mechanical modelling
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- MeSH
- kontrakce myokardu MeSH
- svalová kontrakce MeSH
- teoretické modely MeSH
- Publikační typ
- přehledy MeSH
Autori v práci porovnávajú vypočítané (tstat ) a merané časové konštanty (tdyn) v dvoch skupinách pacientov, ktorí boli dlhodobo ventilovaní ventilačnými režimami CMV, PCV a PSV. Pacienti boli rozdelení do dvoch skupín, prvú skupinu tvorilo 5 pacientov s chronickou obštrukčnou pľúcnou chorobou a druhá skupina pacientov bola bez chronického pľúcneho poškodenia. V exspíriu monitorovali prvú, druhú i tretiu časovú konštantu (tEdyn1,2,3 ), ako aj vypočítanú časovú konštantu ako násobok R . C, t.j. tstat. Zistili, že medzi vypočítanou a meranou časovou konštantou nie je významná korelácia. Pri analýze meraných časových konštánt zistili, že časové konštanty sa od seba líšia nezávisle od aplikovaného spôsobu umelej ventilácie pľúc, a to ako v skupine s CHOPCH, tak v skupine bez predošlého pľúcneho poškodenia. V klinike sa potvrdila teória vyplývajúca z matematického a fyzikálneho modelu, že tEdyn1 > tEdyn2 > tEdyn3. Záverom konštatujú, že v súčasnosti nie je možné ani len teoreticky uvažovať pri hodnotení mechanických vlastností dýchacích orgánov, že časová konštanta je konštantná. Teoretické i klinické merania potvrdzujú, že časové konštanty pri umelej ventilácii pľúc nie sú konštantné.
In the study there are compared calculated (tstat ) and measured time constant (tdyn) in two groups of patients with long-term mechanical ventilation in CMV, PCV and PSV modes. Patients were randomized into two groups: one groups consisted of five COPD patients, the other group consisted of patients with no lung injury. During the expiratory phase, there were monitored first, second and third time constant (tEdyn1,2,3), as well as calculated time constant as the result of R . C i.e. tstat. They found no significant correlation between computed and measured time constant. The analysis of measured time constant revealed differences between time constants irrespectively of the applied mode of mechanical ventilation in both groups with or without COPD. The clinical results confirmed the theory derived from mathematical and physical model that tEdyn1 > tEdyn2 > tEdyn3. In conclusion, when evaluating mechanical characteristics of respiratory organs, we can not even theoretically assume the time constant to be a constant. Theoretical and clinical measurements prove that time constants during mechanical ventilation are not constant.
There is a long history of mathematical and computational modelling with the objective of understanding the mechanisms governing cartilage׳s remarkable mechanical performance. Nonetheless, despite sophisticated modelling development, simulations of cartilage have consistently lagged behind structural knowledge and thus the relationship between structure and function in cartilage is not fully understood. However, in the most recent generation of studies, there is an emerging confluence between our structural knowledge and the structure represented in cartilage modelling. This raises the prospect of further refinement in our understanding of cartilage function and also the initiation of an engineering-level understanding for how structural degradation and ageing relates to cartilage dysfunction and pathology, as well as informing the potential design of prospective interventions. Aimed at researchers entering the field of cartilage modelling, we thus review the basic principles of cartilage models, discussing the underlying physics and assumptions in relatively simple settings, whilst presenting the derivation of relatively parsimonious multiphase cartilage models consistent with our discussions. We proceed to consider modern developments that start aligning the structure captured in the models with observed complexities. This emphasises the challenges associated with constitutive relations, boundary conditions, parameter estimation and validation in cartilage modelling programmes. Consequently, we further detail how both experimental interrogations and modelling developments can be utilised to investigate and reduce such difficulties before summarising how cartilage modelling initiatives may improve our understanding of cartilage ageing, pathology and intervention.
- MeSH
- biologické modely * MeSH
- biomechanika MeSH
- chrupavka patologie fyziologie MeSH
- lidé MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- přehledy MeSH
1st ed. xvi, 595 s.
A three-dimensional finite element model of a vascular smooth muscle cell is based on models published recently; it comprehends elements representing cell membrane, cytoplasm and nucleus, and a complex tensegrity structure representing the cytoskeleton. In contrast to previous models of eucaryotic cells, this tensegrity structure consists of several parts. Its external and internal parts number 30 struts, 60 cables each, and their nodes are interconnected by 30 radial members; these parts represent cortical, nuclear and deep cytoskeletons, respectively. This arrangement enables us to simulate load transmission from the extracellular space to the nucleus or centrosome via membrane receptors (focal adhesions); the ability of the model was tested by simulation of some mechanical tests with isolated vascular smooth muscle cells. Although material properties of components defined on the basis of the mechanical tests are ambiguous, modelling of different types of tests has shown the ability of the model to simulate substantial global features of cell behaviour, e.g. "action at a distance effect" or the global load-deformation response of the cell under various types of loading. Based on computational simulations, the authors offer a hypothesis explaining the scatter of experimental results of indentation tests.
- MeSH
- analýza metodou konečných prvků MeSH
- biologické modely MeSH
- buněčný převod mechanických signálů fyziologie MeSH
- cytoskelet MeSH
- lidé MeSH
- mechanický stres MeSH
- myocyty hladké svaloviny chemie cytologie fyziologie MeSH
- počítačová simulace MeSH
- svaly hladké cévní chemie cytologie fyziologie MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Simulation models in respiratory research are increasingly used for medical product development and testing, especially because in-vivo models are coupled with a high degree of complexity and ethical concerns. This work introduces a respiratory simulation system, which is bridging the gap between the complex, real anatomical environment and the safe, cost-effective simulation methods. The presented electro-mechanical lung simulator, xPULM, combines in-silico, ex-vivo and mechanical respiratory approaches by realistically replicating an actively breathing human lung. The reproducibility of sinusoidal breathing simulations with xPULM was verified for selected breathing frequencies (10-18 bpm) and tidal volumes (400-600 ml) physiologically occurring during human breathing at rest. Human lung anatomy was modelled using latex bags and primed porcine lungs. High reproducibility of flow and pressure characteristics was shown by evaluating breathing cycles (nTotal = 3273) with highest standard deviation |3σ| for both, simplified lung equivalents ([Formula: see text] = 23.98 ± 1.04 l/min, μP = -0.78 ± 0.63 hPa) and primed porcine lungs ([Formula: see text] = 18.87 ± 2.49 l/min, μP = -21.13 ± 1.47 hPa). The adaptability of the breathing simulation parameters, coupled with the use of porcine lungs salvaged from a slaughterhouse process, represents an advancement towards anatomically and physiologically realistic modelling of human respiration.
- MeSH
- biologické modely * MeSH
- lidé MeSH
- mechanika dýchání * MeSH
- plíce MeSH
- počítačová simulace * MeSH
- polymery * MeSH
- umělé dýchání * MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- MeSH
- acetabulum anatomie a histologie fyziologie patologie MeSH
- analýza metodou konečných prvků * využití MeSH
- anatomické modely MeSH
- biomechanika MeSH
- kyčelní kloub * fyziologie patologie MeSH
- kyčelní protézy využití MeSH
- lidé MeSH
- mechanické jevy MeSH
- pánev anatomie a histologie fyziologie patologie MeSH
- počítačová simulace využití MeSH
- statistika jako téma MeSH
- teoretické modely * MeSH
- transplantáty transplantace MeSH
- Check Tag
- lidé MeSH
We combined atomistic molecular-dynamics simulations with quantum-mechanical calculations to investigate the sequence dependence of the stretching behavior of duplex DNA. Our combined quantum-mechanical/molecular-mechanical approach demonstrates that molecular-mechanical force fields are able to describe both the backbone and base-base interactions within the highly distorted nucleic acid structures produced by stretching the DNA from the 5' ends, which include conformations containing disassociated basepairs, just as well as these force fields describe relaxed DNA conformations. The molecular-dynamics simulations indicate that the force-induced melting pathway is sequence-dependent and is influenced by the availability of noncanonical hydrogen-bond interactions that can assist the disassociation of the DNA basepairs. The biological implications of these results are discussed. Copyright 2010 Biophysical Society. Published by Elsevier Inc. All rights reserved.
Understanding the mechanics of the respiratory system is crucial for optimizing ventilator settings and ensuring patient safety. While simple models of the respiratory system typically consider only flow resistance and lung compliance, lung tissue resistance is usually neglected. This study investigated the effect of lung tissue viscoelasticity on delivered mechanical power in a physical model of the respiratory system and the possibility of distinguishing tissue resistance from airway resistance using proximal pressure measured at the airway opening. Three different configurations of a passive physical model of the respiratory system representing different mechanical properties (Tissue resistance model, Airway resistance model, and No-resistance model) were tested. The same volume-controlled ventilation and parameters were set for each configuration, with only the inspiratory flow rates being adjusted. Pressure and flow were measured with a Datex-Ohmeda S/5 vital signs monitor (Datex-Ohmeda, Madison, WI, USA). Tissue resistance was intentionally tuned so that peak pressures and delivered mechanical energy measured at airway opening were similar in Tissue and Airway Resistance models. However, measurements inside the artificial lung revealed significant differences, with Tissue resistance model yielding up to 20% higher values for delivered mechanical energy. The results indicate the need to revise current methods of calculating mechanical power delivery, which do not distinguish between tissue resistance and airway flow resistance, making it difficult to evaluate and interpret the significance of mechanical power delivery in terms of lung ventilation protectivity.
