The effects of curvature and constriction on airflow and energy loss in pathological tracheas

Abstract

This paper considers factors that play a significant role in determining inspiratory pressure and energy losses in the human trachea. Previous characterisations of pathological geometry changes have focussed on relating airway constriction and subsequent pressure loss, however many pathologies that affect the trachea cause deviation, increased curvature, constriction or a combination of these. This study investigates the effects of these measures on tracheal flow mechanics, using the compressive goitre (a thyroid gland enlargement) as an example. Computational fluid dynamics simulations were performed in airways affected by goitres (with differing geometric consequences) and a normal geometry for comparison. Realistic airways, derived from medical images, were used because idealised geometries often oversimplify the complex anatomy of the larynx and its effects on the flow. Two mechanisms, distinct from stenosis, were found to strongly affect airflow energy dissipation in the pathological tracheas. The jet emanating from the glottis displayed different impingement and breakdown patterns in pathological geometries and increased loss was associated with curvature.

A novel method to generate dynamic boundary conditions for airway CFD by mapping upper airway movement with non‐rigid registration of dynamic and static MRI

“…Analysis of the motion of the jaw, tongue, pharyngeal walls, soft palate, and epiglottis revealed how each region of anatomy influences the volume of the airspace and the cross‐sectional area of the upper airway along its length. Many studies have previously shown the relationship between airway cross‐sectional area and airway resistance, with narrower sections increasing the subject's work of breathing. Therefore, mapping the dynamic behavior of the upper airway cross‐section throughout a breath is vital to accurately predicting the airway pressure losses in computational and experimental models.…”

Quantitative Assessment of Regional Dynamic Airway Collapse in Neonates via Retrospectively Respiratory‐Gated 1H Ultrashort Echo Time MRI

“…In order to investigate these possibilities in each patient, the internal pressure forces that act on the tracheal walls and the effect that tracheal motion has on subjects' breathing effort can be calculated through computational fluid dynamics (CFD) simulations. Previously, CFD simulations have been used to calculate the increased tracheal work of breathing in adult subjects with goiters and a transplanted trachea . These simulations rely on high‐resolution imaging to provide the anatomical boundaries of the airway structure, and there is increasing recognition that the accuracy of CFD simulations suffers when airway wall motion is ignored and simplified into a static model …”

Computational fluid dynamics benchmark dataset of airflow in tracheas

“…Analysis of convergence data was performed on one geometry (case B in Bates et al [1] and shown in Fig. 1).…”

“…As an example of typical averaging windows, in Bates et al [1] all computations were simulated for 0.25 s of steady inhalation. Of this period, the first 0.1 s was ignored, to allow for transients caused by the impulsive start to die away.…”