How does sticky mucus reduce gas exchange?

• Mucus blocks the narrow airways of the lungs and the lumen of the bronchi and bronchioles get narrowed. Not enough oxygen gets into the alveoli, which decreases the number of alveoli providing surface area. Also, this decreases the concentration gradient of oxygen across the alveoli, so decreases the rate of diffusion.

  Furthermore, mucus blocks the end of the narrow airways so air can go in but not pass out, this leads to over inflation of lungs which damages the elasticity of the lungs.