= Atrial conduit flow component
The \b[atrial conduit flow component] is <blood> entering the <left atrium> through the <pulmonary veins> during ventricular <diastole> and leaving through the <mitral valve> within that same ventricular <diastole>. The same-phase requirement distinguishes it from the <atrial reservoir flow component> and <atrial delayed-ejection flow component>.<Comprehensive left atrial flow component analysis reveals abnormal flow patterns in paroxysmal atrial fibrillation by Sophia Bäck and others>[Methods, Flow Component Analysis; Figure 1]{ref}
An original two-history example shows why a volume curve alone cannot identify it. During a selected interval, suppose 20 mL enters the <left atrium> and 20 mL leaves through the <mitral valve>, leaving chamber volume unchanged. In history A, all 20 mL entering during that interval passes straight onward; it can qualify as <atrial conduit flow component> if the interval lies within one ventricular <diastole>. In history B, the 20 mL leaving is entirely older atrial <blood>, while the newly entering 20 mL stays behind. The same inflow, outflow and chamber volume change are compatible with different parcel identities.
The boundary balance
$$
V_{\rm LA}(t_1)-V_{\rm LA}(t_0)=\int_{t_0}^{t_1}\bigl(Q_{\rm PV}-Q_{\rm MV}\bigr)\,dt
$$
cannot distinguish these histories. Here $Q_{\rm PV}$ is net inward <volumetric flow rate> at the <pulmonary veins> and $Q_{\rm MV}$ is net outward <volumetric flow rate> at the <mitral valve>. The additional information is the mapping between entry and exit, represented by <pathlines>.
This distinction also explains why <atrial conduit function>, a physiological role, and a particular volume-based proxy need not equal the <atrial conduit flow component>. A parcel volume collected over an interval need not be contained in the chamber simultaneously, so normalization requires an explicitly stated denominator rather than an assumed fraction of maximum atrial volume. The six histories below are constructed examples, not patient measurements.
\Image[/atrial-flow-component-timelines.png]
{title=Six atrial flow components differ by entry and exit history}
{description=Original illustrative parcel histories across two one-second cardiac cycles. Colored background marks ventricular systole and diastole; arrows identify an entry or exit, not measured speed. Pulmonary-vein backflow exits through a different boundary from mitral outflow. The residual and retained examples remain to the observation endpoint.}
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