Respiratory physiology questions

[zmiller5000]

I am having a lot of trouble developing a coherent picture of lung physiology which in turn is making it difficult to understand lung pathophysiology. Here is a list of questions I have been compiling...maybe someone will have some insight.

1. If I drop pleural pressure without allowing air to enter the lungs (contract the diaphragm, but close your epiglottis), do your lungs expand?

My thought: If you took a balloon with an internal pressure of 20 atm in an atmosphere of 0 atm at equilibrium (so elastic recoil pressure is -20 atm), and drop the external atmospheric pressure to -50 atm..the balloon should expand without entry of air.

2. the effort independent part of the lung flow volume curve is attributed to increased pleural pressure compressing small airways..what is said to resist this compression is alveolar tethering/elastic recoil..this doesn't make sense to me.

My thought:
a. I think the majority of the smaller airways are not lined by pleura..so the only way these smaller airways could sense a change in intrapleural pressure is through alveoli tethered to the pleura.
b. I thought the change in intrapleural pressure during expiration was a result of both the lung and chest recoiling toward smaller volumes..so presumably, alveolar elastic recoil force and intrapleural force are in the same direction
c. This would suggest that on the whole..elastic recoil of the lung which microscopically should manifest as elastic recoil of alveoli results in small airway collapse.
d. What I believe maintains a constant resistance is that partial collapse of the small airways causes increased air pressure in the alveoli connected to that airway. This increased air pressure pushes the small airway open acting against the elastic recoil force of the surrounding alveoli.

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[bashwell]

I am having a lot of trouble developing a coherent picture of lung physiology which in turn is making it difficult to understand lung pathophysiology. Here is a list of questions I have been compiling...maybe someone will have some insight.

1. If I drop pleural pressure without allowing air to enter the lungs (contract the diaphragm, but close your epiglottis), do your lungs expand?

My thought: If you took a balloon with an internal pressure of 20 atm in an atmosphere of 0 atm at equilibrium (so elastic recoil pressure is -20 atm), and drop the external atmospheric pressure to -50 atm..the balloon should expand without entry of air.

2. the effort independent part of the lung flow volume curve is attributed to increased pleural pressure compressing small airways..what is said to resist this compression is alveolar tethering/elastic recoil..this doesn't make sense to me.

My thought:
a. I think the majority of the smaller airways are not lined by pleura..so the only way these smaller airways could sense a change in intrapleural pressure is through alveoli tethered to the pleura.
b. I thought the change in intrapleural pressure during expiration was a result of both the lung and chest recoiling toward smaller volumes..so presumably, alveolar elastic recoil force and intrapleural force are in the same direction
c. This would suggest that on the whole..elastic recoil of the lung which microscopically should manifest as elastic recoil of alveoli results in small airway collapse.
d. What I believe maintains a constant resistance is that partial collapse of the small airways causes increased air pressure in the alveoli connected to that airway. This increased air pressure pushes the small airway open acting against the elastic recoil force of the surrounding alveoli.

Check out West's books -- one on physiology and the other on pathophysiology. He also has a series of lectures at UCSD.

 

[futuremdforme]

For the first one: The pleura line the outside of the lungs like a capsule, not the airways themselves. Airways get higher pressure due to lower volume. There are 3 pressures involved: atmospheric, alveolar, and intrapleural. Intrapleural is always lower than atmospheric (by ~4mmHg, give or take). On inspiration, the muscles pull the chest to a larger volume, which pulls on the intrapleural space, decreasing its pressure (pv = pv, and volume just increased). This pulls on the lungs and makes them bigger, with lower pressure, so air rushes in. On expiration, those muscles relax and so the chest cavity gets smaller, increasing alveolar pressure across the lung and pushing air out.

For the main inspiration/expiration, it's better to think of it at the level of the lung than individual alveoli.

 

[ortnakas]

Get a Pathoma account. It'll help.