Clinical research on the deposition of inhaled substances (e.g. inhaled medications, airborne contaminants, fumes) in the lungs necessitates anatomical models of the airways. Current conducting airway models lack three-dimensional (3D) reality as little information is available in the literature on the distribution of the airways in space. This is a limitation to the assessment or predictions of the particle deposition in relation to the subject's anatomy.Detailed information on the full topology and morphology of the airways is thus required to model the airway tree realistically. This paper presents the length, diameter, gravity, coronal and sagittal angles that together describe completely the airways in 3D space. The angle at which the airways branch out from their parent (branching angle) and the rotation angle between successive bifurcation planes are also included. These data are from the study of two sets of airways computed tomography (CT) images. One CT scan was performed on a human tracheobronchial tree cast and the other on a healthy male volunteer. The airways in the first nine generations of the cast and in the first six conducting generations of the volunteer were measured using a computer-based algorithm. The data contribute to the knowledge of the lung anatomy. In particular, the spatial structure of the airways is shown to be strongly defined by the central airways with clear angular lobar patterns. Such patterns tend to disappear with a mean gravity, coronal and sagittal angles of 90 ° in each generation higher than 13-15. The mean branching angle per generation appears independent of the lobe to which the airways belong. Non-planar geometry at bifurcation is observed with the mean ( ± SD) bifurcation plane rotation angle of 79 ± 41 ° ( n = 229). This angle appears constant over the generations studied. The data are useful for improving the 3D realism of the conducting airway structure modelling as well as for studying aerosol deposition, flow and biological significance of non-planar airway trees using analytical and computational flow dynamics modelling.

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Detailed information on biological branching networks (optical nerves, airways or blood vessels) is often required to improve the analysis of 3D medical imaging data. A semi-automated algorithm has been developed to obtain the full 3D topology and dimensions (direction cosine, length, diameter, branching and gravity angles) of branching networks using their CT images. It has been tested using CT images of a simple Perspex branching network and applied to the CT images of a human cast of the airway tree. The morphology and topology of the computer derived network were compared with the manually measured dimensions. Good agreement was found. The airways dimensions also compared well with previous values quoted in literature. This algorithm can provide complete data set analysis much more quickly than manual measurements. Its use is limited by the CT resolution which means that very small branches are not visible. New data are presented on the branching angles of the airway tree.

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Swirling flow associated with non-planar arterial geometry encourages interest in flow in larger human bronchial airways, where bifurcations are planar but consecutive bifurcation planes rotate by an angle (φ) of ca. 90 • . Steady 'inspiratory' flow has been investigated in a two-generation symmetrically bifurcating human bronchial airway model by studying reddening by acid vapour of a litmus-containing coating as an approximate indicator of relative local wall shear (S w ). The inlet tube Reynolds number (Re it ) was 600 or 1800; the branching angle (θ) was 32.5 • at first generation and 32.5 • or 55 • at second generation; φ was 0 • or 90 • between first and second generations; second-generation daughter tube volume flow rates were the same. With φ = 0 • , S w distribution between second-generation daughters was non-uniform. With φ = 90 • , S w distribution between second-generation daughters was uniform and flows were swirling with pitch λ. With φ = 90 • and Re it given, increase of θ reduced λ and increased S w . With φ = 90 • and θ given, increase of Re it reduced λ. Inspiratory flow in larger human bronchial airways is expected to be asymmetric and swirling, with implications for all transport processes including those of particles. The study may have implications for the design of general piping systems. Keywords: bronchial airway flows; planar and non-planar models of bronchial airways; rotation of plane of airway bifurcation; swirling bronchial airflow; bronchial airway transport processes