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NBME 20 Answers
A 52-year-old man is brought to the emergency ...
Increased total peripheral resistance and decreased cardiac output
^ 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.
so why tf do we give beta blockers for hypertension -.-
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
@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.