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Effects of red blood cell concentration on hemostasis and thrombus
formation in a primate model
Y Cadroy and SR Hanson
Roon Research Center for Cardiovascular Disease and Thombosis, Research
Institute of Scripps Clinic, La Jolla, CA.
Because the effects of red blood cell (RBC) concentration on hemostasis and
thrombus formation have not been studied experimentally under conditions of
whole blood flow without anti-coagulation, normal baboons were bled or
transfused to obtain three different groups: a low hematocrit (Ht) group
(20% less than Ht less than 25%), a normal Ht group (35% less than Ht less
than 40%), and a high Ht group (50% less than Ht less than 55%).
Measurements of platelet count, bleeding time, platelet aggregation,
fibrinogen level, and coagulation time (APTT) were equivalent to normal
values in each group. Thrombus formation was induced using a device
composed of collagen-coated tubing followed by two sequentially placed
expansion chambers designed to exhibit flow recirculation and stasis. The
device was exposed for up to 40 minutes in an arterio-venous shunt system.
Wall shear rates in the tubular collagen segment were 100 seconds-1 and 500
to 750 seconds-1. The accumulation of 111In-platelets and
125I-fibrinogen/fibrin was measured radioisotopically; RBC incorporation
was determined from measurements of total thrombus hemoglobin. Thrombus
that formed on the collagen substrate was rich in platelets and poor in
fibrin and RBCs. Under high flow conditions, thrombus composition showed no
dependence on Ht. Surprisingly, under low flow conditions, platelet
thrombus volume was negatively correlated with Ht (r = -.73, P = .005), and
was increased by greater than twofold in the low Ht group as compared with
the high Ht group. Thrombus that formed in the disturbed flow regions
contained relatively few platelets but was rich in fibrin and RBCs. The
predominant finding was a positive correlation between RBC incorporation
and Ht at both high and low shear rates (r = .90, P = .00003; and r = .77,
P = .002, respectively), with thrombus volume increasing three- to sixfold
between the low and high Ht groups. Thus, in vivo variations in Ht ranging
between 20% and 55% did not affect hemostasis, but were found either to
promote or inhibit the net accumulation of thrombus, depending on local
flow conditions.
Volume 75,
Issue 11,
pp. 2185-2193,
06/01/1990
Copyright © 1990 by The American Society of Hematology
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