Use of computational fluid dynamics for respiratory units to simulate air-flow through a radial fan

Track 13. Respiratory Mechanics

Track 13

Respiratory Mechanics 4230 We-Th, no. 1 (P64) Particle distribution in four-generation obstructed lung airways H.Y. Luo, '~ Liu. Department ef Mechanical Engineering, The Heng Keng

Polytechnic University, Hung Hem, Kowloon, Hong Kong Chronic Obstructive Pulmonary Disease (COPD), also called chronic obstructive lung disease, is a kind of common disease in lung. It usually results in an inflammation of the bronchi which would narrow and obstruct the airways. This obstruction alters the flow pattern and particle deposition significantly. In order to investigate the effect of COPD on the particle deposition, the multiphase flow in four different three-dimensional four-generation lung models based on the 23-generation model of Weibel (1963) are carried out using a CFD solver. A symmetric model is built as reference. The other three models are considered to be obstructed at different generation. The fully three-dimensional incompressible laminar Navier-Stokes equations and the particle transport equation are solved using hexahedral meshes. Four Reynolds Numbers, which are based on the mean velocity at the inlet and the diameter of the first-generation tube, ranging from 300 to 1200 with increment of 300, are considered in each model. For each Reynolds Number, five cases with different Stokes Numbers, 0.04, 0.06, 0.08, 0.10 and 0.12, are calculated in order to study the effect of the inertia of the particles on the particle distribution patterns. The calculated results show that particle deposition pattern is influenced significantly by the obstructed airways. Generally, the unobstructed side branches have more particles deposited on the wall. On the obstructed side, particles deposit on the inflamed surface due to inertial impaction. Due to the jet effect of obstruction, more particles would deposit on the conjunction of the bifurcation. 4145 We-Th, no. 2 (P64) Differential regulation o f pulmonary endothelial barrier recovery by varying degrees o f cyclic stretch A.A. Birukova, S. Chatchavalvanich, K.G. Birukov. Department ef Medicine,

the University of Chicago, Chicago, IL, USA Ventilator-induced lung injury is a life-threatening complication of mechanical ventilation at high tidal volumes. Besides activation of pro-inflammatory cytokine production, excessive lung distension directly affects blood-gas barrier and lung vascular permeability. To investigate whether restoration of pulmonary endothelial barrier recovery after agonist challenge is dependent on the magnitude of applied cyclic stretch and how these effects are linked to differential activation of small GTPases Rac and Rho, human pulmonary endothelial cells were subjected to physiologically (5% elongation) or pathologically (18% elongation) relevant levels of cyclic stretch. Pathological cyclic stretch enhanced thrombin-induced (50nM, 5min) stress fiber formation, gap formation, and delayed monolayer recovery (50min after thrombin stimulation). In contrast, physiological cyclic stretch induced nearly complete endothelial barrier recovery accompanied by peripheral redistribution of focal adhesions and cortactin after 50min of thrombin challenge. Consistent with differential effects on monolayer integrity, 18% cyclic stretch enhanced thrombin-induced Rho activation, whereas 5% cyclic stretch promoted Rac activation during endothelial barrier recovery phase. Downregulation of Rac activity by pharmacological inhibitor NSC-23766 (200pM, 1 hr) or Rac protein depletion using siRNAbased approach dramatically attenuated restoration of monolayer integrity after thrombin challenge. In addition, physiological cyclic stretch preconditioning (5% stretch, 24 hrs) enhanced endothelial cell paracellular gap resolution after step-wise increase to 18% stretch (30 min) and thrombin challenge. Our novel data suggest for the first time a critical role for the cyclic stretch amplitude and the balance between small GTPases Rac and Rho in mechanochemical regulation of lung endothelial barrier. 4239 We-Th, no. 3 (P64) Use o f computational fluid dynamics for respiratory units to simulate air-flow through a radial fan N. Sampat, M. Gabi. Department ef Fluid Machinery, Faculty Mechnaical

Engineering, University Karlsruhe, Germany In medical care units for emergency and transport ventilation, respiratory units have been proven to be very useful for patients unable to breath on their own or who have a limited ability for it. Such units can support or even substitute totally the spontaneous gas-exchange between the environment and the lungs. In cases like paralysis of the natural airway, brain-complications or bloodcirculatory disorder, respiratory units become necessary and are based on the natural breathing technique which involves the very delicate lungs.

$593 The common computer-regulated respiratory unit has an air-tank and welldefined medically grounded modes likethe Positive End Expiratory Pressure mode, to pump air in the lungs. An air-tank is heavy and cumbersome and as a first step to replace it, a computer-model of a small radial fan with simple blades and a spiral casing is proposed, which fulfills the medical requirements of a given flow rate and overpressure. In literature, some simplified models do exist in order to predict the air-flow through simple radial blades, yet an exact theoretical concept for the shape and number of blades is not available but some rules can be obtained through the CORDIER-DIAGRAM which is based on experimental work. Based on these limitations, for computer simulations, a trial-and-error method was hence put to practice. The computer model of a radial fan with spiral casing was constructed through commercial software-program ICEM used as the mesh-generator. The flow was treated as incompressible, turbulent and the transient case was solved through the Moving-Reference-Frame technique with computational fluid dynamics software STAR-CD which is based on finite-volume method. Results of the flow-simulations will be presented and compared with the medical requirements of overpressure 4000 Pa and a maximum flow rate of 150 liter per minute. 4401 We-Th, no. 4 (P64) 3D-Spirogram: a combinatory system o f image analysis and computational mechanics H. Kitaoka, T. Kijima, I. Kawase. Dept. of Respiratory Disease, Graduate

School of Medicine, Osaka University, Japan Purpose: We have been developing an integrated system for analyzing and simulating the pulmonary function by the use of multi-phase 3D-CT data set of the lung. "3D-Spirogram" is to estimate intra-pulmonary distributions of ventilation, ventilation-perfusion ratio, airflow conductance, and tissue compliance. Methods: 3D-CT data at FRC, FRC+TV, and TLC were acquired at supine postures. Intra-pulmonary displacement vector field of the lung structure was obtained by a non-rigid image registration technique. Ventilation ratio (VR), defined as the increased volume in lung tissue for a unit volume at expiration, was obtained for each voxel. We defined ventilation-tissue mass ratio (VTR, ml/g) as the inhaled air volume per unit mass of lung tissue which is estimated from the CT value. The VTR is approximately equivalent to ventilation-perfusion ratio (VQR) if there are no exudative changes. Inhaled air flow was simulated by CFD method under the assumption of steady laminar flow with free outlet boundary conditions. Relative flow conductances to respective lobes were then obtained by dividing flow rates to lobar bronchi by lobar volumes at expiratory phase. Distribution of tissue compliance was sought as a reverse problem of linear static structural analysis of the lung FE model so as to reproduce the displacement vector field obtained by real CT data analysis. Results: The spatial distribution of VR was consistent with other clinical tests. Histograms of VTR in normal and emphysema cases were similar to those of VQR in literatures. Calculated spatial distributions of the air flow conductance and the compliance were conceivable, although there are no methods to examine the accuracies. Conclusion: Distributions of ventilation ratio and ventilation-tissue mass ratio are useful and practical as clinical tests. Although estimations of airflow conductance and tissue compliance require more improvements, the 3D spirogram will be a useful method for investigating respiratory pathophysiology. 6480 We-Th, no. 5 (P64) Dexamethasone induces stiffening o f alveolar epithelial cells E Puig, N. Gavara, R. Sunyer, D. Navajas, R. Farr6. Unitat Biofisica i

Bioenginyeria, Facultat Medicina, Universitat Barcelona-IDIBAPS, Barcelona,

spain Acute lung injury is characterized by disruption of the alveolar-capillary barrier. The structural integrity of the alveolar monolayer is regulated by the balance between cell-cell and cell-matrix tethering forces and centripetal forces arising from cytoskeletal tension. Drugs altering cell mechanical properties could modify this force balance and mediate barrier integrity. Dexamethasone, an antiinflammatory drug with protective effects in acute lung injury, has been shown to induce remodelling of cell cytoskeleton. The aim of this work was to study the effects of dexamethasone on the viscoelastic properties of cultured human alveolar epithelial cells. Cell viscoelasticity was assessed by optical magnetic twisting cytometry. Alveolar epithelial cells A549 were plated on 6.4 mm plastic wells. After 24 hours of incubation with dexamethasone 1 ~tM (n = 11 ) or vehicle (0.01% DMSO) (n = 11), ferromagnetic microbeads coated with RGD peptide were attached to the cell surface. The beads were magnetized (150 mT) and sinusoidally twisted (3mT, 0.1 Hz). Cell storage (G/) and loss (G') moduli and the loss tangent ('q = G ' / G ~) were computed from twisting torque and bead displacement. In control cells, G/, G ~ and 'q were 1264.7±81.5Pa, 390.3±32.3Pa and 0.318±0.008, respectively (mean±SE). In dexamethasone treated cells, both G ~ and GPrime; were significantly higher than in controls: G~= 1978±226Pa (p<0.01) and G ' = 5 7 2 . 5 ± 5 3 . 5 P a (p<0.01). The