BANKED BLOOD GROWS STIFF WITH AGE
It may look like fresh
blood and flow like fresh blood, but the longer blood is stored, the less it
can carry oxygen into the tiny microcapillaries of the body, says a new study
from University of Illinois researchers.
Using advanced optical
techniques, the researchers measured the stiffness of the membrane surrounding
red blood cells over time. They found that, even though the cells retain their
shape and hemoglobin content, the membranes get stiffer, which steadily decreases
the cells' functionality.
Led by electrical and
computer engineering professor Gabriel Popescu, the team published its results
in the journal Scientific Reports.
"Our results show
some surprising facts: Even though the blood looks good on the surface, its
functionality is degrading steadily with time," said Popescu, who is also
part of the Beckman Institute for Advanced Science and Technology at the U. of
I.
Nearly 14 million
units of blood are banked annually in the U.S. The established "shelf life"
for blood in blood banks is 42 days. During that time, a lot of changes can
happen to the blood cells -- they can become damaged or rupture. But much of
the blood keeps its shape and, by all appearances, looks like it did the day it
was donated.
Popescu and his
colleagues wanted to quantitatively measure blood cells over time to see what
changed and what stayed the same, to help determine what effect older blood
could have on a patient. They used a special optical technique called spatial
light interference microscopy (SLIM), a method developed in Popescu's lab at
Illinois in 2011. It uses light to noninvasively measure cell mass and topology
with nanoscale accuracy. Through software and hardware advances, the SLIM
system today acquires images almost 100 times faster than three years ago.
The researchers took
time-lapse images of the cells, measuring and charting the cell's properties.
In particular, they were able to measure nanometer scale motions of the cell
membrane, which are indicative of the cell's stiffness and function. The
fainter the membrane motion, the less functional the cell, much like how a
fainter pulse indicates problems with a patient.
The measurements
revealed that a lot of characteristics stay the same over time: The cells
retain their shape, mass and hemoglobin content, for example. However, the
membranes become stiffer and less elastic as time goes by. This is important
because the blood cells need to be flexible enough to travel through tiny
capillaries and permeable enough for oxygen to pass through.
"In
microcirculation such as that in the brain, cells need to squeeze though very
narrow capillaries to carry oxygen," said postdoctoral researcher Basanta
Bhaduri, the lead author of the paper. "If they are not deformable enough,
the oxygen transport is impeded to that particular organ and major clinical
problems may arise. This is the reason why new red blood cells are produced
continuously by the bone marrow, such that no cells older than 100 days or so
exist in our circulation. "
The researchers hope
that the SLIM imaging method will be used clinically to monitor stored blood
before it is given to patients, since conventional white-light microscopes can
be easily adapted for SLIM with a few extra components.
"These results
can have a wide variety of clinical applications," said co-author Krishna
Tangella, U. of I professor of pathology who is also affiliated with the
Christie Clinic in Urbana, Illinois. "Functional data from red blood cells
would help physicians determine when to give red-cell transfusions for patients
with anemia. This study may help better utilization of red-cell transfusions,
which will not only decrease healthcare costs but also increase the quality of
care."
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