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.

PIV Experiments to Measure the Velocity Field Just Downstream of an Oscillating Collapsible Tube

2007 ◽  
Author(s):  
Christopher D. Bertram ◽  
Nicholas K. Truong ◽  
Stephen D. Hall
Keyword(s):  
Cardiac Output ◽  
Cross Section ◽  
Venous Return ◽  
Circular Cross Section ◽  
External Pressure ◽  
Forced Expiration ◽  
Collapsible Tube ◽  
Pulmonary Capillaries ◽  
Pulmonary Airways ◽  
Almost All

Almost all vascular conduits in the human body, being flexible, collapse elastically to a non-circular cross-section when the external pressure sufficiently exceeds the internal. Examples include the brachial artery (sphygmomanometry), veins (everyday manoeuvres), pulmonary airways (forced expiration), pulmonary capillaries (zones 1 and 2), and the urethra (micturition). Venous collapse is involved in regulation of venous return, which in turn regulates cardiac output.

A Nonlinear Model for Dielectric Elastomer Membranes

2005 ◽  
Vol 72 (6) ◽  
pp. 899-906 ◽  
Author(s):  
Nakhiah Goulbourne ◽  
Eric Mockensturm ◽  
Mary Frecker
Keyword(s):  
Large Deformations ◽  
Mathematical Formulation ◽  
Dielectric Elastomer ◽  
External Pressure ◽  
Membrane Area ◽  
System Parameters ◽  
Geometrical Nonlinearities ◽  
Dielectric Elastomer Actuators ◽  
Materials Used ◽  
Dielectric Elastomer Membrane

The material and geometrical nonlinearities of novel dielectric elastomer actuators make them more difficult to model than linear materials used in traditional actuators. To accurately model dielectric elastomers, a comprehensive mathematical formulation that incorporates large deformations, material nonlinearity, and electrical effects is derived using Maxwell-Faraday electrostatics and nonlinear elasticity. The analytical model is used to numerically solve for the resultant behavior of an inflatable dielectric elastomer membrane, subject to changes in various system parameters such as prestrain, external pressure, applied voltage, and the percentage electroded membrane area. The model can be used to predict acceptable ranges of motion for prescribed system specifications. The predicted trends are qualitatively supported by experimental work on fluid pumps [A. Tews, K. Pope, and A. Snyder, Proceedings SPIE, 2003)]. For a potential cardiac pump application, it is envisioned that the active dielectric elastomer membrane will function as the motive element of the device.

Unsteady flow in a collapsible tube subjected to external pressure or body forces

1979 ◽  
Vol 95 (1) ◽  
pp. 1-78 ◽  
Author(s):  
Roger D. Kamm ◽  
Ascher H. Shapiro
Keyword(s):  
External Pressure ◽  
Flow Speed ◽  
Limited Region ◽  
Collapsible Tubes ◽  
Body Forces ◽  
External Pressures ◽  
Highly Nonlinear ◽  
Local Wave ◽  
Nonlinear Flows ◽  
Comparative Results

Flows in thin-walled, collapsible tubes are of fundamental importance to various physiologic phenomena and clinical devices.A one-dimensional, unsteady theory is developed for flows generated either by externally applied pressures or by body forces. Part 1 deals with small-amplitude, linearized flows, part 2 with large amplitude, nonlinear flows. Experimental results for a tube collapsing under external pressure are given in part 3, together with theoretical interpretations and comparative results of numerical simulations.Several new and unanticipated phenomena are revealed. These are in part associated with the highly nonlinear ‘equation of state’ (transmural pressure versus area) for a partially collapsed tube, and in part with whether the flow speed is sub- or supercritical relative to the speed of area waves. For instance, a flow produced by a spatially uniform external pressure applied to a limited region becomes choked at a flow-limiting throat at which point the fluid speed reaches the local wave speed. This throat forms at the edge of the pressurized region. The critical velocity can be exceeded with the application of certain types of spatially graded external pressures.

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.

Dynamic Modeling of Serial Manipulator Arms

1982 ◽  
Vol 104 (3) ◽  
pp. 218-228 ◽  
Author(s):  
M. Thomas ◽  
D. Tesar
Keyword(s):  
Dynamic Modeling ◽  
Simple Form ◽  
Dynamic Properties ◽  
Equations Of Motion ◽  
Model Formulation ◽  
Serial Manipulators ◽  
System Parameters ◽  
Industrial Manipulator ◽  
Influence Coefficients ◽  
Link Model

To design and precisely control a manipulator requires a representative dynamic model of the system. This paper presents the derivation of a rigid-link model for the serial manipulator, which reduces all of the arm’s dynamic properties to their effective values at the generalized inputs. The component terms of the model are readily calculated from the dynamic influence coefficients, which are based only on the geometry of the system. All necessary influence coefficients for serial manipulators are given in a particularly simple form. The model formulation keeps the system parameters and the input dynamics explicit in the controlling equations of motion, such that analysis and dynamic response results can be obtained in the most direct manner. Dynamic analysis results for an industrial manipulator are presented.

Sleeve device functions as a Starling resistor to record sphincter pressure

1985 ◽  
Vol 248 (2) ◽  
pp. G251-G255 ◽  
Author(s):  
J. H. Linehan ◽  
J. Dent ◽  
W. J. Dodds ◽  
W. J. Hogan
Keyword(s):  
Fluid Flow ◽  
Lower Esophageal Sphincter Pressure ◽  
External Pressure ◽  
Transmural Pressure ◽  
Intraluminal Pressure ◽  
Sphincter Pressure ◽  
Collapsible Tubes ◽  
Flow Through ◽  
Esophageal Sphincter

In 1976 Dent (Gastroenterology 71: 263–267) introduced a sleeve-catheter device for obtaining continuous recording of lower esophageal sphincter pressure. The infused sleeve accommodates for axial sphincter movement by providing a large surface of collapsible membrane that is capable of sensing maximal sphincter pressure at any point along the sleeve. Although sleeve performance was tested previously, the precise physical principal of its function has not been delineated. This study tests the hypothesis that the sleeve device functions as a Starling resistor. The term “Starling resistor” is an eponym that designates the physics of fluid flow through collapsible tubes. When pressure at any point along an infused collapsible conduit is greater than the intraluminal pressure at the distal end of the conduit, partial collapse occurs at some axial location along the conduit where the transmural pressure equals zero. The location of zero transmural pressure is termed the “equal pressure point” (EPP). The partial collapse at the EPP causes a local change in luminal resistance that is directly related to the magnitude of the external pressure at the EPP and accompanied by a corresponding change in the pressure upstream from the EPP. A correlate to the performance of Starling resistors is that the pressure upstream to the EPP is not affected by the downstream pressure, so long as the downstream pressure is less than the external pressure. To test our hypothesis, we evaluated sleeve performance in vitro using a two-chambered model that allowed application of static or oscillatory pressures at one or two sites along the sleeve.(ABSTRACT TRUNCATED AT 250 WORDS)

Validation of the Non-Linear Harmonic Approach for Quasi-Unsteady Simulations in Turbomachinery

2009 ◽  
Author(s):  
Michael Hembera ◽  
Andreas Loos ◽  
Andreas Ku¨hrmann ◽  
Florian C. T. Danner ◽  
Hans-Peter Kau ◽  
...  
Keyword(s):  
Main Idea ◽  
Simulation Method ◽  
Computational Time ◽  
Fourier Decomposition ◽  
Axial Compressors ◽  
Sliding Mesh ◽  
Multi Stage ◽  
Unsteady Simulation ◽  
Dependent Flow ◽  
Flow Variables

Unsteady simulations, which are necessary to resolve the time-dependent flow between stationary and rotating parts in axial compressors, require an appropriate rotor-stator interface. For this interface, usually the so called domain-scaling or sliding mesh approach is used. This method requires the pitch of the simulated blades to be equal, to allow the usage of periodic boundary conditions and to cut down the number of represented blade passages in order to save computational time. This is based on the assumption that the flow is identical inside all blade passages. When it comes to the simulation of modern multi-stage compressors, it becomes almost impossible to conduct unsteady simulations with this approach, as blade numbers of different rows usually don’t have common multiples. In order to overcome that problem, a new method called the nonlinear harmonic approach has been introduced. The main idea of the method is, that the different calculated flow variables are divided into a time-averaged part and another part based on a Fourier decomposition, which represents the oscillating influence of the perturbations caused by the adjacent rows. Superimposing these two parts leads to a quasi-unsteady solution. For this simulation method, the pitches of the different blade rows don’t have to be changed, so that it also becomes possible to simulate multistage machines with discretizing only one passage per blade row. For this paper, a full-annulus unsteady simulation with about 40 million gridpoints was performed and the results are compared to a NLH simulation with only 1 simulated blade passage per row with 1.38 million gridpoints. Additionally, a NLH simulation with a much finer mesh with 7 million gridpoints is also included.

Reduction of peak expiratory flow after a 5-meter dive with extreme exertion

2020 ◽  
pp. 461-466
Author(s):  
Nico A.M. Schellart ◽  
◽  
Keyword(s):  
Peak Expiratory Flow ◽  
Pulmonary Ventilation ◽  
Swimming Velocity ◽  
Forced Expiration ◽  
Small Contribution ◽  
Expiratory Muscle ◽  
Open Sea ◽  
Expiratory Flow ◽  
Flow Variables ◽  
Mean Heart Rate

The effects of physically exerting scuba dives on the airways are expected to affect the respiratory system and therefore the spirometric flow indices directly after surfacing. After on-air open-sea dives, the flow indices were examined with standard spirometry (maximal forced expiration) within 10 minutes pre- and post-dive. Twenty volunteers, age 49±14 years (m±SD) equipped with a dive computer to record the dive profile, cylinder pressures and water temperature (27°C), as well as a hear rate monitor, performed 5-meter dives of 27 minutes at maximal swimming velocity (v). Mean pulmonary ventilation (PV) was 48±10 ambient L/minute (aL.min-1). Mean v was 34±6 meters/minute and mean heart rate 143 beats per minute, about 80% of the on-land theoretical maximum. None of the flow variables changed except a decrease of 7.1%±8.3 (p=0.001) of the peak expiratory flow (PEF), pre-dive of 11.2±2.7 L/minute. A likely major cause of the reduction of PEF is expiratory muscle fatigue. A small contribution of subclinical pulmonary edema cannot be excluded. The inhalation of dry air and the cooling of the airways are expected to affect PEF minimally. Although the change is normally clinically irrelevant, during emergency it may be of importance.

Steady Flow in Collapsible Tubes

1977 ◽  
Vol 99 (3) ◽  
pp. 126-147 ◽  
Author(s):  
Ascher H. Shapiro
Keyword(s):  
Steady Flow ◽  
Pressure Difference ◽  
Wave Speed ◽  
Flow Behavior ◽  
External Pressure ◽  
Surface Flow ◽  
Transmural Pressure ◽  
One Dimensional ◽  
Wall Stiffness ◽  
The One

The one-dimensional theory of steady flow in a thin-walled tube, partially collapsed by a negative transmural pressure difference, is developed in a general way. The mechanics of the flow is closely coupled to the mechanics of the tube. The latter is characterized by a “tube law”: the relationship between cross-sectional area and transmural pressure difference. Features analogous to those in gas dynamics and free-surface flow may manifest themselves: a characteristic wave propagation speed; opposite phenomena at flow speeds, respectively, less than and greater than the wave speed; choking; and shocklike transitions. There are many practical examples of such flows, mainly in physiology and medicine. The one-dimensional, steady analysis includes the effects of friction, lengthwise variations in external pressure, variations in elevation, resting area, wall stiffness, and mechanical properties. The speed index S (ratio of flow speed to wave speed), analogous to the Mach and Froude numbers, appears naturally in the results as a controlling parameter of behavior. Various practical ways of passing continuously from subcritical (S < 1) to supercritical (S > 1)speed are suggested. A preliminary theory of shocklike, dissipative transitions is developed, the results of which depend sensitively on the tube law. Explicit working formulas are developed for several simple types of flow (friction alone; changes in rest area alone; changes in external pressure or elevation alone) for a simple, approximate tube law. Various modes of flow behavior for a flow affected by both friction and gravity are explored.

Assessment of exhaled nitric oxide kinetics in healthy infants

2003 ◽  
Vol 94 (6) ◽  
pp. 2384-2390 ◽  
Author(s):  
T. Martı́nez ◽  
A. Weist ◽  
T. Williams ◽  
C. Clem ◽  
P. Silkoff ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Exhaled Nitric Oxide ◽  
Forced Expiration ◽  
Airway Wall ◽  
Compression Technique ◽  
Exhaled No ◽  
Healthy Infants ◽  
Dependent Flow ◽  
Independent Parameters ◽  
Exchange Parameters

Exhaled nitric oxide (Fe NO) measurements provide a noninvasive approach to the evaluation of airway inflammation. Flow-independent NO exchange parameters [airway NO transfer factor (DNO) and airway wall NO concentration (CwNO)] can be estimated from Fe NO measurements at low flows and may elucidate mechanisms of disturbances in NO exchange. We measured Fe NO in sedated infants by using an adaptation of a raised lung volume rapid thoracic compression technique that creates forced expiration through a mass-flow controller that lasts 5–10 s, at a constant preset flow. We measured Fe NO at expired flows of 50, 25, and 15 ml/s in five healthy infants (7–31 mo). Median Fe NO increased [24, 40, and 60 parts per billion (ppb)] with decreasing expiratory flows (50, 25, and 15 ml/s). Group median (range) for DNO and CwNO were 12.7 (3.2–37) × 10−3nl · s−1 · ppb−1and 108.9 (49–385) ppb, respectively, similar to values reported in healthy adults. Exhaled NO is flow dependent; flow-independent parameters of exhaled NO kinetics can be assessed in infants and are similar to values described in adults.

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