[getawayFK]

Hey trux I will get to your question shortly afterwhile as Ive to go now.

Anyway, within your lung, there is a residual volume and within your whole respiratory system there is also whats called "dead space". You can't use whatever volume is in there as the residual volume is simply the amount of air left after a forceful expiration so that your lung doesn't collapse and the dead volume is the volume that air will occupy at any time in your respiratory system. Residual volume can greatly varie (e.g: in asthma or COPD it can occupies up to 60% of your functional volume) etc...

I'll get to your question later.

See ya