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Archive for the ‘cardiac volume’ Category

The right ventricle  is considered as a docile cardiac chamber with passive filling and  emptying  properties .

This belief  was reinforced when Fontan  in early 1970s suggested a principle in the management of  cyanotic heart disease  when  the right side of the heart is underdeveloped. He  proved  RV can be by-passed safely , with  great veins  (IVC/SVC)  by  themselves  take care of filling the pulmonary circulation  without the need of RV pumping function.

While it is true for few complex cyanotic heart disease, largely this a misleading  concept. In clinical cardiology practice  ,sudden or non sudden  RV deaths happen every day in the form of . . .

  • RV Infarction
  • Acute RV dysfunction in massive pulmonary embolism
  • COPD with RV dysfunction
  • Most cases dilated cardiomypathy  the terminal event is due to RV  failure.

So , RV function can never be dispensable in day to day cardiac hemodynamics.

RV has some unique properties in terms of shape , size and  hemodynamics . We are getting more insights from  modern blood pool imaging by MRI , about  how the RV handles the blood volume .

We know RV has a unique shape  triangular ( partially  pyramidal ) . It can be inferred the RV cavity is formed by fusion of  many  eccentric spacial planes. We have always believed  RV handles the blood it receives from right atrium in a unique way .Now we are beginning to understand it .It is now documented the RV segregates the blood it receives into 4 components.

 

right ventricle physiology anatomy hemodynamics

It is curious  to know  RV inflow is connected to the outflow by an invisible   physiologic Bridge . About 44% of  blood traverse the RV in this fashion.

 

RVOT blood flow right ventricle

Note : RV blood flow preferentially enters the RVOT with out transiting RV body and apex.Image courtesy http://ajpheart.physiology.org/

 

Which is the most important part in RV ? (Among Inflow, Body, Apex, Out flow)

After reading this article it seems to me , the mechanical  function of RVOT could be most  vital. If it fails to handle the first increment  which  comes directly from  RV inflow, stasis  is likely in RV body and apex , elevating RVEDP and later promoting stasis leading to clinical events.

Clinical implication of this study

  • Differential dilatation RV chambers to pressure or volume  overload is observed .
  • We need to analyse why RV dilates in some   but   goes for hypertrophy in others when confronted with pressure overload (VPS vs PAH)
  • RV apical clot in restrictive cardiomyopathy  is a direct consequence of stasis  of blood  in RV apical zone .
  • RVOT pacing  may have a hemodynamic advantage  over RV apical pacing  . However , for anatomical reasons RV apical pacing  is  far safer than RVOT pacing where the lead  is subjected to constant life long strain due to this busy RV inflow to outflow express  high way !

Final message

Traditionally we have labeled  RV  as a  passive venous chamber .It is clearly a misnomer.It  has to handle both the venous and pumping function beat to beat with precision  without  back log .Obviously ,  RV has to think and work  more than it’s  big brother !

Reference

I wonder , if  there is  any other site other than APS . . . to  find crucial  answers in cardiac physiology  !

 

Right ventricle physiology blood flow  3d 4d analysisAfter thought

  • There is huge gap between physiologists  who work in research labs and the physicians at bed side .
  • I appeal all young cardiologists  to visit  APS  once in a while ,between your busy cath lab schedule and help narrow this gap.
  • Without understanding the physiology properly how are we going to intervene the pathology ?

 

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Normal  left atrial  (LA) volume is about  22ml/sq.meter body surfacearea  at all ages.Maximum LA volume in physiology is  about 46ml in  females and 56 ml  in males( Average 35 ml)

LV stroke  volume  for each beat is  about  70  ml . . . so where does  the remaining 35ml come from ?

Answer .

  • Pulmonary veins ?
  • Residual LV end systolic volume ?
  • Mix of the two ?

It is logical to assume about 35 ml of fresh  blood  from 4 pulmonary vein*  rushes into LV with every diastolic cycle  .It  never stays in LA  .It just uses LA as a transit  route ,

*In diastole the four PVs,LA  and LV all act like one single chamber .

 

Is this reasoning correct ?.

If we believe the continuity equation this explanation is correct . However still what  we need to know the fate of residual  LV volume (End systolic LV  volume which is also  about 35 ml that would be  in queue for ejection into Aorta  for the next beat !)

Further , we know the LV end systolic volume is not constant .During exertion it  can reach  negligible levels (<10 ml) .At times of vigorous contractions  it can touch near zero as well . Then , It become vital for the  pulmonary venous reservoir  to be act as a  major donor for  LV blood volume for  every ensuing beat.

If the hemodynamics of pulmonary vein LA interface is tricky even in physiology ,  one can imagine the complexities  if the LV diastolic function and left atrial compliance  is affected

Debit and credits of  LV end -diastolic volume .

Let us assume LVEDV is about  1o5  ml .LA blood volume is  roughly one third of LV volume .For every beat equal amounts of fresh blood  from pulmonary vein . These two (LA+PV)  adds to the  residual  blood in LV  to make LVEDV 105   ml . From this 70 ml is ejected as stroke volume leaving behind 35 ml.


lvedv lvesv stroke volume wiggers cycle left atrial volume pressure volume loop residual diastasis

Image template from http://www.cvphysiology.com

 Further questions

LA Chamber volume and blood volume need not be same .What  I struggle to understand is , total anatomical  LA volume  measures  35ml , while the amount of blood it is supposed to hold is also about the same .Does  it mean the LA is completely filled with blood . . . air tight !

Will the LA compliance make it accommodate twice or thrice the blood volume during exercise ?

What is quantum of residual end diastolic  LA volume ?

 

Reference.(Normal LV and LA volumes )

echopedia

 

 

 

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