Concentration polarization of macromolecules in canine carotid arteries and its implication for the localization of atherogenesis

To test the hypothesis that concentration polarization of atherogenic lipids may occur in the arterial system and play an important role in the localization of atherogenesis, we measured in vitro the luminal surface concentration of bovine serum albumin (as a tracer macromolecule) in the canine carotid artery by directly taking liquid samples from the luminal surface of the artery. The experimental results show that the luminal surface albumin concentration, cw, was higher than the bulk concentration, c0 as predicted by our theory. The relative luminal surface albumin concentration, cw/c0, decreased very sharply at low wall shear rate, G, but gradually approached the value of 1.0 asymptotically as G was increased. The experiment shows that water flux rate across the vessel wall, vw, has a profound impact on concentration polarization. For instance, at G=0 and 185 s−1, when vw=8.9±1.7×10−6 cm/s, cw was 65% and 15% higher than c0, respectively, meanwhile when vw=4.8±0.6×10−6 cm/s, cw was only 42% and 5% higher thanc0, respectively. The experiment also revealed that concentration polarization occurred in a thin layer close to the luminal surface of the artery. The thickness of this layer was water flux rate-dependent. The higher the water flux rate, the thicker was the layer. The present study therefore confirms that concentration polarization can indeed occur in the arterial system and our theoretical analysis is accurate in predicting this mass transfer phenomenon.