Atrial conduit function

Atrial conduit function is the passive passage of returning blood through an atrium toward the ventricle, distinguished from temporary storage in atrial reservoir function and active pumping in atrial booster-pump function. For the left atrium, the pathway connects pulmonary vein inflow with mitral valve outflow during ventricular filling.^[ref]

Two measurement descriptions need to be distinguished. A volumetric account compares chamber-volume changes with total ventricular filling. A parcel-based account asks when particular modeled blood enters and leaves the left atrium. A primary study defined conduit flow as entry and exit within the same ventricular diastolic phase and compared such components with volumetric indices.^[ref] The operational definition determines what is counted.

An original bookkeeping model illustrates the volumetric approach. Suppose a periodic system has ventricular stroke volume $S$, and suppose a reservoir release $R$ and direct onward passage $C$ form a complete, nonoverlapping partition of that delivered volume. ThenIf a further idealization identifies $R$ with the atrial excursion $V_{\max }-V_{\min }$, values $S=80$ mL and an excursion of 30 mL give a conduit proxy of 50 mL. The arithmetic is exact for the stipulated partition; the correspondence between that partition and real trajectories is an additional assumption.

For example, simultaneous inflow and outflow can exchange blood while chamber volume remains constant. In the balance $dV/dt=Q_{\mathrm{in}}-Q_{\mathrm{out}}$, equal 100 mL/s flows give zero volume change even though 20 mL passes in 0.2 s. Thus a flat volume trace does not demonstrate absent transport. Geometry, timing and modeled parcel histories supply information that volume extrema alone cannot provide.