Blood, Vol. 91 No. 10 (May 15), 1998:
pp. 3986-3991
Treatment of Myeloproliferative Disorders With Hydroxyurea:
Effects on Red Blood Cell Geometry and Deformability
By
K. Gunnar Engström and
Eva Löfvenberg
From the Departments of Cardiothoracic Surgery and of Hematology,
Umeå University Hospital, Umeå, Sweden.
 |
ABSTRACT |
Hydroxyurea (HU) is used in suppressing the bone marrow and
producing fetal-like red blood cells (RBCs). These RBCs are large in
size and may theoretically disturb the microcirculation. In five
patients with myeloproliferative disorders (MPD), the RBC geometry and
deformability were analyzed before and after 6 to 8 months of HU
treatment. In untreated MPD, the RBC geometry and filterability was
normal. After HU, the RBC membrane area increased 24% and the cell
volume increased 39% (P < .005). This change resulted in a
12% increase in the minimum cylindrical diameter (MCD). From a static
bending model of initial deformation, the RBC diametrical cross-section
had a significantly increased section modulus. However, this increase
in profile stiffness was compensated for by its larger projected cell
area and, thus, pressure load on the RBC corpuscle. The resulting
resistance to initial deformation therefore remained unchanged after
HU. These findings were tested experimentally; with 3-µm filter
membranes, HU treatment caused a significant increase in flow
resistance (P < .02), in accordance with MCD. However, with
5-µm pores, no difference was seen, again in consonance with the
theoretical findings of initial deformation. Because most capillaries
are larger than 3 µm, we suggest that HU is acceptable from a
perspective of cellular microrheology.
| |
INTRODUCTION |
THE CIRCULATING red blood cells (RBCs)
reflect the bone marrow, both cell geometrically and functionally, such
as with growth hormone stimulation1 and with neonatal
RBCs.2 Diseases of the bone marrow may also cause abnormal
geometry of the circulating RBCs, an example being sickle cell anemia,
in which the hemoglobin (Hb) is abnormal with a change in a terminal
amino acid and structural defect of the protein configuration and
solubility. Myeloproliferative disorders (MPD) are another group of
bone marrow diseases, including polycythemia vera (PV), essential
thrombocythemia (ET), and myelofibrosis (MF), with various degrees of
changes in the myelopoiesis and circulating number of erythrocytes and
platelets.3 When there is a need for myelosuppression,
hydroxyurea (HU), a DNA synthesis inhibitor, has been increasingly
used. In both sickle cell anemia4,5 and MPD,6,7
HU has been found useful to modify the gene expression to produce fetal
Hb (HbF).6 HU reduces the production of sickel Hb and
retards the myeloproliferation, respectively. However, a side effect of
HU treatment is megaloblastic change of the RBCs.8
Although the megaloblastic effects of HU has been known for many
years,8 the consequences of this RBC change on the
microcirculation is still under debate. Most of this research is from
sickle cell anemia,9 during which the HU changes per se are
affected and partly masked by the sickle cell disease. Not much is
known about the blood cell rheology in MPD and the possible effects of
HU treatment on relatively normal RBCs. We addressed this problem by
analyzing the geometry and filterability of RBCs on previously untreated patients with MPD before and after 6 to 8 months of HU
treatment. The RBC geometry was analyzed using cell curvature profile
generation with the possibility of calculating and estimating the
theoretical consequences of the HU-induced RBC change.
These theoretical interpretations were also tested experimentally by RBC filterability measurements using both 5-µm and 3-µm Nucleopore membranes. The 5-µm pores measure the effects on initial bending deformation, whereas the 3-µm pores are sensitive to maximum
deformation close to the critical minimum cylindrical diameter (MCD)
limit.
| |
MATERIALS AND METHODS |
Patients and HU treatment.
Five patients with newly diagnosed MPD were selected. Four of the
patients had ET, whereas one was subgrouped to have MF with thrombocytosis. All five patients were about to begin receiving chemotherapy treatment because of thrombocytosis, symptoms,
and/or thrombotic/hemorrhagic complications. The inclusion in
the study had no influence on the clinical routine and treatment. The
patients were analyzed immediately before HU and were then observed 6 to 8 months later during ongoing HU treatment. HU was administered daily, using an oral dose of 0.5 to 1 g/d. Normal controls were healthy
age-matched hospital personal, who were studied in parallel. These
controls were not the same individuals before HU and at the follow-up,
thus producing 5 + 5 control observations.
Blood sampling and media.
Blood samples were from venopuncture using standard heparinized 10-mL
test tubes. The blood was centrifuged at 1,500g for 10 minutes
with buffy coat removal. This was repeated three times to wash the
RBCs, each time by topping up the suspension to 10 mL. Using this
standard routine, most of the plasma, leukocytes, and platelets were
removed. The final resuspension hematocrit for filtration analyses was
set to 5%. The resuspending medium consisted of a Krebs-Ringer
solution (135 mmol/L NaCl, 4.7 mmol/L KCl, 1.2 mmol/L
KH2PO4, 1.2 mmol/L MgSO4) buffered
with 20 mmol/L HEPES and supplemented with 2.56 mmol/L
CaCl2, 5 mmol/L D-glucose, and 0.2 g/L human serum albumin
(Fraction V Albumin; Sigma Chemical Co, St Louis, MO). The pH was set
to 7.40 and the final medium had an osmolality of 299 ± 1 mOsm.
Medium osmolality was measured by freezing-point depression (Osmette
Osmometer; Precision Systems, Inc, Natick, MA). The medium was also
prefiltered through a 0.45-µm Millipore filter (Millipore Corp,
Molsheim, France).
All experimentation was conducted on two parallel blood samples, one
from the MPD patient and one from the matched control. These blood
samples were coded all through the study, after which time the patient
identity was disclosed.
RBC geometry.
About 5 µL of the whole blood was diluted in 1 mL of RBC suspension
medium and incubated for 30 minutes before analysis. A chamber for RBC
geometry measurement was made from coverslips on a microscope slide to
make a rectangular compartment (18 × 10 × 0.17 mm). A drop of suspended RBCs was introduced into the slit entrance of
the chamber, and the openings were sealed with immersion oil. RBCs were
allowed to sediment with the chamber held upside down. After 2 minutes,
the chamber was turned right side up and mounted in the microscope. A
large proportion of the previously settled RBCs were thus hanging
vertically from the upper glass surface. On these vertical RBCs, the
diametrical cross-sections were focused on using bright field
illumination (Carl Zeiss ×100/1.25 oil objective lens; Carl
Zeiss, Oberkochen, Germany). A digitizing table with light-spot cursor
(MOP-Videoplan; Kontron Bildanalyse GmbH, Munich, Germany) was
optically superimposed on the microscopic image. The RBC diameter,
maximum thoroidal thickness, and central thickness were measured. A
thin diffraction band surrounded the RBC cross-sections due to
differences in refractive indices between the RBC and the suspending
medium to which the uniform shell rule was applied during
measurements.10 The method used here is consistent with
that described in previous publications, to which readers are referred
for further details.1,2,11,12 RBCs (50 cells per sample)
were focused on one by one and measured at their diametrical cross-section, a procedure that required about 15 minutes of microscopy per blood sample.
RBC profile calculations.
The above measurements were loaded into equation 1 expressing the RBC
profile curvature, originally derived from Evans and Fung13
and later remodelled11,12:
![y = 0.5(1 − &khgr;<SUP>2</SUP>)<SUP>1/2</SUP>(C<SUB>0</SUB> + C<SUB>1</SUB>&khgr;<SUP>2</SUP>[1 − 0.561&khgr;<SUP>2</SUP>])](/content/vol91/issue10/fulltext/3986/img001.gif)
|
(1)
|
With
the aid of equation 1, the RBC membrane area and volume were computed
by solving the volume integral and using numerical computer integration
for membrane area calculation.11 The cell area-to-volume
ratio was calculated together with the surface area index, which
describes the relative excess of membrane area beyond that required to
enclose the cellular volume. 2,14 MCD was then
derived from the area (A) and volume (V) by a third order
equation11:
|
(2)
|
RBC folding resistance.
It is possible to mathematically calculate the mechanical resistance to
initial bending deformation of the RBC corpuscle in terms of a section
modulus value. The section modulus only considers the RBC shape and
size and not the membrane mechanical properties as such, eg, elastic
shear, dilation, or surface bending moduli or their interrelations. The
section modulus is calculated for the RBC corpuscle, consisting of a
0.01-µm-thick membrane shell model12 with linear elastic
behavior.15 The unit becomes µm3.
The static bending model.
The corpuscle section modulus value is evaluated using a static bending
model in which the RBC is stressed due to a pressure difference between
the two sides of the cell (here set to a fictitious pressure of 1 kPa).
The pressure generates a bending moment and hence a membrane tension,
both having a maximum at the diametrical cross-section of the
RBC12; the higher the tension, the more deformable the RBC.
The tension is mathematically given by the quotient of bending
moment-to-section modulus, with the unit
nanoNewton/µm2 (nN/µm2). This method of
theoretical analysis is useful to evaluate the influence of RBC shape
and size only on corpuscle deformability.11,12
RBC filterability.
The capillary function of RBC was studied by a filterability model on
resuspended cells. This was studied by means of a specially developed
filtration system.1,2,16 This system uses a digital balance
(Mettler PM480; Mettler Toledo AG, Greifensee, Switzerland) in
connection with a computer (IBM PS/2 Model 50; IBM UK Ltd, Greenock,
Scotland) for high precision monitoring of the filtration flow. The
accumulated weight is transmitted by a frequency of 7.5 Hz, with
on-line calculation of flow rate versus time, and is not limited in
volume. This sampling rate gives a sufficient resolution
in time in relation to the obtained flow rate and the resolution of the
balance, corresponding to 1 µL/0.13 seconds. All analyses were made
at room temperature (22°C to 24°C).
A computer was programmed for communication with the balance for data
sampling, experimental timing, calculation of statistics, and storage
of filtration data. The computer program was here designed to find the
peak in initial flow at filtration onset, thus avoiding artifacts
associated with the acceleration of fluids.16 The
filtration is driven by a constant hydrostatic pressure of 600 Pa. The
filtration chamber and filter are vertically located to reduce cell
sedimentation artifacts. Filterability was measured as a function of
time and with respect to the initial filtration rate and clogging rate
and, thus, with the possibility of detecting different measures of
cellular rheology. Nucleopore polycarbonate membranes were used having
pore diameters of 5 and 3 µm and a capillary length of about 11 µm
(lots no. 54F8A36 and 62E0B32, respectively; Nucleopore Corp,
Pleasanton, CA). In the configuration of the filtration system used,
filters were cut from larger sheets (8 × 10 inches to 15-mm wide
strips) and connected so that a roll of filter was made. These rolls (5 and 3 µm) were mounted on the filtrometer and allowed rapid change
between each filtration. A blank filtration was used to calibrate each
filtration. However, the variability in blank filtrations was
negligible, because all filters were from the same batch; furthermore,
within each experiment, all filters were from the same sheet. The
nominal pore density was 4.0 × 105
pores/cm2 and 2.0 × 106
pores/cm2 for the 5-µm and 3-µm filters, respectively.
The active filter area was 70.9 mm2 (open area of the
filter support), which produced a total number of filterable pores of
2.84 × 105 and 1.42 × 106,
respectively.
The erythrocyte filterability indices were calculated by means of a
regression analysis of the flow rate, starting at the initial flow peak
and during a 20-second filtration period. The filterability was
expressed as RBC incremental volume (RBCiv) and clogging
rate (RBCcr). The filtration rate decreased with time due to pore
clogging of rigid erythrocytes and some contaminating leukocytes. The
initial filtration rate (FRBC) was extrapolated from the
regression line to time 0, thus reflecting the filtration rate before
pore clogging. The RBC incremental volume (RBCiv) was
calculated based on the initial filtration rate of blood
(FRBC) and that of cell-free medium (Fm) and
with correction for the RBC particle concentration (RBCc):
|
(3)
|
This
equation expresses the relative decrease in filtration rate due to RBCs
as compared with that of medium alone, Fm. The concentration of RBCs in the suspension, RBCc, is also
considered. More precisely, the RBCiv (expressed as
nanoliters per RBC) is the volume of medium that is
hindered from passing a narrow pore due to the presence of an RBC
within it.
The decrease in filtration rate is due to clogging particles
(RBCcr). The clogging rate can be evaluated by relating the
slope, k (filtration rate as a function of filtration time) to the
initial filtration rate, FRBC:
|
(4)
|
Np
is the average number of initially open filter pores (see above). The
unit for clogging particles will be RBC per second. The calculations in
the present report are, in principle, in accordance with those
described by Matrai et al,17 except that the filtration rate is expressed here as a function of time instead of as a function of volume.
Statistics.
Data are presented as the mean values ± SEM. For statistical
differences, both paired and unpaired t-tests were used for
matched analyses with respect to differences induced by HU and for
analysis versus control individuals, respectively. With unpaired
testing, correction was made for unequal variance and different number of observations between groups. The different numbers of observation are indicated in the tables (n). Five levels of significance were tested; P < .051, P < .022,
P < .013, P < .0054, and
P < .0015.
| |
RESULTS |
Clinical response.
The patients were diagnosed according to required criteria for MPD. The
Hb concentration varied with the MPD spectrum. One patient had
supranormal Hb and an MPD profile towards PV, but with normal RBC mass
and classified as ET; the Hb was reduced after HU. In another patient,
the Hb was subnormal (MF) and increased during HU treatment. In the
remaining three patients, an isolated ET was observed in which the Hb
remained largely unaffected by HU (Table
1). In all included patients, the platelet counts were increased and
became successfully reduced after HU (P < .05).
The mean corpuscular Hb concentrations (MCHC) were at normal levels in
all patients and remained unaffected by HU (Table 1). The mean
corpuscular volume (MCV) was normal but increased markedly during HU
treatment. It is noteworthy that this MCV was derived from electronic
sizing, which indicated a volume increase from 89.0 ± 1.0 µm3 to 116.4 ± 4.4 µm3 (P < .01). The patients tolerated the HU treatment well, and all five patients had clinical benefits from the myelosuppression; in
all patients, the symptoms or complications at diagnosis resolved or
improved (Table 1).
Effects of HU on the RBC geometry.
The circulating RBCs of patients with MPD were normal in cell geometry,
with close to identical cross-section profiles to those of matched
normal control individuals (Table 2). After HU treatment, the RBC geometry was increased dramatically (Table 2).
This was seen in both diameter and thoroidal thickness by 10.0% ± 2.0% and 15.1% ± 2.6%, respectively. The central thickness remained unchanged. The resulting cell profile was generated by computer iteration to produce a larger RBC with marked increase in both
membrane area and cell volume by 24.0% ± 4.5% and 39.0% ± 6.3%, respectively. The area-to-volume ratio decreased, whereas the
surface area index remained unchanged.
Effects of HU on calculated RBC deformability.
The patients with MPD had normal RBC geometry and, thus, no difference
in calculated deformability indices (Table 2). However, the HU-induced
change in RBC size produced highly significant alterations in these
calculated RBC deformability indices. These changes were found in terms
of both maximum deformation, represented by MCD, and initial bending
rigidity, as judged from the static bending model. The MCD increased
significantly by 11.7% ± 0.9%; furthermore, the percentage of RBC
having an MCD greater than 3.5 µm increased by 263% ± 39%
(Table 2). This dramatic percentage increase suggests a larger
resistance to pass a narrow capillary and with more capillary blockage.
The bending section modulus that was calculated for each RBC
diametrical cross section indicated a significantly more rigid RBC
membrane shell profile; this increase was by 23.6% ± 1.9% (Table 2). However, although the corpuscle profile was
associated with a larger calculated bending resistance, when the larger
projected surface area was taken into consideration and thus the larger pressure load on the RBC to initiate deformation, the generated membrane tension was almost the same before and after HU treatment (Table 2).
Effects of HU on the measured RBC filterability.
The RBC filterability in patients with untreated MPD was not
significantly different from those of normal controls. This was seen
using both 3-µm and 5-µm pore filters, although there was a small
tendency for a decreased filterability in MPD patients using the 5-µm
filtration model (interpreted as a small increase in both
RBCiv and RBCcr;
Table 3). After HU treatment, a significant reduction in filterability was recorded with 3-µm filters as the RBCiv increased by 221% ± 63% (P < .02).
There was also a 23% ± 13% increase in the the corresponding
RBCcr, but without becoming significant. No significant
changes were seen using the 5-µm pore size (Table 3).
| |
DISCUSSION |
The oxygen delivery from the blood to the surrounding tissue is
promoted by the narrow dimensions of the capillaries. The RBC are
folded in the capillaries because these are narrower than the cell
diameter, of the order of 4 to 5 µm.18 The RBC therefore relies on its ability to deform (ie, cellular deformability), which in
large part is due to the relative excess of membrane area to cell
volume. RBCs of unfavorable shape and size may impair the blood flow in
the macrocirculation by viscosity increase, but more obviously in the
microcirculation with retarded cell passage through the capillary
network. Impaired RBC deformability is thought to
contribute to the sequestration of senescent cells.19
HU has become a useful treatment to alter the gene expression of the
bone marrow and thus the circulating blood cells.5,20 This
is achieved by a change in the ribonucleotide reductase
during the mitotic S-phase.21 Regardless of treated
disease, HU produces fetal-like RBCs with HbF.22 Fetal RBCs
are known to be larger in size2,14 and are similar to the
cells seen with HU treatment.8 In MPD, the administration
of HU is aimed at altering the concentration of circulating RBCs and
platelets by suppressing the abnormal myelopoiesis in favor of the
fetal gene expression.6 This is done to reduce the clinical
symptoms of MPD, such as thrombotic and hemorrhagic
complications.23 However, the beneficial effects of HU are
paralleled by a possible disadvantage of having large-size fetal RBCs.
Intuition tells us that these large cells would more easily be trapped
in the microcirculation. Our aim was to analyze this
phenomenon by parallel experimental and theoretical observations on MPD
patients before and after HU treatment and to compare the data to
normal controls.
In each patient, the cross-sectional profiles of 50 random RBCs were
carefully measured by computerized image processing. From triplicate
size measurements, the RBC curvature equation was computer generated,
and various RBC deformability indices were calculated. These indices
were calculated according to (1) a static bending model12
to simulate the initial corpuscle bending deformation at capillary
entrance and (2) MCD calculation to find the minimum capillary diameter
the RBC can pass without lysis.11,14 The theoretical data
were compared with those of experimental filtration measurements using
(1) 5-µm pore membranes to simulate the initial deformation (cf, RBC
static bending model) and (2) 3-µm pore membranes to analyze the
final stage of deformation (cf, MCD).
The tested MPD patients had normal RBC geometry and a filterability
resistance comparable to that of the matched controls. In the
literature there are no absolute answers as to how the circulating
blood cells are affected in MPD; this may depend on the wide spectrum
of MPD diseases with dysplastic erythropoiesis and, in many cases,
possible coexistence of iron deficiency24 and thus altered
RBC geometry. The present patients showed normal RBC geometry, which
makes the interpretation of the HU more strict. Note, our microscopy
data suggest slightly oversized RBCs (in MPD patients and normal
controls), with an average cell volume of 105.7 ± 3.3 µm3 and membrane area of 141.4 ± 3.0 µm2 in the control group. These recordings are about 10%
larger than that recorded using micropipette aspiration of RBC (93.2 ± 1.5 µm3 and 133.3 ± 1.6 µm2,
respectively).25 Similar reference values on RBC geometry are available based on microscopy interference
holography,13 although larger size reference values,
similar to those recorded here, also exist.26,27 Thus, the
exact geometry of the average RBC is not known, and the variations in
reference value depend on the used techniques. This is due in part to
the optical limits with light microscopy. With the present data, the
RBC geometry is derived from diametrical cross-sections. This technique
requires a consistent tracing routine of a diffraction band that
outlines the cell and is the result of the light resolution and the
difference in refractive indices between the RBC and the surrounding
medium. The RBC diffraction phenomenon was first analyzed by
Ponder28 and later reevaluated by Korpman et
al.10 With the Korpman rule,10 the cell
membrane is thought to be found in the middle of the diffraction band,
which is the guideline today. However, there is probably no exact
tracing rule for the membrane edge, a fact that may account for the
apparent oversizing of the normal RBC in this study. As an example of
optical effects, by assuming an error on the linear scale corresponding
to the light-microscopy resolution of approximately 0.2 µm, an RBC
diameter of 8 µm has a potential optical error of ±2.5%. The
second and third power errors, membrane area and cell volume, are 5.1%
and 7.7%, respectively. This example simplifies the true calculations,
because the cell diameter is only one of three measured parameters from
which the RBC curvature is synthesized. The optical limits may thus
introduce apparent discrepancies in baseline cell size. However, this
does not affect the interpretations made in this study because of the systematic nature of the membrane-tracing routine. Note also that electronic orifice sizing of RBC (ie, Coulter counter) is affected by a
shape factor correction29 and does not represent exact estimates of the RBC geometry, especially not shape-changed RBCs. In
MPD with discoid RBCs, one would assume that the shape-factor error
would be rather consistent to yield a good estimate of the true MCV. In
this study, the Coulter counter indicated a 30.9% ± 5.3% increase
in MCV due to HU, which did not differ significantly from the
microscopy data (39.0% ± 6.3%). Microscopy measurements on
vertical RBCs and diametrical cross-section profiles are far more
time-consuming than using Coulter counting; however, the microscopy
technique has been made more available due to modern computer
technology and the use of a modified RBC curvature
equation.12 Furthermore, with the curvature equation, not
only the RBC volume is derived but also membrane area and various
deformability indices based on the RBC cross-sectional profile (see
below).
After HU treatment, the trombocythemia was reduced and, in most cases,
normalized. From a clinical perspective, the HU treatment was
successful, with no signs of disturbed microcirculation. The RBC
concentration was reduced in the patient having Hb in the upper range,
whereas it was increased in the patient with a clinical profile towards
MF. The cell size was dramatically increased, whereas the average MCHC
remained at normal level. In this study, we analyzed the start and end
points before and after 6 to 8 months of HU. Our previous research has
indicated a close to linear increase in MCV with time of HU treatment,
until a steady-state occurred at about 5 months.30 During
this initial period, two separate pools of RBC were seen: those with
normal MCV and those with HU-affected geometry, respectively. This was
followed by a complete replacement with HU-RBC.30
Previously in the literature, the terms responders versus nonresponders
have been attributed the pattern of HbF increase in HU-treated MPD
patients.6 Although we did not measure HbF or detailed
temporal dynamics of RBC geometry change, it is tempting to look at the
different end-point RBCs as possible responders or nonresponders. All
patients showed a dramatic increase in MCV, whereas the MCHC varied.
However, there was no correlation between the rate of MCV increase
versus MCHC change in a way that could reflect different response
patterns. Further research may highlight this issue.
Our Coulter counter data in HU-treated MPD patients seem comparable to
results in sickle cell anemia. However, our 131% ± 5%
increase in MCV appears somewhat larger than in many sickle cell
reports.31,32 This may be attributed the hemolytic anemia in sickle patients with an increase in reticulocytes and thus an
increase in MCV before HU treatment. It could also reflect errors
associated with the shape-factor correction of sickle RBCs in Coulter
counting. In our study on MPD, the average MCHC appeared unaffected by
HU; this is again paralleled by observations in HU-treated dogs and in
many sickle cell studies.31
The RBC microscopy measurements, as with the Coulter data, also showed
a dramatic increase in RBC size; the cell diameter and thickness were
significantly increased, whereas the central thickness (dimple)
remained unchanged. The RBC curvature calculation produced a
significant increase in both RBC membrane area and cell volume. These
changes resulted in a significant decrease in RBC area-to-volume ratio,
whereas the surface area index remained unchanged. The calculation of
MCD gave a significant increase of 12%.
When the RBC cross-sectional profile of HU-treated patients was
analyzed using the static bending model, a significantly larger section
modulus was generated, suggesting a greater required force to initiate
deformation of the corpuscle. However, the larger RBC diameter after HU
also resulted in a larger projected surface area and thus deforming
pressure load. This increased pressure load balanced the increase in
section modulus to generate similar membrane tension and deformation in
the RBC before and after HU.
The filtration analyses of HU-RBC correlated well with the theoretical
observations and geometry. With 3-µm pore membranes, a significantly
increased filtration resistance was produced by HU. This increase
drives the attention to the increase in MCD and the percentage of RBC
having an MCD larger than 3.5 µm from 17% to 59% after HU (cells
that would effectively be trapped within the filter). With 5-µm
pores, there were no significant differences associated with HU
treatment. This lack of difference using the 5-µm filtration
correlated with the theoretical findings given by the static bending
model. The RBC geometry change after HU produced a more stiff corpuscle
shell profile; however, this profile was balanced by a larger projected
cell area and hence deforming pressure load. The
resistance to initiate RBC folding thus remained larger without change
after HU treatment. It is noteworthy that, with 5-µm pores, the RBC
will required only minor folding to pass for which the static bending
model appears relevant.
In conclusion, patients with MPD have RBCs of normal shape, geometry,
and rheological function. With HU treatment, the bone marrow is
suppressed to produce fetal-like large RBCs. The present detailed
microscopic measurements of individual RBC cross-sectional profiles
confirms this geometry change; not only is the cell volume increased,
but also the membrane area. However, in addition to mere cell geometry,
the calculations were extended to also analyze the mathematical
deformability; an obvious impairment in micropore function (MCD
increase) was seen, whereas the initial corpuscle bending deformability
appeared unaffected. These calculations were confirmed by 3-µm and
5-µm filterability measurements, respectively. Because the
capillaries in the circulation are larger in diameter than 3 µm,18 we suggest that the HU-induced change in RBC
geometry is acceptable from a perspective of cellular microrheology.
| |
FOOTNOTES |
Submitted August 12, 1997;
accepted January 13, 1998.
Supported by grants from the Swedish Medical Research Council
(12x-11204), the Swedish Diabetes Association, the Swedish Society of
Medicine, the Medical Faculty at Umeå University, and the Sahlberg Fund.
Address reprint requests to K. Gunnar Engström, MD, PhD,
Department of Cardiothoracic Surgery, Umeå University Hospital, S-901
85 Umeå, Sweden.
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 18 U.S.C. section
1734 solely to indicate this fact.
| |
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Abstract
Introduction
Abstract
