Effects of Epinephrine and Phenylphrine on Diastolic Blood Pressure! - USMLE Forums
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Old 06-12-2011
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Heart Effects of Epinephrine and Phenylphrine on Diastolic Blood Pressure!

Can someone explain to me the physiology of diastolic blood pressure? What controls it and what major factors affect it?

Also, how would epinephrine administration decrease diastolic BP while phenylephrine increases it?

Thanks!
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Old 06-12-2011
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So, for me, when I think about DBP, I think in TPR = resistance of the arterioles

phenylephrine = alpha 1 agonist = vasoconstriction = increase TPR

Epi = alpha (1&2) and beta (1&2) agonist...b2 are present in the vessels in skeletal muscle (and also liver) -> dilates vessels -> decrease TPR
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Old 06-12-2011
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waoooo
thats good question thanks i always have crave for it..
and i hope bebix explanation is also good..
WHY epinephrine has al alpha 1 2 and beta 1 2 effects i mean actually i m messed up..
pardon me but i have not done pharma yet
can u really make it simple??

Last edited by INCOGNITO; 06-12-2011 at 06:24 PM.
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Old 06-12-2011
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Quote:
Originally Posted by bebix View Post
So, for me, when I think about DBP, I think in TPR = resistance of the arterioles

phenylephrine = alpha 1 agonist = vasoconstriction = increase TPR

Epi = alpha (1&2) and beta (1&2) agonist...b2 are present in the vessels in skeletal muscle (and also liver) -> dilates vessels -> decrease TPR
I want to add that, the above is true in low concentration.

If you have a little bit of Epi, the predominant action is on Beta receptors. If you increase the concentration (or dose), the actions will be on Alpha.
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Old 11-14-2012
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kindly correct me if im wrong

EPI @ LOW Dose = b1, b2 response
EPI @ HIGH Dose = a1, a2 response

b1 respose = INCREASED Systolic BP (coz increased contractility)
b2 response = DECREASED Diastolic BP (coz vasodilation)
(combine both and we have a wide Pulse Pressure)

a1 response = INCREASED TPR and since
MAP = COxTPR
so we have an INCREASED MAP
and since
MAP is also = 2/3 Diastolic + 1/3 Systolic
BOTH Systolic and Diastolic BP are INCREASED
TPR affects both Systolic and Diastolic pressures, increasing both
(ignore a2 response)

HENCE

EPI @ LOW Dose = b1, b2 response = INC. Systolic & DEC. Diastolic
EPI @ HIGH Dose = a1, a2 response = INC. Systolic & INC. Diastolic
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Old 11-14-2012
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Quote:
Originally Posted by pukhtoon123 View Post
kindly correct me if im wrong

EPI @ LOW Dose = b1, b2 response
EPI @ HIGH Dose = a1, a2 response

b1 respose = INCREASED Systolic BP (coz increased contractility)
b2 response = DECREASED Diastolic BP (coz vasodilation)
(combine both and we have a wide Pulse Pressure)

a1 response = INCREASED TPR and since
MAP = COxTPR
so we have an INCREASED MAP
and since
MAP is also = 2/3 Diastolic + 1/3 Systolic
BOTH Systolic and Diastolic BP are INCREASED
TPR affects both Systolic and Diastolic pressures, increasing both
(ignore a2 response)

HENCE

EPI @ LOW Dose = b1, b2 response = INC. Systolic & DEC. Diastolic
EPI @ HIGH Dose = a1, a2 response = INC. Systolic & INC. Diastolic
One might expect a reflex bradycardia after a while with a high dose of epinephrine which might thus lower the systolic blood pressure. But the overall BP would still be high because the major component of MAP is still the diastolic pressure (2/3). That's what I thought I understood. Your reasoning is correct otherwise, I think.
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Old 04-02-2015
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very good point
coz with alpha response we can get a reflex bradycardia coz no beta agonism
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Old 10-22-2015
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Bt in low dose if b2 receptor is causing vasodilatation that means the peripheral resistance is decreased nd as u said tpr affects both sys as well as diastolic bp so the b action shud also decrease systolic bp n not only diastolic. Please help me with this doubt?
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Old 01-20-2016
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Default Point of thought:

Quote:
Originally Posted by volvo View Post
One might expect a reflex bradycardia after a while with a high dose of epinephrine which might thus lower the systolic blood pressure. But the overall BP would still be high because the major component of MAP is still the diastolic pressure (2/3). That's what I thought I understood. Your reasoning is correct otherwise, I think.
I there, I know it was a long time ago but I am sure it is still relevant to some of us:
You said that in high doses Epi works on Alpha1+2 rather than on beta 1+2.
More accurately the affinity increases for Alpha receptors than to beta receptors no?(this is a question)
a
And someone can explain also why it changes its affinity to the receptors?
Thanks in advance folks.
Dan
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