Lung Constant-Pressure Inflation: Fluid Dynamic Factors are the Basis of Airway Overpressure During Bronchoconstriction

1993 ◽  
Vol 28 (3) ◽  
pp. 185-192 ◽  
Author(s):  
Giuseppe Marano ◽  
Guelfo Pulci Doria
Keyword(s):  
Constant Pressure ◽  
Fluid Dynamic ◽  
Dynamic Factors

Theoretical Investigation of a Peristaltic Magneto-Fluid Dynamic Induction Compressor-2

1965 ◽  
Vol 9 (02) ◽  
pp. 56-65
Author(s):  
Joseph L. Neuringer ◽  
Eugene Migotsky ◽  
James H. Turner ◽  
Robert M. Haag
Keyword(s):  
Scaling Laws ◽  
Electromechanical Coupling ◽  
Constant Pressure ◽  
Fluid Dynamic ◽  
Pressure Rise ◽  
Magnetic Reynolds Number ◽  
Design Parameters ◽  
Propulsion Systems ◽  
Geometric Scaling ◽  
Axial Mass

In Part 3, the nature of the electromechanically induced motions inside the compressor both of the fluid conductor and of the pumped fluid when the electromechanical coupling is weak, i.e., in the limit of small magnetic Reynolds number, is investigated. The analysis predicts the development of a constant pressure gradient in the pumped fluid when the condition is imposed that the time-average axial mass flow across the conducting fluid annulus is zero. In Part 4, a preliminary feasibility study is made to determine whether the induction compressor has the potential to provide the pressure rise required to propel large and small undersea craft by means of jet propulsion systems for reasonable power and current-sheet inputs. Also determined here are the geometric scaling laws for the appropriate operating and design parameters.

Fluid dynamic factors in tracheal pressure measurement

1981 ◽  
Vol 51 (1) ◽  
pp. 218-225 ◽  
Author(s):  
H. K. Chang ◽  
J. P. Mortola
Keyword(s):  
Endotracheal Tube ◽  
Pressure Measurement ◽  
Fluid Dynamic ◽  
Theoretical Explanation ◽  
Apparent Paradox ◽  
Cross Sectional ◽  
Tracheal Cannula ◽  
Dynamic Factors ◽  
Tracheal Pressure

Because tracheal pressure measurement generally involves the use of a cannula or an endotracheal tube, fluid dynamic factors may cause a considerable artifact. We present a theoretical explanation of the observed apparent paradox in which the resistance of a tracheal cannula or an endotracheal tube is isolation was found to exceed the resistance of the airways plus the cannula or the tube in situ. By estimating the viscous dissipation and the kinetic energy change in a conduit with sudden variation of cross-sectional area, a predictive model is derived. The predictions are verified by a series of in vitro experiments with both steady and oscillatory flows. The experiments showed that the pressure recorded from the sidearm of a tracheal cannula or endotracheal tube contains an error which, in general, increased with the mean Reynolds' number of the through flow and also depends on the diameter ratio between the trachea and the tube or cannula, the position of the pressure tap, and the frequency of ventilation. When feasible, direct measurement with a needle in the trachea is suggested as a way to avoid the possible artifacts arising from the use fo a side tap of the cannula. Theoretical considerations, as well as in vitro and animal experiments, indicate that adding a properly chosen expansion to the tracheal cannula makes it possible to alter inspiratory and expiratory pressures selectively. This device may prove useful in control of breathing studies.

Interaction of fluid dynamic factors in the migration and accumulation of natural gas

2002 ◽  
Vol 47 (14) ◽  
pp. 1207-1211 ◽  
Author(s):  
Yan Song ◽  
Xinyu Xia ◽  
Zhenliang Wang ◽  
Yi Wang ◽  
Shengbiao Hu
Keyword(s):  
Natural Gas ◽  
Fluid Dynamic ◽  
Dynamic Factors

DIAGNOSTIC AND THERAPEUTIC TREATMENTS OF PLAQUES IN THE CAROTID BIFURCATION — STUDIES IN MODELS WITH STENTS AND FILTERS

2014 ◽  
Vol 14 (03) ◽  
pp. 1450030
Author(s):  
D. LIEPSCH ◽  
A. BALASSO ◽  
C. ZIMMER ◽  
H. BERGER ◽  
R. BURKHART ◽  
...  
Keyword(s):  
Flow Rate ◽  
Fluid Dynamic ◽  
Flow Behavior ◽  
Carotid Bifurcation ◽  
Flow Rate Ratio ◽  
Shear Stresses ◽  
Dynamic Factors ◽  
Rate Ratios ◽  
Visualization Techniques

Fluid dynamics, especially forces and velocity distribution, influence the development of plaques. Flow parameters: pulsatility, the non-Newtonian flow behavior of blood and wall elasticity are considered. Flow visualization techniques (dyes and birefringent solution with a photo-elasticity apparatus) and LDA measurements demonstrate the importance of the flow. Accurate in vivo velocity measurements are necessary to calculate shear stresses. Different bifurcation angles and flow rate ratios were tested in true to life artery models. The most important fluid dynamic factors at bifurcations are the flow rate ratio and the geometry which create flow separation regions which are responsible for platelet aggregation and intima damage. It is necessary to measure all three velocity components to calculate the velocity vector. The highest shear stresses in a healthy carotid artery are 16 Pa and are found just at the apex. In artery models with 90% stenosis, shear stresses up to 250 Pa were found. Distally, vortices were created where particles remained over several pulse cycles. Measurements show that stents must be selected carefully and placed precisely. Filters must be closed during the systolic phase before removal, so that no trapped particles can escape.

PULSATILE FLOW FIELDS IN A MODEL OF ABDOMINAL AORTA WITH ITS PERIPHERAL BRANCHES

2003 ◽  
Vol 15 (05) ◽  
pp. 170-178 ◽  
Author(s):  
D. LEE ◽  
J. Y. CHEN
Keyword(s):  
Flow Field ◽  
Steady Flow ◽  
Abdominal Aorta ◽  
Pulsatile Flow ◽  
Fluid Dynamic ◽  
Flow Behavior ◽  
Computer Code ◽  
Flow Fields ◽  
Dynamic Factors ◽  
Recirculation Zones

In a previous study by the authors, steady flow fields in a model of abdominal aorta with its seven peripheral branches were reported. In the present study, the some aorta model was simulated numerically with a pulsatile inlet waves for both the resting and exercise conditions. The baseline pulsatile flow field was presented in terms of velocity vectors and iso-velocity contours as well as the wall shear stress (WSS) distribution and the recirculation zones. The time-averaged behavior of the flow field represented by the fluid dynamic factors was discussed. The results were consistent with those obtained experimentally and numerically by other investigators. It was also found that under the present conditions, the steady flow behavior could adequately describe the time-averaged behavior of its corresponding pulsatile case, particularly in the regions where convective flow dominated. The present computer code may provide a platform for clinical simulations.

Flowfield Investigation of the Effect of Rib Open Area Ratio in a Rectangular Duct

1998 ◽  
Vol 120 (3) ◽  
pp. 504-512 ◽  
Author(s):  
Tong-Miin Liou ◽  
Chih-Wen Kao ◽  
Shih-Hui Chen
Keyword(s):  
Computational Models ◽  
Fluid Dynamic ◽  
Fluid Flows ◽  
Area Ratio ◽  
Open Area ◽  
Height Ratio ◽  
Mean Velocity ◽  
Dynamic Factors ◽  
Nusselt Number Distribution ◽  
Spatially Periodic

The spatially periodic turbulent fluid flows and friction in a rectangular passage of width-to-height ratio of 4:1 with perforated rectangular ribs mounted on one wall have been studied using laser Doppler velocimetry and pressure probing. The parameters fixed were rib height to duct hydraulic diameter ratio of 0.106, rib width-to-height ratio of 0.76, rib pitch-to-height ratio of 10, and Reynolds number of 2 × 104, while the main parameter investigated was the rib open-area ratio (β) with values of 0%, 10%, 22%, 38%, and 44%. Two critical ranges of β and three characteristic flow regimes were identified, which provides useful references of practical tests of computational models. The results also showed that the dominant fluid dynamic factors responsible for the reported peak values of local Nusselt number distribution could be recognized. Moreover, the secondary-flow mean velocity components were found to be one to two orders of magnitude smaller than the bulk mean velocity.

Analysis of Volumetric Residence Time of Blood Elements in Stenosed Arteries

2003 ◽  
Author(s):  
M. C. Kim ◽  
C. S. Lee ◽  
C. J. Kim
Keyword(s):  
Residence Time ◽  
Transient Flow ◽  
Fluid Dynamic ◽  
Viscous Drag ◽  
Shear Stresses ◽  
Drag Forces ◽  
Area Reduction ◽  
Dynamic Factors ◽  
Recirculation Zones ◽  
Computational Fluid Dynamics Cfd

Blood flow in arteries is known to be closely related to atherosclerosis. Presence of recirculation zones, and low, high, and oscillatory wall shear stresses have been suggested to be important fluid dynamic factors causing development and progress of atherosclerosis. Our study was motivated to develop fluid mechanical indices between residence time of blood particles in arteries and atherosclerosis. In rigid models of stenosed arteries with 75% area reduction, trajectories of blood particles were numerically computed and used to determine local volumetric residence time (VRT) of platelets. The motion of particles in the model artery was computed by considering viscous drag forces between blood particles and presolved transient flow field from computational fluid dynamics (CFD). Many cardiac cycles were considered in the computation to reflect temporally accumulative characteristics of VRT in the recirculation zones. Our results showed that VRT in the recirculation zone was relatively low in the first cardiac cycle. However it increased in the subsequent cycles as more particles were trapped in the same zone. The results suggested that VRT contour calculated in the present study would be an effective indicator of the presence of atherosclerosis.

Thromboembolic Reaction Following Wall Puncture in Arterioles and Venules of the Rabbit Mesentery

1988 ◽  
Vol 59 (01) ◽  
pp. 023-028 ◽  
Author(s):  
Mirjam G A oude Egbrink ◽  
Geert Jan Tangelder ◽  
Dick W Slaaf ◽  
Robert S Reneman
Keyword(s):  
Vessel Wall ◽  
Fluid Dynamic ◽  
Video Microscopy ◽  
Dynamic Factors ◽  
Wall Injury

SummaryThe walls of rabbit mesenteric arterioles and venules (diameter 20 to 40 pm) were punctured with glass micropipets (tip diameter 6 to 8 pm). Thromboembolic reactions resulting from this standardized, small mechanical vessel wall injury could be quantified in vivo with the use of intravital video-microscopy. Following induction of the injury thrombus growth started immediately (<0.1 s). Bleeding times were short, on the average less than 2 s, and did not differ between arterioles and venules. The duration of the embolization process was significantly longer in arterioles than in venules (median 101 and 17 s, respectively), and more emboli were produced in arterioles than in venules (median 6 and 1, respectively). Arteriolar thrombi were more effective in plugging the punctured holes than venular thrombi. The differences in thromboembolic reaction between arterioles and venules, as found in the present study, can probably not be explained by fluid dynamic factors.

Experimental Study of Steady and Pulsatile Flows in Cerebral Aneurysm Model of Various Sizes at Branching Site

1997 ◽  
Vol 119 (3) ◽  
pp. 325-332 ◽  
Author(s):  
T.-M. Liou ◽  
W.-C. Chang ◽  
C.-C. Liao
Keyword(s):  
Volume Flow Rate ◽  
Fluid Dynamic ◽  
Flow Rate Ratio ◽  
Parent Vessel ◽  
Fluctuation Intensity ◽  
Dynamic Factors ◽  
Middle Range ◽  
Forced Vortex ◽  
Maximum Fluctuation ◽  
Pulsatile Flows

Pulsatile and steady flow fields in cerebrovascular aneurysm models of various sizes are presented in terms of laser-Doppler velocimetry measurements and flow visualization. The bifurcation angle was 140 deg and volume flow rate ratio between the branches was 3:1. The mean, peak, and minimal Reynolds numbers based on the bulk average velocity and diameter of the parent vessel were 600, 800, and 280, respectively. It is found that among the tested sizes there exists a middle range of aneurysm sizes, above and below which the forced-vortex inside the aneurysmal model is weaker and lacking, respectively, whereas in the middle range of the tested sizes the forced vortex is stronger and the fluctuation level is higher near the dome. The present results also identify the major fluid dynamic factors of the aneurysmal promotion or rupture for the medium and larger aneurysms, respectively. Furthermore, the maximum fluctuation intensity is found to increase with aneurysm size. The locations of the maximum fluctuation intensity are found to occur in the bifurcation area or at the neck instead of intra-aneurysm.

Periodic flow at airway bifurcations. II. Flow partitioning

1990 ◽  
Vol 69 (2) ◽  
pp. 553-561 ◽  
Author(s):  
A. Tsuda ◽  
R. Kamm ◽  
J. J. Fredberg
Keyword(s):  
Fluid Dynamic ◽  
Flow Distribution ◽  
Flow Conditions ◽  
Time Constants ◽  
Dynamic Factors ◽  
Velocity Flow ◽  
Small Flow ◽  
Underlying Mechanisms ◽  
Temporal Events ◽  
Upstream Flow

The distribution of flow among parallel pathways is believed to be determined by the balance of downstream mechanical loads or time constants. We studied the influence of upstream flow conditions and airway geometry vs. downstream mechanical impedances in determining flow partitioning at airway bifurcations. Each model consisted of a single rigid bifurcation with various branching angles and area ratios but having identical pathway impedances. Sinusoidal volumetric oscillations were applied at the parent duct with various frequencies and tidal volumes. Measuring the terminal pressures continuously, we calculated the flow distribution. When flow amplitude was small, flow partitioning was homogeneous and synchronous, as expected in a system possessing homogeneous pathway impedances and time constants. But when flow amplitude was large and frequency was high, appreciable heterogeneity and asynchrony of flow partitioning arose; during midinspiration the high-velocity flow stream preferentially favored the axial pathway. This effect vanished in the absence of a net area change at the bifurcation. For a given bifurcation geometry, these observations could be organized using only two nondimensional parameters, neither of which incorporated consideration of fluid friction. The description of temporal events required, in addition, a nondimensional time. Therefore these flow-dependent phenomena and their underlying mechanisms differ fundamentally from those described in classical impedance models. The complex pattern of nonuniform interregional behaviors apparent in whole lungs when tidal volume and frequency are large (Allen et al., J. Clin. Invest. 76: 620-629, 1985) is reiterated faithfully in models consisting of only two compartments with homogeneous time constants. As such, the behaviors observed in lungs would appear to be attributable in large part to fluid dynamic factors in central airways.

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