= Vascular graft compliance mismatch
\b[Vascular graft compliance mismatch] is a difference between the pressure-dependent deformation of a <vascular graft> and that of the adjoining <blood vessel>, compared under specified loading conditions. Equal unloaded diameters do not imply equal diameter changes during a pressure pulse. The comparison must specify both the geometric observable and the pressure interval.
For the <diameter compliance of a vascular graft>, one useful definition is
$$
C_D=\frac{1}{D}\frac{dD}{dp},\qquad
\overline C_D=\frac{D_2-D_1}{D_1(p_2-p_1)}.
$$
Both have inverse-pressure units; the second is an interval estimate referenced to $D_1$. This differs from the volume-based <vascular compliance> $C_V=dV/dp$. For a cylindrical segment of fixed length, $V=\pi D^2L/4$, so differentiation gives $C_V/V=2C_D$. A diameter convention and a volume convention cannot be compared merely because both are called compliance.
Suppose two stipulated segments each have diameter $4.0\,\mathrm{mm}$ at $80\,\mathrm{mmHg}$. At $120\,\mathrm{mmHg}$ their diameters are $4.4$ and $4.1\,\mathrm{mm}$. The fractional diameter increases are 10 percent and 2.5 percent, giving
$$
\overline C_{D,1}=0.0025\,\mathrm{mmHg^{-1}},\qquad
\overline C_{D,2}=0.000625\,\mathrm{mmHg^{-1}}.
$$
One interval compliance is four times the other despite equal initial diameters. Attaching these segments constrains their deformation near the join; this calculation alone does not determine the resulting local stress or biological response.
In a primary experiment on engineered bovine arteries, a video motion analyzer tracked vessel edges while a pressure transducer recorded loading. A bellows pump supplied pulsatile loading; static loading was assessed separately. The authors observed lower dynamic than static compliance overall, illustrating that the loading history and analysis method belong in the measured property.<Morphologic and mechanical characteristics of engineered bovine arteries by Laura E. Niklason and others>[Printed pp. 631–632: video, transducer and pump apparatus; Figure 9 and accompanying Results: static versus dynamic response]{ref} Their diameter-based values expressed as percent per 100 millimeters of mercury require a factor of $10^4$ relative to fractional change per millimeter of mercury.
A mismatch assessment should therefore compare like observables at comparable pressure, frequency and reference diameter. It is distinct from <vascular graft burst pressure>, which concerns rupture, and from <graft patency>, which concerns whether the conduit remains open.
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