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 ?
- 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.
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 )