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NBME 23 Answers

nbme23/Block 2/Question#42

A 63-year-old woman comes to the physician because ...

FVC: decreased;
FEV1/FVC: decreased;
Peak expiratory flow rate: decreased;
Peak inspiratory flow rate: decreased

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 +7  upvote downvote
submitted by nwinkelmann(187),

@gh889 "Because the obstruction is above the alveolar regions there is a decrease in air flow, not lung volumes, which would make this an obstructive pathology" is the most helpful explanation. If you know the most basic definition/pathophysiology of obstructive vs restrictive (which I do, just didn't in that most simplified way), then you can figure anything out. If something is impacting airway flow = obstructive, if something is impacting airway volume = restrictive. THANK YOU!

burningmoon  How about emphysema? airway volume changed but it's obstructive. +1  
almondbreeze  i think OP meant to say that something DECREASING airway volume = restrictive +2  

 +4  upvote downvote
submitted by .ooo. (20),

I personally thought of this questions thinking of it in these terms.. Since the patient has a mass in the trachea peak expiratory and inspiratory flow will be interrupted, and would therefore be decreased. FVC1 would also have to decrease by this. This eliminated all the other choices.

charcot_bouchard  Are you Me? +1  

 +3  upvote downvote
submitted by xkno(3),

I overthought this one big time. Since the question said the mass was pressing on the outside of the trachea, I figured that during inspiration, b/c the chest expands, so more space, so the mass would have less effect on the trachea as the chest expands (and conversely, it'd have more of an effect during expiration as the chest wall retracts). Apparently, it was just straight up blockage and I thought waaay to hard. Oops.

Like any of the COPD, the patient has a difficult time exhaling the inspired air (thus its called an obstructive disease)

COPD results in FVC decrease, FEV1/FVC ratio decrease, FRC increase, and peek expiatory flow decrease.

A tumor or any other object that would compress on or narrow these the air way tract would present as a COPD.

Inhaling and exhaling would be limited

It could be that this is a fixed upper airway obstruction, which would prevent inflation and deflation of the airways due to the tumor clamping down on the trachea.

Hi guys can someone please elaborate on these findings. I understand she has lung cancer that's impeding her trachea. But how is this representative of an obstructive disorder? Aren't lung cancers restrictive if anything? Thanks

nlkrueger  I agree that it's confusing but I looked at it as a physical *obstruction* since it's impinging on the airway.... but yeah idk this is weird +  
ferrero  Doesn't the trachea have cartilage rings so it wouldn't collapse which makes it seem less like a typical obstructive disorder? I'm really not sure why FVC would change because I don't see how total lung capacity or residual volume would change because those are static conditions where there is no airflow at all. I understand FEV1, peak expiratory flow, peak inspiratory flow etc. +2  
mousie  Agree this is a really tough Q but I also think I really over thought it... I eliminated all with a normal Ratio bc something obstructing would obviously produce an obstructive pattern although I don't know why FVC would be decreased. I wasn't sure about both peak expiratory and inspiration flow being decreased can someone help me with this or tell me I'm totally overthinking again.. are they both decreased simply bc theres an obstruction ..? +2  
mimi21  Yea I got confused on this question. But I guess they wanted us to look at it as a obstructive disease . If this were the case all of those function tests would dec. ( See FA ) +  
gh889  Because the obstruction is above the alveolar regions there is a decrease in air flow, not lung volumes, which would make this an obstructive pathology. +2  
charcot_bouchard  FVC here dec same way it dec in Obstructive lung disease. Read the concept of Equal pressure point of BnB. There he says in bronchitis we have onstructive pattern because inflammed airways gen more resistance. so EPP comes early. I guess here due to tracheal narrowing pressure inc downstream. which collapses smaller airway. result in air trapping. +1  

 +0  upvote downvote
submitted by mrglass(6),

I figured this was a variable intrathoracic obstruction and got it wrong.

According to UpToDate, INTRAluminal tracheal obstruction is varaible, while EXTRAluminal tracheal obstruction (like in this case) is fixed.

To think about this simply, it literally is an obstruction so you can just choose the answer with the COPD like PFTs.

It's a bit counterintuitive that the FVC would be decreased, but the reason for this is because at the end expiration for FVC, the positive pleural pressure pushing the air out has equalized with the pressure of the atmosphere / airway wanting to keep the alveoli open. With an increase in the airway resistance from the obstruction, this equalization point comes at a higher FVC. Somebody fact check me please

"disproportionate reduction in the peak expiratory flow rate or maximum minute volume compared with the forced expiratory volume in one second (FEV1). It should be noted, however, that there can be a significant loss in airway cross-sectional area before the textbook flattening of the inspiratory or expiratory loops are visualized."