Platelet retention in columns packed with glass beads has been theoretically
analyzed in a manner similar to that commonly used to describe the behavior of
fixed-bed adsorbers. Combining the results of this analysis with experimental observations
has confirmed that the process of platelet deposition from whole blood
onto glass bead surfaces is entirely adsorption controlled. In contrast to this finding,
a theory often used to predict the performance of a wide range of filtration
processes has been utilized to show that platelet deposition from PRP is dominated
not by the adsorption step, but by resistances to platelet transport which are confined
to the plasma phase. Furthermore, a direct relationship between platelet retention
in glass bead columns and hematocrit has been observed using whole blood
and ghost cell suspensions. These results, which are in accord with observations
made by Zucker et al. (1972), strongly suggest that ADP released from red cells
cannot account for the increased retention with increased hematocrit. This behavior
can be explained, however, by recognizing that the effective platelet diffusivity
is considerably enhanced by increasing the hematocrit of red cell or ghost cell suspensions
and consequently the frequency of cell-cell interactions. As confirmed
experimentally, these physical interactions, as opposed to biochemical factors, are
primarily responsible for determining the observed changes in platelet retention
when the suspending medium is gradually changed from PRP (0% hct) to normal
hematocrit values.
Furthermore, theoretical and experimental techniques are described which
permit, for the first time, a quantitative measure of platelet retention in columns
packed with glass beads which is independent of both hemodynamic factors and
column geometry. This new measure of platelet retention is shown to relate
directly to the affinity of platelets for one another and for solid surfaces in vitro,
thereby offering the possibility of using glass bead columns as highly sensitive diagnostic
tools for the detection of hemorrhagic disorders.