Abstract
BackgroundLeft pulmonary artery sling (LPAS) is a rare but severe congenital anomaly, in which the stenoses are formed in the trachea and/or main bronchi. Multi-detector computed tomography (MDCT) provides useful anatomical images, but does not offer functional information. The objective of the present study is to quantitatively analyze the airflow in the trachea and main bronchi of LPAS subjects through computational fluid dynamics (CFD) simulation.MethodsFive subjects (four LPAS patients, one normal control) aging 6-19 months are analyzed. The geometric model of the trachea and the two main bronchi is extracted from the MDCT images. The inlet velocity is determined based on the body weight and the inlet area. Both the geometric model and personalized inflow conditions are imported into CFD software, ANSYS. The pressure drop, mass flow ratio through two bronchi, wall pressure, flow velocity and wall shear stress (WSS) are obtained, and compared to the normal control.ResultsDue to the tracheal and/or bronchial stenosis, the pressure drop for the LPAS patients ranges 78.9 - 914.5 Pa, much higher than for the normal control (0.7 Pa). The mass flow ratio through the two bronchi does not correlate with the sectional area ratio if the anomalous left pulmonary artery compresses the trachea or bronchi. It is suggested that the C-shaped trachea plays an important role on facilitating the air flow into the left bronchus with the inertia force. For LPAS subjects, the distributions of velocities, wall pressure and WSS are less regular than for the normal control. At the stenotic site, high velocity, low wall pressure and high WSS are observed.ConclusionsUsing geometric models extracted from CT images and the patient-specified inlet boundary conditions, CFD simulation can provide vital quantitative flow information for LPAS. Due to the stenosis, high pressure drops, inconsistent distributions of velocities, wall pressure and WSS are observed. The C-shaped trachea may facilitate a larger flow of air into the left bronchus under the inertial force, and decrease the ventilation of the right lung. Quantitative and personalized information may help understand the mechanism of LPAS and the correlations between stenosis and dyspnea, and facilitate the structural and functional assessment of LPAS.
Highlights
Left pulmonary artery sling (LPAS) is a rare congenital anomaly, where the left pulmonary artery (LPA) starts from the proximal portion of right pulmonary artery; initially runs to the right, passes behind the right main bronchus, turns left and crosses between the trachea and esophagus, and reaches the hilum of the left lung [1,2]
Once the computational fluid dynamics (CFD) simulations are done for all subjects, the average inlet pressure, outlet sectional area, minimum sectional area and mass flow rates are calculated and summarized in Table
Using geometric models extracted from CT images and patient-specified inlet boundary conditions, CFD simulation can provide vital airflow information including flow features and the quantitative parameters for LPAS
Summary
Left pulmonary artery sling (LPAS) is a rare congenital anomaly, where the left pulmonary artery (LPA) starts from the proximal portion of right pulmonary artery; initially runs to the right, passes behind the right main bronchus, turns left and crosses between the trachea and esophagus, and reaches the hilum of the left lung [1,2]. The anomalous LPA forms a “sling” around the distal trachea. Subjects with LPAS commonly present with respiratory problems resulting from external trachea and main bronchus compression. Surgeries including left pulmonary re-implantation with simultaneous repair of the tracheal stenosis are often carried out after diagnosis [3,4,5]. Left pulmonary artery sling (LPAS) is a rare but severe congenital anomaly, in which the stenoses are formed in the trachea and/or main bronchi. The objective of the present study is to quantitatively analyze the airflow in the trachea and main bronchi of LPAS subjects through computational fluid dynamics (CFD) simulation
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