Human Lung Morphology Models for Particle Deposition Studies

Abstract

Knowledge of human lung morphology is of paramount importance in calculating deposition patterns of inhaled particulate matter (PM) to be used in the definition of ambient air quality standards. Due to the inherently complex nature of the branching structure of the airway network, practical assumptions must be made for modeling purposes. The most commonly used mathematical models reported in the literature that describe PM deposition use Weibel's model A morphology. This assumes the airways of the lung to be a symmetric, dichotomously branching system. However, computer simulations of this model, when compared to scintigraphy images, have shown it to lack physiological realism (Martonen et al., 1994a). Therefore, a more physiologically realistic model of the lung is needed to improve the current PM dosimetry models. Herein, a morphological model is presented that is based on laboratory data from planar gamma camera and single-photon emission computed tomography (SPECT) images. Key elements of this model include: The parenchymal wall of the lung is defined in mathematical terms, the whole lung is divided into distinct left and right components, a set of branching angles is derived from experimental measurements, and the branching network is confined within the discrete left and right components (i.e., there is no overlapping of airways). In future work, this new, more physiologically realistic morphological model can be used to calculate PM deposition patterns for risk assessment protocols.

3D In Silico Modeling of the Human Respiratory System for Inhaled Drug Delivery and Imaging Analysis

“…Our contribution is that we have adapted the concept to the respiratory system. The most recent descriptions of 3D asymmetric branching networks have been presented by Martonen et al, 31,32 Guan and Martonen, 45 and Spencer et al 46 The elements of asymmetry include: variations in bifurcation angles, and differences in airway dimensions throughout lungs. In Figure 3, centerline pathways are presented from different viewing perspectives.…”

“…It will have obvious mathematical advantages to begin this complex process with a welldefined geometric form. We shall employ a truncated cone 32 because the resultant 3D surface can reasonably approximate outer (i.e., thoracic wall) and inner (i.e., heart cavity) in vivo features, and its cross-sections match the transverse slices of SPECT images (see Fig. 5).…”

Simulation of the regional manifestation of asthma

“…The lung morphology employed in this study is founded on the work of Martonen et al 25 That investigation has established how branching networks of airways can be formulated in such a manner that the resultant anatomical systems are compatible with the human subject images from clinical studies using SPECT.…”

Simulation of Three-Dimensional Particle Deposition Patterns in Human Lungs and Comparison with Experimental SPECT Data

“…Airway diameters, lengths, branching, and gravity angles were based on published morphometric data, while the boundary of the lung was generated from magnetic resonance images (MRI) (Burton et al 2004). Our approach differs from that of Martonen et al (2000) in that individual paths are constructed for each inhaled particle within the boundary of the lung. Thus instead of visualizing the whole airway system, it is the three-dimensional deposition pattern that was visualized in the present study.…”

“…In order to utilize these SPECT data for model validation, particle deposition models must be able to predict three-dimensional deposition patterns. Martonen et al (2000) developed a three-dimensional model of the spatial arrangement of the entire airway network for the analysis of SPECT images (Schroeter et al 2002). Airway diameters, lengths, branching, and gravity angles were based on published morphometric data, while the boundary of the lung was generated from magnetic resonance images (MRI) (Burton et al 2004).…”