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NBME 20 Answers

nbme20/Block 4/Question#25 (47.6 difficulty score)
A 52-year-old man is brought to the emergency ...
Increased total peripheral resistance and decreased cardiac outputπŸ”,πŸ“Ί
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 +0 
submitted by hungrybox(1108),
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..o.S oltrcitlhyeae an aslteiod recesade ni HR duolw srieeacn OC due to .inc loeadr,p ?tgrhi

tuB OC descaseer in htsi asec /cb teh eftfce of c.ni RTP si roem ?opleuwrf

kernicterusthefrog  @hungrybox: No. Isolating HR, you would look at CO like this: CO=HR*SV so if HR or stroke volume go down, CO goes down. The change in preload wouldn't affect the CO as much as the change in rate of flow. So, the decrease in CO is solely due to the beta1 blocking effect on the AV node to decrease HR. +  



 +0 
submitted by maxillarythirdmolar(40),
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eerWh osde hte lreo fo 1B onlismauitt of ASAR ocme inot t?sih ounl'Wdt het B1 iontca escau erseaedc AR?SA Taht gnebi sda,i I nca also nntadseurd if thsat' a nlog tmer gnith dna shti si a oestnqui tobau eth iamiemetd .c.seff?et.




 -1 
submitted by strugglebus(172),
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olnoloarpP si a sninvle-ecoet teBa kcblo.re So royu HR wlli esceader ,)B(1 hcwih illw cuaes a eptoormsnayc iareecsn ni .PTR

home_run_ball  ^ Above is partially right: Propranolol is non-selective Beta blocker: Beta1 stimulation causes inc HR, therefore blocking it will dec HR and dec Cardiac output Beta 2 stimulation causes vasodilation, therefore blocking it will CAUSE UNOPPOSED alpha1 activation --> therefore increasing total peripheral resistance. +43  
amarousis  so why tf do we give beta blockers for hypertension -.- +6  
dr_jan_itor  I would also add that the patient was previously on an a2 inhibitor (clonidine), which he ran out of. So he is rebounding on that with upregulated a1 receptor activity. Adding labetalol would cause a greater degree of unopposed alpha, increasing tpr +1  
llamastep1  @amarousis They are used for hypertension because the hypotensive effect of the reduced CO is greater than that of the effect of the increase of TPR. Cheers. +8  
hungrybox  @dr_jan_itor Adding labetalol would not cause unopposed Ξ±1 because labetalol and carvedilol are Ξ±1 blockers in addition to being nonspecific Ξ² blockers (great name btw, I love scrubs haha) +2  
mw126  Beta 1 blockade in the kidney (JG cells) would also decrease renin release, which would also help with HTN. FA2019 pg 245 +  
rockodude  @dr_jan_itor clonidine is an a2 agonist not an a2 inhibitor +1  
feanor  I believe that in addition to the compensatory increase in TPR due to the decreased CO; Beta blockers such as propanol which are nonselective Beta Antagonists also have an effect on the B2 receptors to a certain degree, which would explain the increase in the sudden TPR. +  
feanor  sudden increase** P.S. Ignore my OCD(egodystonic), Thanks! +