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NBME 21 Answers

nbme21/Block 3/Question#2

A 40-year-old man with interstitial pulmonary ...

Increased radial traction on airways

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submitted by benzjonez(15),

Uworld Qid 1543 has a good explanation as to how pulmonary fibrosis increases the radial traction on the airway walls.

cienfuegos  I think this is it -pulmonary fibrosis increases elastic recoiland widens airway 2/2 increased outward force (radial traction) by fibrotic tissue thus decreasing airflow resistance thus supernormal expiratory flow rates (higher than nl following correction for lung volume) +  

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submitted by nwinkelmann(111),

In case anyone is a dense as I am and just didn't understand/remember what exactly expiratory flow is = FEV1. In restrictive conditions, FEV1 is normal or increased due to decreased FVC. Interstitial fibrosis = increased airway parenchyma scaffold around the airways, which is what provides radial traction. The greater the radial traction, the lower the collapsing force, and so expiratory flow is increased.

champagnesupernova3  FEV1 is increased due to greater recoil of the lung tissue. FEV1/FVC is increased bc of that and bc of decrease in FVC +  

Pulmonary fibrosis will involve granulation tissue (as it is fibrosis). Granulation tissue includes myofibroblasts, which will "pull" on the airways, thereby increasing radial traction.

sahusema  The fibrosis causes contraction, the airways are pulled open giving less resistance to airflow +