View the Transcript.

15:52:12 evolved to try to keep the external environment15:52:16 from getting inside us, with the exception of15:52:20 obviously we have to breathe air all the time. So15:52:23 molecular oxygen, we want to get that down into15:52:25 our alveoli, but particles bigger than oxygen,15:52:28 it's not desirable. We have a torturous route in15:52:34 the upper airway. You consider the hairs in the15:52:36 nose, the nasal turbinates. The nose will filter15:52:41 out particles that go down as small as 1 micron in15:52:44 size. Even if one is breathing through the mouth,15:52:46 you certainly have a torturous route to go beneath15:52:49 the vocal cords with a 90‐degree turn in the back15:52:52 of the throat. And it's really thought that15:52:54 breathing through the mouth particles of 5 microns15:52:57 or larger are filtered out.15:53:0015:53:00 Once you get down into the lower airway, we all15:53:03 know that the airway branches over and over and15:53:05 over again. There is something call the Weibel15:53:09 model of airway branching where there are 23 315:53:11 generations of airways, and each time there's a15:53:13 branch point, that's a corner that medications15:53:19 have to negotiate to get down to the target15:53:21 region. In asthma we're certainly looking at15:53:23 delivering medications to smaller airways down15:53:25 here. The same could be said for cystic fibrosis.15:53:29