Poster Q10 - Computational Pulmonary Edema

Introduction: We present a microvascular model of fluid transport in the alveolar septa related to pulmonary edema. It consists of a two-dimensional capillary sheet coursing by several alveoli. The alveolar epithelial membrane runs parallel to the capillary endothelial membrane with an interstitial layer in between, making one long septal tract. See Figure 1.

Materials and

Methods: A coupled system of equations is derived using lubrication theory for the capillary blood, Darcy flow for the porous media of the interstitium, a passive alveolus, and the Starling equation at both membranes. The solution method involves the use of Fourier series expansions in the x-direction with y-dependent coefficients for the pressures and velocities

Results, Conclusions, and Discussions: Case examples include normal physiology, cardiogenic pulmonary edema, noncardiogenic edema ARDS and hypoalbuminemia, and the effects of PEEP. COVID-19 has dramatically increased ARDS in the world population, raising the urgency for such a model to create an analytical framework. Under normal conditions fluid exits the alveolus, crosses the interstitium, and enters the capillary. For edema, this crossflow is reversed with fluid leaving the capillary and entering the alveolus. Because both the interstitial and capillary pressures decrease downstream, the reversal can occur within a single septal tract, with edema upstream and clearance downstream. Overall, the interstitial pressures are found to be significantly more positive than values used in the traditional physiological literature. That creates steep gradients near the upstream and downstream end outlets, driving significant flows towards the distant lymphatics. See Figure 2. This new physiological flow resolves a puzzle, noted since 1896, of how pulmonary lymphatics can function so far from the alveoli: the interstitium can be self-clearing. For the large majority of the septal tract away from the ends, the flow is directly across the interstitial layer and locally one-dimensional. Simple algebraic solutions to pressure and velocity are investigated which can be clinically useful for diagnosis and therapy. See Grotberg JB, and Romanò F. Computational pulmonary edema: A microvascular model of alveolar capillary and interstitial flow. APL Bioengineering 7: 036101, 2023.

Acknowledgements (Optional): Supported by NIH grants T32 HL007317 (JCG) and RO1 HL136141 (JBG,FR).