How is intrapleural pressure related to breathing?

[USC 22]

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This is driving me insane.

I know the diaphragm and intercostal muscles contract, which increases the chest cavity (lung volume), causing air to rush in. But how is this related to the intrapleural pressure? How does intrapleural pressure have anything to do with air rushing in?

 

[doctor sock]

Assuming the atmospheric pressure to be constant, the relationship between intra-alveolar pressure and atmospheric pressure determines whether or not air moves into the lungs. Intrapleural pressure is the pressure within the pleural space. Due to the elastic forces of the lung (tending to contract) and the chest wall (tending to expand) under normal conditions Pip is negative. The magnitude of Pip varies with each phase of ventilation. During inspiration as the chest wall expands Pip decreases (more negative). During expiration as the chest wall recoils Pip increases (less negative). The air coming into the lung is driven by these pressure gradients.

Example with arbitrary numbers.

Inspiration: intra-alveolar pressure decreases from 0 to -1 by the action of the diaphragm and external intercostal muscles. Air will flow in until the intra-alveolar pressure returns to 0. See Boyle's law. During inspiration, intra-pleural pressure will also decrease from -4 to -6 mmHg

Expiration: Intra-alveolar pressure increases during expiration from 0 to +1. Air will flow out until the intra-alveolar pressure returns to 0. During expiration, intra-pleural pressure increases from -6 to -4.

 

[USC 22]

Assuming the atmospheric pressure to be constant, the relationship between intra-alveolar pressure and atmospheric pressure determines whether or not air moves into the lungs. Intrapleural pressure is the pressure within the pleural space. Due to the elastic forces of the lung (tending to contract) and the chest wall (tending to expand) under normal conditions Pip is negative. The magnitude of Pip varies with each phase of ventilation. During inspiration as the chest wall expands Pip decreases (more negative). During expiration as the chest wall recoils Pip increases (less negative). The air coming into the lung is driven by these pressure gradients.

Example with arbitrary numbers.

Inspiration: intra-alveolar pressure decreases from 0 to -1 by the action of the diaphragm and external intercostal muscles. Air will flow in until the intra-alveolar pressure returns to 0. See Boyle's law. During inspiration, intra-pleural pressure will also decrease from -4 to -6 mmHg

Expiration: Intra-alveolar pressure increases during expiration from 0 to +1. Air will flow out until the intra-alveolar pressure returns to 0. During expiration, intra-pleural pressure increases from -6 to -4.

Thanks for your response. I understand everything you have just said. I know the intrapleural pressure keeps the lungs from collapsing, but how does this have to do with air rushing into the lungs? I don't see how it's actually involved in the "air rushing in" process.

 

[loveoforganic2]

1----------------------
................................ <-- Lung space
2----------------------
................................ <-- Intrapleural space
3---------------------- <-- Diaphragm

The intrapleural space is isovolumic, the lung space is not

By contracting the diaphgram (bringing 3 down lower), you exert a vacuum force on the intrapleural space, which causes the lung space to expand (as the pleural space cannot)

 

[adrakdavra]

There are two things to keep in mind 1) the intrapleural cavity has a constant negative pressure. This allows the outside pressure (alveolar pressure) to exert force and maintain proper background inflation of the lungs to prevent complete collapse. at normal lung at rest the intrapleural pressure is -3mmgh, and during inhalation the pressure drops to - 6 mmghand the tidal volume increases to 500ml 2) (volume increase pressure decrease) and the ATM pressure is higher and the inside of the lung volume increase and you know the rest ......
Just close your eye and imagine if the air is water what is going to happen?
then Imagine if you were standing at Everest what happen to pressure and breating?