Distant hemodynamic impact of local geometric alterations in the arterial tree

Thesis (Ph. D.)--Harvard-MIT Division of Health Sciences and Technology, 2003.Includes bibliographical references (leaves 164-169).Hemodynamics has long been identified as a major factor in the determination and localization of atherosclerotic lesions. While the precise mechanism by which different hemodynamic factors act is not yet clear, the fact that they correlate highly with atherogenesis suggests that local disturbances in flow through blood vessels can promote arterial disease. These issues have become increasingly acute as physicians seek to alter the pathological arterial anatomy with bypass grafting or endovascular manipulations such as angioplasty or stenting. We proposed that local vascular interventions might cause previously unforeseen effects elsewhere in the arterial tree. As an example of these interactions, manipulation of one branch of a bifurcation might adversely affect the contralateral branch of the bifurcation. The goal of this work was to study the distant impact of local flow alterations, as well as to classify and evaluate the different parameters that determine their severity. Dynamic flow models of the arterial system were developed that allowed for the continuous alteration of model geometry in a controlled fashion to simulate the healthy and diseased states as well as the entire range in between. Moreover, these models permit simulation of different strategies of clinical intervention. Flow through the models was investigated using both qualitative and quantitative tools. Boundary layer separation and vascular resistance in one location of the arterial tree varied with geometrical alterations in another. In-vivo models were developed that allowed investigation of the effect of side branch occlusion or dilation on the acute and chronic outcome of main branch stenting in a bifurcation. Chronic side branch occlusions were protective of main branch stenting as reflected by a reduction in in-stent neo-intimal hyperplasia.(cont.) This protective influence was mediated by an acute modulation of monocyte adhesion and accumulation on the lateral wall of the main branch, correlating with the location of flow disturbance demonstrated by the flow models. Chronic main branch vascular remodeling plays a major role in achieving this beneficial effect. The results of this study could have important implications for the diagnosis, treatment and long-term follow-up of the large number of patients who suffer from complex arterial diseases and undergo vascular interventions. In clinical manipulation of one arterial site one may well need to consider the hemodynamic impact on vascular segments at a distance.by Yoram Richter.Ph.D

Distant hemodynamic impact of local geometric alterations in the arterial tree

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2000.Includes bibliographical references (leaf 96).Hemodynamics has long been identified as a major factor in the determination and localization of atherosclerotic lesions. Atherosclerosis is focal and often forms in specific locations in the arterial tree such as bifurcations. Many different aspects of fluid mechanics have been suggested as the trigger for atherogenesis - non-laminar and/or unstable flow, flow separation, regions of higher/lower and/or oscillatory shear stress etc. While the precise mechanism by which these hemodynamic factors act is not yet clear, the fact that they correlate highly with atherogenesis suggests that local disturbances in flow through blood vessels can promote arterial disease. These issues have become increasingly acute as physicians seek to alter the pathological arterial anatomy with bypass grafting or endovascular manipulations such as angioplasty or stenting. We proposed that vascular interventions might cause previously unforeseen effects in the arterial tree especially at branch points. Manipulation of one branch of a bifurcation might adversely affect the contralateral branch of the bifurcation. The goal of this work was to study the distant impact of local flow alterations, as well as to classify and evaluate the different parameters that determine their severity. Dynamic flow models of the arterial system were developed that allowed for the continuous alteration of model geometry in a controlled fashion. This property allows for the simulation not only of the healthy or diseased states, but also of the entire range in between. Moreover, these models permit simulation of different strategies of clinical intervention. Flow through the models was investigated using both qualitative (flow visualization) and quantitative (flow and pressure readings) tools. Flow separation and vascular resistance in one location of the arterial tree varied with geometrical alterations in another. The results of this study could have important implications for the diagnosis, treatment and long-term follow-up of the large number of patients who suffer from these diseases and undergo vascular interventions. Clinical arterial manipulation of one arterial site may well need to consider the hemodynamic impact on vascular segments at a distance.by Yoram Richter.S.M

Suppression of environmental health scientists: real-world examples as a basis for action

Pressures on epidemiologists, toxicologists, and on public health scientists to suppress their work are known to occur worldwide. In this article, we share six stories from environmental health scientists about the pressures they faced in their jobs after bringing public health problems to light. The method used to document each of the stories was to invite scientists who attended meetings of the International Society for Environmental Epidemiology to tell their own stories of having experienced research suppression. We then extracted the salient features of each experience into a coherent story, providing references as corroboration where possible. The specific purpose in going public with the six stories presented in this article is to open a conversation to better equip colleagues to stand up to pressures to suppress their work. By publicly sharing the pressures experienced by these scientists in attempts to suppress their scientific work, including intimidation, harassment, threats and/or bullying, other scientists may be better able to withstand such pressures. In the absence of a larger collection of stories, we are unable to identify common approaches taken against suppression. It appears that a focus on scientific excellence and tenacity are two major factors likely to have contributed to the ability to withstand pressure. We encourage others to tell their stories. Bringing examples of these instances to attention will make them familiar enough to be less intimidating should others experience anything similar. Additional documented experiences will expand the base of stories and thus help colleagues to withstand the pressures wielded by special interests. Shining a light on these pressures will remove barriers, not only to advancing the science, but also to protecting the public interest

The role of open abdomen in non-trauma patient : WSES Consensus Paper

The open abdomen (OA) is defined as intentional decision to leave the fascial edges of the abdomen un-approximated after laparotomy (laparostomy). The abdominal contents are potentially exposed and therefore must be protected with a temporary coverage, which is referred to as temporal abdominal closure (TAC). OA use remains widely debated with many specific details deserving detailed assessment and clarification. To date, in patients with intra-abdominal emergencies, the OA has not been formally endorsed for routine utilization; although, utilization is seemingly increasing. Therefore, the World Society of Emergency Surgery (WSES), Abdominal Compartment Society (WSACS) and the Donegal Research Academy united a worldwide group of experts in an international consensus conference to review and thereafter propose the basis for evidence-directed utilization of OA management in non-trauma emergency surgery and critically ill patients. In addition to utilization recommendations, questions with insufficient evidence urgently requiring future study were identified.Peer reviewe

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements