Intrapleural pressure and lung recoil

[Dr.Bajaber]

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hello
I know this really has been asked multiple times but I searched and still not clear to me. My question is how the lung wanting to recoil and the chest wall wanting to expand will make the intrapleural pressure negative?
I really need an explanation of the physics behind it imagine If I know nothing about physics. second question when we inspire how the increase in the recoil of the lung will make the intrapleural pressure even more negative.
thank you

 

[DrPicard]

If you stretch a rubber band, it will attempt to shrink back into its natural position.

Our anatomy is such that both the chest wall and our lungs are under a bit of stretch; this means they both want to spring back into their natural positions. For the chest wall, that would be expanding and moving outwards a little bit. For the lungs, this is to shrink into a smaller volume. The thing, though, is that the chest wall and lungs are connected by the IPP, and they both want to move in opposite directions (chest out, lungs in). This makes the IPP negative, since the volume of this space is increasing without introducing any new molecules in it to maintain pressure. This decreasing IPP applies a sort of suction on both the chest wall and the lung, thus preventing them from expanding and shrinking respectively.

Just like increasing pressure creates a force to do work, so does decreasing pressure - just in the opposite direction. Think about the flow equation: Q = P1 - P2. We can increase Q by either increasing P1 or decreasing P2.

So for the chest wall that wants to spring outwards, the negative IPP applies an inward force and doesn't allow it to completely do so. Similarly, the IPP prevents the lung from recoiling completely.

If we allow air to enter the intrapleural pressure, eg pneumothorax, we disrupt the negative pressure inside the IPP and in a sense disconnect the chest wall with the lung. Hence the chest wall springs outwards, and the lungs recoil to a smaller volume.

Whether the lungs increase or decrease in volume depends on the sum of the forces acting on it. If the IPP is greater than recoil, lungs will expand. If the IPP is smaller, lungs will shrink. If both forces are equal, lungs wont change volume.

In restrictive diseases, recoil of the lungs is increased. The only way to expand your lungs now would be to apply a greater (ie more negative) IPP.

 

[SpaceOfDisse]

That was a remarkably clear explanation, much better than how my professor explained it!!!


Sent from my iPhone using SDN mobile app

 

[Dr.Bajaber]

If you stretch a rubber band, it will attempt to shrink back into its natural position.

Our anatomy is such that both the chest wall and our lungs are under a bit of stretch; this means they both want to spring back into their natural positions. For the chest wall, that would be expanding and moving outwards a little bit. For the lungs, this is to shrink into a smaller volume. The thing, though, is that the chest wall and lungs are connected by the IPP, and they both want to move in opposite directions (chest out, lungs in). This makes the IPP negative, since the volume of this space is increasing without introducing any new molecules in it to maintain pressure. This decreasing IPP applies a sort of suction on both the chest wall and the lung, thus preventing them from expanding and shrinking respectively.

Just like increasing pressure creates a force to do work, so does decreasing pressure - just in the opposite direction. Think about the flow equation: Q = P1 - P2. We can increase Q by either increasing P1 or decreasing P2.

So for the chest wall that wants to spring outwards, the negative IPP applies an inward force and doesn't allow it to completely do so. Similarly, the IPP prevents the lung from recoiling completely.

If we allow air to enter the intrapleural pressure, eg pneumothorax, we disrupt the negative pressure inside the IPP and in a sense disconnect the chest wall with the lung. Hence the chest wall springs outwards, and the lungs recoil to a smaller volume.

Whether the lungs increase or decrease in volume depends on the sum of the forces acting on it. If the IPP is greater than recoil, lungs will expand. If the IPP is smaller, lungs will shrink. If both forces are equal, lungs wont change volume.

In restrictive diseases, recoil of the lungs is increased. The only way to expand your lungs now would be to apply a greater (ie more negative) IPP.

Thanks a lot.I have read many resources but I could not understand it well. but finally you made crystal clear.Thank you.SO the more negative it is the more it expands the lung and this negativity is a result of the increasing volume because of the lung tendency to collapse and the thoracic wall to expand so in inspiration the diaphragm will contract thus will increase the volume more which will make the intrapleural pressure more negative and thus the lung will expand right?

 

[DrPicard]

Yep, thats right. Glad I could help!