= Mitral annulus
The \b[mitral annulus] is the supporting attachment region around the <mitral valve> between the <left atrium> and <left ventricle>. It supplies a reference for the <valve leaflets> but is not adequately described as a rigid, flat circle. Its spatial shape and motion form part of the coupled valve apparatus.
A primary left-heart simulator study compared flat and saddle-shaped annular configurations in eleven human valve specimens. The investigators measured <chordae tendineae> forces in selected experiments and found a redistribution of those forces with annular shape.<Effects of a saddle shaped annulus on mitral valve function and chordal force distribution: an in vitro study by Jorge Hernan Jimenez and others>[Abstract, Methods and Results]{ref} This tests a geometrical variable directly rather than assuming that one diameter captures the complete attachment boundary.
An original circular approximation illustrates why fractional diameter and area changes differ. If a hypothetical ring's diameter changes from $D$ to $0.9D$, its planar area changes from $\pi D^2/4$ to $0.81\pi D^2/4$. A $10\%$ diameter decrease gives a $19\%$ area decrease in this model. The equation is not a claim that the native <mitral annulus> is circular or planar.
Motion adds another geometrical contribution. In a rigid-piston model, translation of a boundary with area $A$ by distance $\Delta z$ changes the represented volume by $\Delta V=A\Delta z$. Stipulated values 10 cm$^2$ and 0.4 cm give 4 mL. Actual <mitral annular excursion> occurs in a deforming <heart>, so this does not assign all <stroke volume> to one translating plane.
Annular area, shape, position and leaflet <coaptation> are therefore related but distinct observations. Comparisons need consistent landmarks and phases, while models must specify which parts of the surrounding apparatus are allowed to move.
Back to article page
