Influence of pulsatility and inlet velocity profiles on tracheal airflow characteristics

Abstract

Patient-specific simulation is a powerful and emerging tool for studying human airway physiological and pathological characteristics. Decision-based systems for clinicians based on the patient airflow characteristics play a critical role in tailored medical treatment, from drug delivery to surgical planning. Computational methods are commonly employed and easily executable to investigate and understand the biofluid mechanics of the airflow in simplified or patient-specific tracheal geometries. One of the key considerations in setting up computations is choosing the correct inlet boundary conditions (BCs). The most common BCs employed in previous studies are a) flat, b) parabolic, c) Womersley, and e) real velocity profiles. In many situations, an idealized velocity profile must be selected if the patient-specific velocity information is unavailable. In addition, the flow patterns change with different breathing frequencies, which might be due to underlying lung disease or physical activity. In order to examine the influence of choosing different inlet conditions and breathing frequencies, the current study executes the simulations of the inhalation-phase airflow in ten patient-specific healthy tracheas for normal and rapid breathing conditions with various inlet velocity profiles mentioned above. Qualitative results for various inlet conditions are presented using velocity and vorticity contours in the trachea's axial and sagittal planes. In contrast, quantitative flow metrics are studied by evaluating net pressure drop, Time-Averaged Wall Shear Stress (TAWSS), and Oscillatory Shear Index (OSI). These results indicate that flat profiles are the least representative of the realistic situations under both breathing conditions. Further, the Parabolic and Womersley profiles led to similar flow patterns and values of TAWSS and OSI for normal breathing conditions. However, in rapid breathing conditions, Womersley profiles better represent the real velocity profiles than parabolic profiles.