= Aortic sinus
An \b[aortic sinus] is one of the bulging spaces of the <aortic root> behind an <aortic valve> leaflet. In the usual three-leaflet arrangement, two sinuses give origin to the <coronary arteries>; the third is noncoronary. The distal sinus boundary is associated with the <sinotubular junction>.<Surgical anatomy of the aortic valve and root—implications for valve repair by Ruggero De Paulis and Andrea Salica>[General considerations; Figures 1–3]{ref} A sinus is thus a local part of the root geometry, rather than the whole <ascending aorta> or the central passage alone.
The geometry has an experimentally testable role in valve motion. <B. J. Bellhouse> and <L. Talbot> placed a rigid-walled valve model in a pulsatile water tunnel. Their primary report describes a trapped circulating flow and a downstream <stagnation point> within each sinus, with much of leaflet closure occurring before net forward flow had ended.<The fluid mechanics of the aortic valve by B. J. Bellhouse and L. Talbot>[Abstract, model and closure mechanism]{ref} This is evidence from a controlled physical model, not direct observation of every patient or proof that root walls are rigid.
A local circulation can coexist with net forward transport. For an original accounting example, suppose an ideal central stream carries 80 mL/s downstream, while an adjacent recirculating region carries 10 mL/s across a selected internal surface in each direction. The circulating contributions cancel in the net flux through that surface even though the fluid there is moving. Thus net <volumetric flow rate> alone does not specify the spatial <velocity> field near a leaflet.
The same distinction matters for washout. A sinus can contain rapidly moving fluid whose paths mostly recirculate; speed alone does not establish how quickly that fluid is replaced. Replacement depends on exchange with the through-flow and can be investigated using a tracer or modeled <pathlines>. The <aortic sinus> therefore connects a visible anatomical shape with questions about leaflet loading, local flow and transport history.
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