Asymmetric redirection of flow through the heart

Through cardiac looping during embryonic development(1), paths of flow thro ugh the mature heart have direction changes and asymmetries whose topology and functional significance remain relatively unexplored. Here we show, usi ng magnetic resonance velocity mapping(2-5), the asymmetric redirection of streaming blood in atrial and ventricular cavities of the adult human heart , with sinuous, chirally asymmetric paths of flow through the whole. On the basis of mapped flow fields and drawings that illustrate spatial relations between flow paths, we propose that asymmetries and curvatures of the loop ed heart have potential fluidic and dynamic advantages. Patterns of atrial filling seem to be asymmetric in a manner that allows the momentum of inflo wing streams to be redirected towards atrio-ventricular valves, and the cha nge in direction at ventricular level is such that recoil away from ejected blood is in a direction that can enhance rather than inhibit ventriculo-at rial coupling(6). Chiral asymmetry might help to minimize dissipative inter action between entering, recirculating and outflowing streams(7). These fac tors might combine to allow a reciprocating, sling-like, 'morphodynamic' mo de of action to come into effect when heart rate and output increase during exercise(6).