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Old 03-28-2012
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Heart Transplanted heart with no nerves!

NOTE: this is a USMLE Consult-"inspired" question, so look away if you plan on using USMLE Consult as a measure of your progress.


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A 61-year-old man underwent a heart transplantation for congestive cardiomyopathy. Following heart transplantation, the interruption of cardiac innervation results in which of the following?

A. Decrease in stroke volume at any level of cardiac filling pressure
B. Failure of coronary arterioles to dilate with exercise
C. Greater than normal heart rate in response to exercise
D. Lack of response of cardiac muscle to circulating epinephrine
E. Less than normal tachycardia in response to acute hypotension
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E. Less than normal tachycardia in response to acute hypotension

Because you take away the sympathetic innervation..
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E. Less than normal tachycardia in response to acute hypotension

Because you take away the sympathetic innervation..
i agree but wouldnt we also take away the vagus innervation? :S
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Oh man, I am pretty sure its C
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i agree but wouldnt we also take away the vagus innervation? :S
I was thinking that .. the parasympathetics wouldn't be there and so you wouldn't be able to slow down the heart rate when needed. Also if the heart is not innervated does that mean the efferents are not there or both efferents and the afferents (baroreceptor reflexes from CN IX & X) are not present ?
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I was thinking that .. the parasympathetics wouldn't be there and so you wouldn't be able to slow down the heart rate when needed. Also if the heart is not innervated does that mean the efferents are not there or both efferents and the afferents (baroreceptor reflexes from CN IX & X) are not present ?
You cut the vagus and aorta just above the coronary arteries, so most of the ascending part is still there...
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Originally Posted by Hope2Pass View Post
I was thinking that .. the parasympathetics wouldn't be there and so you wouldn't be able to slow down the heart rate when needed. Also if the heart is not innervated does that mean the efferents are not there or both efferents and the afferents (baroreceptor reflexes from CN IX & X) are not present ?
I think only the efferents are not there , I think its C, as it would involve the heart into a fake feeling of low BP or something like that.. i dont know how to explain it :S
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Heart has automaticity and B1, B2 receptors
and M2 receptors (Ach) from vagus to slow it down
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Ok so I'm guessing as you exercise, the epinephrine will increase your HR & BP and then the afferents will shoot up to the medulla telling it to slow down (increase parasympathetics) but since there's no innervation, it will not be able to slow down hence option C) Greater than normal heart rate in response to exercise


Is that correct ?
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Heart has automaticity and B1, B2 receptors
and M2 receptors (Ach) from vagus to slow it down
yup so no control from PNS the heart will race as f...k! ;D
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Heart has automaticity and B1, B2 receptors
and M2 receptors (Ach) from vagus to slow it down
yup thats correct -


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No autonomic reflexes are pissible in isolated preparations
Denervated tissue dont respond to indirect acting agonist.
its C
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guys want the answer or do you want to keep discussing it?
mad braincells in work in this thread, i like it.
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guys want the answer or do you want to keep discussing it?
mad braincells in work in this thread, i like it.
I'd like the answer lol can you also post an explanation for your questions specially since these are Usmle consult based. That would be helpful. Thanks.
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Default answer = E.

Quote:
Originally Posted by Hope2Pass View Post
I'd like the answer lol can you also post an explanation for your questions specially since these are Usmle consult based. That would be helpful. Thanks.
the answer is E: Less than normal tachycardia in response to acute hypotension.

explanation was you have eliminated the baroreflex apparatus.
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the answer is E: Less than normal tachycardia in response to acute hypotension.

explanation was you have eliminated the baroreflex apparatus.
Weeeeird!!!

What baroreflex apparatus r u talking though?
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Originally Posted by DocSikorski View Post
Weeeeird!!!

What baroreflex apparatus r u talking though?
"The increase in heart rate occurring with hypotension is a result of the baroreflex, which is mediated by changes in cardiac nerve activity. The baroreflex function is eliminated by a cardiac transplantation." - Usmleconsult

this is literally the full explanation

this qbank is terrible for explanations, they are seldom longer than 2,3 sentences.
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Hah .. I was right but got persuaded to change my answer .... Everything sounded so right in those explanations lol
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Hah .. I was right but got persuaded to change my answer .... Everything sounded so right in those explanations lol
so what exactly is being lesioned here?
the aortic arch sinus fibers?
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Originally Posted by Dr.NickRiviera View Post
so what exactly is being lesioned here?
the aortic arch sinus fibers?
Ok this is how I thought of it -

Since the question said that there is no innervation to the heart, I assumed that it is the efferents they're talking about. So you still have the IX & X afferent activity from the baroreceptors .. but there is no reflex coz there are no efferents. The afferents are always active. When there is increased afferent activity, the parasympathetic's are activated to slow down the HR. When there is low afferent activity it tells the brain that the BP is low and it fires off Sympathetics to increase the HR.

So when you have acute hypotension, there will be a lesser response as the afferents have less activity, the brain tries to fire off the sympathetic but there is no increased in heart rate and contractility. But you do get increased venous return and preload so you will get a lesser tachycardic response.

I think thats the right explanation I'm not too sure. Its all about applying the concepts but often what seems right to me might not correct because I might not have applied the concept correctly
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Ok I got it, I did some reading:

SNS fatens PNS slows the heart through B1 and M2 respectively.

When the heart is transplanted, both nervous pathways are severed so there is no more autonomic regulation of the heart. (both aortic arch and carotid body baroreceptors are intact).

The heart rate at rest is higher than normal in the transplant. The heart regulation depends only on the circulating levels of catecholamines.
==============================================

Plus, there is no chest pain in the heart transplant indicating ischemia which is directly associated with sudden death in heart transplant patients.


==========

Good job Hope2Pass!!!
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