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Old 02-18-2012
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Lungs FVC in Asthma; Normal or Decreased?

A 30-year-old patient with a history of mild persistent asthma (baseline peak expiratory flow rate of 85%) presents to the emergency department with shortness of breath and wheezing that has not relieved by her albuterol inhaler for the past 12 hours. She was able to tolerate pulmonary function tests and a set was performed. Which of the following is the most likely test result?
(A) Decreased FEV 1, normal/increased FVC, decreased FEV 1:FVC ratio, with post-bronchodilator FEV 1 increased by 13%
(B) Decreased residual volume and total lung capacity
(C) Increased FEV 1, increased FVC, normal FEV 1:FVC ratio
(D) Increased residual volume, increased total lung capacity, increased FEV 1


here answer is A, but then in asthma FVC is decreased. Isn't it?
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Old 02-19-2012
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Arrow FVC is normal in obstructive lung diseases

The FVC is normal in Asthma and other obstructive lung diseases.
The FEV1 is decreased in Asthma and other obstructive lung diseases.
Therefore FEV1/FVC ratio is decreased in obstructive lung diseases.

In Restrictive lung diseases, both FVC and FEV1 are low, therefore you have normal FEV1/FVC ratio.

The reason why we have normal or even sometimes increased FVC in obstructive lung diseases is because there's air trapping (increased expiratory reserve volume).

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Old 02-19-2012
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dont agree.
kaplan page 283 figure at top, FVC in obstructive is 3.1 as compared to 5 of normal. that means its decreased in asthma. what say?
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Old 02-19-2012
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Quote:
Originally Posted by tyagee View Post
dont agree.
kaplan page 283 figure at top, FVC in obstructive is 3.1 as compared to 5 of normal.that means its decreased in asthma. what say?
i agree, i know that in obstructive lung disease TLC , RV increase and ratio
FEV1 : FVC & other lung volumes decrease.

can you mention the reference sabio.
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Old 02-19-2012
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You guys are absolutely right, except that you are talking about the ratio of FEV1:FVC.
Now let's say that the FVC is decreased in asthma, think with me and tell me what would you except to happen to the ratio ?
according to this the ratio should either Increase or stay within the normal limits (based on that FEV1 is also decreased in asthma)
Now how come that the ratio is decreased in asthma ??
Mathematically to decrease the ratio you need to :
Either Decrease the FEV1 or Increase the FVC.
think about it again and re-read Sabio's explanation it should make sense.

Best Regards,
Sam
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Old 02-19-2012
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You are right guys.

I had a mistake in my initial post above.

The FVC does decrease in asthma. But it decreases to a lesser extent than that of FEV1 and that keeps the FVC/FEV1 ratio lower.

Therefore, I think the question in the first post above is poorly written.

References:
N Engl J Med. 1994;331(1):25
Am Rev Respir Dis. 1991;144(5):1202

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