Rheology of blood by NMR

Pipe flow of blood in tubes of 1 and 7 mm inner diameter, respectively, was investigated employing two-dimensional NMR velocity imaging and PFG propag ator measurements at different Reynolds numbers between 10 and 3500. The re sults are compared to flow of a water/glycerol mixture of matching viscosit y under identical conditions. The transition from laminar to turbulent flow is observed by both a flattening of the velocity profile and a change of t he propagator shape. For blood flow this transition is found to be shifted toward higher Reynolds numbers as compared to the transition of the water/g lycerol mixture. This observation is in agreement with predictions from hyd raulic measurements and is a consequence of the non-Newtonian flow characte ristics of blood as a suspension of erythrocytes and plasma. Likewise, a de viation from the laminar flow condition is observed for blood at low Reynol ds numbers between 10 and 100. This phenomenon is unknown for Newtonian liq uids and is explained by the onset of a geometrical arrangement of the eryt hrocytes, the so-called rouleaux effect. (C) 2001 Academic Press.