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Role of Plasma Viscosity in Platelet Adhesion
By Hans H.F.I. van Breugel, Philip G. de Groot, Robert M. Heethaar, and Jan J. Sixma
Platelet adhesion t o the vessel wall is initiated by transport
of blood platelets from the bulk flow t o the wall. The process
of diffusion and convection of the platelets is affected by
rheological conditions such as wall shear rate, red blood cell
(RBC) deformability, and viscosity of the medium. To study
the effect of plasma viscosity on platelet adhesion, perfusion
experiments with a rectangular perfusion chamber were
performed. Reconstituted blood, consisting of washed platelets and washed RBCs, was circulated through this chamber
for 5 minutes at a wall shear rate of 300 s-’. Different albumin
concentrations were made, t o obtain different medium viscosities (0.89 t o 1.85 mPa s). Platelet adhesion decreased with
increasing medium viscosity up t o viscosities of 0.95 mPa . s,
but increased with medium viscosity above this value. Instead of human albumin solution, different plasma viscosities were obtained by dilution of Waldenstriim plasma with
buffer. Plasma was depleted of fibronectin, which gave a final
plasma viscdsity of 2.0 mPa . s, and was dialyzed against
HEPES buffer and subsequently diluted with the dialysis
buffer in different fractions (0.89 t o 2.00 mPa .s). Perfusions
were performed over a purified von Willebrand factor coating
on glass, or over an endothelial cell matrix, preincubated
with von Willebrand factor. With both surfaces, platelet
adhesion was dependent on the plasma viscosity in a similar
way: at low plasma viscosities, adhesion was decreased with
increasing plasma viscosity, while at higher plasma viscosities, adhesion increased with plasma viscosity. Adhesion
values at higher plasma viscosity or at higher human albumin
concentrations could be explained by effects of the medium
on the rigidity of the RBCs, since platelet adhesion is known
to be increased by enhanced RBC rigidity. Effects of the
medium on the deformability of the RBCs were measured
separately with the laser diffraction method. These experiments confirmed that presence of human albumin or plasma
in the measuring suspension increased the rigidity of RBCs.
To prevent influence of the medium on the RBCs in perfusion
experiments, the RBCs were fixated with glutaraldehyde.
Perfusion experiments with fixated RBCs in plasma over a
von Willebrand factor preincubated endothelial cell matrix,
showed a consequent decrease in adhesion with increasing
plasma viscosity, according t o the diffusion theories, whereas
the increase of adhesion at high plasma viscosities was
lacking. This suggests that the latter effect was entirely due
t o increased transport of platelets by more rigid RBCs.
o 1992by The American Society of Hematology.
P
the Stokes-Einsteinian beha~i0ur.l~
This could be ascribed
to the fact that the medium is not a continuum.
All theories on platelet transport show that platelet
diffusivity is strongly dependent on the shear rates of the
flow. Therefore, two limiting cases for platelet adherence to
the wall can be distinguished6: a diffusion-controlled platelet adherence when the wall shear rate is very low (<300
s-l), and a reaction-controlled adherence when high shear
rates are present ( > 1,300 s-l), with the area between 300
and 1,300 s-l as intermediate.
In this report, the effect of the plasma viscosity on
platelet adhesion is studied. Convective diffusion theories
predict that adhesion decreases with increasing medium
viscosity. We found such a decrease up to values of 0.95
mPa . s, but higher viscosities caused increased adhesion.
Studies on RBCs showed an increased rigidity under these
conditions. Previous studies have shown increased platelet
adhesion with more rigid RBCs. It is likely that the
paradoxical effect of increased plasma viscosity is due to
this phenomenon.
-
LATELET ADHESION to the vessel wall is dependent on transport of blood platelets to the wall.
Various rheological factors that are of importance for the
platelet transport have been
Transport of platelets in the flow is regulated by the processes of diffusion and
con~ection.~
Convection refers to the movement of particles
in conformity with the movement of the medium in which
the particles are placed. In convection, the particles follow
the streamlines of the fluid. In diffusion, the movement of
particles is relative to the motion of the fluid, and motion of
an entity in a stationary or smoothly flowing fluid is random
when viewed particle by particle, but the net result of the
random movements results in movement of particles from
regions of high particle concentration to regions of low
particle concentration.
The mass transport in blood can be described by the
convective diffusion t h e ~ r y .Platelet
~ , ~ diffusivity was found
to be dependent on wall shear rate, due to shear induced
red blood cell (RBC) motion.2,6A power law was assumed
between this diffusion resistance and wall shear
Rotation of larger particles (RBCs) could enhance diffusivity of molecules and smaller particles (blood platelets) in
the surrounding area.lOJ1This effect is also dependent on
the rigidity of the larger particles, as the mixing effect that is
responsible for the increase in diffusivity will be smaller in
case of more deformable particles, since the so-called
swept-out volume12 will be smaller. Calculation of the
brownian diffusion coefficient shows a small contribution of
this mechanism to the total platelet transport. Convective
diffusion due to fluid shear stresses and rotation of particles
(RBCs) is the main contributor. Gravitational effects will
be negligible compared with this convective diffusion. From
polymer dynamics, we know that large particles move
through polymer solutions more rapidly than expected from
Blood, VOI 80, N O 4 (August 15). 1992: pp 953-959
From the Departments of Hematology and Medical Physics, University Hospital Utrecht, The Netherlands.
Submitted June 18,1991; acceptedApril 18,1992.
Address reprint requests to Jan J. Sixma, MD, Department of
Hematology, University Hospital Utrecht, PO Box 85500, 3508 GA,
Utrecht, The Netherlands.
The publication costs of this article were defrayed in part by page
charge payment. This article must therefore be hereby marked
“advertisement”in accordance with I8 U.S.C. section 1734 solely to
indicate this fact.
0 I992 t
y The American Society of Hematology.
0006-4971I92 l8004-0018$3.00/0
953
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954
VAN
MATERIALS AND METHODS
Preparation ofperfusate. Whole blood was collected into 0.1 vol
of 110 mmol/L citrate. RBCs and platelets were separated by
centrifugation (45% for 10 minutes at 20°C). RBCs were washed
three times with saline (150 mmol/L NaCI, 5 mmol/L aD-glUCOSe)
and centrifuged (2,OOOg for 5 minutes at 20°C). Platelets were
aspirin-treated and washed with Krebs-Ringer buffer as previously
described.14 Platelets and RBCs were suspended in either human
albumin solutions (HAS) or plasma. Human albumin (Sigma
Chemical, St Louis, MO) was dissolved in Krebs-Ringer buffer (4
mmol/L KCL, 2 mmol/L NazS04, 107 mmol/L NaCI, 20 mmol/L
NaHC03,19 mmol/L sodium citrate, 2.5 mmol/L CaC12,5 mmol/L
aD-glUCOSe, pH 7.35) in a concentration of 160 g/L, and dialyzed
overnight against this buffer. Dilution of the HAS was prevented by
a tightly fitted dialysis bag. To obtain different albumin concentrations, the 16% HAS was diluted with the dialysis buffer to
concentrations of OS%, 1%, 2%, 4%, and 8% HAS.
Plasma from a patient suffering from Waldenstrom disease15
(with a plasma viscosity of 2.5 mPa.s, 27 g/L IgM-K) was
fibronectin-depleted by affinity chromatography on gelatinSepharose as previously described.16J7 Column fractions were
screened and selected by viscosity measurements, and the final
viscosity of the used fraction pool was 2.0 mPa . s. Different plasma
viscosities were obtained by dilution of the plasma with HEPES
buffer (150 mmol/L NaCI, 10 mmol/L HEPES, 11mmol/L sodium
citrate, pH 7.35). Plasma was first dialyzed, in a tightly fitted
dialysis bag, against this buffer, and afterwards diluted to different
concentrations (6.25%, 12.5%, 25%, and 50% plasma).
Platelets were resuspended in plasma or HAS at a final platelet
concentration in the medium of 190 x 103/p,L. RBCs were added
to avolume fraction of 40% of totalvolume of the perfusate (15 mL
total volume), 5 minutes before perfusion.
RBCs were fixated by incubating equal volumes of washed RBCs
and a 1% glutaraldehyde solution in saline for 1 hour at room
temperature. After fixation, the cells were washed three times in
saline to remove free glutaraldehyde. Since the viscosity of concentrated fixed cells is too high to pipette the packed cells, these cells
were first resuspended in the plasma, and platelets were added to
the perfusate 5 minutes before perfusion.
Endothelial cell matrix. Cell matrices on glass coverslips were
obtained from human umbilical vein endothelial cells as previously
described.18Coating of the matrix with von Willebrand factor was
performed by incubation of the matrix with purified von Willebrand factor19(10 p,g/mL in phosphate-buffered saline [PBS] being
the average plasma von Willebrand factor Concentration) for 1
hour at room temperature. After coating with von Willebrand
factor, coverslips were kept in PBS (pH 7.4) until perfusion on the
same day. From previous
we know that von Willebrand
factor is not removed by PBS or shear stresses after coating.
Coating of coverslips. Glass coverslips were cleaned overnight
by a chromium trioxide solution, and rinsed with distilled water
before coating. Coating was performed by incubating a coverslip
with 10 p,g/mL purified von Willebrand f a c t ~ r ’in~ PBS
, ~ (pH 7.4)
for 1 hour at room temperature, followed by a 1-hour incubation
with 4% human albumin solution to block further proteitl binding
to the glass. The von Willebrand factor concentration on glass was
approximately 50 ng/cm2 by this method.20 After coating, coverslips were kept in PBS until perfusion.
Perfusion procedure. The perfusion system with a flat chamber
as developed by Sakariassen et aI2l was used for all perfusion
experiments. Before perfusion, the perfusate was prewarmed for 5
minutes at 37T, and this temperate was held constant during
perfusion. After perfusion, the coverslips were washed with HEPES
BREUGEL ET AL
buffer (150 mmol/L NaCI, 10 mmol/L HEPES, pH 7.35) and
fixated by 0.5% glutaraldehyde in PBS.
Evaluation of the platelet coverage was done by staining the
coverslips (May-Griinwald/Giemsa) and determining the average
surface coverage by means of light microscopy with the aid of an
image ana1y~er.I~
Vucosity and cell deformability measurements. Viscosities of the
plasma dilutions atid the human albumin solutions were determined in a Contraves Low Shear 30 viscosimeter (Contraves AG,
Zurich, Switzerland) at 37°C as described by Merri11.22Viscosity
was measured at different shear rates (6.0 to 128.5 s-l) to enhance
accuracy of the final (newtonian) viscosity value.
RBC deformability was determined by the laser diffraction
t e c h n i q ~ e . ~A~ -system
~
constructed around a Contraves Low
Shear 30 viscosimeter was
in which shear rates could be
varied between 0.56 and 410.5 s-l. Human albumin was dissolved
in Krebs-Ringer buffer (290 mOsm/L, pH 7.4) at a concentration
of 160 g/L, and dialyzed against this buffer. After dialysis,
polyvinyl-pyrrolidone (PVP) was dissolved in the HAS and in the
dialysis buffer in a concentration of 70 g/L. Mixtures of the
albumin solutions and Krebs-Ringer buffer (both with 7% PVP)
were made, resulting in PVP medium with human albumin concentrations of 0.5%, 1%, 2%, 4%, 8%, and 16%. The fibronectin-free
plasma from the Waldenstrom patient was dialyzed against HEPES
buffer (290 mOsm/L, pH 7.4). After dialysis, PVP was dissolved in
the plasma and in the dialysis buffer in a concentration of 70 g/L.
These plasma/PVP and buffer/PVP solutions were mixed in
different plasma/buffer mixtures with loo%, 50%, 25%, 12.5%,
and 6.25% plasma (vol/vol).
The differences in viscosity caused by the various plasma or
albumin concentrations are negligible in comparison to the high
viscosity of the PVP (60 mPa . s). Measurement samples were 5 KL
washed RBCs suspended in 2.25 mL of these different media.
During measurement, temperature was held constant at 37°C.
Deformation was expressed as the elohgation index5of the diffraction pattern of the cells as a function of the shear stress: E =
(a - b)/(a b), where E is the elongation index, a is the length of
long axis of the diffraction pattern, and b is the length of short axis
of the diffraction pattern.
+
RESULTS
Adhesion studies. Reconstituted blood consisting of a
human albumin solution with added RBCs and platelets
was circulated over an endothelial cell matrix. A human
albumin solution of 160 g/L in Krebs-Ringer buffer was
dialyzed against this buffer, and diluted with the dialysis
buffer to different concentrations ( O S % , 1%,2%, and 4%
human albumin). The viscosities of the human albumin
solutions were between 0.89 and 1.85 mPa . s (Fig 1A).
Perfusions were performed for 5 minutes at a wall shear
rate of 300 s-l, in order to approximate a diffusion
controlled platelet adhesion process6 (Fig 1B). Platelet
coverage decreased with increasing HAS concentration at
the lower medium viscosities; at a HAS viscosity of 0.95
mPa . s (20 g/L), platelet coverage was approximately 52%
of the adhesion value at the lowest HAS concentration (5
g/L, 0.89 mPa . s). At higher HAS concentrations, platelet
adhesion increased with an increasing medium viscosity. At
the highest albumin concentration (160 g/L, 1.85 mPa . s),
platelet adhesion was at the same level as the adhesion at
the lowest albumin concentration.
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ROLE OF PLASMA VISCOSITY IN PLATELET ADHESION
2.0
-
1.0
-
1.6
-
955
10
T
8
6
1.4 -
-
4
1.2
1.0
-
2
10
2
0
100
.89
-90
.95
1.05
Viscosity HAS
Albumin conc. [gAI
1.24
1.85
[mPa.s]
Fig 1. (A) Viscosity of 160 g/L human albumin in Krebs-Ringer buffer, at different volume fractions, diluted with buffer. (6) Perfusion
experiments with different HAS concentrations (Fig 4). Perfusions were performedover an ehdothelial cell matrix, at a shear rate of 300 0-1 for 5
minutes (SEM for n = 4). Hematocrit of the perfusate was 0.4, with a platelet concentration of 190 x lOJ/pL.
Similar results might be obtained when albumin would be
a cofactor for platelet adhesion. To exclude the possibility
that albumin has a direct effect on platelet adhesion, we
performed perfusion experiments for 5 minutes at a higher
wall shear rate of 1,800 s-l, conditions at which platelet
adhesion is reaction-controlled. No significant effect due to
a change in human albumin concentration on platelet
adhesion was observed at this shear rate (Fig 2), indicating
that albumin has no direct effect on the adhesive process.
When plasma instead of HAS was used for the perfusion
experiments, the adhesive proteins in the plasma, which are
T
1
a
HAS concentration [gA]
2
4
I
16
Fig 2. Perfusion experiments with different HAS concentrations.
Perfusionswere performedover an endothelialcell matrix, at a shear
rate of 1,800 s-l for 5 minutes (SEM for n = 12). Hematocrit of the
perfusate was 40%. with a platelet concentration of 190 x I O 3 / pL.
also diluted by dilution of the plasma, had to be excluded as
determining factors of the adhesive process. The main
adhesive proteins in the plasma are von Willebrand factor17,27-29
and f i b r o n e ~ t i n . 2 ~Plasma
, ~ ~ , ~ ~can be easily depleted of fibronectin by affinity chromatography." To
obtain a wide range of different plasma viscosities, plasma
of a patient with Waldenstrom's disease (having a high
plasma viscosity of 2.5 mPa . s) was made fibronectin-free
by this method. After pooling the column fractions, the final
plasma viscosity was 2.0 mPa . s. The plasma was dialyzed
against HEPES buffer, and was diluted 1:l with the dialysis
buffer. By subsequent dilutions of 1:l with the buffer, a
plasma viscosity range was obtained (0.89, 0.90, 0.92, 0.95,
1.04, 1.28, and 2.00 mPa. s) (Fig 3A). To eliminate the
contribution of the von Willebrand factor in the plasma,
glass coverslips, coated with 10 p,g/mL purified von Willebrand factor for 1hour, were used as adhesive surface.20To
block any further binding of adhesive proteins from the
plasma to this surface, the coverslips were subsequently
coated with a 4% human albumin solution for 1 hour.
Perfusion studies with the fibronectin-depleted plasma
over the purified von Willebrand factor surface at a shear
rate of 300 s-l for 5 minutes (Fig 3B) showed a similar
behavior as in the previous experiments. Platelet adhesion
decreased when plasma viscosity was enhanced up to a
plasma viscosity of 0.95 mPa . s, resulting in an adhesion
value at this plasma viscosity of approximately 50% of the
adhesion at a plasma viscosity of 0.89 mPa . s. At higher
plasma viscosities ( > 0.95 mPa . s), adhesion values increased with plasma viscosity up to an adhesion of 160% of
the minimum adhesion value at the highest plasma viscosity
(2.00 mPa . s).
Endothelial cell matrix as adhesive surface has been
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956
VAN
2.0
-
1.8
-
BREUGEL ET AL
8 -
6 .
1.6 -
1.4 -
4
1.2 1.0
2
L1
0.8
10
1
0
100
.89
Plasma fraction
[%I
B
.90
.92
.95
1.04 1.28 2.00
Plasma viscosity [mPa.sl
Fig 3. (A) Viscosity of fibronectin-depleted plasma from a Waldenstrem patient, diluted with buffer, at different volume fractions of the
plasma. (B)Perfusion experiments with different plasma fractions (Fig 1). Perfusions were performedwith fibronectin-free plasma over a glass
coverslip coated with purifiedvon Willebrandfactor and human albumin, at a shear rate of 300 s-' for 5 minutes (SEMfor n = 4). Hematocrit of the
perfusate was 0.4, with a platelet concentration of 190 x 10JIpL.
shown to be independent of plasma von Willebrand factor.28A possible effect of differences in plasma von Willebrand factor was further minimized by incubating the
endothelial cell matrix with 10 pg/mL (corresponding to
the mean plasma concentration) of von Willebrand factor.
By using this preincubated endothelial cell matrix in combination with the fibronectin-free plasma (Fig 4), a similar
adhesion dependence on plasma viscosity was found as
previously. At lower plasma viscosities, platelet coverage
decreased with increasing plasma viscosity. At a plasma
15
-s
u
r
IT
T
viscosity of 1.04 mPa . s, platelet adhesion was 33% of the
adhesion value at the lowest plasma viscosity of 0.89 mPa . s.
At plasma viscosities above 1.04 mPa s, adhesion increased
with increasing plasma viscosity; platelet adhesion at the
highest viscosity (2.00 mPa s) was approximately 150% of
the minimum adhesion at a plasma viscosity of 1.04 mPa . s.
Deformability of the RBCs. We suspected that the increased adhesion at higher medium viscosities was due to
increased rigidity of the RBCs. Effects of plasma proteins
on RBC rigidity were therefore studied.
Deformability of the RBCs was determined by laser
diffra~tometry.23-~
The effect of the presence of human
albumin or plasma on RBC rigidity was studied using
suspending medium in which human albumin or plasma was
present in corresponding concentrations as in the perfusion
studies.
Deformation of the cells was expressed as the elongation
index of the diffraction pattern at different shear stresses.
The presence of human albumin in the suspending medium
decreased the deformability of the cells, since the elongation index was smaller at the same shear stress in presence
of plasma (Fig SA). The presence of plasma also decreased
the deformability, to an even greater degree than the
presence of human albumin (Fig SB).
Adhesion studies with firated RBCs. Possible effects of
the Dlasma on the rigidity of the RBCs in adhesion
experiments were eliminated by fixation of the cells. The
RBCs were washed three times in saline and fixated in 0.5%
glutaraldehyde for 1 hour. After fixation, the cells were
again washed three times in saline. The cells were resuspended in the fibronectin-free plasma, and perfusions were
performed over an endothelial cell matrix that was preincubated with von Willebrand factor. Perfusions were per-
-
I
~ 3 9 90
92
-95
1.04
1.28
2.00
Plasma viscosity [mPa.sl
Fig 4. Perfusion experiments with different plasma fractions (Fig
1). Perfusions were performed with fibronectin-free plasma over an
endothelial cell matrix preincubated with von Willebrand factor, with
a shear rate of 300 s-7 for 5 minutes (SEM for n = 4). Hematocritofthe
perfusate was 0.4, with a platelet concentration of 190 x 103/pL.
_
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957
ROLE OF PLASMA VISCOSITY IN PLATELET ADHESION
___---.
__---.
_._.-.--.--I.>.,._--
0.0
'
0.6 r
I
0
5
A
10
20
15
0
25
B
Shear stress [N/m2]
5
10
15
20
25
Shear stress [N/m21
Fig 5. (A) Deformability experiments with laser diffractometry. Washed RBCs (5 pL) were added to PVP solutions in buffer with a human
albumin concentration of 160 (-),
80 (-4
40 (---), 20 (-4
and 10 g/L (--). (B) Deformabilityexperiments with laser diffractometry.Washed
RBCs (5 NL) were added to PVP solutions in buffer with plasma fractions in the medium of 100% (-),
50% (--),
25% (---),
12.5% (---), and
6.25% (-).
formed at a wall shear rate of 300 s-l for 5 minutes (Fig 6).
Platelet adhesion now decreased with increasing plasma
viscosity over the whole range of plasma viscosities. At the
highest plasma viscosity of 2.00 mPa . s, platelet adhesion
was approximately 50% of the maximum value at the lowest
plasma viscosity of 0.89 mPa . s.
DISCUSSION
According to the convective diffusion theory, platelet
adhesion was expected to decrease when medium viscosity
is increased. From the results reported here, the effects of
medium viscosity are more complex; at higher plasma
.89
.90
.92
.95
1.04
1.28 2.00
Plasma viscosity [mPa.sl
Fig 6. Perfusion experiments with different plasma fractions (Fig
1). Perfusions were performed with fibronectin-free plasma over an
endothelial cell matrix preincubated with von Willebrand factor, with
a shear rate of 300 s-1 for 5 minutes. RBCs were fixated in 0.5%
glutaraldehyde for 1 hour and were added to the perfusate in a
volume fraction of 0.4 (SEM for n = 4). Platelet concentration was
190 x lW/pL.
viscosities, platelet adhesion increased with an increasing
viscosity of human albumin solution or plasma.
Experiments were performed in which blood platelets
and RBCs were resuspended in HAS and perfused over an
endothelial cell matrix (Fig 1B). The use of various albumin
concentrations (and so various medium viscosities) showed
that platelet adhesion decreased with increasing HAS
viscosity at low medium viscosities, but increased at higher
medium viscosities. Minimum adhesion was found at a HAS
viscosity of 0.95 mPa s. Since human albumin does not
contribute to the adhesive process of the platelets (Fig 2),
the observations were due purely to differences in medium
viscosity.
When plasma dilutions were used as suspending medium
for the platelets and RBCs, contribution of adhesive proteins in plasma to platelet adhesion had to be excluded.
Since von Willebrand f a ~ t o r ~and
~ f, i~b r~o-n ~e ~~t i n ~are
v~~-~~
the two main factors in plasma involved in platelet adhesion, these factors had to be accounted for. This was done
by depletion of fibronectin from the plasma, and by perfusing over a purified von Willebrand factor surface.20 Since
this surface was coated afterwards with human albumin, no
adhesive proteins from the plasma could adhere to this
surface. Results were similar to those found in previous
experiments (Fig 2). Also in this case, the typical changes in
platelet adhesion could only be due to changes in plasma
viscosity.
Preincubation of an endothelial cell matrix with purified
von Willebrand factor prevented the von Willebrand in the
plasma from adhering to the surface (Fig 4). Incubation
concentration of the von Willebrand factor was 10 kg/mL,
since this is the average plasma concentration. From other
s t ~ d i e s , ~we
~ J know
~ , ~ ~that platelet adhesion is mainly
dependent on von Willebrand factor at high wall shear rates
(>SO0 s-l), Using this system, adhesion values again
showed a decrease at increasing plasma viscosity for low
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958
VAN
medium viscosities, and an increase in adhesion at higher
plasma viscosities.
With all three methods of perfusion, comparable adhesion dependencies on the medium viscosity were thus
found. The increase in adhesion with medium viscosity at
higher medium viscosities could be explained by an effect of
the medium on RBC rigidity.
To study the effect of presence of plasma proteins on
RBC deformability separately, deformability measurements were performed. From the measurements represented in Fig 5A, it was seen that presence of human
albumin in the suspending medium decreased the deformability of the RBCs. Similar experiments with plasma
showed also a decrease of the deformability of the RBCs in
presence of plasma (Fig 5B). A more detailed study on the
effects of plasma proteins on the deformability of RBCs will
be reported separately.26 To exclude influence of the
medium on the RBCs in perfusion studies, RBCs were
fixated with glutaraldehyde (Fig 6). From these experiments, it seemed clear that in the previous experiments
using untreated RBCs, effects of the medium on the RBCs
were responsible for the results. Adhesion experiments
with these fixated cells showed a predicted behavior according to the diffusion theories, where increased medium
viscosity gives rise to a decreased platelet transport.
Experimental in vitro increase of RBC rigidity causes
decrease in adhesi0n.I Since increased RBC rigidity increases platelet adhesion, the deformability measurements
could explain the results of the adhesion experiments at
different medium viscosities. Decrease of platelet diffusion
BREUGEL ET AL
by an increase in medium viscosity, and increase of diffusion
by an increase in RBC rigidity, were simultaneously present
in our experiments. At low medium viscosity, effects of the
increase in cell rigidity were not yet significantly active. At
high medium viscosity, rigidity of the cells is that high that
the increase in adhesion by an increase in rigidity is higher
than the decrease in adhesion by an increased medium
viscosity.
When considering plasma viscosities in the physiological
range (> 1.2 mPa . s), an increase of platelet adhesion with
increasing plasma viscosity is found. Since several patient
groups have an increased plasma viscosity (eg, diabetes
mellitus and intermittent claudication), RBC rigidity in
native plasma will be increased in these patients, and
therefore an increased platelet adhesion will occur. This
could probably contribute to the thrombotic tendency of
these patient groups. These data are obviously of major
importance for the understanding of the hyperviscosity
syndrome observed in Waldenstroms macroglobulinemia.
The hyperviscosity is clearly caused not only by the increase
in plasma viscosity, but also by a change in RBC rigidity.
These consequences will be more fully discussed elsewhere.26 The present study indicates that hyperviscosity
may be associated with an increased tendency to thrombosis due to increased platelet adhesion. The current data
may also be of importance in patients with a nephrotic
syndrome in whom plasma viscosity in total is not increased,
but in whom the changed plasma protein composition
affects RBC rigidity.
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1. Goldsmith HL, Turitto VT: Rheological aspects of thrombosis and haemostasis: Basic principles and applications. Thromb
Haemost 55:415,1986
2. Turitto VT,Weiss HJ: Rheological factors influencing platelet interaction with vessel surfaces. J Rheol23:735,1979
3. Leonard EF, Grabowski EF, Turitto V T The role of convection and diffusion on platelet adhesion and aggregation. Ann NY
Acad Sci 201:329,1972
4. Turitto V T Mass transfer in annuli under conditions of
laminar flow. Chem Engl Sci 30:503,1975
5. Turitto VT, Baumgartner HR: Platelet interaction with subendothelium in flowing blood: Effect of blood shear rate. Microvasc
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6. Turitto VT, Baumgartner HR: Platelet deposition on subendothelium exposed to flowing blood: Mathematical analysis of
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7. Aarts PAMM, Heethaar RM, Sixma JJ: Red blood cell
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8. Grabowski EF, Friedman LI, Leonard E F Effects of shear
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surface. Ind Eng Chem Fundam 11:224,1972
9. Turitto VT, Benis AM, Leonard EF: Platelet diffusion in
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10. Keller KH: Effect of fluid shear on mass transport in flowing
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11. Wang NH, Keller KH: Solute transport induced by erythrocyte motion in shear flow. Trans Am SOCArtif Organs 25:14,1979
12. Chien S: The biophysical behaviour of the red cells in
suspension, in Surgenor DM (ed): The Red Blood Cell. New York,
NY, Academic, 1975
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1992 80: 953-959
Role of plasma viscosity in platelet adhesion
HF van Breugel, PG de Groot, RM Heethaar and JJ Sixma
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