[Chivalrous (OP)]

I've read that: "Trans-pulmonary pressure is the difference between the intra-alveolar pressure and the intra-pleural pressure in the lungs."

I'll be very grateful if anyone could please explain that in more details.
(Note: I've read about the intra-alveolar and the intra-pleural pressures, but I still can't understand how the trans-pulmonary pressure can be the difference between them.)

[cheryl j]

It might help to google transpulmonary pressure under google images and look at some diagrams. You understand that when when you breath in, the diaphragm and rib muscles expand the the size of the thoracic cavity?  The pleural membrane is a double membrane with one layer tightly adhering to the walls of the chest cavity, with a small space between it and the second layer around the lungs. When the thoracic cavity expands, the pressure inside the lungs decreases, drawing in air. When inhaling, the pressure will begin decreasing in the pleural space first, and hold for a while at slightly more negative.   (If I'm stating the obvious, I apologize.)

[cheryl j]

another diagram

[evan_au]

That's pretty impressive - our normal breathing works at around 0.3% of an atmosphere pressure!

I'm sure our lungs can produce more pressure than that, for example, when blowing up a balloon...

[alancalverd]

Maximum exhalatory pressure is about 60 - 90 cm water gauge. One atmosphere is about 10 m water gauge. 

[Chivalrous (OP)]

cheryl j, Thanks a lot for your help, your second diagram was very useful. I got it! []
evan_au & alancalverd, Thanks for your replies.