Why do opposing chest wall expansion and lung collapse add up to a negative intrapleural pressure, why does the pressure get more negative as lung volume increases during inspiration, and become (briefly) positive in forced expiration? Didn't get it M1 year, don't get it now. Any explanation greatly appreciated-hate just memorizing.
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Step I Respiratory Phys. Confusion
Started by artsydoc
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Boyle's Law. P1V1 = P2V2
Contract the diaphragm, increase volume of pleural space, compensatory pressure drop, and lungs expand.
Contract the diaphragm, increase volume of pleural space, compensatory pressure drop, and lungs expand.
When you push an object away... you are applying force and that's in essence positive force (i.e. pressure).. that's the same analogy I use for expiration, you need to push air out of your lungs, so you need positive pressure.
On the other hand, when you want to bring air in your lungs, you are not pushing air away, rather you are sucking it in... so it will be negative pressure...
I also look at the chest as a huge syringe, with your diaphragm being the sucker or pusher - when you pull out the syringe (diaphragm), you get negative pressure which will suck air in... but when you want to push air out of it, you need to apply force (pressure) on the diaphragm to push out the air...
Goljan says remember one thing and the other one's the other one. So just remember that pushing air out is +ve pressure. I know I was being redundant, but hope it helps.
