[Postsurgical changes of the calculated wall shear stress in autogenous interpositional venous grafts by blood flow...

This investigation was designed to evaluate the postsurgical changes of autogenous, interpositional venous grafts in terms of the calculated wall shear stress by blood flow waveform analysis. In a model of tethered elastic tube, mean wall shear stress (tau) was obtained by the following equation: tau = 32 microQ/(pi.D3). Twenty-four grafts in repairing limb arterial injuries from 24 patients were examined with Doppler ultrasonic image instrument (7.5 MHz) for follow-up studies. Three mongrel dogs were selected for experimental studies. A segment of femoral vein (4-5 cm) was excised, reversed and interpositionally grafted into the femoral artery. The mean wall shear stress was calculated at 1 hour, 24 hours, 1 week, 4 and 12 weeks after implantation. Two occluded grafts were demonstrated in one femoral and one popliteal artery. The value of mean wall shear stress was higher in upper limb group (over 1.1 N/m2) than in lower limb group (five over 1.1 N/m2 and seven below 1.1 N/m2). The value of mean wall shear stress of grafts with follow-up time of more than 24 weeks was over 1.1 N/m2 in 6 grafts including one from lower limb while that was below 1.1 N/m2 in 6 grafts (all from lower limbs). No significant difference was found between the mean flow velocity values in upper and lower groups. The results from the experiment revealed that the value of mean wall shear stress decreased at one hour after operation, and increased and reached a fixed value beyond 1 week postsurgery. The vein graft in upper limb has better early and long-term result than that in lower limb because wall shear stress is correlated with the intimal hyperplasia, then the outcome of autogenous vein graft. In conclusion, we propose that wall shear stress be applied for follow-up studies on vascular grafts in limb arterial injuries and hemodynamic factors be considered for arterial reconstructive procedures.