Treatment of Myeloproliferative Disorders With Hydroxyurea:
Effects on Red Blood Cell Geometry and Deformability
K. Gunnar Engström and
Eva Löfvenberg
From the Departments of Cardiothoracic Surgery and of Hematology,
Umeå University Hospital, Umeå, Sweden.
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.
Blood, Vol. 91 No. 10 (May 15), 1998:
pp. 3986-3991
© 1998 by The American Society of Hematology.
