Less bronchial lumen diameter in the lung bases: There's not enough evidence that bronchial lumen diameter variations significantly affect the accumulation or removal of mucus in cystic fibrosis.

Presence of more alveoli in the lung bases: Alveolar count does not significantly influence mucus accumulation in cystic fibrosis, although their destruction due to the disease can decrease respiratory function.

In cystic fibrosis, thick mucus accumulates in airways, causing obstruction and infection risk. Lung bases have increased perfusion, providing a richer blood supply that helps dilute and/or metabolize mucus, thereby slowing disease progression.

Increased lymphatic drainage in the lung bases: While lymphatics play an important role in the lung's immune response, they don't significantly influence mucus accumulation in cystic fibrosis.