NBME 23 4.5 (NBME Answers)

Retired NBME 23 Answers

nbme23/Block 1/Question#50 (reveal difficulty score)
A 45-year-old woman with coronary artery ...
4.5 🔍 / 📺 / 🌳 / 📖
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+6 upvote downvote
submitted by ∗welpdedelp(270)

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30* 0.15. Think about it, there is x flow with an oxygen concentration of y--so to find out the delivery you just multiply them together.

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yotsubato One of those questions too simple to believe its actually the right answer +32

mimi21 Right, I was like this is too simple lol ! im not sure if this is also a good tip but I tend to look at the units they are asking for and double check my math to make sure I end up with them. +9

osgood-schlatter what equation is it exactly? +

arcanumm Literally did not even conceptualize this question, just looked at the units. +7

stunna216 when you just multiply the only 2 numbers given in the question together and its actually an answer choice (insert surprised Pikachu meme) +

chaosawaits I came here just to repeat what everyone above has said. Sometimes you can get the answer right just by looking at the units without having any idea about what is going on conceptually at all. +1

step1dreamteam This is the equation: Myocardial oxygen consumption: coronary blood flow × arteriovenous O2 difference. Now, in the vignette venous O2 content is missing. What is the reasoning that allows to not consider venous O2 content? +

+5 upvote downvote
submitted by ∗sam1(22)

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What about the additional flow through the circumflex?

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maddy1994 exactly man i got 4.5 and i thought he asked ventricle and left circumflex should be there so i put 5 ...glad someone thought like me.i was just cursing myself for over thinking. +11

djtallahassee Yea put 5 here too. they are essentially saying the myocardial oxygen supply to the left ventricle comes from the LAD. Not sure if true or not but figured that the LCX would at least contribute 20% of the blood +1

justherefortheyield 100% agree. This is definitely a better answer. I assumed the # would be beyond 5 but that it was closest to the right value. +1

+3 upvote downvote
submitted by ∗nor16(70)

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all those non maths guys here, dont skip these questions, try to arrange the units, here you´d easily find out that you just have to multiply! Give it a try :-)

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charcot_bouchard This was like Filtered Load ques of Renal. Where u multiply icoming fluid (GFR) with the desired substances conc (Px) so FIltered load of A is GFR x Pa Same here. Myocardial O2 supply is Blood flow x Conc of O2 in that blood flow +4

powerhouseofthecell For us non math folk, how do you compare the mL/min to mLO2/mL to get mLO2/min? Sorry. Do you just find out that when you have the units beside each other, cross multiplying them gives you the correct one? I need to know this trick. I can't find this on google. +

abcdefbhiximab mL/min * mLO2/mL = (mLmLO2)/(mLmin) where the mL's cancel out = mLO2/min +

+2 upvote downvote
submitted by thelupuswolf(9)

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This question is not good. The math is simple, sure. But the PDA (which is most of the time a branch of the RIGHT coronary artery) supplies 2/3 posterior walls of the ventricles (FA 2019 p.281) which I'm sure is a significant portion of the left ventricle. The LAD specifically does not account for the entirety of the oxygen supply to the left ventricle, but about 45-55% according to wiki. If the question asked, "How much oxygen is delivered to the left ventricle by the LAD" it would have been acceptable.

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+1 upvote downvote
submitted by ∗chaosawaits(92)

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For any non-math oriented person, as a test strategy in general, I automatically skip all questions that have any form of calculation in them. For me, this takes all the pressure off having to get the calculation right in the middle of the test because I'll finish the first round of 50 question with about 10-15 minutes and there's usually no more than 3 calculations in a block.

In general, learning to skip the questions that give you anxiety early to come back to tends to help increase scores.

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+0 upvote downvote
submitted by ∗guillo12(58)

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Fick principle: CO= Rate of O2 consumption/arterivenous O2 concentration

CO means cardiac output or Flow of blood

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charcot_bouchard This wasnt Fick +1

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