mechanical modeling
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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.
- MeSH
- kontrakce myokardu MeSH
- svalová kontrakce MeSH
- teoretické modely MeSH
- Publikační typ
- přehledy MeSH
Interdisciplinary applied mathematics
1st ed. xliii, 634 s., barev. il.
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
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.
In the present study, inflation tests with free axial extension of 15 human vena saphena magna were conducted ex vivo to obtain data suitable for multi-axial constitutive modeling at overloading conditions (pressures up to approximately 15kPa). Subsequently the data were fitted with a hyperelastic, nonlinear and anisotropic constitutive model based on the theory of the closed thick-walled tube. It was observed that initial highly deformable behavior (up to approximately 2.5kPa) in the pressure-circumferential stretch response is followed by progressive large strain stiffening. Contrary to that, samples were much stiffer in longitudinal direction, where the observed stretches were in the range 0.98-1.03 during the entire pressurization in most cases. The effect of possible residual stress was evaluated in a simulation of the intramural stress distribution with the opening angle prescribed to 0°, 10°, 20°, 30°, 40°, and 50°. The result suggests that the optimal opening angle making the stress distribution through the wall thickness uniform is about 40°. The material parameters presented here are suitable for use in mechanobiological simulations describing the adaptation of the autologous vein wall after bypass surgery.
- MeSH
- biologické modely * MeSH
- dospělí MeSH
- lidé středního věku MeSH
- lidé MeSH
- mechanický stres MeSH
- senioři MeSH
- testování materiálů MeSH
- tlak * MeSH
- vena saphena anatomie a histologie fyziologie MeSH
- zatížení muskuloskeletálního systému MeSH
- Check Tag
- dospělí MeSH
- lidé středního věku MeSH
- lidé MeSH
- mužské pohlaví MeSH
- senioři MeSH
- ženské pohlaví MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
INTRODUCTION: There is a striking difference in the reported mean response of abdominal aortic aneurysm tissue in academic literature depending on the type of tests (uniaxial vs biaxial) performed. In this paper, the hypothesis variability caused by differences in experimental protocols is explored using porcine aortic tissue as a substitute for aneurysmal tissue. METHODS: Nine samples of porcine aorta were created and both uniaxial and biaxial tests were performed. Three effects were investigated. (i) Effect of sample (non) preconditioning, (ii) effect of objective function used (normalised vs non-normalised), and (iii) effect of chosen procedure used for mean response calculation: constant averaging (CA) vs fit to averaged response (FAR) vs fit to all data (FAD). Both the overall shape of mean curve and mean initial stiffness were compared. RESULTS: (i) Non-preconditioning led to a much stiffer response, and initial stiffness was about three times higher for a non-preconditioned response based on uniaxial data compared to a preconditioned biaxial response. (ii) CA led to a much stiffer response compared to FAR and FAD procedures which gave similar results. (iii) Normalised objective function produced a mean response with six times lower initial stiffness and more pronounced nonlinearity compared to non-normalised objective function. DISCUSSION: It is possible to reproduce a mechanically inconsistent response purely by using the chosen experimental protocol. Non-preconditioned data from failure tests should be used for FE simulation of the elastic response of aneurysms. CA should not be used to obtain a mean response.
- MeSH
- aneurysma břišní aorty * MeSH
- aorta abdominalis MeSH
- aorta MeSH
- biomechanika MeSH
- mechanický stres MeSH
- počítačová simulace MeSH
- prasata MeSH
- zvířata MeSH
- Check Tag
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
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Vyd. 1. 145 s. : il. ; 30 cm
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.
