Suspensions of human red cells in citrated plasma, in Ringer solution, and in Ringer solution containing albumin were passed through straight and curved glass and plastic hollow fibers (diameter range, 100–1,000 μ). Pressure-flow relations were measured over the pressure range of 0.1– 800 mm water, corresponding to a shear stress range of 0.01– 80 dynes/cm2. The suspensions were tested simultaneously in a rotational viscometer. It was found that red cell suspensions exhibit a yield shear stress only if the plasma protein fibrinogen is present. Experimental pressure-flow data in hollow fibers were in excellent agreement with rotational viscometer measurements and with analytical predictions based on the assumptions that blood flows as a homogeneous continuum and that the velocity at the wall is zero. Effects of tube surface characteristics and curvature on the pressure drop-flow rate relation were not discernible. microcirculation models; model blood flow; yield stress of blood; capillary blood flow and viscometry; fibrinogen and blood flow in hollow fibers; non-Newtonian flow of blood in hollow fibers Submitted on July 20, 1964

Platelet diffusivity was measured in flowing blood by a technique based on the classical experiment of Taylor. Values of diffusivity were calculated from experimental data with the aid of theoretical results obtained by Ananthakrishnan, ef a/. Values ranged between 0.5 and 2.5 X 10-7 cm2/sec for a series of hematocrits (H = 0-50) and shear rates (->-w = 40-440 sec-1). These values imply significant enhancement of diffusivity due to red cell motion. The experiment was not sensitive enough to detect the dependence of diffusivity on either shear rate or hematocrit, although on the assumption of power-law dependence of diffusivity on shear rate the data indicated a power-law coefficient of less than 0.5. At high shear rates (>200 sec-1) results were found to be influenced by nonrandom cell migration; however, upon correction for this migration, these results were consistent with the results obtained at low shear rate.

No abstract

The effect of hematocrit on pressure-flow relations was studied in the perfused isolated hindpaw of the dog. Blood and suspensions of erythrocytes (RBC) in albumin-Ringer solution, hematocrit range of 0 to 80%, were used as perfusates. Flow resistance was found to increase markedly with hematocrit. No significant difference was found between pressure-flow data obtained with blood and RBC in albumin-Ringer solution when comparisons were made at comparable hematocrits, indicating negligible effect of RBC aggregation when blood was the perfusion fluid. Computations of flow resistance relative to cellfree perfusate indicated that non-Newtonian viscosity, as well as vessel distensibility, contributed to the nonlinearity of pressure-flow curves. Perfusion of paws with two Newtonian fluids of different viscosities allowed computation of inertial pressure losses under conditions of steady flow. At physiological perfusion pressures, inertial losses accounted for about 40% of the total pressure drop for cell-free albumin-Ringer solution, and dropped to about 5% for a hematocrit of 50. The results suggest that inertial losses, rather than a Fahraeus-Lindqvist effect, play an important role in pressure-flow relations in the hindpaw. 1047 at UNIV OF NORTH DAKOTA on May 15, 2015 http://circres.ahajournals.org/ Downloaded from 1048 BENIS, USAMI, CHIEN pressure-flow relations. The results do not support the existence of a Fahraeus-Lindqvist effect in the perfused hindpaw. Methods PERFUSIONS WITH RBC SUSPENSIONS AT DIFFERENT HEMATOCRITS Colled.d Blood Weight FIGURE 1 (A) Schematic drawing of perfusion circuit. Cannulated paw on balance is perfused by dog's natural blood (connections to femoral artery and vein) or by syringe pump. Inset shows cannula manifolds.(B) Variables displayed on multichannel recorder include venous pressure (P T ), arterial pressure (P 8 ), paw weight (W p ) and weight of collected fluid (W q ).