What abnormal conditions can increase the diffusion path length?
1. Fibrotic thickening of alveolar and capillary walls
2. interstitial edema fluid, separating alveolar and capillary membranes
3. fluid alveoli
4. interstitial fibrotic processes that thicken the interstitial space.
5. dilated, engorged capillaries, which allow red cells to flow side by side.