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An experimental investigation on airflow in human airway
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Journal of Biomechanics 2006, Vol. 39 (Suppl 1)
[4] Subramaniam et al. Inhalation Toxicolology 1998; 10: 91-120. 4942 Th, 11:45-12:00 (P41) An experimental investigation on airflow in human airway S.-K. Chu 1, S.K. Kim 2 . 1Dept. ef ORL-HNS, Samsung Medical Center, School
of Medicine, Sungkyunkwan University, South Korea, 2Dept. Mechanical Engineering, Konkuk University, South Korea Knowledge of airflow characteristics in nasal cavities is essential to understand the physiological and pathological aspects of nasal breathing. Several studies have utilized physical models of the nasal cavities to understand the patterns of the airflow. Creating accurate transparent flow passages is essential to analyze the flow by particle image velocimetry (PIV). We established a procedure to construct a transparent rectangular box containing a model of the nasal cavity for PIV measurement by combining the rapid prototyping and the curing of clear silicone. Thin sliced CT data and meticulous refinement of model surface under the ENT doctor's advice provided more sophisticated nasal cavity models. The CBC (Correlation based correction) algorithm with window offset (64 64 to 32 32) is used for vector searching in PIV analysis. From tomographic flow data of sagittal planes, a 3 dimensional velocity data set can be reconstructed. The authors have investigated nasal airflows in normal and abnormal nasal cavities by tomographic PIV; Airflow in nasal cavity and nasopharynx with different degree of adenoid vegetation, changes of airflow after resection of meddle turbinate. We also visualized the airflow pattern during quiet nasal breathing with a periodic pumping system, designed to simulate human breathing. The phase averaged mean and RMS velocity distributions in sagittal and coronal planes were obtained for 17 phases in a respiratory cycle. Recently, we applied these techniques to visualize the respiratory gas flow in human airway including nasal cavities, larynx, trachea, and second bifurcation of the bronchi. Flow characteristics related with abnormalities in nasal cavities are conjectured in some cases. The methodology in this paper can be applied to any other otorhinolaryngological diseases and contributes to help ENT doctors in diagnosis and treatments of these diseases 6735 Th, 12:00-12:15 (P41) Characterisation of nasal geometry and flow A. Gambaruto, D. Doorly. Dept. Aeronautics, Imperial College, London, UK There is a large diversity in the geometric form of the human nasal cavity geometry, and a general lack of understanding of the impact of nasal cavity airway topology on the complex air flow patterns engendered. It is now possible however using MRI or CT techniques to determine nasal cavity geometry invivo, and particularly with CT, with relatively high accuracy. In this study, we present three novel approaches to classify the detailed three-dimensional form of the nasal cavity geometry: discrete harmonic maps, Fourier descriptors and skeletonisation. These procedures also prove useful as techniques for geometry reconstruction, providing objective means to simplify and manipulate the geometry. They act as geometric compression tools for the mesh surface data, with possible application to non-nasal cavity topologies. We present details of the techniques used to obtain common stencils on which to compare the resulting flow features for the different subjects. Classification of the nasal cavity allows for idealisation of the various topologies and hence the formulation of a common norm, permitting the study of significance of patient specific topologies with respect to this norm. This can be seen as a measure of patient deviation from the norm and a rational approach to the study of morphological variations. The methods used in this work thus provide well-defined procedures to compare different subject anatomies and to relate corresponding characteristic geometric variations to differences in the effectiveness of airflow and transport. 7567 Th, 12:15-12:30 (P41) Airflow in the human nasal cavity D.J. Taylor1,2, D.J. Doorly 1, R.C. Schroter2. 1Department of Aeronautics and
2Department of Bioengineering, Imperial College London, London, UK The nose performs many important physiological functions, including: heating, humidifying and filtering inspired air, as well as sampling air to smell. The successful functioning of the nose is highly dependent on the fluid dynamic characteristics of airflow through the nasal cavities. Significant advances in the fields of toxicology, particle deposition, drug delivery and surgical planning could be achieved through an improved understanding of nasal airflow. Although Computational Fluid Dynamics (CFD) has been applied to investigate nasal airflow properties at quiet breathing rates, its predictions are constrained by the complex and unsteady nature of the flow within the complicated geometry. CFD predictions require experimental validation. However, in vive and in vitro flow is confounded by the inaccessibility of the nasal passages. The approach of using optical measurements obtained in transparent model structures is particularly attractive in this situation.
Oral Presentations Transparent nose models were manufactured by casting transparent silicone around twice-scale inverse rapid-prototype geometries of one half of the nasal cavity; these had been previously created by image segmentation of Computed Tomography (CT) medical images. A fidelity survey of the silicone model was also undertaken to ensure it accurately represented the initial virtual CT based geometry. Refractive index matched recirculating liquid was pumped through the nominally normal, anatomically accurate, transparent models to simulate the airflow. Particle Image Velocimetry (PIV) and dye visualisation methods were used to quantify gross flow patterns and velocities in the nose and to assess the stability of the flow, for a range of steady inspiratory flow rates. The results obtained of the gross flow characteristics were compared for two different nasal geometries. Airflow through these geometries was found to be laminar for quiet restful breathing (Reynolds numbers up to 1000), but became transitional at higher flow rates. An insight into the effects that nasal anatomy has on flow can clearly be seen by comparison of the flow patterns and velocities through a normal and "simplified" model, created from the same CT dataset.
Track 14
Cardiovascular Mechanics
14.1. Aneurysms 14.1.1. Aneurysms 7584 Mo, 08:15-08:45 (P6) Analysis of the importance of the ratio of aneurysm size to parent artery diameter on hemodynamic conditions H. Zakaria 1, H. Yonas 2, A.M. Robertson 1. 1Department of Mechanical Engineering, University of Pittsburgh, Pittsburgh, PA, USA, 2Department of Surgery, School of Medicine, University of New Mexico, Albuquerque, NM, USA The geometry of saccular aneurysms is often characterized by three lengths: neck width (N), dome height (H), and dome diameter (D), (e.g. [1]). Aneurysm size has also been found to be strongly correlated with rupture as well as extent of SAH [2]. However, to date, no study has been performed analyzing the impact of aneurysm size on hemodynamics relative to a length scale external to the aneurysm, for example, the parent diameter (P). In this work, we systematically analyze the effect of aneurysm size on hemodynamics by varying the ratio P/N for fixed H/N and D/H. Namely, the shape of the aneurysm is fixed and the size is scaled relative to the parent artery. Three-dimensional models of non-symmetric, saccular aneurysms at symmetric bifurcations were created using a recently developed parametric model. The aspect ratios of the aneurysm were fixed at H/D= 1.1 and H/N = 1.6 while the value of P/N was chosen as (0.47, 0.7, 1.4). The upper and lower choices for P/N correspond to scaling the aneurysm dimensions by a factor of 1.5 and 0.5 respectively. Flow simulations were based on the unsteady Navier-Stokes equations for rigid walled vessels and solved by the finite element method using ADINA software (ADINA Inc.). Aneurysm size was found to have both a qualitative and quantitative effect on the hemodynamics in and around the aneurysm including pathlines, influx rate and location of maximum wall shear stress (WSS). With increasing size, the normalized influx rate was found to decrease and the location of maximum WSS moved away from the aneurysm neck. The results suggest that aneurysm size relative to the parent vessel diameter is an important ratio to consider in evaluating the hemodynamic conditions of saccular aneurysms. References [1] Parlea P, Rebecca F, Holdsworth DW, Lownie SP, AJNR 1999; 20: 1079-1089. [2] Russell SM, Lin K, Hahn SA, Jafar JJ, J Neurosurg 2003; 99(2): 248-53 6660 Mo, 08:45-09:00 (P6) Mechanical stress in abdominal aneurysm: influence of GEOMETRY and material anisotropy J.F. Rodriguez1, C. Ruiz 1, G. Holzapfel2, M. Doblar61 . 1Group of structural
mechanics and material modelling (GEMM), Aragon Institute of Engineering Research (13A). University of Zaragoza, Spain, 2Institute of Structural Analysis-Computational Biomechanics, Graz University of Technology, Austria Biomechanical studies suggest that risk for rupture of an abdominal aortic aneurysm (AAA) is more precisely related to mechanical wall stress. In this regard, a reliable and accurate stress analysis of an in vivo AAA requires the use of suitable constitutive models. To date, all stress analysis conducted on
Journal of Biomechanics 2006, Vol. 39 (Suppl 1)
[4] Subramaniam et al. Inhalation Toxicolology 1998; 10: 91-120. 4942 Th, 11:45-12:00 (P41) An experimental investigation on airflow in human airway S.-K. Chu 1, S.K. Kim 2 . 1Dept. ef ORL-HNS, Samsung Medical Center, School
of Medicine, Sungkyunkwan University, South Korea, 2Dept. Mechanical Engineering, Konkuk University, South Korea Knowledge of airflow characteristics in nasal cavities is essential to understand the physiological and pathological aspects of nasal breathing. Several studies have utilized physical models of the nasal cavities to understand the patterns of the airflow. Creating accurate transparent flow passages is essential to analyze the flow by particle image velocimetry (PIV). We established a procedure to construct a transparent rectangular box containing a model of the nasal cavity for PIV measurement by combining the rapid prototyping and the curing of clear silicone. Thin sliced CT data and meticulous refinement of model surface under the ENT doctor's advice provided more sophisticated nasal cavity models. The CBC (Correlation based correction) algorithm with window offset (64 64 to 32 32) is used for vector searching in PIV analysis. From tomographic flow data of sagittal planes, a 3 dimensional velocity data set can be reconstructed. The authors have investigated nasal airflows in normal and abnormal nasal cavities by tomographic PIV; Airflow in nasal cavity and nasopharynx with different degree of adenoid vegetation, changes of airflow after resection of meddle turbinate. We also visualized the airflow pattern during quiet nasal breathing with a periodic pumping system, designed to simulate human breathing. The phase averaged mean and RMS velocity distributions in sagittal and coronal planes were obtained for 17 phases in a respiratory cycle. Recently, we applied these techniques to visualize the respiratory gas flow in human airway including nasal cavities, larynx, trachea, and second bifurcation of the bronchi. Flow characteristics related with abnormalities in nasal cavities are conjectured in some cases. The methodology in this paper can be applied to any other otorhinolaryngological diseases and contributes to help ENT doctors in diagnosis and treatments of these diseases 6735 Th, 12:00-12:15 (P41) Characterisation of nasal geometry and flow A. Gambaruto, D. Doorly. Dept. Aeronautics, Imperial College, London, UK There is a large diversity in the geometric form of the human nasal cavity geometry, and a general lack of understanding of the impact of nasal cavity airway topology on the complex air flow patterns engendered. It is now possible however using MRI or CT techniques to determine nasal cavity geometry invivo, and particularly with CT, with relatively high accuracy. In this study, we present three novel approaches to classify the detailed three-dimensional form of the nasal cavity geometry: discrete harmonic maps, Fourier descriptors and skeletonisation. These procedures also prove useful as techniques for geometry reconstruction, providing objective means to simplify and manipulate the geometry. They act as geometric compression tools for the mesh surface data, with possible application to non-nasal cavity topologies. We present details of the techniques used to obtain common stencils on which to compare the resulting flow features for the different subjects. Classification of the nasal cavity allows for idealisation of the various topologies and hence the formulation of a common norm, permitting the study of significance of patient specific topologies with respect to this norm. This can be seen as a measure of patient deviation from the norm and a rational approach to the study of morphological variations. The methods used in this work thus provide well-defined procedures to compare different subject anatomies and to relate corresponding characteristic geometric variations to differences in the effectiveness of airflow and transport. 7567 Th, 12:15-12:30 (P41) Airflow in the human nasal cavity D.J. Taylor1,2, D.J. Doorly 1, R.C. Schroter2. 1Department of Aeronautics and
2Department of Bioengineering, Imperial College London, London, UK The nose performs many important physiological functions, including: heating, humidifying and filtering inspired air, as well as sampling air to smell. The successful functioning of the nose is highly dependent on the fluid dynamic characteristics of airflow through the nasal cavities. Significant advances in the fields of toxicology, particle deposition, drug delivery and surgical planning could be achieved through an improved understanding of nasal airflow. Although Computational Fluid Dynamics (CFD) has been applied to investigate nasal airflow properties at quiet breathing rates, its predictions are constrained by the complex and unsteady nature of the flow within the complicated geometry. CFD predictions require experimental validation. However, in vive and in vitro flow is confounded by the inaccessibility of the nasal passages. The approach of using optical measurements obtained in transparent model structures is particularly attractive in this situation.
Oral Presentations Transparent nose models were manufactured by casting transparent silicone around twice-scale inverse rapid-prototype geometries of one half of the nasal cavity; these had been previously created by image segmentation of Computed Tomography (CT) medical images. A fidelity survey of the silicone model was also undertaken to ensure it accurately represented the initial virtual CT based geometry. Refractive index matched recirculating liquid was pumped through the nominally normal, anatomically accurate, transparent models to simulate the airflow. Particle Image Velocimetry (PIV) and dye visualisation methods were used to quantify gross flow patterns and velocities in the nose and to assess the stability of the flow, for a range of steady inspiratory flow rates. The results obtained of the gross flow characteristics were compared for two different nasal geometries. Airflow through these geometries was found to be laminar for quiet restful breathing (Reynolds numbers up to 1000), but became transitional at higher flow rates. An insight into the effects that nasal anatomy has on flow can clearly be seen by comparison of the flow patterns and velocities through a normal and "simplified" model, created from the same CT dataset.
Track 14
Cardiovascular Mechanics
14.1. Aneurysms 14.1.1. Aneurysms 7584 Mo, 08:15-08:45 (P6) Analysis of the importance of the ratio of aneurysm size to parent artery diameter on hemodynamic conditions H. Zakaria 1, H. Yonas 2, A.M. Robertson 1. 1Department of Mechanical Engineering, University of Pittsburgh, Pittsburgh, PA, USA, 2Department of Surgery, School of Medicine, University of New Mexico, Albuquerque, NM, USA The geometry of saccular aneurysms is often characterized by three lengths: neck width (N), dome height (H), and dome diameter (D), (e.g. [1]). Aneurysm size has also been found to be strongly correlated with rupture as well as extent of SAH [2]. However, to date, no study has been performed analyzing the impact of aneurysm size on hemodynamics relative to a length scale external to the aneurysm, for example, the parent diameter (P). In this work, we systematically analyze the effect of aneurysm size on hemodynamics by varying the ratio P/N for fixed H/N and D/H. Namely, the shape of the aneurysm is fixed and the size is scaled relative to the parent artery. Three-dimensional models of non-symmetric, saccular aneurysms at symmetric bifurcations were created using a recently developed parametric model. The aspect ratios of the aneurysm were fixed at H/D= 1.1 and H/N = 1.6 while the value of P/N was chosen as (0.47, 0.7, 1.4). The upper and lower choices for P/N correspond to scaling the aneurysm dimensions by a factor of 1.5 and 0.5 respectively. Flow simulations were based on the unsteady Navier-Stokes equations for rigid walled vessels and solved by the finite element method using ADINA software (ADINA Inc.). Aneurysm size was found to have both a qualitative and quantitative effect on the hemodynamics in and around the aneurysm including pathlines, influx rate and location of maximum wall shear stress (WSS). With increasing size, the normalized influx rate was found to decrease and the location of maximum WSS moved away from the aneurysm neck. The results suggest that aneurysm size relative to the parent vessel diameter is an important ratio to consider in evaluating the hemodynamic conditions of saccular aneurysms. References [1] Parlea P, Rebecca F, Holdsworth DW, Lownie SP, AJNR 1999; 20: 1079-1089. [2] Russell SM, Lin K, Hahn SA, Jafar JJ, J Neurosurg 2003; 99(2): 248-53 6660 Mo, 08:45-09:00 (P6) Mechanical stress in abdominal aneurysm: influence of GEOMETRY and material anisotropy J.F. Rodriguez1, C. Ruiz 1, G. Holzapfel2, M. Doblar61 . 1Group of structural
mechanics and material modelling (GEMM), Aragon Institute of Engineering Research (13A). University of Zaragoza, Spain, 2Institute of Structural Analysis-Computational Biomechanics, Graz University of Technology, Austria Biomechanical studies suggest that risk for rupture of an abdominal aortic aneurysm (AAA) is more precisely related to mechanical wall stress. In this regard, a reliable and accurate stress analysis of an in vivo AAA requires the use of suitable constitutive models. To date, all stress analysis conducted on