Posts Tagged ‘componets of LV stroke volume’

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 )





Read Full Post »