The role of collateral paths in long-range diffusion of 3He in lungs.

Rationale And Objectives: The hyperpolarized (3)He long-range diffusion coefficient (LRDC) in lungs is sensitive to changes in lung structure due to emphysema, reflecting the increase in collateral paths resulting from tissue destruction. However, no clear understanding of LRDC in healthy lungs has emerged. Here we compare LRDC measured in healthy lungs with computer simulations of diffusion along the airway tree with no collateral connections.

Role of collateral paths in long-range diffusion in lungs.

The long-range apparent diffusion coefficient (LRADC) of (3)He gas in lungs, measured over times of several seconds and distances of 1-3 cm, probes the connections between the airways. Previous work has shown the LRADC to be small in health and substantially elevated in emphysema, reflecting tissue destruction, which is known to create collateral pathways. To better understand what controls LRADC, we report computer simulations and measurements of (3)He gas diffusion in healthy lungs.