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 +0  (nbme23#45)

A very similar question I have seen in Qbanks will ask why a patient with right heart failure does not develop edema and the answer is increased lymphatic drainage. I got this question wrong originally because I answered along this line of reasoning but I think in this case it all has to do with WHERE the extra pressure is coming from. In this question the pt has diastolic hypertension so you can think about the pressure as coming "forward" so constricting precapillary sphincters can prevent an increase in pressure in the capillary bed. However for right heart failure this extra fluid is coming from the OPPOSITE direction (backwards from the right heart) and constricting precapillary sphincters can do nothing (on opposite side of capillary bed) - the only way to prevent edema is to increase lymphatic drainage.


 +18  (nbme23#45)

A very similar question I have seen in Qbanks will ask why a patient with right heart failure does not develop edema and the answer is increased lymphatic drainage. I got this question wrong originally because I answered along this line of reasoning but I think in this case it all has to do with WHERE the extra pressure is coming from. In this question the pt has diastolic hypertension so you can think about the pressure as coming "forward" so constricting precapillary sphincters can prevent an increase in pressure in the capillary bed. However for right heart failure this extra fluid is coming from the OPPOSITE direction (backwards from the right heart) and constricting precapillary sphincters can do nothing (on opposite side of capillary bed) - the only way to prevent edema is to increase lymphatic drainage.

seagull  The question clearly lead us to think about Osmotic pressure by talking about protein and urine. I wonder how many people used that line of reasoning (like myself)?
mousie  Great explanation, I chose lymphatic drainage for the same reasoning (similar Q on different bank)
sympathetikey  My reasoning was much more simplistic (maybe too simple) but in my mind, systolic BP is determined by Cardiac Output and diastolic BP is determined by arterioles. Therefore, what comes before the capillary and regulates resistance? Arterioles. That's why I said that pre-capillary resistance.
cr  the main difference between the 2 cases is that in this case the patient has high BP
link981  So in kindergarten language the question is essentially asking how high pressure in the arterial system is NOT transmitted to the venous system (which is where EDEMA develops). But you know they have to add all this info to try confuse a basic principle and make you second guess yourself. (Got it wrong by the way) because of what @ferrero said of Qbank questions.
hello  @ferrero what are you talking about? lymphatic drainage is the wrong answer...
hello  ok never mind. i got it. hard to understand b/c it was a big block of text.
asteroides  I think they may be talking about the myogenic compensatory mechanism: https://www.ncbi.nlm.nih.gov/books/NBK53445/figure/fig4.1/?report=objectonly "Increased arterial or venous pressure also induces myogenic constriction of arterioles and precapillary sphincters, which raises arteriolar resistance (thereby minimizing the increase in capillary pressure) and reduces the microvascular surface area available for fluid exchange. For example, because vascular smooth muscle in arterial and arteriolar walls contracts when exposed to elevated intravascular pressures, this myogenic response increases precapillary resistance and protects capillaries from a concomitant rise in their intravascular pressure."




Subcomments ...

submitted by docred123(3),

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. +  
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 ..? +1  
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. +