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Old 02-23-2012
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Default Can anybody please explain this?

I'm so confused about positive-pressure ventilation and why it's used in ARDS. Can anybody explain this?
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Old 02-23-2012
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Its like you have a plastic bag in front of you and it is very sticky inside...
You blow in - it expands (if you blow too hard - it over expands or even ruptures) if you let the air come out - it will collapse and get glued to each other, cuz its sticky inside... so you try not to let all the air to come out, but allways keep some in.
Positive pressure.
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Old 02-23-2012
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That makes sense but my understanding is that during inspiration, the increasing -ve intrapleural pressure along with a -1 alveolar pressure is responsible for expansion because air can rush in due to the pressure difference from outside air. Opposite occurs during expiration and alveolar pressure goes from -1 to +1 which causes air to flow out.

So what I don't get is the + pressure causes the alveoli to become smaller during expiration..so why would you give positive-pressure ventilation if your goal is to keep the alveoli from getting smaller and collapsing? Wouldn't it make sense to give negative pressure?
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Old 02-23-2012
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I think DocSikorski is right.

The pos. pressure during expiration that you explained here is different from the pos. pressure-ventilation that is the treatment in ARDS.

Pos. pressure during expiration in the normal lungs --> exactly as you have told us.

Pos pressure ventilation: (ARDS treatment)
- refers to a setting in a mechanical ventilator
- the machine is just basically giving a continuous flow of O2 into the lungs so that the alveoli won't collapse.
- because the walls in ARDS are "sticky" due to lack of surfactant (in the case of neonates) or other pathology; like DocSikorski explained in the above post

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Old 02-24-2012
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As rightly explained the Positive pressure during expiration is the positive pressure created by lungs..

In positive pressure respiration we have a mask( very similar to the O2 masks) and that maintains a continuous pressure in the lungs preventing the lungs from collapsing..

Something similar is also used in people with obstructive sleep apnea and is called CPAP (continuous positive airway pressure)
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