Constant Surface Tension (respir physio)

[coffeebythelake]

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Quick question. I'm trying to understand alveolar instability which assumes constant surface tension. If I was to replace surfactant in a lung with saline solution, would this cause constant surface tension?

 

[ubcredfox]

Quick question. I'm trying to understand alveolar instability which assumes constant surface tension. If I was to replace surfactant in a lung with saline solution, would this cause constant surface tension?

No. Surfactant has specific properties inherent to it which allow it to maintain near constant surface tension at varying alveolar volumes. A saline solution would not have this property, and surface tension would vary with volume. The problem with that is, that smaller volume alveoli would experience proportionately greater surface tension and collapse.

I think that's the right answer anyhow. But, an excellent read on the subject is Lange's Pulmonary Physiology. It answers your question exactly. It covers most things well, except for dynamic compression.

 

[DoctaJay]

Yeah ubcredfox basically answered it. Its the specific properties of surfactant (the amphiphatic DPPC molecules, which acts like a detergant) that breaks the affinity of the surface liquid molecules for each other, decreasing the surface tension. Saline just doesn't have the composition to do the same thing.

Also,I know costanzo had an example of surface tension with a saline filled lung (instead of an air filled lung), but I'm not sure if you were talking about that too.

 

[SeventhSon]

Quick question. I'm trying to understand alveolar instability which assumes constant surface tension. If I was to replace surfactant in a lung with saline solution, would this cause constant surface tension?

what do you mean constant surface tension? Surface tension being constant during what? Surface tension is a property of the two components of a phase interface and is a function of temperature. There is a force associated with surface tension that changes as the interphasic length/area increases, but surface tension itself is constant

Surface tension is an effect that is due to the solid-gas phase change interface. When saline is in the lung, surface tension is essentially abolished because surface tension between a solid and liquid is very low.

 

[TMP-SMX]

There is no surface tension due to a lack of a fluid-air interface.

I think you are trying to make the connection between the alveolar instability and the Von Neergaard expieriments. In order to get surface tension you have to inflate the lungs with air and not water. Inflating with liquid only causes recoil due to the elastic and collagen fibers.

And guys don't think I know what I'm talking about I just go to the same school as eikenhein and it's in our notes.