Towards a comprehensive computational model for the respiratory system

Abstract

SUMMARYThis paper is concerned with computational modeling of the respiratory system against the background of acute lung diseases and mechanical ventilation. Conceptually, we divide the lung into two major subsystems, namely the conducting airways and the respiratory zone represented by lung parenchyma. Owing to their respective complexity, both parts are themselves out of range for a direct numerical simulation resolving all relevant length scales. Therefore, we develop detailed individual models for parts of the subsystems as a basis for novel multi-scale approaches taking into account the unresolved parts appropriately. In the tracheobronchial region, CT-based geometries up to a maximum of approximately seven generations are employed in fluid-structure interaction simulations, considering not only airway wall deformability but also the influence of surrounding lung tissue. Physiological outflow boundary conditions are derived by considering the impedance of the unresolved parts of the lung in a fully coupled 3D-1D approach. In the respiratory zone, an ensemble of alveoli representing a single ventilatory unit is modeled considering not only soft tissue behavior but also the influence of the covering surfactant film. Novel nested multi-scale procedures are then employed to simulate the dynamic behavior of lung parenchyma as a whole and local alveolar ensembles simultaneously without resolving the alveolar micro-structure completely.

Local Strain Distribution in Real Three-Dimensional Alveolar Geometries

“…This has the advantage, that these models could much simpler and more efficiently be included in our overall lung model. 32 With this model it will be possible to investigate how novel ventilation strategies, e.g., how variable tidal volume ventilation affect the deformations at the alveolar level. This will be done by first considering how the airflow distributes in the large airways, 4 how this couples down to the more peripheral levels and then finally via the aforementioned multiscale approach the deformation in the alveolar wall.…”

Hypo-elastic model for lung parenchyma

“…Most of these are numerical models, e.g., Frankus and Lee (1974), Dale et al (1980), Karakaplan et al (1980), Wilson and Bachofen (1982), Kowe et al (1986), Fung (1988, Denny and Schroter (1995), Tawhai and Burrowes (2003), and Wall et al (2010). Finite elements are called upon to solve these 'constitutive models'.…”

“…Because it is our intention that our material model be used as a constitutive model within a computational mechanics code, where analyses are to be done on whole breathing lungs, it is imperative that the selected material model be efficient, foremost. An alveolar constitutive model for use at Gauss points within a finite element model of a lung, which is itself a finite element model, would not be efficient, although such multi-scale analyses have been done, e.g., Tawhai and Burrowes (2003); Wall et al (2010).…”

Nanoparticle transport in a realistic model of the tracheobronchial region

“…Although this gives useful insight into overall transport mechanisms, the simplified transport dynamics probably affect the regional distribution of particles in the lung (specifically particles at the smaller end of the scale). One alternative method in order to consider the whole conducting tree is to use space filling algorithms [23,24] and then utilize a reduced-dimensional model for the lower regions since cross-sectional distribution will become relatively small in the peripheral regions. A further limitation is the profile shape at the inlet of the domain.…”