Modeling the Nonlinear Motion of the Rat Central Airways

Abstract

Advances in volumetric medical imaging techniques allowed the subject-specific modeling of the bronchial flow through the first few generations of the central airways using computational fluid dynamics (CFD). However, a reliable CFD prediction of the bronchial flow requires modeling of the inhomogeneous deformation of the central airways during breathing. This paper addresses this issue by introducing two models of the central airways motion. The first model utilizes a node-to-node mapping between the discretized geometries of the central airways generated from a number of successive computed tomography (CT) images acquired dynamically (without breath hold) over the breathing cycle of two Sprague-Dawley rats. The second model uses a node-to-node mapping between only two discretized airway geometries generated from the CT images acquired at end-exhale and at end-inhale along with the ventilator measurement of the lung volume change. The advantage of this second model is that it uses just one pair of CT images, which more readily complies with the radiation dosage restrictions for humans. Three-dimensional computer aided design geometries of the central airways generated from the dynamic-CT images were used as benchmarks to validate the output from the two models at sampled time-points over the breathing cycle. The central airway geometries deformed by the first model showed good agreement to the benchmark geometries within a tolerance of 4%. The central airway geometry deformed by the second model better approximated the benchmark geometries than previous approaches that used a linear or harmonic motion model.

Effect of static vs. dynamic imaging on particle transport in CT-based numerical models of human central airways

“…This method provides arguably the most physiologically-realistic boundary conditions to human lung models, although Ibrahim et al (2015) took advantage of a vascular tree to reproduce more realistic sub-lobar ventilation of their rat lung model. Regarding airway geometry, most of the previous studies used rigid airways, while more recent studies used deforming airways based on static or dynamic images of the rat (Mead-Hunter et al, 2013; Ibrahim et al, 2016) and human lungs (Yin et al, 2013). Airway geometry based on static images may reflect very slow respiratory rates.…”

“…Yin et al (2013) simulated air flow in a rigid, linearly deforming, and nonlinearly deforming imaging-based models of a human lung using one to three static images to compare regional ventilation and pressure drop. Ibrahim et al (2016) studied nonlinear deformation of the rat central airways using dynamic images. Therefore, the objective of this study is to investigate the effects of rigid vs. deforming airways, linear vs. nonlinear deformations, and static vs. dynamic imaging on particle transport in the human central airways with a CFD with airway geometric models derived from different numbers of dynamic or static images.…”