Mathematical simulation of forced expiration

1988 ◽  
Vol 65 (1) ◽  
pp. 14-25 ◽  
Author(s):  
D. Elad ◽  
R. D. Kamm ◽  
A. H. Shapiro
Keyword(s):  
Smooth Transition ◽  
Forced Expiration ◽  
Flow Limitation ◽  
One Dimensional ◽  
Collapsible Tubes ◽  
Mouth Pressure ◽  
Flow Speeds ◽  
Realistic Representation ◽  
Pressure Area ◽  
Trans Asme

Flow limitation during forced expiration is simulated by a mathematical model. This model draws on the pressure-area law obtained in the accompanying paper, and the methods of analysis for one-dimensional flow in collapsible tubes developed by Shapiro (Trans. ASME J. Biomech. Eng. 99: 126-147, 1977). These methods represent an improvement over previous models in that 1) the effects of changing lung volume and of parenchymal-bronchial interdependence are simulated; 2) a more realistic representation of collapsed airways is employed; 3) a solution is obtained mouthward of the flow-limiting site by allowing for a smooth transition from sub- to supercritical flow speeds, then matching mouth pressure by imposing an elastic jump (an abrupt transition from super- to subcritical flow speeds) at the appropriate location; and 4) the effects of levels of effort (or vacuum pressure) in excess of those required to produce incipient flow limitation are examined, including the effects of potential physiological limitation.

scholarly journals Numerical solutions for unsteady gravity-driven flows in collapsible tubes: evolution and roll-wave instability of a steady state

1999 ◽  
Vol 396 ◽  
pp. 223-256 ◽  
Author(s):  
B. S. BROOK ◽  
S. A. E. G. FALLE ◽  
T. J. PEDLEY
Keyword(s):  
Shallow Water ◽  
Numerical Solutions ◽  
Godunov Method ◽  
Test Case ◽  
Interesting Phenomenon ◽  
One Dimensional ◽  
Collapsible Tubes ◽  
Highly Nonlinear ◽  
Pressure Area ◽  
The One

Unsteady flow in collapsible tubes has been widely studied for a number of different physiological applications; the principal motivation for the work of this paper is the study of blood flow in the jugular vein of an upright, long-necked subject (a giraffe). The one-dimensional equations governing gravity- or pressure-driven flow in collapsible tubes have been solved in the past using finite-difference (MacCormack) methods. Such schemes, however, produce numerical artifacts near discontinuities such as elastic jumps. This paper describes a numerical scheme developed to solve the one-dimensional equations using a more accurate upwind finite volume (Godunov) scheme that has been used successfully in gas dynamics and shallow water wave problems. The adapatation of the Godunov method to the present application is non-trivial due to the highly nonlinear nature of the pressure–area relation for collapsible tubes.The code is tested by comparing both unsteady and converged solutions with analytical solutions where available. Further tests include comparison with solutions obtained from MacCormack methods which illustrate the accuracy of the present method.Finally the possibility of roll waves occurring in collapsible tubes is also considered, both as a test case for the scheme and as an interesting phenomenon in its own right, arising out of the similarity of the collapsible tube equations to those governing shallow water flow.

Choking Phenomena in a Lung-Like Model

1987 ◽  
Vol 109 (1) ◽  
pp. 1-9 ◽  
Author(s):  
David Elad ◽  
Roger D. Kamm ◽  
Ascher H. Shapiro
Keyword(s):  
Fluid Flow ◽  
Flow Patterns ◽  
Physical Parameters ◽  
Forced Expiration ◽  
Flow Limitation ◽  
Conducting System ◽  
Dimensional Model ◽  
One Dimensional

A simple, continuous, one-dimensional model for the geometry and structure of the bronchial airways is used for the analysis of fluid flow patterns which have been observed in forced expiration maneuvers. Various phenomena within the conducting system associated with flow limitation are investigated: (a) the conditions in which a “choke” (flow limitation) can occur in a compliant system; (b) theoretical flows that are physically impossible; (c) the possibility of having elastic jumps downstream of the choke point; (d) perturbations in the physical parameters of the conducting system.

scholarly journals Viscoelasticity of the trachea and its effects on flow limitation

2006 ◽  
Vol 100 (2) ◽  
pp. 384-389 ◽  
Author(s):  
Nikolai Aljuri ◽  
Jose G. Venegas ◽  
Lutz Freitag
Keyword(s):  
Wave Speed ◽  
Mathematical Representation ◽  
Forced Expiration ◽  
Flow Limitation ◽  
Time Dependency ◽  
Cross Sectional ◽  
Elastic Tubes ◽  
Forced Expiratory Flow ◽  
Expiratory Flow ◽  
The Relationship

To test the hypothesis that peak expiratory flow is determined by the wave-speed-limiting mechanism, we studied the time dependency of the trachea and its effects on flow limitation. For this purpose, we assessed the relationship between transmural pressure and cross-sectional area [the tube law (TL)] of six excised human tracheae under controlled conditions of static (no flow) and forced expiratory flow. We found that TLs of isolated human tracheae followed quite well the mathematical representation proposed by Shapiro (Shapiro AH. J Biomech Eng 99: 126–147, 1977) for elastic tubes. Furthermore, we found that the TL measured at the onset of forced expiratory flow was significantly stiffer than the static TL. As a result, the stiffer TL measured at the onset of forced expiratory flow predicted theoretical maximal expiratory flows far greater than those predicted by the more compliant static TL, which in all cases studied failed to explain peak expiratory flows measured at the onset of forced expiration. We conclude that the observed viscoelasticity of the tracheal walls can account for the measured differences between maximal and “supramaximal” expiratory flows seen at the onset of forced expiration.

Steady compressible flow in collapsible tubes: application to forced expiration

1989 ◽  
Vol 203 ◽  
pp. 401-418 ◽  
Author(s):  
David Elad ◽  
Roger D. Kamm ◽  
Ascher H. Shapiro
Keyword(s):  
External Pressure ◽  
Forced Expiration ◽  
Simple Description ◽  
System Parameters ◽  
Collapsible Tubes ◽  
Influence Coefficients ◽  
Cross Section Area ◽  
Wall Stiffness ◽  
Dependent Flow ◽  
Flow Variables

Steady, one-dimensional flow of a compressible fluid through a collapsible tube is analysed. A general model is employed, incorporating axial variations in the parameters of the conducting system, such as the tube unstressed cross-section area and wall stiffness, the external pressure and energy exchange with the environment. The flow variables are described in differential form as functions of the conduit system parameters. A coupled set of equations for the dependent flow variables is summarized in a table of influence coefficients, which provides a clear and simple description of the effects produced by the system parameters. Examples of the effects of fluid compressibility in the respiratory system are presented for forced expiration manoeuvres. The effects are found to be generally small, but are most accentuated when breathing heavy gases and when the airways are pathologically stiffened.

Mechanism of reduced maximum expiratory flow in dogs with compensatory lung growth

1986 ◽  
Vol 60 (2) ◽  
pp. 441-448 ◽  
Author(s):  
H. W. Greville ◽  
M. E. Arnup ◽  
S. N. Mink ◽  
L. Oppenheimer ◽  
N. R. Anthonisen
Keyword(s):  
Control Flow ◽  
Sham Operation ◽  
Forced Expiration ◽  
Flow Limitation ◽  
Lung Growth ◽  
Lung Volumes ◽  
Flow Rates ◽  
Compensatory Lung Growth ◽  
Maximum Expiratory Flow ◽  
Expiratory Flow

We examined the mechanism of the reduced maximum expiratory flow rates (Vmax) in a dog model of postpneumonectomy compensatory lung growth. During forced expiration, a Pitot-static tube was used to locate the airway site of flow limitation, or choke point, and to measure dynamic intrabronchial pressures. The factors determining Vmax were calculated and the results analyzed in terms of the wave-speed theory of flow limitation. Measurements were made at multiple lung volumes and during ventilation both with air and with HeO2. Five of the puppies had undergone a left pneumonectomy at 10 wk of age, and 5 littermate controls had undergone a sham operation. All dogs were studied at 26 wk of age, at which time compensatory lung growth had occurred in the postpneumonectomy group. Vmax was markedly decreased in the postpneumonectomy group compared with control, averaging 42% of the control flow rates from 58 to 35% of the vital capacity (VC). At 23% of the VC, Vmax was 15% less than control. Choke points were more peripheral in the postpneumonectomy dogs compared with controls at all volumes. The total airway pressure was the same at the choke-point airway in the postpneumonectomy dogs as that in the same airway in the control dogs, suggesting that the airways of the postpneumonectomy dogs displayed different bronchial area-pressure behavior from the control dogs. Despite the decreased Vmax on both air and HeO2, the density dependence of flow was high in the postpneumonectomy dogs and the same as controls at all lung volumes examined.

Application of negative expiratory pressure during expiration and activity of genioglossus in humans

1998 ◽  
Vol 84 (3) ◽  
pp. 1076-1082 ◽  
Author(s):  
Claudio Tantucci ◽  
Selma Mehiri ◽  
Alexandre Duguet ◽  
Thomas Similowski ◽  
Isabelle Arnulf ◽  
...  
Keyword(s):  
Reflex Response ◽  
Reflex Activity ◽  
Steady Increase ◽  
Flow Limitation ◽  
Upper Airways ◽  
Experimental Conditions ◽  
Surface Electromyogram ◽  
Genioglossus Muscle ◽  
Mouth Pressure ◽  
Muscle Reflex

The application of negative expiratory pressure (NEP) at end expiration has been shown to cause reflex-mediated activation of the genioglossus muscle in awake humans. To test whether a reflex contraction of pharyngeal dilator muscles also occurs in response to NEP applied in early expiration, the effect on genioglossus muscle reflex activity of NEP pulses of 500 ms, given 0.2 s after the onset of expiration and during the end-expiratory pause, was assessed in 10 normal awake subjects at rest. The raw and integrated surface electromyogram of the genioglossus (EMGgg) was recorded with airflow and mouth pressure under control conditions and with NEP ranging from −3 to −10 cmH2O. Intraoral EMGgg was also recorded under the same experimental conditions in two subjects. The application of NEP at the end-expiratory pause elicited a consistent reflex response of EMGgg in seven subjects with a mean latency of 68 ± 5 ms. In contrast, when NEP was applied at the onset of expiration, EMGgg reflex activity was invariably observed in only one subject. No relationship was found between steady increase or abrupt fall in expiratory flow and the presence or the absence of a reflex activity of genioglossus during sudden application of NEP at the beginning of expiration. Our results show that a reflex activity of genioglossus is elicited much more commonly during application of NEP at the end rather than at the onset of expiration. These findings also suggest that when NEP is applied in early expiration to detect intrathoracic flow limitation the absence of upper airways narrowing does not imply the occurrence of a reflex-mediated activation of genioglossus and vice versa.

Biotinylated Polythiophene Copolymer – a Novel Electroactive Biomaterial Utilizing the Biotin-Streptavidin Interaction

1992 ◽  
Vol 292 ◽  
Author(s):  
Jeong-Ok Lim ◽  
Manjunath Kamath ◽  
Kenneth A. Marx ◽  
Sukant K. Tripathy ◽  
David L. Kaplan ◽  
...  
Keyword(s):  
Binding Sites ◽  
Solid Substrate ◽  
Emission Peak ◽  
One Dimensional ◽  
Langmuir Blodgett ◽  
Significant Area ◽  
Pressure Area ◽  
Biotin Binding ◽  
Monolayer Assembly ◽  
Area Expansion

AbstractA novel hierarchical biomaterial capable of incorporating any biotinylated biomolecule has been created. Our strategy is to biotinylate one-dimensional electroactive polymers and use a bridging streptavidin protein on Langmuir-Blodgett (LB) organized films. The following copolymeric system which enables functionalization of other molecules and formation of good monolayers was employed. Biotinylated poly(3-methanolthiophene-co-3-undecylthiophene) (B-PMUT) demonstrated a significantly better isotherm implying superior molecular packing compared to poly(3-methanolthiophene-co-3-undecylthiophene) (PMUT) on the LB airwater surface. The isotherm showed significant area expansion when streptavidin was injected below the B-PMUT monolayer in 0.1mM NaH2PO4/0.1 M NaCl buffer (pH 6.8) subphase. We then incorporated biotinylated phycoerythrin (B-PE) into this novel biomaterial by binding the unoccupied biotin binding sites on the bound streptavidin (4 sites total). The pressure-area isotherm of the protein injected monolayer showed area expansion. A characteristic fluorescent emission peak at 576nm was detected from the monolayer transferred onto a solid substrate. These observations demonstrated the function of B-PMUT in hierarchical monolayer assembly of molecules incorporating the biotin / streptavidin interaction.

Subcritical Flutter in Collapsible Tube Flow: A Model of Expiratory Flow in the Trachea

1991 ◽  
Vol 113 (1) ◽  
pp. 21-26 ◽  
Author(s):  
C. Walsh ◽  
P. A. Sullivan ◽  
J. S. Hansen
Keyword(s):  
Fluid Model ◽  
One Dimensional ◽  
Shell Effects ◽  
Collapsible Tubes ◽  
Dimensional Modeling ◽  
Axial Tension ◽  
Normal Wall ◽  
Axial Curvature ◽  
The One ◽  
Axial Stretching

Using an axisymmetric geometry that retains certain qualitative features of the trachea, we extend one-dimensional modeling of flow in collapsible tubes to include both curved shell effects and, for untethered tubes, wall inertia. A systematic scaling of the finite deformation membrane equations leads to an approximate set which is consistent with the one-dimensional fluid model; axial and normal wall variables are coupled elastically, but only axial inertia is retained. Transverse curvature causes elastic coupling that can give rise to axial wall motion and a flutter instability. The source of instability is the product of a nonzero reference axial curvature with axial tension variation due to axial stretching. The numerical results suggest that this mechanism may be significant even in processes which cannot be assumed one-dimensional.

High-Fidelity Rendering of Contact With Virtual Objects

2015 ◽  
Vol 137 (7) ◽  
Author(s):  
Arash Mohtat ◽  
József Kövecses
Keyword(s):  
Contact Force ◽  
Constitutive Relations ◽  
Sampling Rate ◽  
Smooth Transition ◽  
Virtual Object ◽  
High Fidelity ◽  
Unified Approach ◽  
One Dimensional ◽  
The Core ◽  
The One

When interacting with a virtual object (VO) through a haptic device, it is crucial to feedback a contact force to the human operator (HO) that displays the VO physical properties with high fidelity. The core challenge, here, is to expand the renderable range of these properties, including larger stiffness and smaller inertia, at the available sampling rate. To address this challenge, a framework entitled high-fidelity contact rendering (HFCR) has been developed in this paper. The framework consists of three main strategies: an energy-based rendering of the contact force, smooth transition (ST) between contact modes, and remaining leak dissipation (LD). The essence of these strategies is to make the VO emulate its continuous-time counterpart. This is achieved via physically meaningful modifications in the constitutive relations to suppress artificial energy leaks. The strategies are first developed for the one-dimensional (1D) canonical VO; then, generalization to the multivariable case is discussed. Renderability has been analyzed exploring different stability criteria within a unified approach. This leads to stability charts and identification of renderable range of properties in the presence and absence of the HO. The framework has been validated through simulation and various experiments. Results verify its promising aspects for various scenarios including sustained contact and sudden collision events with or without the HO.

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