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NBME 21 Answers

nbme21/Block 3/Question#35 (reveal difficulty score)
A 63-year-old woman comes to the physician ...
Increased resting cardiac output 🔍 / 📺 / 🌳
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 +29 
submitted by drdoom(1046),
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’sreeH enotrah vrey niec eno hatt rsispupeesmo hte pwtayah oont a iilfsmidpe sambtienr idgrawn ic(ne ofr het clnotmaaia ioaer:slt)n

b/ea2G5he-syswrdo2ap:-..N2Fhu/thnoi.ami.geesps/g-w/etOuRecpfetLui/Iec/yo

Source tliecr:a

awpparpih2/5u/ttm/heeel-fceadp.iameltctl-triyoboa2s/hu.e.unege:ehwstmhnys/hoo.oure

oT ees neev rm,eo ytr ggoole igmea esrcah on ed“mali giadnnilutlo calf”cssuu:i

oha+/wmtoslmgatuul+oacwtdgmtquislse?emcabwls.e=/ca&d:pifphigcin/.;h=rnisolc


 +20 
submitted by cellgamesgojan(42),
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AV ulsatsiF ot-erru lobod form hte araretil sstyem ot eht suovne ses,tym p-ybganssi hte Ailreserot = eaecnrIs LP -t--&;g NAECSERI RV. llA ni all = aIcnesre OC.

Adorcignc ot oWrdlU, hte raosrtieel era a amjor useroc of rntecseisa ... os syainsbpg teh rolreeista sseltru in a eeercsad in aloTt ariPpherel tensecisaR ... nagucsi na nsierace ni the reta and uovmel fo dbool nturgneir ot het rth.ae I am epytrt eurs eethr si omre to teh lshpyogoiy nbideh t,sih but I eoph sthi edixplane a itllte.

big92  "Immediately following creation, arteriovenous fistula (AVF) is associated with an increase in cardiac output (CO), achieved predominantly through a reduction in systemic vascular resistance, increased myocardial contractility, and an increase in stroke volume (SV) and heart rate. Over the following week, circulating blood volume increases in conjunction with increases in atrial and brain natriuretic peptides. These alterations are associated with early increases in left ventricular (LV) filling pressure with the potential for resultant impact on atrial and ventricular chamber dimensions and function." (PMID: 25258554) There's also another study by Epstein from the 1950s looking at the effects of AVF's effect on CO in men (PMID: 13052718). Apparently, the increase in resting CO is a big problem because it can lead to high-output cardiac failure (LVH). +31  
hungrybox  Jesus big92 you went in on the research lmao u must be MSTP +6  
temmy  big92 you are right. that is why pagets disease pagets have high output cardiac failure because of the av shunts. +4  
kevin  what is "increase PL" +3  
jhan17  According to wiki "When an arteriovenous fistula is formed involving a major artery like the abdominal aorta, it can lead to a large decrease in peripheral resistance because it by pass arteriole (where major BP is formed) . This lowered peripheral resistance causes the heart to increase resting cardiac output to maintain proper blood flow to all tissues." +  



 +4 
submitted by azibird(218),
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I d'nto lfee ikel yna fo eesht oecsmntm haev lfuyl daeddsesr why teh tintaep cltyurren ash isnecarde senrgit OC nda OTN saeedercd V.S Here is how a rdenif of mnei naiepldex t:i

MAP (ta ngriste )HR = 2/3 BDP + 13/ BSP = 77 mgmH ni shit petnit,a hwchi si oerlw hatn mroanl 39( gmmH fi you sue .018/)20 So APM si saddereec adn eth hiers/kdeyton nrogsa na'ter etgnigt hte rouensipf yeht n,eed lndaeig to SRAA cititvnoaa dna md.eBSOa/e PAM = OC × TR,P so stih cdluo be eud ot wlo CO eailetvr to PRT hawt( ew asulylu t)cxepe ro olw RPT aiervlte ot C.O iTsh tteapsni' gaelr VA aiutslf ash pdordpe erh TPR yevr ,wol hwhci naems rhe OC utms haev nebe eryv hihg rof the tspa 51 erysa ot pmanocseet hg(hi uoputt tahre ier.aluf eSh has oynl 5 syda of mmsotsp,y ichhw mneas hes si alyre on ni rhe HF. enciS esh had cuhs a high CO ot egnib hi,tw hre odpr ni SV sith arlye on wodlu tlisl aevel rhee htwi na RDENACISE SV armdoepc ot a lmonar apitt.ne nsleUs rhe elups is espru hgh,i erh hrtae smut be uppmnig a amvsies ostkre vuemol to iatnmian a mlnroa ssotiylc oolbd eprsesru twhi shcu a wol RPT PMA( = SV x HR x .)TPR nlvEtuay,el reh SV may cdseeear to eb bowel mo,lran tub ont so ryela no.

rFo nmoc tstes:poNele rceesedda elartira 2O tas uecbsae oblod si fnoiwlg mofr raeyrt ot i,ven not het rthoe way Nrn.daut oo eaerddecs meidx nsoeuv O2 sat uaseebc aarierlt odlob is lgifodon hte anubsvaicl iven thgri rebfeo xedim O2 tsa ldwuo be emuta.sdoeNr ednsaeirc RSV caeuseb fo the gealr AV f.ilstua




 +2 
submitted by the260guy(18),
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Btu e'resh ym meplobr thwi sith tuneis:qo ti ysas atth hse has a 5 ady oithysr of SBO dan nseolwl les.g oS uoiyvobsl teh heart si gliaf.ni I ipkdce ecasDeedr kSoter eumlVo orf ttha anso.re

nwinkelmann  AV fistulas are one cause of high-output cardiac failure. This person presents with heart failure, but it is due to chronically increased resting CO. +2  
lukin4answer  @nwinkelmann yes thats right, he has failing heart. but question is asking what is the finding of this patient, I understand the cause is Fistula causing high output failure, but they didn't ask the reason of his HF, they are asking the finding. I choose decrease Stroke VOlume :/ +  
happyhib_  This was my logic and got to decreased stroke volume as well; they arent asking what caused his HF or anything it says what is the most likley finding in this patient. If his heart is failing due to LVH from consistent increased CO wouldnt he AT THIS VERY MOMENT WITH his heart failing have decreased stroke volume?.. +  



 +2 
submitted by usmleuser007(438),
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OC si aderisenc twhi ) 1 arsdeeecd oedrlafa)t 2 ecaesrdni el3roa) dp dIansecre oynitlrcttaic

nA ruesenoivaot afstilu crteesa an neaattervil urtoe ofr rtlaai boodl tion het nosuev ccurniialot ow/ ggino pats eth ereialsrto h(te ojmra caseu fo ) tsnTa.icu,eesshr yb iondg os het PTR )fraalto(de saeedcers dan hte OC is re.nsiecad




 +1 
submitted by uslme123(80),
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sF'VA = nraiseecd accrdai oTtt uB.Upu thsi ni'st ewn fro ihts ep?rsno I wiev stih sa a rahet htta ash nfilyal bueng to ilaf -- ecdserdae icetvffee oyltccairru uomvle t--;g& eacrdsein .SVR

tuB i usegs uoy ntc'a have B eofrbe A -- treewhva \--

happyhib_  his bp was something like 130/50; with diastolic around 50 I figured he couldnt have increased SVR because his diastolic would be higher? +1  
trazobone  I had this same reasoning I completely glossed over the BP 🤦🏻‍♀️ +  



 +1 
submitted by nuts4med(7),
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onnyeA haev na aeid why the eesarcedd taiaelrr 2O nisoruttaa si erictcnor? msAunisg esh ahs mlup dmeea ecnsi esh ahs LE ed,ame tlwdou'n a lwoer 2O sat be tcxedpee o?ot

haliburton  I believe there would be no decrease in O2 saturation because oxygenated blood (high pressure) is shunted into deoxygenated circuit. As long as the lungs can keep up, this should increase venous oxygenation on average. +7  
hungrybox  ty both of you for this, was wondering the same thing +  
coxsack  O2 sat won’t change b/c you’re not adding deoxygenated blood to the arterial side. You’re just taking arterial blood and putting it into venous blood. Same reason why L->R cardiac shunts don’t decrease O2 sat (while in contrast, a R->L shunt would). +5  
hungrybox  just realized: the high pressure of the arterial system keeps out low-pressure venous blood in an AV fistula (probably obvious to most ppl but it was a eureka moment for me lol) +2  
chandlerbas  ya you wont have decreased arterial O2 sat because oxygenation of blood is perfusion limited (FA19 --654) therefore oxygenation of the blood happens within the first .3seconds of entering the pulmonary capillary that you could even handle having more deoxygenated blood enter +  



 +0 
submitted by step1soon(48),
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eatrH urfiael: hiTs si eth tsmo susoeir aioimpoclntc fo grael itrooaesuvnre atf.ussli iencS ryuo lodbo wflos emro cuiklyq uthorgh an toeoesnavirur utifsla naht ti doluw if yrou oobdl wolfed hruogth a almrno sucoer of terae,irs laielricpsa and n,sevi ryuo terha pspum darrhe to tmcepesnao fro hte podr in obldo ureprses lalec(d ihh-ottuugp ahert ria.)eulf ervO i,emt het enicaedrs stinnyeit fo yoru har'est mpnipug nca kweena ryuo etrah s,mluce dlienag to rteha aflr.uei




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