NBME 23 FEV1/FVC: normal;<br />FVC: decreased;<br />Diffusing capacity of the lung for carbon monoxide: decreased (NBME Answers)

Retired NBME 23 Answers

nbme23/Block 2/Question#21 (reveal 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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submitted by momof21234(6)

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the patient has asbestos which is restrictive (clue was pleural plaques) DLCO is decreased in intra-thoracic conditions (interstitial lung dz etc) and normal on extra-thoracic conditions (muscular issues)

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usmlecharserssss how FEV1/FVC is normal i cannot get that +4

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. +4

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 +7

llamastep1 To add to what @drzed said, fibrosis causes radial traction on the airways therefore increasing FEV1/FVC. Theres a Uworld q on it +1

ankigravity And just to add to what @llamastep1 said, radial traction is the relative force exerted on the airways by the interstitial tissues. It is increased in fibrotic conditions due to tensing of the tissue and decreased in conditions that destroy or reduce strength of interstitial tissue. +

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.

+2/- mdmikek89(6)

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submitted by ∗imgdoc(183)

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30 years construction worker, insulation, shipbuilding, plumbing? Asbestosis fine inspiratory crackles = restrictive lung disease bilateral parenchymal opacities, RETICULAR pattern = pulmonary fibrosis pattern on CXR PLEURAL PLAQUES = Cherry on top, extra info, Asbestosis.

All of this points to a restrictive lung disease with an INTERSTITIAL pattern. Even if you didn't get asbestosis, but understood that this pathologic process is restrictive in nature, you can get the right set of changes on PFT. This is a pathologic interstitial disease, not myasthenia gravis or polio, so DLCO will decrease. IF this was myasthenia gravis, and it asked for the same set of findings your DLCO WOULD BE NORMAL, your Alveolar arterial gradient would be normal!!

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submitted by docred123(9)

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Are all interstitial/restrictive lung diseases indicative of a LOW DLCO?

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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. +10

305charlie94 Actually polio is one of the restrictive lung diseases that have a normal diffusing capacity for carbon monoxide (FA 2019 p.661) +1

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