A computational study of the respiratory airflow characteristics in normal and obstructed human airways

Abstract

Obstructive lung diseases in the lower airways are a leading health concern worldwide. To improve our understanding of the pathophysiology of lower airways, we studied airflow characteristics in the lung between the 8th and the 14th generations using a three-dimensional computational fluid dynamics model, where we compared normal and obstructed airways for a range of breathing conditions. We employed a novel technique based on computing the Pearson׳s correlation coefficient to quantitatively characterize the differences in airflow patterns between the normal and obstructed airways. We found that the airflow patterns demonstrated clear differences between normal and diseased conditions for high expiratory flow rates (>2300ml/s), but not for inspiratory flow rates. Moreover, airflow patterns subjected to filtering demonstrated higher sensitivity than airway resistance for differentiating normal and diseased conditions. Further, we showed that wall shear stresses were not only dependent on breathing rates, but also on the distribution of the obstructed sites in the lung: for the same degree of obstruction and breathing rate, we observed as much as two-fold differences in shear stresses. In contrast to previous studies that suggest increased wall shear stress due to obstructions as a possible damage mechanism for small airways, our model demonstrated that for flow rates corresponding to heavy activities, the wall shear stress in both normal and obstructed airways was <0.3Pa, which is within the physiological limit needed to promote respiratory defense mechanisms. In summary, our model enables the study of airflow characteristics that may be impractical to assess experimentally.

How design characteristics of tracheostomy tubes affect the cannula and tracheal flows

“…During exhalation, a region of high velocity and shear stress was formed superior to the bifurcation in the trachea due to merging of the flow from the mainstem bronchi. With these current observations in agreement with previous studies, clinicians should consider the effect of WSS within the lower trachea and at the carina that may cause impingement of the tracheal flow on the cartilage or airway mucosa, which can potentially lead to tissue inflammation and injury. Previous experimental studies involving tracheal epithelium tissue cultures from Fischer 344 rats exposed to transmembrane pressures showed the induction of early growth response‐1 (Egr‐1), endothelin‐1, and transforming growth factor‐B1 .…”

“…The effect of various airway surgeries performed to correct obstructive sleep apnea, expressed as a change in the work of breathing, were evaluated preoperatively using CFD modeling . CFD modeling has also been effective in estimating three‐dimensional variations in flow‐induced frictional stresses, which are hypothesized to influence the inflammation of soft and cartilaginous tissue through the trauma induced by the flow of air against the tissue . Spatial variation in airflow turbulence, determined as a function of the inner cannula diameter, can be evaluated more accurately than in vitro or in vivo studies using CFD …”

A voxel image‐based pulmonary airflow simulation method with an automatic detection algorithm for airway outlets

“…A highly complex geometry of the lung airway usually must be simplified before the mesh generation process. For this reason, most previous studies have used the simplified central airway model with collections of pipes representing the airway geometry . In this study, we propose a novel simulation approach based on the voxel image data directly extracted from the medical CT.…”

“…For this reason, most previous studies have used the simplified central airway model with collections of pipes representing the airway geometry. [18][19][20] In this study, we propose a novel simulation approach based on the voxel image data directly extracted from the medical CT. This can avoid substantial effort being wasted on the mesh generation and the imposition of boundary conditions.…”

Numerical assessment of airflow and inhaled particles attributes in obstructed pulmonary system

“…An anatomically-inspired model of the lung acinus featuring a bifurcating tree of alveolated airways with moving walls has been developed [20], [21]. Moreover, the airflow characteristics of human airways between the 8 th and 14 th generations have been examined [22]. The aforementioned methodologies utilize several turbulence models to evaluate the behavior of the airflow as well as the inhaled particles.…”