Using a classic paper by Robin Fåhraeus and Torsten Lindqvist to teach basic hemorheology

Abstract

"The viscosity of the blood in narrow capillary tubes" by Robin Fåhraeus and Torsten Lindqvist (Am J Physiol 96: 562-568, 1931) can be a valuable opportunity for teaching basic hemorheological principles in undergraduate cardiovascular physiology. This classic paper demonstrates that a progressive decline in apparent viscosity occurs when blood flows through glass capillary tubes of diminishing radius, which was later designated as the "Fåhraeus-Lindqvist effect." Subsequent studies have shown that apparent viscosity continues to decline at diameters that correspond to the arteriolar segments of the systemic vascular tree, where the majority of the total peripheral resistance resides and is actively regulated in vivo. The Fåhraeus-Lindqvist effect thus reduces microvascular resistance, thereby maintaining local tissue perfusion at a relatively lower blood pressure. The paper by Fåhraeus and Lindqvist can be used as a platform for a plenary discussion of these concepts as well as of the relationships among hematocrit, vessel diameter, red blood cell deformability, and resistance to blood flow and how these factors may affect the work of the heart.

Role of particle size, shape, and stiffness in design of intravascular drug delivery systems: insights from computations, experiments, and nature

“…In parallel, there is increased appreciation in the scientific community on how natural blood cells such as RBCs, WBCs, and platelets may already provide certain physicomechanical and biochemical design paradigms for vascular DDS and how these bioinspired cues can be incorporated into semi‐synthetic and synthetic particle platforms for creating DDS with enhanced performance. To this end, building on the Fåhraeus phenomenon that renders RBC volume localization at the center of flowing blood in blood vessels, several researchers have modeled platelet‐RBC interactions to elucidate how collisions of smaller stiffer biconvex discoid platelets with larger softer biconcave discoid RBCs helps laterally pushing the platelets into an RBC‐free plasma zone closer to the vascular wall such that the probability of platelet's interaction with a vascular injury site (when needed) is enhanced (see Box ) . Figure shows a concept diagram of how the various blood cells are distributed radially in blood flow, and how an injected DDS particle will need to traverse across this volume of blood components to marginate to the vessel wall to bind target cells at the wall, release drug payload at the wall, or in specific cases of pathologies (e.g., tumor‐associated leaky blood vessels) they might traverse past the endothelial barrier into the tissue.…”

Micro-Needle with Polygonal Structure of Micro-Channel for Stress and Blood or Drug Flow Optimization

“…During laminar flow through a tube, the concentric layers of plasma shearing against each other when it is caught between two layers [25]. This multiphase fluid nature of blood is the physical reason behind the Fahraeus effect where the correlation is when the tube diameter is decreased, the average velocity of blood is increased and so does the wall shear stress but decreased in apparent blood viscosity [24][25].…”

“…6. This type of migration is known to be due to the formation of a cell-free layer near the wall and shear induced diffusion caused by a decrease of granular temperature at the center of the tube due to inelastic collisions hence drop of pressure through the narrow vessel [25]. This relationship can be applied to the polygonal shape of channel where the hydraulic diameter of polygonal channel has less area compared to the total are of diameter of circular channel.…”

Effects of dexmedetomidine on the deformability of erythrocytes in vitro and in anesthesia

“…This is the reason for using patients undergoing laparoscopic cholecystectomy as research subjects in the current study. The value of EI was affected by the Hct measured by the viscosity method (13). In the clinical experiment of the present study, Hct did not change significantly prior to and following surgery (P>0.05) in the two groups of patients.…”