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Old 04-28-2015
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Default confusing terms in cardio

I have some questions, each having connection with each other, can anybody pls clarify my doubts.

1. Is preload and venous return exactly same, if not,in what terms are they different?
2. Normally, venous return means venous return to rt. atrium or venous return to Lt. ventricle? OR, phrasing in other words, preload means, venous return to rt. atrium OR simply it means Lt. ventricular end diastolic volume? In U-world, somewhere venous return is used with regard to rt. atrium and somewhere it is used with regard to Lt ventricle, so I am really confused.
3. If venous return to rt. atrium increases, venous return to Lt. ventricle decreases or increases?

Thanks in advance.
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Originally Posted by Aumsai View Post
I have some questions, each having connection with each other, can anybody pls clarify my doubts.

1. Is preload and venous return exactly same, if not,in what terms are they different?
2. Normally, venous return means venous return to rt. atrium or venous return to Lt. ventricle? OR, phrasing in other words, preload means, venous return to rt. atrium OR simply it means Lt. ventricular end diastolic volume? In U-world, somewhere venous return is used with regard to rt. atrium and somewhere it is used with regard to Lt ventricle, so I am really confused.
3. If venous return to rt. atrium increases, venous return to Lt. ventricle decreases or increases?

Thanks in advance.
venous return is the volume of blood coming back to the heart. It could be from IVC+SVC to the R heart or from the pulmonary veins from the lung to L side

preload is blood in the L ventricle right before it pumps it so basically it is the same as venous return because whatever comes in the heart goes back out

The only difference maybe is that preload is more related to the stretch of the myocardium, as in more preload more stretch = frank starling = greater stroke volume pumped

lastly if venous return to right heart increases then it also increased in the left heart beacause its all circulating around; nothing is lost in between the right and left heart
hope i make sense
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Quote:
Originally Posted by Aumsai View Post
I have some questions, each having connection with each other, can anybody pls clarify my doubts.

1. Is preload and venous return exactly same, if not,in what terms are they different?
2. Normally, venous return means venous return to rt. atrium or venous return to Lt. ventricle? OR, phrasing in other words, preload means, venous return to rt. atrium OR simply it means Lt. ventricular end diastolic volume? In U-world, somewhere venous return is used with regard to rt. atrium and somewhere it is used with regard to Lt ventricle, so I am really confused.
3. If venous return to rt. atrium increases, venous return to Lt. ventricle decreases or increases?

Thanks in advance.
1.

Preload is basically End-Diastolic Myocardial Fibre Length. So lets explain what is End-Diastolic Myocardial Fibre Length....

End-Diastolic Myocardial Fibre Length is the length of the myocardial fibre after diastole as the name suggests. So what does this depend upon?

This depends upon End Diastolic Volume. So what does end diastolic volume depend upon?

Venous return to the heart.

In short preload is the load which is already placed on the heart even before it begins contraction and is directly related to end-diastolic volume.

2,3.

A very basic concept will clear your doubts regarding the right and left heart and the different chambers!

Remember Stroke Volume is approx 70mL/beat

Does this mean both the RV and LV stroke out 70mL/beat....offcourse yes!!!!

Think of a situation when RV beats out 55mL and LV beats out 70mL...there will be a vacuum in between so what comes in is what goes out.

So if the venous return to the right atrium is increased then the venous return to the right ventricle is increased,left atrium is increased and left ventricle is also increased........this is true for 99% of cases unless the pulmonary vasculature dilates to hold that excess blood(dont think about this)

So when Venous Return is increased in rt heart it will be increased in the left heart too, think of the whole system as a pipe!

And when we are talking about venous return we are normally referring to the right heart and EDV(end diastolic volume) so Right ventricular EDV to be more specific!
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Old 04-28-2015
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Thank you so much for your answers.

But, In U-world it is mentioned that,

During inspiration, venous return to rt. atrium increases, venous return to Lt. ventricle decreases
Vs.
IN supine hypotension syndrome, venous return decreases and subsequently decreases cardiac output.
In the 2nd condition (during inspiration), the logic given by you satisfies but not in 1st condition (ie during inspirtion). So, even more confused.
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sorry, I mean to say,In the 2nd condition (supine hypotension syndrome), the logic given by you satisfies but not in 1st condition (ie during inspirtion). So, even more confused.
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Quote:
Originally Posted by Aumsai View Post
Thank you so much for your answers.

But, In U-world it is mentioned that,

During inspiration, venous return to rt. atrium increases, venous return to Lt. ventricle decreases
Vs.
IN supine hypotension syndrome, venous return decreases and subsequently decreases cardiac output.
In the 2nd condition (during inspiration), the logic given by you satisfies but not in 1st condition (ie during inspirtion). So, even more confused.

sorry, I mean to say,In the 2nd condition (supine hypotension syndrome), the logic given by you satisfies but not in 1st condition (ie during inspirtion). So, even more confused.
I knew you or someone will point this so I mentioned it in my previous post where I said:

Quote:
So if the venous return to the right atrium is increased then the venous return to the right ventricle is increased,left atrium is increased and left ventricle is also increased........this is true for 99% of cases unless the pulmonary vasculature dilates to hold that excess blood(dont think about this)
Now think about this

Normally think of the whole thing as a pipe what comes in goes out but in case of inspiration when the chest volume increases there is decrease in intrapleural pressure as well as decrease in pressure of the whole thorax...this leads to two things:

1.More blood return from the abdomen....so venous return increases to the right side of the heart

2.Since the thorax as a whole expanded so the lungs got stretched and the vasculature in the lung being highly complaint will also dilate to hold this extra amount of blood returning from the abdomen...so although there was a increase in VR to the right heart since the pulmonary vasculature got dilated so it somehow accomodated the more amount of blood...

A point to ponder about is that now actually the RV pumps more blood than the left ventricle so we get a splitting of the 2nd heart sound that is the P2 is delayed than the A2


Hope this clears all problems
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Thank you for your superb explanation. It cleared my doubts.
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Just want to add one more relevant query,
Then what happens in expiration, the venous return to rt. atrium compared to the Lt. side.?
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Quote:
Originally Posted by Aumsai View Post
Just want to add one more relevant query,
Then what happens in expiration, the venous return to rt. atrium compared to the Lt. side.?
Like I said before during inspiration there is splitting of heart sound P2 occurs after A2 due as RV will pump a little more blood than LV which will result in delay in the closing of pulmonary valve...

Considering normal respiration to be a passive process much will not be affected that is S2(A2,P2) will occur together,in such case what I think will happen is both the ventricles will pump the same amount of blood as there wont be much reduction in Venous return since expiration is a slow passive process

But is expiration is forceful then there might be a decrease in VR so RV will actually pump less blood in that case but again whole thing is a pipe so the pulmonary vasculature will compress this time and will add that extra blood to LV return so that Stroke Volume is maintatined...but this theory is doubtful...


What happens during the inspiration is proven by the splitting of heart sound dont worry much about the expiration process
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That makes sense. Thanks a lot.
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