Hydraulic conductivity and low-density lipoprotein transport of the venous graft wall in an arterial bypass

BACKGROUND: Blood flow condition may have influence upon the hydraulic conductivity of venous graft (L(p,vein)) in an arterial bypass, then affecting the accumulation of low-density lipoproteins (LDLs) within the graft wall. To probe this possibility, we first measured in vitro the filtration rates of swine lateral saphenous vein segments under different flow rates, and the correlation of L(p,vein) with wall shear stress (WSS) was then obtained. RESULTS: The experimental results showed that when WSS was very low, L(p,vein) would increase drastically with WSS from 1.16 ± 0.15 × 10(−11) m/s Pa at 0 dyn/cm(2) to 2.17 ± 0.20 × 10(−11) m/s Pa at 0.7 dyn/cm(2), then became constant of approximately 2.33 × 10(−11) m/s Pa as the WSS increased further. Based on the experimental results, we assumed three different cases of L(p,vein) and numerically simulated the LDLs transport in an arterial bypass model with venous graft. Case A: L(p,vein) = 2.33 × 10(−11) m/s Pa; Case B: L(p,vein) = 1.16 × 10(−11) m/s Pa (static condition with WSS of 0); Case C: L(p,vein) was shear dependent. The simulation showed that the deposition/accumulation of LDLs within the venous graft wall in Case A was greatly enhanced when compared with that in Case B. However, the LDL accumulation in the graft wall was similar for Case A and Case C. CONCLUSIONS: Our study, therefore, indicates that when the venous graft was implanted as a bypass graft, the L(p,vein) might remain nearly constant along its whole length except for very few areas where the value of WSS was extremely low (less than 0.7 dyn/cm(2)) and the effects of L(p,vein) modulated by blood flow on LDL transport may be neglected.