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NBME 22 Answers

nbme22/Block 1/Question#9

A 54-year-old man has an aneurysm in the distal ...


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 +14  upvote downvote
submitted by keycompany(185),

Flow Rate = Velocity x Cross-Sectional Area

2 cm^2 x 20 cm/sec x 60 sec/min x 1 L/1,000 cm^3 = 2.4 L/min

1,000 cm^3 = 1 L

seagull  Well, I missed this one. I don't even feel bad. +13  
link981  @keycompany a small typo, 100 cm^3 = 1 L not 1000cm^3. 1000 mL^3= 1 L +  
hello  @keycompany how did you edit your original comment to fix your typo? +  
winelover777  Pretty sure @keycompany was correct. 1 L = 1000 cm^3. Otherwise the answer would be 24. +  

if one still doesn't understand to add on .. 1000 cm^3 = 1000 ml 1000ml = 1 Litre

+2/- ribosome01(-2),

 +7  upvote downvote
submitted by nwinkelmann(188),

I've never been good at converting units :( lol so had to ask my brother. He told me that:

distance × distance = distance2 = area


distance × distance × distance = distance2 × distance = distance3 = volume

Gotta love public school for never been taught that ... geesh (obviously I've done the equations and stuff, just never been told it that way/that simple before). Knowing that makes figuring out the equation much easier:

Flow rate = velocity × CSA = 20 cm/sec × 2cm2 = 40cm3/sec

To convert to L/min, just multiply:

40cm3/sec × 60 sec/min × 1L/1,000cm3 = 2400 L/1,000 min = 2.4 L/min

Hope this helped!

impostersyndromel1000  to all my public school peeps out there (and not the nice public schools in rich areas, the real public schools)... we made it! +2  
angelaq11  Thankfully I was taught how to convert units, but let me tell you that I was SO lost on this one. It's USELESS to know how to do it if you (I, I mean I) don't know the damn formula xD. Obviously got this one wrong, but it's good to know that if it ever comes up again (and I know it won't) I already know it. +1  

This is all you need for conversions:

1cm3 = 1 ml ... thus 40 cm3 = 40 ml

So to make it faster I would do it like this

40 ml/sec * 60 sec/1min * 1L/1000ml = 2.4 L/min

+/- majoav1(0),

 +1  upvote downvote
submitted by seracen(5),

Ugh, sorry, getting used to the formatting, and accidentally posted it in the wrong place.

Anyways, to reiterate, I always just look at the units. It wants L/min, I'm given cm^2 and cm/sec

So I multiply, to get volume out of it (cm^3), then convert seconds to minutes.

Thus, it's basically 2x2x6, in some shape or form after placing the decimals appropriately. Good thing they didn't add that particular wrinkle, I'll take my remedial math skills and bug out, haha...

Just in case that lovely little equation provided by @keycompany wasn't quite enough for you, here's a link to a more complete explanation by Kahn Academy. Helped me, when I looked at the equation and said, whaaaa?

If, like me, you dislike memorizing formulas, but are okay doing the actual math, I always just look at the units. It wanted L/min, and I had to get it using cm^2 and cm/sec...

Well, I know cm^3 gives volume (L) after bashing out a few conversions, so multiply it is!

Then I know to turn seconds into minutes, so multiply by 60.

Now, at this point, I knew my decimals were off, but still, 4x6 = 24, so it's some version of that. Had they included 24 or .24 as answers, I'd have actually had to pay attention to my conversions.

Anyways, I hope that helps!

+2/- seracen(5),