Ex vitro experimental study on concentration polarization of macromolecules (LDL) at an arterial stenosis

To verify the previous theoretical prediction that the disturbed flow distal to a stenosis enhances lipid accumulation at the blood/arterial wall interface, we designed a canine carotid arterial stenosis model and measured ex vitro the luminal surface concentration of bovine serum albumin (as a tracer macromolecule) by directly taking liquid samples from the luminal surface of the artery. The experimental results showed that due to the presence of a filtration flow, the luminal surface albumin concentration c(w) was higher than the bulk concentration c(0) as predicted by our theory. The measurement revealed that the luminal surface concentration of macromolecules was indeed enhanced significantly in regions of the disturbed flow. At Re = 50, the relative luminal surface concentration c(w)/c(0) was 1.66 +/- 0.10 in the vortex region, while the c(w)/c(0) was 1.37 +/- 0.06 in the laminar flow region. When Re increased to 100, the c(w)/c(0) in the vortex flow region and the laminar flow region reduced to 1.39 +/- 0.07 and 1.24 +/- 0.04, respectively. The effect of the filtration rate, v(w), on the luminal surface concentration of albumin was remarkably apparent. At Re = 50 and 100, when v(w) = 8.9 +/- 1.7 x 10(-6) cm/s, c(w) in the vortex region was 77% and 52% higher than c(0) respectively, meanwhile when v(w) = 4.8 +/- 0.6 x 10(-6) cm/s, c(w) in the vortex region was only 66% and 39% higher than c(0) respectively. In summary, the present study has provided further experimental evidence that concentration polarization can occur in the arterial system and fluid layer with highly concentrated lipids in the area of flow separation point may be responsible for the formation and development of atherosclerosis.