Augmentation of Axial Dispersion by Intermittent Oscillatory Flow

The efficiency of axial gas dispersion during ventilation with high-frequency oscillation (HFO) is improved by manipulating the oscillatory flow waveform such that intermittent oscillatory flow occurs. We therefore measured the velocity profiles and effective axial gas diffusivity during intermittent oscillatory flow in a straight tube to verify the intermittency augmentation effect on axial gas transfer. The effective diffusivity was dependent on the flow patterns and significantly increased with an increase in the duration of the stationary phase. It was also found that the ratio of effective diffusivity to molecular diffusivity is two times greater than that in sinusoidal oscillatory flow. Moreover, turbulence during deceleration or at the beginning of the stationary phase further augments axial dispersion, with the effective diffusivity being over three times as large, thereby proving that the use of intermittent oscillatory flow effectively augments axial dispersion for ventilation with HFO.

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Gas Dispersion in a Model Pulmonary Bifurcation During Oscillatory Flow

Journal of Biomechanical Engineering ◽

10.1115/1.2796095 ◽

1997 ◽

Vol 119 (3) ◽

pp. 309-316 ◽

Cited By ~ 11

Author(s):

M. Nishida ◽

Y. Inaba ◽

K. Tanishita

Keyword(s):

Velocity Profile ◽

Axial Velocity ◽

Oscillatory Flow ◽

Gas Transport ◽

Main Bronchus ◽

High Frequency Oscillation ◽

Laser Doppler Velocimeter ◽

Straight Tube ◽

Gas Dispersion ◽

Axial Velocity Profile

In order to clarify the gas transport process in high-frequency oscillation, we measured the axial velocity profile and the axial effective diffusivity in a single asymmetric bifurcating tube, based on the Horsfield airway model, with sinusoidally oscillatory flow. The axial velocity profiles were measured using a laser-Doppler velocimeter, and the effective diffusivities were evaluated using a simple bolus injection method. The axial velocity profile was found to be nonuniform, promoting axial gas dispersion by the spread of the concentration profile and lateral mixing. The geometric asymmetry of the bifurcation was responsible for the difference in gas transport between the main bronchi. The axial gas transport in the left main bronchus was 2.3 times as large as that of the straight tube, whereas the gas transport in the right main bronchus was slightly larger than that of the straight tube. Thus localized variation in gas transport characterized the heterogeneous respiratory function of the lung.

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OSCILLATORY FLOW OF HFV DISTRIBUTED IN LEFT AND RIGHT LUNGS: A MODEL-BASED EXPERIMENT AND INVESTIGATION

Journal of Mechanics in Medicine and Biology ◽

10.1142/s0219519414400156 ◽

2014 ◽

Vol 14 (06) ◽

pp. 1440015

Author(s):

YUEYANG YUAN ◽

CHONGCHANG YANG ◽

ZHE LI ◽

ZHIXIN CAO ◽

SIMON ZHANG ◽

...

Keyword(s):

High Frequency ◽

Oscillatory Flow ◽

Flow Distribution ◽

Lung Compliance ◽

High Frequency Oscillation ◽

High Frequency Ventilation ◽

Signal Acquisition ◽

Airflow Distribution ◽

Frequency Ventilation ◽

Left And Right

The human respiratory system is not entirely symmetric, and regional respiratory diseases can further enlarge this difference in most cases. Therefore, the lungs perform differently. This paper explored the possibilities of suppressing and enhancing the performance of a diseased lung with different high-frequency ventilation (HFV) frequencies by experimenting, as well as modeling, the oscillatory airflow distribution between the left and right lungs. The experimental setup mainly consisted of a physical respiratory model, a signal acquisition device, and a high-frequency oscillation ventilator. This ventilator outputs a positive sinusoidal air-pressure during inspiration. On these bases, a series of experiments were also conducted with different compliances and resistances in the left and the right lungs. The experiments demonstrated that the oscillatory flow distribution is primarily correlated with the oscillation frequency and the regional lung compliance.

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Bolus Contaminant Dispersion in Oscillatory Tube Flow With Conductive Walls

Journal of Biomechanical Engineering ◽

10.1115/1.2895507 ◽

1993 ◽

Vol 115 (4A) ◽

pp. 424-431 ◽

Cited By ~ 25

Author(s):

Yahong Jiang ◽

James B. Grotberg

Keyword(s):

Total Mass ◽

Functional Dependence ◽

Asymptotic Methods ◽

Effective Diffusivity ◽

Expansion Method ◽

Axial Dispersion ◽

Dimensionless Frequency ◽

Straight Tube ◽

Derivative Expansion ◽

Small Conductance

Dispersion of a bolus contaminant in a straight tube with oscillatory flows and conductive walls is solved by using a derivative-expansion method. Using asymptotic methods when small conductance exists, the axial dispersion, as measured by the time-averaged effective diffusivity, increases over the insulated case, as long as the dimensionless frequency (Womersley parameter), α, is smaller than a critical value. When α exceeds this value, axial dispersion is diminished by wall conductance. The functional dependence of this critical α on the system parameters is investigated. We examine the radial wall transport both for total mass and localized flux, which is found to be independent of velocity field, and compute the time-dependent total mass of wall transport and asymptotic Sherwood number for large times as a function of the wall conductance.

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Flow Separation, an Important Mechanism in the Formation of Mean Pulmonary Pressure During High-Frequency Oscillation

Journal of Biomechanical Engineering ◽

10.1115/1.3168333 ◽

1989 ◽

Vol 111 (1) ◽

pp. 17-23 ◽

Cited By ~ 4

Author(s):

E. H. Bush ◽

D. R. Spahn ◽

P. F. Niederer ◽

E. R. Schmid

Keyword(s):

Flow Separation ◽

High Frequency ◽

Oscillatory Flow ◽

Stationary Flow ◽

General Mechanism ◽

High Frequency Oscillation ◽

Frequency Oscillation ◽

Mean Pressure ◽

Dependent Flow

Mean pressures within the lungs and lung volume, respectively, are clinically important parameters. During ventilation by way of high-frequency oscillation (HFO), these parameters have been shown to be strongly frequency dependent. To identify mechanisms leading to mean pressure formation during HFO, findings of the theory of stationary flow were extended to oscillatory flow by a quasi-stationary approach. To confirm the theoretical findings, in-vitro experiments on HFO-models were performed. Flow separation was found to be an important mechanism in the formation of mean pressure. Flow separation causes a significant flow resistance, which may be distinctly different for in- and outflow. During oscillatory flow, a mean pressure difference thus results. This mechanism is of particular importance in bifurcations, which are present in the HFO-circuit as well as in the airways. With the direction-dependent flow separation, a general mechanism was found, which accounts for differing mean pressure values within the lungs with different HFO-circuits. This mechanism also contributes to interregionally different mean pressure values within the lungs.

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Bolus Contaminant Dispersion for Oscillatory Flow in a Curved Tube

Journal of Biomechanical Engineering ◽

10.1115/1.2796015 ◽

1996 ◽

Vol 118 (3) ◽

pp. 333-340 ◽

Cited By ~ 5

Author(s):

Yahong Jiang ◽

James B. Grotberg

Keyword(s):

Stokes Equations ◽

Time History ◽

Local Maximum ◽

Effective Diffusivity ◽

Axial Position ◽

Radius Of Curvature ◽

Local Concentration ◽

Straight Tube ◽

Molecular Diffusivity ◽

Curved Tube

The dispersion of a bolus of soluble contaminant in a curved tube during volume-cycled oscillatory flows is studied. Assuming a small value of δ (the ratio of tube radius to radius of curvature), the Navier-Stokes equations are solved by using a perturbation method. The convection-diffusion equation is then solved by expanding the local concentration in terms of the cross-sectionally averaged concentration and its axial derivatives. The time-averaged dimensionless effective diffusivity, 〈Deff/D〉, is calculated for a range of Womersley number α and different values of stroke amplitude A and Schmidt number Sc, where D is the molecular diffusivity of contaminant. For the parameter values considered, the results show that axial dispersion in a curved tube is greater than that in a straight tube, and that it has a local maximum near α = 5 for given fixed values of Sc = 1, A = 5 and δ = 0.3. Finally it is demonstrated how the time history of concentration at a fixed axial position can be used to determine the effective diffusivity.

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Gas mixing in lung model ventilated by high frequency oscillation: Effect of tidal volume, frequency and molecular diffusivity

Medical & Biological Engineering & Computing ◽

10.1007/bf02446299 ◽

1991 ◽

Vol 29 (1) ◽

pp. 75-78 ◽

Cited By ~ 2

Author(s):

A. Ben-Jebria

Keyword(s):

Tidal Volume ◽

High Frequency ◽

Lung Model ◽

High Frequency Oscillation ◽

Gas Mixing ◽

Frequency Oscillation ◽

Oscillation Effect ◽

Molecular Diffusivity

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Shear dispersion and anomalous diffusion by chaotic advection

Journal of Fluid Mechanics ◽

10.1017/s0022112094002880 ◽

1994 ◽

Vol 280 ◽

pp. 149-172 ◽

Cited By ~ 41

Author(s):

S. W. Jones ◽

W. R. Young

Keyword(s):

Effective Diffusivity ◽

Axial Dispersion ◽

Slip Condition ◽

Chaotic Advection ◽

Local Analysis ◽

Axial Position ◽

Solid Boundary ◽

Transverse Mixing ◽

Molecular Diffusivity ◽

Shear Dispersion

The dispersion of passive scalars by the steady viscous flow through a twisted pipe is both a simple example of chaotic advection and an elaboration of Taylor's classic shear dispersion problem. In this article we study the statistics of the axial dispersion of both diffusive and perfect (non-diffusive) tracer in this system.For diffusive tracer chaotic advection assists molecular diffusion in transverse mixing and so diminishes the axial dispersion below that of integrable advection. As in many other studies of shear dispersion the axial distribution ultimately becomes Gaussian as t → ∞. Thus there is a diffusive regime, but with an effective diffusivity that is enhanced above molecular values. In contrast to the classic case, the effective diffusivity is not necessarily inversely proportional to the molecular diffusivity. For instance, in the irregular regime the effective diffusivity is proportional to the logarithm of the molecular diffusivity.For perfect tracer chaotic advection does not result in a diffusive process, even in the irregular regime in which streamlines wander throughout the cross-section of the pipe. Instead the variance of the axial position is proportional to t in t so that the measured diffusion coefficent diverges like In t. This faster than linear growth of variance is attributed to the trapping of tracer for long times near the solid boundary, where the no-slip condition ensures that the fluid moves slowly. Analogous logarithmic effects associated with the no-slip condition are well known in the context of porous media.A simple argument, based on Lagrangian statistics and a local analysis of the trajectories near the pipe wall, is used to calculate the constants of proportionality before the logarithmic terms in both the large- and infinite-Péclet-number limits.

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