Effects of elevated hematocrit on cerebral blood flow
William Olbricht (Cornell University), Puifai Santisakultarm (Cornell University), Gregory Farber (Cornell University), Nozomi Nishimura (Cornell University), Chris Schaffer (Cornell University)
Complex Fluids: Suspensions, Emulsions, and Gels
Wed 1:30 - 2:50
Barus-Holley 160
The rheological properties of blood depend strongly on hematocrit – the volume fraction occupied by red cells in blood. Myeloproliferative diseases are characterized by an overproduction of red cells leading to elevated hematocrit, which affects rheology and flow, especially in smaller blood vessels. We report results of measurements of microcirculatory blood flow in the brain cortex of live anesthetized rodents. Using a two-photon excited fluorescence (2PEF) microscope as a velocimeter, we have measured red cell velocity profiles inside arterioles, capillaries, and venules, both in healthy animals and in animals with elevated hematocrit due to myeloproliferative disease. Results demonstrate that the spatial resolution of the method is sufficient to construct detailed velocity profiles, despite the high concentration of red cells in whole blood, which limits other measurement methods. Furthermore, the temporal resolution of 2PEF microscopy is sufficient to determine how local velocity profiles depend on heartbeat and respiration in individual blood vessels and at vessel bifurcations. The data show that the time-averaged blood flow speed decreases with vessel diameter in arterioles and in capillaries, and increases in venules. Furthermore, animals with elevated hematocrit show an abnormally large number of “stalled” capillaries that have little or no blood flow. A simple empirical model of capillary networks suggests these capillary stalls start as a result of hemodynamics and rheology. The experiments show that they can persist for long times, which can be a consequence of cell adhesion to the vessel wall. Diminished cerebral blood flow may be a cause of cognitive decline associated with myeoloproliferative disease.