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NBME 23 Answers

nbme23/Block 2/Question#21 (34.6 difficulty score)
A 55-year-old man comes to the physician ...
FEV1/FVC: normal;
FVC: decreased;
Diffusing capacity of the lung for carbon monoxide: decreased
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 +6 
submitted by momof21234(6),
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usmlecharserssss  how FEV1/FVC is normal i cannot get that +2  
sammyj98  I think this is standard for restrictive lung diseases. In obstructive the airways collapse during expiration so it's hard to expire, but there's a long drawn out end to epiration as little by little it escapes, leading to a decreased FEV1/FVC. In restrictive pt's just aren't able to move and expand their lungs enough, so when they expire it's of a small volume, but there isn't any collapse involved. It's like a normal expiration just with a restricted volume, making the FEV1/FVC normal. +  
spow  @usmlecharserssss In restrictive lung diseases, the ratio is either normal or increased. +1  
drzed  And the reason why FEV1/FVC is either normal or increased in restrictive lung disease is very simple: the FEV1 and FVC both decrease because you are restricting airflow, but the FVC will decrease MORE than the FEV1, and thus because the denominator is larger, the fraction either stays normal, or increases slightly Contrast this to obstructive lung disease where you have an obstruction to air FLOW, e.g. the FEV1 will decrease more than the FVC, leading to a low ratio by defition +2  
llamastep1  To add to what @drzed said, fibrosis causes radial traction on the airways therefore increasing FEV1/FVC. Theres a Uworld q on it +  

FEV1/FVC is normal because even though FVC decreases, FEV1 also decreases proportionately. There for the FEV1/FVC would be normal if both values decrease.

+1/- mdmikek89(1),


 +0 
submitted by docred123(6),
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Aer all setitvri/stcteniirteiarl nulg esesasdi vcdiineait of a LWO O?LCD

nlkrueger  only if it's an interstitial lung disease i believe. like polio can cause a "restrictive lung disease" but it's due to muscle effort and would expect to see a decrease in diffusing capacity (FA 2018 pg 657.2) +6  
meningitis  Construction worker, Diffuse reticular opacities screamed restrictive and low DLCO for me. Anything that either adds fibrosis to alveoli, or thickens the diameter between alveoli and alveolar capillaries will cause low DLCO. +8  
305charlie94  Actually polio is one of the restrictive lung diseases that have a normal diffusing capacity for carbon monoxide (FA 2019 p.661) +