COMPARATIVE MECHANICAL BLOOD PROPERTIES 
p. L. Blackshear and R. J. Forstrom* 
The red cells in mammalian and non-mammalian 
species display a range of size, shape, membrane flexi- 
bility, tendency to aggregate and intracellular viscosity 
characteristic of each species. These parameters influ- 
ence the ability of the cells to resist mechanical trauma, 
and along with the properties of the plasma, influence 
the rheological behavior of the blood. In this paper, 
(1) the relevant mechanical properties of the erythro- 
cytes of several species obtained in the laboratory of 
Shu Chien are summarized along with the resulting 
rheological influences. (2) The mechanical hemolysis 
results of Forstrom's jet test for several species are 
summarized in the light of the mechanical properties of 
the erythrocytes. (3) The role of cell size and deforma- 
bility in influencing the diff'usion of extracellular solutes 
in the presence of a velocity gradient is calculated (but 
not demonstrated experimentally). (4) The role of cell 
size and deformability in influencing the cell concentra- 
tion distribution near walls during flow is qualitatively 
predicted (but not demonstrated experimentally). (5) 
The way these factors determine the degree to which 
model experiments can be related to human blood is 
summarized. 
INTRODUCTION 
Shu Chien, et have combined the micro- 
rheological considerations pioneered by Gold- 
smith and Mason," Cokelet,^ Rand,* and others 
with the cell deformability determinations of 
Weed, et al ^ and LaCelle and Weed ^ and with 
supplemental experiments have formulated a 
set of defined properties of cells that aid greatly 
in understanding the macrorheological behavior 
of blood of various mammalian and non-mam- 
malian species. 
Because this work is so germaine to the pres- 
ent topic we will, with Professor Chien's per- 
mission, review the useful microrheological and 
physical properties of several species published 
by him. We find that Chien's defined quantity, 
the sphericity ratio, helps greatly in classify- 
ing the strong dependence of cell lysis stress on 
cell volume reported in the Forstrom jet test.'^ 
* Bioengineering Laboratory, Department of Mechanical Engineer- 
ing, University of Minnesota, Minneapolis, Minnesota. 
Diffusion induced by cell motion predicted by 
the model experiments of Collingham^ and 
Singh ^ and measured in blood by Overcash and 
Keller,^° also is dependent upon cell size and 
sphericity ratio. The cell depleted layer near a 
wall in flowing blood should be similarly de- 
pendent upon these two cell properties.^^-^^ 
These mechanical blood properties will be 
discussed in the sections that follow. We will 
show that size, shape and deformability on 
which these properties depend are themselves 
apparently interrelated. Thus, red blood cell 
volume alone may well be the single quantity 
required to predict the mechanical blood prop- 
erties considered. 
COMPARATIVE MACRORHEOLOGICAL 
BEHAVIOR OF BLOOD AND ITS DEPENDENCE 
UPON RED BLOOD CELL PROPERTIES 
In this section we will review some of the re- 
sults of Chien and his collaborators as pub- 
lished in ref. (1). Figures 1-7 in this section are 
from ref. (1). 
The shear rate dependence on viscosity of sev- 
eral mammalian and non-mammalian species is 
shown in Figure 1. At low shear rates, the 
viscosity of mammalian blood falls into one of 
two groups, whereas at high rates of shear the 
results converge. (Note: hematocrit is not the 
same in this comparison.) 
Cell suspensions of equal hematocrit display 
viscosities that depend upon shear rate and 
apparently upon the volume swept by the cell 
(or rouleaux) as it rotates.^ This volume is 
thought to be a function of cell or rouleaux 
size, shape, and resistance to deformation. These 
influences on the viscosity of human blood are 
shown in Figure 2. Starting from a low shear 
rate of lO^^ sec-^, large rigid rouleaux make 
human blood nearly 10 times as viscous as when 
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