Interstitial Fibrosis and FEV1

[misery]

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Goljan says FEV1 is decreased in this? Wouldn't it be increased due to the fact that the lungs are more elastic, therefore greater air is expelled on expiration in one second. I know that FVC will be lowered simply due to a decrease in TLC/IC. Am I missing something?

 

[UCLAstudent]

Both FEV1 and FVC are decreased with interstitial fibrosis --- however, the FEV1/FVC ratio is increased (greater than 80%) due to the higher lung elasticity.

 

[misery]

Right, but why wouldn't the FEV1 be increased as well. Maybe I'm just thinking about it too much.

 

[SOUNDMAN]

This is definitely an example of a restrictive lung disease and not an obstructive lung disease. So UCLA was right in saying both FVC and FEV1 will decrease, and ratio of FEV1/FVC will remain the same or increase from what I remember. However I don't know why you are stating that with fibrosis your lungs become more elastic. I would ascertain that they become less elastic. Thus you can't fill your lungs as much (decreased FVC) and can't get out what you filled, as fast (decrease FEV1). What am I missing?

 

[misery]

I see your point let me further explain my thought. Your right, they don't get more elastic in the way of having more elastin/collagen deposited. But the way I have always remember this, is as though it a ballon that gets stiffer (as you say). If you increase it's stiffness, ie decrease its compliance and put a positive pressure in it, will the pressure not equalize at a faster rate? I think I have it straight in my head now, I may be thinking ass backwards but it's working for me, so I won't repost. Thanks for helping my work through it though.

 

[somnolent]

However I don't know why you are stating that with fibrosis your lungs become more elastic. I would ascertain that they become less elastic. Thus you can't fill your lungs as much (decreased FVC) and can't get out what you filled, as fast (decrease FEV1). What am I missing?

Everything's compliance vs elasticity. Restrictive lungs are less compliant, and more elastic. It's kinda like thinking of that ball-bearing experiment from high school. Comparing it to a bouncy ball, you would think that the bouncy ball would naturally "bounce" higher, but technically the ball-bearing is more elastic (bouncy)...thus FEV1/FVC increases.

 

[misery]

Yeah when I saw your avitar, a light bulb went off. I finally figured out why I had things backwards.

 

[Taus]

i was confused about this at first too....especially as I noticed that the FEV1 and FVC are both decreased in restrictive AND obstructive conditions......then I realized that its just all about the ratio of which value is decreased more....ie FVC takes the biggest hit in restrictive and FEV1 goes down more in obstructive

 

[Hallm_7]

I had a question about this on Qbank recently. The question explanation said that because radial traction on the airways is increased that at a given volume the expiratory flow rate will be increased when compared to normal lungs.

This kinda confused me for a minute because FEV1 is slightly decreased. I think the difference is that in a restrictive lung disease the total volume present at the time FEV1 is measured will be less than the total volume of a normal lung when FEV1 is measured. As lung volumes increase in both normal and fibrotic lungs expiratory rates will be greater than they were at a smaller total lung volume.

So FEV1 is really a combination of two factors: 1. The elasticity in the lung is directly correlated with expiratory flow rate (fibrotic lung will be more elastic and would have a higher expiratory flow rate at a given lung volume compared to normal). 2. Volume of the lung at which FEV1 is measured. The larger the volume, the larger the FEV1 value. And the converse, the smaller the lung volume the smaller the FEV1.

The reason (at least in my mind) that FEV1 is decreased in restrictive lung diseases is because of the decreased TLC is a more negative force on FEV1 than the increased elasticity is a positive force.

 

[SOUNDMAN]

Ok I think I actually get it, Compliance and elasticity are opposing forces that occur with the lung during inhalation and exhalation? I did good in this part of physiology but it was too long ago. Plus physiology is my one class that I had some minor difficulties with compared to my other classes.

Phys >>> me