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Incidents – Markers of Resilience or Brittleness?
Published in Erik Hollnagel, David D. Woods, Nancy Leveson, Resilience Engineering, 2017
David D. Woods, Richard I. Cook
These complexities are illustrated by one kind of pattern in adaptive response called ‘decompensation.’ Cases of ‘decompensation’ constitute a kind of incident and have been analyzed in highly automated systems such as aircraft or cardiovascular physiology (Cook et al., 1991; Woods, 1994; Sarter et al., 1997). The basic decompensation pattern evolves across two phases. In the first phase, automated loops compensate for a growing disturbance; the successful compensation partially masks the presence and development of the underlying disturbance. The second phase of a decompensation event occurs because the automated response cannot compensate for the disturbance indefinitely. After the response mechanism’s capacity is exhausted, the controlled parameter suddenly collapses (the decompensation event that leads to the name).
Basic Patterns in How Adaptive Systems Fail
Published in Erik Hollnagel, Jean Pariès, David Woods, John Wreathall, Resilience Engineering in Practice, 2017
David D. Woods, Matthieu Branlat
In this pattern, breakdown occurs when challenges grow and cascade faster than responses can be decided upon and effectively deployed. A variety of cases from supervisory control of dynamic processes provide the archetype for the basic pattern. Decompensation occurs in human cardiovascular physiology, for example, the Starling curve in cardiology. When physicians manage sick hearts they can miss signals that the cardiovascular system is running out of control capability and fail to intervene early enough to avoid a physiological crisis (Feltovich et al., 1989; Cook et al., 1991; Woods and Cook, 2006). Decompensation also occurs in human supervisory control of automated systems, for instance in aviation. In cases of asymmetric lift due to icing or slowly building engine trouble, automation can silently compensate but only up to a point. Flight crews may recognise and intervene only when the automation is nearly out of capacity to respond and when the disturbances have grown much more severe. At this late stage there is also a risk of a bumpy transfer of control that exacerbates the control problem. Noticing early that the automation has to work harder and harder to maintain control is essential (Norman, 1990; Woods and Sarter, 2000 provide examples from cockpit automation). Figure 10.1 illustrates the generic signature for decompensation breakdowns.
Optimization and Dose Reduction in Hybrid Imaging: PET/CT and SPECT/CT
Published in Lawrence T. Dauer, Bae P. Chu, Pat B. Zanzonico, Dose, Benefit, and Risk in Medical Imaging, 2018
Adam M. Alessio, Frederic H. Fahey
PET has an established role for imaging cardiovascular physiology and pathology. In this domain, PET is most commonly used to assess myocardial perfusion using 82Rb. PET offers the added value over cardiac SPECT in being able to quantify myocardial blood flow under conditions of rest and pharmacologic stress.60,61 This quantification has become fairly widespread, with advances in dynamic data processing software offering reproducible estimates of coronary flow reserve.62,63 There are a plethora of other cardiovascular applications including evaluation of myocardial metabolism,64,65 cardiac innervation,66,67 and atherosclerotic plaque evaluation.68
Effects of cardiac growth on electrical dyssynchrony in the single ventricle patient
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2023
O. Z. Tikenoğulları, M. Peirlinck, H. Chubb, A. M. Dubin, E. Kuhl, A. L. Marsden
Following recent developments in computational modeling, cardiac simulations are increasingly able to replicate the mechanisms of cardiovascular physiology and, as such, deliver more and more opportunities for clinical use (Peirlinck et al. 2021c). Computational models can help to understand the cause of, and improve treatment therapies for, congenital heart defects (Salman and Yalcin 2021; Trusty et al. 2018). In this aspect, lumped parameter network models have become a standard method to study the hemodynamics of congenital heart defects (Marsden and Feinstein 2015), including a.o. the effect of dobutamine in Fontan circulation (Sughimoto et al. 2019) and the performance of total cavopulmonary connection on single ventricle circulation (Sundareswaran et al. 2008). More advanced studies develop personalized coupled three-dimensional computational fluid dynamics models with lumped parameter models, as in Schwarz et al. (2021); Yang et al. (2015) where authors simulated hemodynamics of cavopulmonary grafts. Electrophysiology and growth-and-remodeling of CHDs have received less attention (Lee et al. 2018) and are often modeled with reduced-order lumped parameter network models (Hayama et al. 2020). To the authors’ best knowledge, this study is the first attempt to simulate personalized electrophysiology and growth mechanics in single ventricle physiology.
Mock circulatory test rigs for the in vitro testing of artificial cardiovascular organs
Published in Journal of Medical Engineering & Technology, 2019
The design and functioning of an MCTR significantly influence the reliability, precision, and accuracy of the test results. Thus design and fabrication of MCTRs are among the major topics in cardiovascular research. Ideally, there should be some national or international standards compiled and published by government organisations, which should clearly define the system configurations, performance requirements, and operating procedures of the MCTR. The MCTRs in design and in use, whether in-house built or commercially manufactured, should all meet these fundamental criteria. This will effectively minimise the equipment-related experimental errors, increase repeatability and reproducibility and facilitate the comparison of experimental results from different research groups. Indeed there are some relevant standards presently in use, which specify the testing requirements for certain specific medical devices. Examples of these include the British standard for cardiac and vascular implants [1], the US FDA standard for cardiac monitor devices [2], and the ISO standard for cardiac valve prostheses [3]. However, given the wide range of testing needs and lack of coordination among the authorities in different countries, a formal standard for the MCTR is still not available at present. Researchers and manufacturers generally build the MCTR systems based on their own needs and understanding of the cardiovascular physiology.
Heparinized PCL/keratin mats for vascular tissue engineering scaffold with potential of catalytic nitric oxide generation
Published in Journal of Biomaterials Science, Polymer Edition, 2018
Xiuzhen Wan, Yanfang Wang, Xingxing Jin, Pengfei Li, Jiang Yuan, Jian Shen
NO plays a crucial role in the cardiovascular physiology because it inhibits platelet activation and aggregation, prevents atherosclerosis, suppresses vascular SMC proliferation while enhances HUVEC adhesion, proliferation and migration [28,29,32]. Figure 6b shows the effect of GSNO concentration on the HUVEC viability. Keratin was able to promote GSNO to release NO in the presence of GSH. It can be explained that the residual disulfide bonds of keratin are first reduced into thiols by GSH, which then promote the NO transfer from GSNO and the following release [33]. Regarding 1 ∼ 3 μM GSNO, HUVEC viability was improved due to NO release. However, for 4 μM GSNO, the growth of HUVEC was inhibited. It was because the higher GSNO concentration would release excess amount of NO, which brought toxicity to HUVEC cells. Figure 6c shows the NO release as a function of time, ensuring the NO generation from keratins. Previously, our group demonstrated that keratin could catalyze the GSNO to release NO.