田中 学

This study deals with the exchange flow of two different gases (He-air, Ar-air, and SF6-air) through a rectangular channel that has a 5-mm width, a 50-mm height, and a 200-mm length. The net exchange flow rate is measured by an electronic mass balance, and velocity distribution is measured by a laser-Doppler anemometer. Flow patterns of the exchange flow are made visual with a tracer method using smoke. The effects of gas densities, molecular diffusion coefficients, inclination angles (χ) of the channel, on the flow patterns and the net exchange flow rates, are discussed. Based on the experimental results, the net exchange flow data are correlated by the equation derived by dimensional analysis: Q*=2.87 × 10-7 Gr2.17 Sc0.41 χ-1.09.

The efficiency of axial gas dispersion during ventilation with high-frequency oscillations (HFO) can be improved by manipulating the oscillatory flow waveform such that intermittent oscillatory flow occurs. To clarify the augmentation of axial gas transfer during intermittent oscillatory flow, we measured the axial and secondary velocity profiles during intermittent oscillatory flow through a model human central airway. We used a rigid model of human airways consisting of asymmetrical bifurcations up to third generation. Velocities in the axial and radial directions were measured with two-color laser-Doppler velocimetry. Secondary flow was accelerated at the beginning of the stationary period, particularly in the trachea, which resulted in enhanced gas transport during intermittent oscillatory flow.

Axial and secondary velocity profiles were measured in a model human central airway to clarify the oscillatory flow structure during high-frequency oscillation. We used a rigid model of human airways consisting of asymmetrical bifurcations up to third generation. Velocities in each branch of the bifurcations were measured by two-color laser-Doppler velocimeter. The secondary velocity magnitudes and the deflection of axial velocity were dependent not only on the branching angle and curvature ratio of each bifurcation, but also strongly depended on the shape of the path generated by the cascade of branches. Secondary flow velocities were higher in the left bronchus than in the right bronchus. This spatial variation of secondary flow was well correlated with differing gas transport rates between the left and right main bronchus. © 1999 by ASME.

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. © 1998 by ASME.

The rate of local axial gas transport in oscillatory flow through a model of human central airways was measured to evaluate gas exchange during high-frequency oscillation. A rigid model of human central airways consists of asymmetrical bifurcations up to 3-5 generation, of which geometries were determined by the study of Horsfield et al. (J. Appl. Physiol., 31 (1971), 207.). A bolus of CO_2 washout profiles. The rate of increase of effective diffusivity depends on the local flow conditions and differs with branches. The effective diffusivity in the left main bronchus is 3.2 times greater than that in the straight tube, whereas no significant difference is observed in the right main bronchus. In addition, the presence of a stationary period augments axial gas transport in intermittent oscillatory flow because it provides time for the occurrence of lateral mixing in the radial direction, i.e., axial diffusivity is 1.6 times greater on the average than that in sinusoidally oscillatory flow.

The rate of local axial gas transport in oscillatory flow through a model human central airways was measured to evaluate the gas exchange during high-frequency oscillation. A rigid model of human airways consists of asymmetrical bifurcations up to third generation, of which geometries were determined by the study of Horsfield et. al. (1971). A bolus of CO2 tracer was injected into the trachea, and effective diffusivities as a function of location in the airways were obtained by CO2 washout profiles. The rate of increase of effective diffusivity depends on the local flow conditions and differs with branches. The effective diffusivity in the left main bronchus becomes 3 times greater than that in the straight tube, whereas no significant effect is observed in the right main bronchus.

Ventilation by high-frequency oscillation (HFO) has gained widespread attention in clinical medicine because of its potential benefits to respiratory insufficiency. The axial dispersion in oscillatory flow is one of the important factors influencing gas transport during HFO. In this study, the gas transport in sinusoidally oscillatory and intermittent laminar flow in a straight circular pipe was numerically simulated to reveal the mechanism of dispersion. The diffusion of substance was simulated according to the random walk technique and its diffusive nature was evaluated by tracking the path of marked particles. The presence of a stationary period enhances the axial gas transport in the oscillatory flow, and the maximum ratio of effective diffusivity to the molecular diffusivity is twice that of sinusoidal oscillatory flow.