In a saphenous vein casting, steady and pulsatile flow resulted in overall pressure drops 130 to 360 percent higher than Poiseuille flow, with complex flow patterns observed around the valve.
Flow visualization and pressure measurements were carried out in a singel valve saphenous vein casting which was made from a saphenous vein segment obtained from a bypass patient at Cedars Sinai Medical Center. Dye was injected to understand the flow around the valve. The dye showed very complex flow patterns around the valve and in the valve sinus, and the cavity formed by a ligated branch. For steady flow, pressure drops across the valve were 0.72, 2.0 and 6.3 mmHg for the physiological flow rates of 45, 84, and 169 ml/min, respectively. Overall pressure drop across the casting (compared to Poiseuille flow for a straight tube) increased with the flow rate, being 130 to 290 percent higher over this flow rate range. In the case of pulsatile flow, pressure drops across the valve were 0.95 and 3.0 mmHg for the flow rates of 47 and 87 ml/min which were 26 and 43 percent higher than those of steady flow. Overall pressure drop was 220 and 360 percent higher for those flow rates compared to Poiseuille flow. The measured spatial pressure distributions along the casting and flow visualization indicated the global nature of the flow field with the accelerated flow through the valve separating and reattaching downstream along the wall in the pressure recovery region. Atherosclerosis may be prone to occur in the lower shear region along the wall beyond the valve tip in the reattachment region, as we have observed in vivo in rabbit experiments.
Kwack et al. (Wed,) conducted a other in Aortocoronary Bypass Graft (n=1). Steady and pulsatile flow vs. Poiseuille flow for a straight tube was evaluated on Pressure drop across the valve and casting. In a saphenous vein casting, steady and pulsatile flow resulted in overall pressure drops 130 to 360 percent higher than Poiseuille flow, with complex flow patterns observed around the valve.