Atrial booster-pump function

Atrial booster-pump function is the active contribution of atrial contraction to ventricular filling. In the left atrium, contraction late in ventricular diastole helps drive blood through the open mitral valve. It supplements earlier filling associated with atrial conduit function, rather than accounting for all filling during the cardiac cycle.^[ref]

A volumetric descriptor compares the chamber volume just before contraction, $V_{\mathrm{preA}}$, with the subsequent minimum, $V_{\min }$. Their difference is the observed active-phase volume loss; the left atrial active emptying fraction usesFor constructed values 50 and 40 mL, the volume loss is 10 mL and this fraction is $20\%$. Choosing the denominator is part of defining the descriptor.

That loss is not automatically all of the blood flow through the mitral valve during the interval. Integrating the left atrium's balance giveswhere $V_{\mathrm{PV}}$ is signed net pulmonary vein inflow over the same interval. If $V_{\mathrm{PV}}=8$ mL in the constructed example, 18 mL leaves through the mitral valve despite a chamber-volume decrease of only 10 mL.

A primary atrial flow component analysis reconstructed flow from time-resolved computed tomography and computational fluid dynamics, distinguishing modeled passage and residence histories.^[ref] This helps separate a phase-associated volume measurement from the route taken by each parcel. Likewise, an observed contraction-associated volume loss is not itself a controlled measurement of how much less ventricular filling would have occurred without contraction; pressure, timing and continuing inflow can also differ.

Left atrial active emptying fraction is a volumetric descriptor of the relative decrease in left atrium volume during its active emptying phase. With volume $V_{\mathrm{preA}}$ immediately before atrial contraction and subsequent minimum volume $V_{\min }$,The phase choice distinguishes this quantity from a fraction formed using the maximum atrial volume over the entire cardiac cycle. Atrial contraction normally contributes to late ventricular filling after earlier passive filling.^[ref]

An original comparison uses $(V_{\mathrm{preA}},V_{\min })=(50,40)$ mL and $(25,15)$ mL. Both chambers lose 10 mL, but their fractions are $20\%$ and $40\%$. The denominator converts an absolute volume decrease into a relative one; it does not add an independent measurement of forward transport.

Timing is part of the measurement. With the first pair, choosing an earlier or later frame that gives $V_{\mathrm{preA}}=48$ mL instead of 50 mL changes the calculated fraction to $8/48\approx 16.7\%$, even if $V_{\min }$ is unchanged. Consistent boundaries and phase identification therefore matter alongside image segmentation precision.

The fraction describes chamber-volume change, not all concurrent mitral valve flow. Pulmonary vein inflow during the interval contributes to the balance $V_{\mathrm{out}}=V_{\mathrm{preA}}-V_{\min }+V_{\mathrm{in}}$. Nor does the observed volume decrease isolate the causal effect of contraction from every other changing condition. A primary CT-based atrial flow component analysis compared volumetric indices with modeled transport components, illustrating the separation between volume measurements and parcel histories.^[ref] Atrial booster-pump function is the physiological contribution; this fraction is one specified descriptor of its associated volume behavior.