycobacterium tuberculosis. Methods. We compared the cellular expression of granulysin and perforin cytolytic molecules in cord blood and peripheral blood from 10-week-old infants vaccinated at birth with either Japanese or Danish BCG, administered either intradermally or percutaneously. Results. In cord blood, only CD56+ NK cells expressed granulysin and perforin constitutively. These cytolytic mediators were upregulated in CD4+ and CD8+ cord blood cells by ex vivo stimulation with BCG but not with PPD. Following BCG vaccination of neonates, both BCG and PPD induced increased expression of granulysin and perforin by CD4+ and CD8+ T cells. There was no difference in expression of cytolytic molecules according to vaccination route or strain. Conclusions. Constitutive expression of perforin and granulysin by cord blood NK-cells likely provides innate immunity, while BCG vaccination-induced expression of these cytolytic mediators may contribute towards protection of the neonate against tuberculosis

Risky behaviour and psychosocial correlates in adolescents - is there a link with tuberculosis?

Reasons for the increase in incidence of Tuberculosis (TB) in late adolescence are poorly understood. One hypothesis is that psychological and behavioural variables associated with adolescence may increase risk of developing TB. The study aimed to determine whether psychosocial and behavioural variables affect incidence of TB disease in adolescents. Methods: A case control study design was used in adolescents who were participants in a TB epidemiological study. Cases were adolescents diagnosed with TB disease. Approximately half of the controls had no TB disease but a positive TST indicative of latent TB. Half had neither TB disease nor latent TB. A self-administered questionnaire was completed by participants. The questionnaire consisted of a combination of standardised psychosocial instruments. Results: Of 292 participants, 62 were cases, 112 had latent TB and 118 neither TB disease nor latent TB. There were no significant differences in instrument scores between cases and controls. There was a trend for certain adverse life events to be more common in the TB-disease group. Conclusion: In adolescents, a trend for association between TB incidence and psychosocial and behavioural variables was not statistically significant. Given the trend, research with larger samples, and more comprehensive assessment of the relationship between stressors and TB, is warranted