NBME Answers : anu's page

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why is option D ) there is an increased likelihood of statistically significant findings... wrong ?

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micray There is a decreased likelihood of statistically significant findings due to the much higher threshold (lower p-value). +5

drpee The lower you make your p-value, the harder it will be to prove the relationship. That's why I always go with a p-value of .49 in my research. +2

lba9587 Because BOTH values are significant. PValue of Less than or equal to 0.05 is significant. +1

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what about the increase in pulmonary vascular resistance ? doesnt PCWP fall in hemorraghic shock

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ibestalkinyo I think this may have something to do with hypoxic vasoconstriction? +2

medguru2295 PCWP falls because there is less blood going into the Lungs and therefore, less blood coming out (decreased preload). However RESISTANCE is a measure of how difficult it is for blood to flow. That essentially means constriction. As stated above, it is likely hypoxic vasoconstriction as well as just global sympathetic attempt to maintain BP. If it said pressure in pulmonary arteries, it would likely be decreased as the vasoconstriction cannot full compensate the blood loss! +2

sharpscontainer Actually I don't think this is due to hypoxic vasoconstriction. The alveolar oxygen content of the lungs remains high, so there's still a good amount of oxygen getting into the pulmonary vessels, even if less of it can bind to Hb. I think instead it's that there's tons of sympathetic stimulation from hypovolemia, so alpha 1 in the pulmonary blood vessels is activated (which is separate from beta 2 bronchodilation which is a smooth muscle thing). https://www.ncbi.nlm.nih.gov/pubmed/10378571 +11

avocadotoast PVR = (PAP - PCWP) / CO. There is a decrease in cardiac output in hypovolemic shock. Given its inverse relationship with pulmonary vascular resistance, we should choose an increase in PVR for this question. +4

topgunber in hypovolemic/hemorrhagic shock there is a decrease in systemic blood pressure , there is an Increase in TPR (it's a compensation) to maintain flow. I think it's safe to apply the same logic to the pulmonary circulation where there is decreased blood pressure there will be an increase in TPR to maintain flow. (due to the sympathetic activation from the baroreceptor reflex). As someone said, the PCWP will fall, the increase in TPR is a compensation just like in systemic circulation. There will be absorption - we wouldn't want to lose more intravascular volume when you've lost blood. I'm not 100% if its due to hemoconcentration or a severe decrease in hydrostatic pressure in the capillaries, though +1