On the Stokes number and characterization of aerosol deposition in the respiratory airways

Aerosol deposition in the respiratory airways has traditionally been examined in terms of the Stokes number based on the reference flow timescale. This choice leads to large scatter in deposition efficiency when plotted against the reference Stokes number because the velocity and length scales experienced by advected particles deviate considerably from the reference values. A time-average of the particle local Stokes number should be adopted instead. Our results demonstrate that this average, or effective, Stokes number can deviate significantly from the reference value, in particular in the intermediate Stokes number range where variation across subjects is largest

Inertial and gravitational effects on aerosol deposition in the conducting airways

In most inhaled drug delivery applications, aerosol deposition in the upper airways occurs primarily via impaction. However, the effects of gravity become important as particle size increases and flow rate decreases. Sedimentation can therefore be significant in the smaller airways of the tracheobronchial tree, where velocities decrease due to the large increase in cross-sectional area, as well as the larger airways at low inhalation flow rates. In order to assess the relative importance of impaction and sedimentation, particle transport and deposition is examined under different steady inhalation conditions in a mouth-throat and a bifurcation model, using direct numerical simulations. The results are also compared to computations without the effect of gravity on the particles. Two important parameters characterize particle motion: (i) the Stokes number, StkStk, and (ii) the ratio of the gravitational settling velocity to the fluid velocity, View the MathML sourceVg*. The ratio of these two parameters is the Froude number, which measures the relative importance of inertial to gravitational forces. Instantaneous definitions of the Stokes number, non-dimensional settling velocity and Froude number are derived, based on the local flow properties, which provide a more accurate representation of the particle trajectories compared to the reference parameters based on characteristic flow scales. Results show that, in certain regions of the flow, the instantaneous Froude number can be three to four orders of magnitude smaller than the reference value. In these regions, deposition via sedimentation is shown to be significant, and the reference parameter underestimates gravitational effects. In the extrathoracic airways, particles with high View the MathML sourceVg* deposit primarily in the mouth, via sedimentation, while particles with high StkStk deposit mainly in the larynx and trachea, via impaction. In the bifurcation, different orientation angles of the airway geometry are shown to result in non-negligible variation in deposition. Impaction is the dominant mechanism for deposition on the carinal ridge, while sedimentation occurs along airway walls at an angle to the gravity direction. In the daughter branches, both impaction and sedimentation contribute to deposition

The psychosocial contract: Its nature and effects fro Greek industry

[Δε διατίθεται περίληψη / no abstract available]The basic focus of this paper lies in the definitionof the «psychosocial contract» as a new concept inorganization theory, and the discussion of its potentialtheoretical and practical usefulness. Thisconcept derived out of a research study in the Greekindustry and is supported by current organizationtheory and traditional political philosophy.The basic problem of the Greek study centeredaround the topic of success of industrial firmswithin the Greek economy, success being defined interms of a systems-effectiveness model. The findings,while supporting previous contingency theoriesdeveloped in other Western industrial settings,further extended them by adding «Social Accountability» as a major predictor of organizationalsuccess. A conceptual model, supported by theGreek data, provided an adequate explanation ofdifferences in success among Greek industrial firms,and suggested a workable «psychosocial contract.»The psychosocial contract, as a theoretical construct,helped to explain the Greek data moreconveniently than would be possible without it

Prediction of flow and aerosol deposition in the extrathoracic airways using an implicit immersed boundary method

The effect of intrasubject variation on the turbulent flow and aerosol deposition in the extrathoracic airways is studied in two realistic mouth-throat geometries from the same subject. An immersed boundary method is applied which simplifies the task of grid generation for the complex extrathoracic geometries and allows the use of a structured grid solver. Curvilinear grids that roughly follow the shape of the geometries are adopted, allowing for much higher resolution within the geometries than Cartesian grids commonly used in IB methods. An added advantage is that the grid lines are approximately aligned with the streamlines, which reduces numerical diffusive errors. The numerical simulations allow us to explain in vitro aerosol deposition data in the literature for the same mouth-throat models. The position of the tongue during inhalation is shown to have a significant impact on both the mean flow patterns and the turbulence intensities, which in turn affects extrathoracic deposition

The effect of mouth-throat geometry on regional deposition in the tracheobronchial tree

In silico methods offer a valuable approach to predict localized deposition in the tracheobronchial tree, important in the topical treatment of respiratory diseases and the systemic administration of drugs with limited lung bioavailability. In this study, we examine the effect of extrathoracic airway variation on regional deposition in order to assess whether standard mouth-throat models can be adopted for more efficient predictions. Despite large qualitative differences in the extrathoracic airways, deposition patterns and efficiencies in the tracheobronchial region remain largely unaffected for particles smaller than 6 microns. The findings suggest that for drug delivery applications, standard mouth-throat models could be adopted to predict deposition in the central airways