Here is another one for ya--you love Physi.!

Discussion in 'Medical Students - MD' started by rsweeney, Apr 8, 2004.

  1. rsweeney

    rsweeney Senior Member
    15+ Year Member

    Joined:
    Jan 6, 2003
    Messages:
    355
    Likes Received:
    9
    Why does right atrial [central venous pressure] rise as left ventricular cardiac output falls?

    Also, with aortic stenosis and mitral regurgitation, since CVP rises as CO falls, then why does right ventricular end diastolic volume decrease? You would think that if you have a rise in CVP then MORE bood would enter the right ventricle thus increasing right ventricular end diastolic volume. But, when you review cases of mitral regurgitation and aortic stenosis, right ventricular end diastolic volume falls, yet the right atrial pressure is elevated!! Doesn't that seem a little paradoxial? If right atrial pressure is up then you would expect right ventricular end diastolic volume to keep going up as the condition worsens--aayyaya--maybe it's a flow thing. :rolleyes:

    This question is related to the previous aortic stenosis thread, but I figured this question is equally important:D

    -Another challenge for ya!

    -Y'all love me:love:

    -Richard
     
  2. omarsaleh66

    omarsaleh66 Senior Member
    10+ Year Member

    Joined:
    Jul 10, 2003
    Messages:
    952
    Likes Received:
    7
    Status:
    Attending Physician
    if cardiac output falls, then u increase sympathetic outflow. This increases Heart rate and constricts arterioles and veins to increase venous return.

    But my thoughts are maybe the increase in right atrial pressure cannot fully compensate for the decrease in CO, so u have a total decrease in EDV in ur right ventricle where even the increased venous pressure cannot compensate the lowered Cardiac Output to full recovery.



    peace

    Omar
     
  3. IlianaSedai

    IlianaSedai Senior Member
    7+ Year Member

    Joined:
    Nov 9, 2002
    Messages:
    325
    Likes Received:
    2
    I really think the easiest way to think about this is to just visualize the four chambers of the heart. Remember this is a PATHOLOGIC (inappropriate) drop in left ventricular cardiac output (not an appropriate or PHYSIOLOGIC drop). When the LV can't pump out, the blood backs up. Thus, you get increased left atrial pressure, then increased right ventricular pressure, then increased right atrial pressure.

    There is a drop in systemic arterial pressure when the LV cardiac output falls, so several things happen in order to raise the BP back to normal (so brain gets adequate perfusion, blah blah). You do get sympathetic increases in HR and you get vasoconstriction; you also get renal retention of sodium and water in order to raise the blood volume. All of this puts MORE strain on the heart and makes the situation worse, not better-- because you get increased venous return to the heart (which also increased right atrial pressure) WITHOUT increase in left ventricular cardiac output.

    There, I've answered assuming that you're talking about a PATHOLOGIC process.
     
  4. rsweeney

    rsweeney Senior Member
    15+ Year Member

    Joined:
    Jan 6, 2003
    Messages:
    355
    Likes Received:
    9
    When the LV can't pump out, the blood backs up. Thus, you get increased left atrial pressure, then increased right ventricular pressure, then increased right atrial pressure.

    But if blood backs up in the left trium as a result of the stenosis the left ventricle is still going to eject less blood. So, why does right atrial pressure go up just because the left atrium is backed up? Does right ventricular pressure go up first? Is it because the right ventricle has more trouble pumping into the congested pulmonary circulation, which resulted from the back-up in the left atrium? And then, since right ventricular pressure goes up, an increase in right atrial pressure will follow?

    The reason I ask is because I was told that simply decreasing cardiac output will cause an increase in right atrial pressure. And then the same person told me that since right atrial pressure goes up right ventricular end-diastolic volume will go up too--thus the right ventricle will eject more blood. That scenerio just cant be, though. Since the left ventricle is "forced" to eject less, the right ventricle will have no "choice" but to also eject less in order to adjust to the decreased left ventricular stroke volume. Thus, an increase in right atrial pressurr would imply a greater right ventricular stroke volume, and this can't be! When you look at PV-loops for aortic stenosis and mitral regurgitation, right ventricular end-diastolic decreases more and more and the problem gets worse. This would imply a derease in right atrial pressure right? Where am I lost.

    -Thank you

    -Richard
     
  5. IlianaSedai

    IlianaSedai Senior Member
    7+ Year Member

    Joined:
    Nov 9, 2002
    Messages:
    325
    Likes Received:
    2
    Whoops, re-reading that, I did skip a few steps. Yes, the RV pressure goes up. In fact, pressure in all four cardiac chambers goes up -- the heart fills faster than it can pump. Here is what happens:

    LV failure --> increased LA pressure --> pulmonary congestion --> increased RV pressure + increased venous return to heart --> increased RA pressure

    where increased venous return to the heart is caused by increased sympathetic activity causing vasoconstriction, and activation of the renin-angiotensin-aldosterone axis by decreased renal perfusion.

    Take out your physio book and just find the diagram of the entire heart-lung circuit. Then follow it through with your eyes. You'll see.
     
  6. IlianaSedai

    IlianaSedai Senior Member
    7+ Year Member

    Joined:
    Nov 9, 2002
    Messages:
    325
    Likes Received:
    2
    You got it backwards. In end-stage congestive heart failure secondary to aortic stenosis or mitral regurg, RV end diastolic pressure increases. RA pressure increases. The blood backs up beginning in the left side of the heart, and the pressure is transmitted (through back-up in the lungs) to the right side.
     
  7. rsweeney

    rsweeney Senior Member
    15+ Year Member

    Joined:
    Jan 6, 2003
    Messages:
    355
    Likes Received:
    9
    Thanks for pointing that out to me. I realized I had it backwards after finding out the that the loops I was referring to were incorrect. The loops were a computer animation and did not take into account the pulmonary congestion which ultimately leads to elevated right ventricular and atrial pressures (it also did not take into account sympathetic stimulation). Thank you so much for your help, as I am sure you are very busy. I appreciate it.

    Richard
     

Share This Page