Non-reflecting boundary conditions and tensile instability in smooth particle hydrodynamics

This thesis aimed at the understanding and further development of smoothed particle hydrodynamics (SPH). The first part described the implementations of non-reflecting boundary conditions for elastic- waves in SPH. The second part contains a stability analysis of the semi-discrete SPH equations and a new method for stabilising basic SPH in tension

Oral and small intestinal sensitivity to fats in lean and obese humans : implications for energy intake regulation in obesity.

The research presented in this thesis focuses on the complex and interrelated oral and gastrointestinal mechanisms involved in the regulation of appetite and energy intake in lean and obese individuals. The three broad areas of research that have been investigated in the thesis include: i) the gastrointestinal motor and hormonal functions involved in the regulation of energy intake in healthy individuals; ii) the effects of oral and intraduodenal nutrients on gastrointestinal motility and hormone release, appetite and energy intake in obese compared with lean individuals; and iii) the effects of acute and prolonged energy restriction on gastrointestinal function, appetite and energy intake. Following ingestion of a meal, the interaction of nutrients with receptors in the small intestinal lumen modulates gastro-pyloroduodenal motility, stimulates the release of gastrointestinal hormones, and suppresses appetite and energy intake. It appears that modulation of gastrointestinal functions, that is, gastrointestinal motility and hormone release/suppression, mediate the regulation of appetite and acute energy intake in humans, at least in part. Changes in motility and hormone secretion occur concurrently with changes in appetite; however, there is little information regarding which, if any, of these factors are independent determinants of energy intake. In the study presented in Chapter 5, we determined independent predictors of energy intake and identified specific changes in gastrointestinal motor and hormone functions (i.e. stimulation of pyloric pressures and plasma cholecystokinin) that are associated with the suppression of acute energy intake in healthy lean males. The incidence of obesity is rapidly increasing and, currently, the therapies used for the prevention and management of obesity have limited long-term benefits. In addition, the available therapies have largely ignored the pivotal role of the gastrointestinal tract in the regulation of appetite. There is evidence that gastrointestinal function in obesity is modified, which may be the result of the eating habits of obese individuals and, in turn, may also contribute to the maintenance of obesity by causing insufficient suppression of energy intake. However, much of the literature relating to gastrointestinal function in the obese is inconclusive and controversial. A better understanding of any adaptations that occur in obesity is important, particularly in regards to treatment approaches for weight loss. There is also evidence that previous patterns of energy intake, in excess or in restriction, even when sustained for short periods, have the capacity to modify gastrointestinal function and energy intake. For example, in humans following a high fat diet for two weeks, gastric emptying and mouth-to-caecum transit in response to a high fat test meal were faster. In contrast, fasting had the opposite effect and a four-day fast slowed gastric emptying of a glucose drink in both lean and obese subjects, suggesting that a reduction in nutrient exposure may increase the sensitivity of gastrointestinal responses to nutrients in the obese. Although many studies have addressed aspects of gastrointestinal function in the obese, there is a lack of studies that have evaluated gastric emptying and gastrointestinal hormone release specifically GLP-1 and GIP, given the risk of diabetes in obesity, as well as previous patterns of nutrient intake concurrently. In the study presented in Chapter 6, we evaluated the effects of oral ingestion of a nutrient liquid on gastric emptying, oro-caecal transit, plasma GLP-1 and GIP, appetite and energy intake, as well as, habitual energy and fat intake in lean, overweight and obese individuals. We reported no differences in gastric emptying, intragastric distribution or oro-caecal transit between the lean, overweight and obese groups. After the drink, blood glucose and plasma insulin were greater in the obese, when compared with both the lean and overweight groups, however, there were no differences in plasma GLP-1 or GIP concentrations, appetite and energy intake at the buffet meal or habitual energy intake between the groups. In the obese, the magnitude of the rise in blood glucose was inversely related to the gastric emptying, suggesting that obesity per se, in the absence of differences in habitual energy intake, has no effect on gastric emptying or incretin hormone release and that gastric emptying influences postprandial blood glucose in the obese. In Chapter 7, we investigated the hypothesis that gastrointestinal and oral sensitivity to fat is compromised in the obese and directly related to their high fat/energy consumption. For this purpose, we investigated the effects of an intraduodenal infusion (to bypass gastric emptying), of a fatty acid (oleic acid) on gastrointestinal function, appetite and energy intake, and relationships with habitual energy intake and oral fatty acid detection threshold in lean and obese individuals. We report that pyloric pressure, which plays a major role in the regulation of gastric emptying, was lower in response to intraduodenal oleic acid infusion, with trends for reduced cholecystokinin stimulation and energy intake responses in the obese compared with lean. Oral fatty acid detection thresholds were higher in obese compared with lean subjects, and obese subjects also had greater habitual energy and fat intakes than lean subjects. The results suggest that the ability to detect fats both orally and within the gastrointestinal tract is compromised in obese males, probably due to their increased fat consumption. In the study presented in Chapter 8, we evaluated the hypothesis that in obese individuals, the effects of duodenal fat on gastrointestinal motor and hormone function, and appetite would be enhanced by a short period on a very low calorie diet. We demonstrated that following a 70% four-day very low calorie diet there was a significant increase in pyloric pressure and the stimulation of PYY and suppression of ghrelin was greater during an intraduodenal lipid infusion. In addition, following the four-day very low calorie diet, appetite perceptions and energy intake in response to intraduodenal lipid were reduced, indicating that gastrointestinal function, appetite and energy intake in obese can be enhanced over a short period. Given that gastrointestinal function is sensitive to changes even over short periods of dietary restriction, it is important to determine whether these changes are maintained in the long term in order to determine the efficacy of energy restriction therapies for obesity. To maintain dietary restriction and weight loss in the longer term, we used a 30%, as opposed to 70%, energy-restricted diet. In the study presented in Chapter 9, we evaluated the effects of an acute (in lean and obese) and prolonged (in obese only) 30% energy restriction on gastrointestinal function and appetite in response to an intraduodenal lipid infusion. In contrast to the previous 70% very low calorie diet study, there were no differences in gastrointestinal motor or hormonal function in the obese following the acute or prolonged 30% dietary restriction period, although there was a trend for energy intake to be reduced. However, in the lean, there was a decrease in plasma CCK and an increase in ghrelin concentrations following the acute period of dietary restriction with no differences in gastrointestinal motility or energy intake, suggesting that a 30% energy-restricted diet diminishes gastrointestinal hormone responses in lean, but not obese, which may suggest that obese are less sensitive to this caloric restriction. These observations will contribute to the advances in basic appetite physiology and will have clinical implications for further development of dietary interventions for the treatment of obesity.Thesis (Ph.D.) -- University of Adelaide, School of Medicine, 201

Effect of a 4-week weight maintenance diet on circulating hormone levels: implications for clinical weight loss trials

Summary The majority of weight loss studies fail to standardize conditions such as diet and exercise via a weight maintenance period prior to commencement of the trial. This study aimed to determine whether a weight stabilization period is necessary to establish stable baseline hormone concentrations. Fifty-one obese male participants with a body mass index of 30–40 kg m−2 and aged 25–54 years underwent 4 weeks on an energy balance diet that was designed to achieve weight stability. Blood samples were collected in the fasting state at commencement and completion of the 4-week period, and circulating concentrations of 18 commonly measured hormones were determined. During the 4-week weight maintenance period, participants achieved weight stability within −1.5 ± 0.2 kg (−1.4 ± 0.2%) of their initial body weight. Significant reductions in serum insulin (by 18 ± 6.5%) and leptin (by 21 ± 6.0%) levels occurred, but no significant changes were observed for gut-derived appetite-regulating hormones (ghrelin and peptide YY), nor thyroid, adrenal, gonadal or somatotropic hormones. There were no significant correlations between the change in body weight and the change in circulating concentrations of insulin or leptin over the 4-week period, indicating that the observed changes were not due to weight loss, albeit significant negative correlations were observed between the changes in body weight and plasma ghrelin and peptide YY levels. This study demonstrates the need for baseline weight maintenance periods to stabilize serum levels of insulin and leptin in studies specifically investigating effects on these parameters in the obese. However, this does not apply to circulating levels of gut-derived appetite-regulating hormones (ghrelin and peptide YY), nor thyroid, adrenal, gonadal or somatotropic hormones

Open complete dislocation of trapezium with a vertically split fracture: a case report

Open complete dislocation of the trapezium is an extraordinarily rare injury with only a few cases reported so far in literature. The association of a vertically split fracture makes this injury even rare and hence worth reporting. A 14 year old Kashmiri boy presented to us with a history of massive trauma to the non dominant left hand sustained as a result of a blow from a heavy hammer. The thenar area was burst out and the trapezium was vertically split apart into two halves which were dislocated from the articular surfaces of the scaphoid as well as the first metacarpal. The mechanism of injury as in other such reported cases was a massive direct force localized over the carpal bone which causes its enucleation and fracture. Although some authors have recommended excision of the dislocated trapezium, open reduction of the fracture dislocation and fixation with K wires was carried out under General anesthesia. At the end of one year although there was some functional deficit in the affected thumb, especially in opposition, the patient was quite satisfied with the outcome as this was the non dominant hand

Accuracy of hands v. household measures as portion size estimation aids

Accurate estimation of food portion size is critical in dietary studies. Hands are potentially useful as portion size estimation aids; however, their accuracy has not been tested. The aim of the present study was to test the accuracy of a novel portion size estimation method using the width of the fingers as a 'ruler' to measure the dimensions of foods ('finger width method'), as well as fists and thumb or finger tips. These hand measures were also compared with household measures (cups and spoons). A total of sixty-seven participants (70 % female; age 32·7 (sd 13·7) years; BMI 23·2 (sd  3·5) kg/m(2)) attended a 1·5 h session in which they estimated the portion sizes of forty-two pre-weighed foods and liquids. Hand measurements were used in conjunction with geometric formulas to convert estimations to volumes. Volumes determined with hand and household methods were converted to estimated weights using density factors. Estimated weights were compared with true weights, and the percentage difference from the true weight was used to compare accuracy between the hand and household methods. Of geometrically shaped foods and liquids estimated with the finger width method, 80 % were within ±25 % of the true weight of the food, and 13 % were within ±10 %, in contrast to 29 % of those estimated with the household method being within ±25 % of the true weight of the food, and 8 % being within ±10 %. For foods that closely resemble a geometric shape, the finger width method provides a novel and acceptably accurate method of estimating portion size

Fast versus slow weight loss: development process and rationale behind the dietary interventions for the TEMPO diet trial

OBJECTIVE AND METHODS: Finding effective solutions to curb the obesity epidemic is a great global public health challenge. The need for long‐term follow‐up necessitates weight loss trials conducted in real‐world settings, outside the confines of tightly controlled laboratory or clinic conditions. Given the complexity of eating behaviour and the food supply, this makes the process of designing a practical dietary intervention that stands up to scientific rigor difficult. Detailed information about the dietary intervention itself, as well as the process of developing the final intervention and its underlying rationale, is rarely reported in scientific weight management publications but is valuable and essential for translating research into practice. Thus, this paper describes the design process and underlying rationale behind the dietary interventions in an exemplar weight loss trial – the TEMPO Diet Trial (Type of Energy Manipulation for Promoting optimal metabolic health and body composition in Obesity). This trial assesses the long‐term effects of fast versus slow weight loss on adiposity, fat free mass, muscle strength and bone density in women with obesity (body mass index 30–40 kg m(−2)) that are 45–65 years of age, postmenopausal and sedentary. RESULTS AND CONCLUSIONS: This paper is intended as a resource for researchers and/or clinicians to illustrate how theoretical values based on a hypothesis can be translated into a dietary weight loss intervention to be used in free‐living women of varying sizes