Airflow Oscillation Research Articles

Symmetrical-Waveform High-Frequency Oscillation Increases Artificial Mucus Flow Without Changing Basal Mucus Transport in In Vitro Ovine Trachea

The efficacy of symmetrical-waveform high-frequency oscillating (HFO) air flow for airway secretion clearance is controversial and debated in the literature. We conducted in vitro experiments with ovine tracheae to investigate the effects of symmetrical-waveform HFO on tracheal transport of artificial mucus. We mounted each trachea as an intact tube, with a 15(o) head-down tilt, infused artificial mucus (10 mL over one hour) at the caudal end of the trachea, and measured mucus-transport velocity as the time between the beginning of infusion and the first appearance of artificial mucus over 2 near-infrared sensors at the rostral end of the trachea and by measuring the amount of mucus emerging. In a second series of experiments we opened each trachea flat and with video microscopy we measured the transport velocity of plaques over the endogenous mucus sheet. In the intact-trachea preparation, HFO at 20 Hz and 50 cm H(2)O increased mucus-transport velocity from 5.8 mm/min to 7.8 mm/min. HFO led to nearly half the artificial mucus being cleared during the infusion period. In the opened-trachea experiments the mean control transport velocity was 8.7 mm/min, and HFO, at 14 Hz or 20 Hz (and 50 cm H(2)O), did not significantly alter that velocity. Symmetrical-waveform HFO increases mucus-transport velocity and mucus clearance when a thick layer of mucus is present. This may be important when considering the mechanisms of mucus clearance and using HFO for secretion clearance.

Buoyancy and inertial force on oscillations of thermal-induced convective flow across a vent

Natural vents are commonly installed in buildings for smoke control. Air motion is induced by buoyancy of the thermal sources inside the building. Hot smoke is expected to be exhausted out of the vent. However, directions of air flowing across the vent might be oscillating under some conditions. The ratio B of buoyancy to inertial force defined by the Grashof number over the square of the Reynolds number is the key parameter in determining airflow oscillations. In this paper, effects of buoyancy, pressure, and the combined effect of buoyancy and pressure denoted by B will be studied by simple flow equations. A room fire with a horizontal vent is taken as an example. The results indicate that pressure is the driving force for the airflow oscillations when B < 0.1. Buoyancy is the dominating factor when B > 10. However, the combined effect of pressure and buoyancy is important when B is close to 1. Results are useful for designing smoke exhaust systems with natural vents.

Numerical Study of High-Frequency Oscillatory Air Flow and Convective Mixing in a CT-Based Human Airway Model

High-frequency oscillatory ventilation (HFOV) is considered an efficient and safe respiratory technique to ventilate neonates and patients with acute respiratory distress syndrome. HFOV has very different characteristics from normal breathing physiology, with a much smaller tidal volume and a higher breathing frequency. In this study, the high-frequency oscillatory flow is studied using a computational fluid dynamics analysis in three different geometrical models with increasing complexity: a straight tube, a single-bifurcation tube model, and a computed tomography (CT)-based human airway model of up to seven generations. We aim to understand the counter-flow phenomenon at flow reversal and its role in convective mixing in these models using sinusoidal waveforms of different frequencies and Reynolds (Re) numbers. Mixing is quantified by the stretch rate analysis. In the straight-tube model, coaxial counter flow with opposing fluid streams is formed around flow reversal, agreeing with an analytical Womersley solution. However, counter flow yields no net convective mixing at end cycle. In the single-bifurcation model, counter flow at high Re is intervened with secondary vortices in the parent (child) branch at end expiration (inspiration), resulting in an irreversible mixing process. For the CT-based airway model three cases are considered, consisting of the normal breathing case, the high-frequency-normal-Re (HFNR) case, and the HFOV case. The counter-flow structure is more evident in the HFNR case than the HFOV case. The instantaneous and time-averaged stretch rates at the end of two breathing cycles and in the vicinity of flow reversal are computed. It is found that counter flow contributes about 20% to mixing in HFOV.

Hovering of a rigid pyramid in an oscillatory airflow

We investigate the dynamics of rigid bodies (hollow ‘pyramids’) placed within a background airflow, oscillating with zero mean. The asymmetry of the body introduces a net upward force. We find that when the amplitude of the airflow is above a threshold, the net lift exceeds the weight and the object starts to hover. Our results show that the objects hover at far smaller air amplitudes than would be required by a quasi-steady theory, although this theory accounts qualitatively for the behaviour of the system as the body mass becomes small.

Interactions of Airflow Oscillation, Tracheal Inclination, and Mucus Elasticity Significantly Improve Simulated Cough Clearance

Viscoelastic properties of simulated mucus, angle of tracheal inclination (theta), and high-frequency airflow oscillations on median displacement of simulated mucus during simulated cough were investigated in this study. Mucus simulants with viscoelastic properties similar to healthy individuals and patients with COPD were prepared using locust bean gum (LBG)-water solution (0.38 g LBG in 100 mL water) cross-linked with 3-mL and 12-mL borax-water solution (0.02 M), respectively. Aliquots of 0.3 mL of simulants were placed on a dry Plexiglas insert inside a D-shaped clear Plexiglas tracheal model. Movement of aliquots of mucus simulants was measured during cough of 0.3 s duration. Cough velocities studied (5-30 m/s) are typical of patients with weak expiratory muscles and airway obstruction. Studies were conducted with tracheal model placed horizontally (0 degrees) and at increasing theta (15 degrees, 30 degrees, and 45 degrees), with and without superimposed airflow oscillations during coughs. Effects of different parameters and their interactions on displacements of aliquots were compared using analysis of covariance (n = 849). Significant positive nonlinear associations existed between displacement and cough velocity for both 3-mL and 12-mL simulants (P < .0001). Displacement was greatest for the cohesive 12-mL simulant at all cough velocities. Displacement increased significantly (P < .0001) as theta was increased for both types of simulants. Largest displacements at low cough velocities occurred with 12-mL simulant in the presence of oscillations at 45 degrees angle. Results support the use of airflow oscillations and sitting upright to facilitate mucus displacement during cough, particularly with thick, elastic mucus found in patients with COPD (P < .0001).

W204 乱流オリフィス流れの計測融合シミュレーション(WS2-2 CFDとEFDの融合研究,ワークショップ2)

Visualizing the state of real turbulent flow is important in many applications such as safe operation and diagnosis of fault in plant or pipeline. However, visualization of flow field is difficult in many actual cases. We target a visualization of an oscillating air flow through an orifice, which is widely used in industry, in a circular pipe. As a visualization method, measurement-integrated (MI) simulation using a standard k-ε model is employed to reduce computation time. In this paper, we induct the apparatus of our MI simulation by comparing with experiment and ordinary CFD analysis in steady and unsteady condition.

Viscoelasticity and fractal structure in a model of human lungs

This paper provides a model of the human respiratory system by taking into account the fractal structure of the airways and the viscoelastic properties of the tissue. The self-similarity of airway distribution is admitted up to the 24th generation. Due to periodic breathing which results in sinusoidal excitation of the respiratory system, an electrical equivalent model is developed. The periodic current in this electrical network, that preserves the geometry of the human respiratory tree, is equivalent to the oscillatory air-flow. The model is expressed by Navier–Stokes equations under cylindrical symmetry, linked with an equation responsible for the motion of viscoelastic tissue of airway walls. By use of both electro-mechanical analogies, the total impedance of the respiratory system is determined and compared to the measured data in the clinical range of 4–48 Hz, as well as in the low-frequency range of 0.1–5 Hz. We propose also a lumped model of fractional orders, which is able to capture frequency-dependent variations in both clinical as well as in the low-frequency ranges. The models proposed in this paper can be further used to determine the effects of disease on the lung morphology.

Application of MI Simulation Using a Turbulent Model for Unsteady Orifice Flow

Measurement-integrated (MI) simulation is a numerical simulation in which experimental results are fed back to the simulation. The calculated values become closer to the experimental values. In the present paper, MI simulation using a turbulent model is proposed and applied to steady and unsteady oscillatory airflows passing an orifice plate in a pipeline. Velocity and pressure feedbacks are conducted and both feedback methods showed good agreement with the experimental results. Moreover, the calculation times between the MI simulation and ordinary simulation were compared in steady and unsteady conditions. The calculation time was demonstrated to be significantly reduced compared with ordinary simulation.

Large eddy simulation of high frequency oscillating flow in an asymmetric branching airway model

The implementation of artificial ventilation schemes is necessary when respiration fails. One approach involves the application of high frequency oscillatory ventilation (HFOV) to the respiratory system. Oscillatory airflow in the upper bronchial tree can be characterized by Reynolds numbers as high as 10 4, hence, the flow presents turbulent features. In this study, transitional and turbulent flow within an asymmetric bifurcating model of the upper airway during HFOV are studied using large eddy simulation (LES) methods. The flow, characterized by a peak Reynolds number of 8132, is analysed using a validated LES model of a three-dimensional branching geometry. The pressures, velocities, and vorticity within the flow are presented and compared with prior models for branching flow systems. The results demonstrate how pendelluft occurs at asymmetric branches within the respiratory system. These results may be useful in optimising treatments using HFOV methods.

Experimental analysis of oscillatory airflow in a bronchiole model with stenosis

As the mechanism of gas transport and exchange in human respiratory ventilation, the complicated processes of mixing and diffusion in airways of human lungs are considered. However the mechanism has not been clarified enough. On the other hand, the analysis of detailed mechanism in the case of artificial ventilation like HFOV (High Frequency Oscillatory Ventilation) is strongly required for the development of clinical treatments on patients with respiration disorder. In HFOV, it is considered that pendelluft becomes one of the important factors of gas transport and exchange because of high frequency ventilation in comparison with natural breathing. As increase of the frequency, the different time constants of lung units generate phase lag of ventilation in airways of lungs. The phase lag of ventilation causes to generate pendelluft. The time constant is determined by compliance and flow resistance of lung unit. In order to investigate the effect of the different time constants induced by the difference of flow resistance in a part of respiratory bronchiole of human lungs, the experimental study has been carried out by using multi-bifurcated micro channels as a model of bronchiole. The flow resistance in the model channels was produced by a stenosis. The velocity distributions of ventilation flows in the channels with and without the stenosis have been measured by using μ-PIV technique. The results obtained show the frequency effects on the flow pattern in the bronchiole model channels and the appearance of pendelluft.

Oscillating behaviour of fire-induced air flow through a ceiling vent

Oscillations of fire-induced air flow through a ceiling vent in a compartment will be studied in this paper. The equations describing the oscillations of air flow induced will be discussed first. Air flow through the vent is found to be induced by buoyancy or by pressure. A wave function was introduced as a perturbation to a control volume concerned. Oscillation growth, amplification, response and frequency will then be studied by solving these key equations under practical conditions. Useful semi-empirical formula on those parameters is derived for fire safety engineering design. The predicted results will be discussed and compared with experimental data available in the literature.

The effects of airway closure in central apneas and obstructed respiratory efforts in mixed apneas in preterm infants

Airway closure during central apnea could allow for better gas exchange. However, the return of inspiratory efforts against a closed airway may cause greater desaturation and prolongation of apnea. To investigate the effect of patency of the airway and obstructed respiratory efforts on the length of apneas and the degree and slope of O(2) desaturation and bradycardia. All mixed apneas observed in 15 preterms were matched 1:2 with the longest central apneas in each infant. Central apneas were further classified using the amplified cardiac airflow oscillation in those with airway open and in those with airway closed. No differences were found in the length of apnea, slope of O(2) desaturation, delay between the onset of apnea and onset of desaturation, lowest post-apneic SpO(2), and time of recovery of SpO(2) between central apneas with and without airway closure. Although mixed apneas were significantly longer than central apneas, their initial central component was significantly shorter than the length of central apneas. In mixed apneas, the onset of O(2) desaturation occurred faster, SpO(2) decreased lower, and recovered slower compared with central apneas. The slope of O(2) desaturation after the obstructed respiratory efforts was significantly greater than before the obstructed respiratory efforts. In preterm infants: (1) airway closure during central apneas does not limit oxygen desaturation; (2) respiratory efforts against a closed airway prolong apnea and worsen the degree of desaturation and bradycardia. Although respiratory efforts are not necessary to induce airway closure, inspiratory efforts against a closed airway could trigger inhibitory cardio-respiratory responses causing significant desaturation, bradycardia, and prolongation of apnea.

Transport and deposition of inertial aerosols in bifurcated tubes under oscillatory flow

The transport and deposition of aerosol particles in a single bifurcation tube under oscillatory airflow condition are investigated via experiments and numerical simulations. In the experimental study, a novel stabilized laser-photodiode measurement technique is used to quantify the effects of frequency of oscillatory airflow and airflow rate on surface deposition of particles within the bifurcation tube. Surface deposition in the parent and daughter tubes is measured by orientating the laser-photodiode device parallel and perpendicular to the bifurcation plane and calculated using a transmission loss model. In the numerical simulation study, the same bifurcation tube is constructed using a two- and three-dimensional computer mesh in COMSOL ® to model particle mobility and deposition characteristics, considering the simultaneous effects of inertial impaction, gravitational settling and interception. The effects of frequency of oscillatory airflow, airflow rate and particle size on the particle trajectory and spatial deposition pattern are examined.

Numerical and Experimental Studies of Oscillatory Airflows Induced by Rotation of a Grass-Cutting Blade

Three-dimensional oscillatory airflows induced by a rotating grass-cutting blade in a cylindrical chamber are studied experimentally and numerically in this paper. Experimental pressure results are obtained using a sound pressure transducer and a data acquisition system. The measured pressure data contain background noise and high-frequency sound signals due to the blade vibrations. The background noise is separately measured; its effect on the signal is determined from a spectral subtraction algorithm. A time-accurate finite volume numerical solution to the three-dimensional incompressible unsteady Navier–Stokes equations is also sought using the sliding frame technique and the unstructured tetrahedral mesh. Convergence studies are conducted using various combinations of mesh sizes and time increments to ensure the stability of the numerical scheme. The experimental and numerical pressure results are in good agreement.

613 呼吸時の鼻腔・咽頭内の往復気流に関する生体外モデル実験(GS-2 生体内の流れ)

613 呼吸時の鼻腔・咽頭内の往復気流に関する生体外モデル実験(GS-2 生体内の流れ)

Experimental Analysis of Oscillatory Air Flow in a Model of Respiratory Bronchiole with Pendelluft

Experimental Analysis of Oscillatory Air Flow in a Model of Respiratory Bronchiole with Pendelluft

Alan Arthur Wells. 1 May 1924 — 8 November 2005

Alan Wells was probably best known for his seminal contributions to studies of brittle fracture and fracture mechanics conducted during his period at the British Welding Research Association (BWRA) from 1951 to 1964. He was Professor of Structural Science at Queen's University Belfast from 1964 to 1977, when he returned to the Welding Institute (as the BWRA had then become) as Director General until his retirement in 1988. In his later years, he worked on wave energy devices and was responsible for the development of the innovative ‘Wells’ turbine, a device that continues to rotate in the same direction under oscillatory air flows.

Experimental investigation of oscillatory air flow in a bronchial tube model with HFOV mode

Mechanical ventilations for artificial respiration have been developed to improve the medical treatment of the patients showing respiratory disorder. In various types of ventilation, High Frequency Oscillatory Ventilation (HFOV) is one of the most effective techniques of medical care for pulmonary disease patients, especially, infants or premature infants. HFOV is a ventilation technique with high breathing rate in comparison with the normal breathing rate. Some successful studies have focused on the effect of treatment using HFOV. However, the mechanism of gas exchange in bronchial tube under the medical treatment by HFOV has not been clarified. In this study, the oscillatory flow in a micro-channel model of bronchial with single bifurcation in HFOV mode has been investigated experimentally with micro Particle Image Velocimetry (micro PIV) technique. The phase averaged velocity profiles changing with the driving frequency of HFOV have been investigated.

Physiological effects of vibration in subjects with cystic fibrosis

The physiological mechanisms by which vibration and other physiotherapy interventions may clear secretions in subjects with cystic fibrosis are unknown. The main aim of this study was to compare the expiratory flow rates and frequencies of airflow oscillation of vibration to those of Acapella(R), Flutter(R), positive expiratory pressure and percussion. Respiratory flow rates were measured during interventions, the order of which was randomised. The oscillation of the airflow of the interventions was determined by frequency spectral analysis. In 18 young adult subjects with cystic fibrosis, the mean peak expiratory flow rate of vibration was greater than Flutter(R), percussion, Acapella(R) and positive expiratory pressure. The mean+/-sd of the oscillation of the airflow of vibration (8.4+/-0.4 Hz) was lower than Acapella(R) (13.5+/-1.7 Hz) and Flutter(R) (11.3+/-1.5 Hz) but similar to percussion (7.3+/-0.3 Hz). Theoretically, the higher peak expiratory flow rate of vibration compared to the other physiotherapy interventions may promote secretion clearance. In addition, the frequency of oscillation of vibration was within the range demonstrated to increase mucus transport. This study has provided some evidence for the physiological rationale for the use of vibration to aid secretion clearance.

1506 細気管支モデル内の振動気流計測(1)(OS15-2 生体流体解析とその応用,OS15 生体流体解析とその応用,オーガナイズドセッション)

1506 細気管支モデル内の振動気流計測(1)(OS15-2 生体流体解析とその応用,OS15 生体流体解析とその応用,オーガナイズドセッション)