(emsl3427)Computational Fluid Dynamics applied to airflow problems in animal and human lungs.
EMSL Project ID
3427
Abstract
With the advent of innovative treatments for lung diseases, the necessity for accurately determining the presence and regional distribution of lung abnormalities has become essential. The long-term objective of this project is to develop a model of the normal human lung, which will consist of an atlas of normal anatomy down to the sub-lobar segments. Coupled to these sub-lobar segments will be parameters of the normal range and distribution of airway and blood vessel geometries, compliance, tissue texture and perfusion, and regional ventilation. This model will allow for the use of dynamic and volumetric x-ray CT to assess the lung. By understanding normal, we will be in a better position to determine abnormal.Regional ventilation of the lungs is measured by following the wash in and wash out of the radio-dense, non-radioactive xenon gas using multi-detector row CT (MDCT). In previous studies in sheep, time constants for xenon wash-in and wash-out were assumed identical. However, it has been observed that xenon wash out takes longer than wash in, particularly in the apical lung regions. The finding cannot be explained by the xenon solubility in blood, as that would cause wash-out to be longer than wash-in. The monopodial geometry of the sheep lung is hypothesized to be the cause of the currently observed differences in wash-in and wash-out. The monopodial branching pattern in sheep may provide greater conductance to the dorsal-basal lung during wash-in as compared to the lung apices because of the nearly 180 degree turn and more rapid narrowing of the upper lobe bronchi. This observation provides an exciting opportunity to begin link experiments in which we model gas flow in realistic lung geometry based upon imaging to match the predicted flow differences with direct observations. At our disposal are xenon and krypton gases along with gas mixtures, which include xenon, krypton, oxygen and helium. Through a study of the various gases via imaging, and comparing the gas distributions to models of gas flow derived from computational fluid dynamics (CFD), we have an exciting opportunity to gain new insights into the determinants of regional ventilation and the delivery of foreign gases to the lung.
The main aim of implementing CFD modeling is to support the above-mentioned hypothesis. The short-term aim is to create a CFD model of the sheep airway tree using suitable imaging modalities, which represents 10 generations of the lung. Realistic breathing pattern is simulated using the flow data gathered from sheep experiments. Then this model is extended up to 23 generations with the help of diameter ratios and branching patterns already published in journals. Previously only smaller numbers of airway generations have been simulated at a time due to technical limitations, piecewise simulations being combined to reconstruct the entire lung. A majority of CFD models of the lung to date have considered only steady state flow condition. We have the possibility, through imaging, of being able to accurately specify multiple intermediary states of the airway tree between end-inspiratory and end-expiratory states.
Further studies will involve an eventual comparison of gas flow between the monopodial branching of the sheep and the bipodial branching in humans. This will provide an opportunity to understand the interplay between structure and function in the lung.
Project Details
Project type
Capability Research
Start Date
2003-06-01
End Date
2005-08-02
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members