question regarding the pressure inside of pleural space

[hyhero89]

hi I am a nurse on ward.

I was just looking through thoracic cage anatomy

And this sentence needs to be understood to me.

"subatmospheric pressure in pleural space is responsible for continued expansion of lungs"

you can just explain it to me or suggest any link that may help. thanks for your attention.

[vandydani]

They are referring to the pleura, which is the membrane covering on the outside of your lungs (visceral pleura) and also lines your chest wall (parietal pleura). There is a pocket of air and some fluid between the two pleura that has a negative pressure (subatmospheric) and that creates a kind of vacuum force that pulls your lungs open and the air fills your lungs. So on inspiration your intercostal muscles tense, your diaphragm contracts, and your chest wall expands. When it expands that negative pressure brings the lungs with it, lungs fill with oxygen. On expiration those muscles relax and the chest wall moves back to where it was pre-inspiration. That negative pressure means that the lungs and the chest wall do not touch. The pressure forces the carbon dioxide out of your lungs for expiration. This also explains the mechanism of a pneumothorax. This is a collection of more air than usual in the pleural space. The pleural space loses that negative pressure and the patient ends up with a "collapsed" lung because the lung is no longer inflating and expanding without the negative pressure from the chest wall. Hope this helps and is not super confusing!!

[hyhero89]

Vandydani / thank you very much for your detailed explanation first! But I don' get it still especially the part 'the pleural pressure is negative so it makes lungs open'... maybe I should check the whole respiratory mechanism?

[Rose_Queen, BSN, MSN, RN]

Maybe not the best example and a bit simplified, but think about drawing up meds from a vial into a syringe without injecting air into the vial- when you pull back on the plunger, the pressure inside the syringe is much less than the pressure inside the vial (and will actually be a negative pressure). Law of physics means that the pressure in the vial and the syringe will try to equalize, causing fluid to flow from the vial into the syringe. The lungs and air work much the same way- when the diaphragm contracts during inspiration, it's causing the negative pressure inside the chest cavity. To equalize the pressure between the atmosphere and the chest cavity, air rushes into the lungs. When the diaphragm relaxes, the pressure inside the chest cavity increases, causing air to be expelled from the lungs via exhalation.

[vanilla bean]

As PP mentioned, there is a visceral membrane lining the lung(s) and a parietal membrane lining the chest wall(s). The space in between is filled with a small amount of pleural fluid. Negative pressure (relative to atmospheric pressure) is generated between the two pleural layers because of opposing forces - the outward pull of the thoracic cavity (chest wall) and the inward pull of the lung(s).

The lungs are normally in a constant state of elastic recoil and the chest wall, although can change size and shape somewhat during normal breathing, is otherwise quite rigid and these two opposing states maintain the negative pressure in the pleural space.

I've heard a good comparison of this to help illustrate the mechanics: say you have a glass of an icy cold beverage on a hot day sitting on a heavy coaster. You attempt to pick up said tasty beverage and the coaster comes along with it. You've cause an upward direction of the glass while the coaster tries to maintain a downward direction, and the thin layer of liquid that has accumulated between the two simultaneously attempts to maintain contact with the glass and the coaster. This creates a situation of negative pressure in that small amount of fluid. This is what is happening with the lung and chest wall.

I bet Khan academy or similar site will have good video illustrations of this if you are more of a visual learner.

[nursej22, MSN, RN]

There are many videos on the internet demonstrating how to make a lung model using a bottle and balloons, like this:

If this video could go one step further, and withdraw the air between the inner bottle wall and the balloon, this would cause the balloon to stay inflated. This is because of negative pressure pulling on the outside of the balloon.

A tube withdrawing the air would be similar to a chest tube, withdrawing air from a pneumothorax.

[kool-aide, RN]

If this statement is in reference to inspiration of room air, and not necessarily relating to pneumothorax as other posters are speaking of....

What I was taught in school is that when one takes a breath in, it's not truly the work of the pt consciously "breathing in" but it is the pressure in the atmosphere around us moving room air from an area of higher pressure(the atmosphere) to an area of lower pressure(the interior of our lungs).