Abstract
Ektacytometry has been the primary method for evaluating deformability of red blood cells (RBCs) in both research and clinical settings. This study was designed to test the hypothesis that the flow of RBCs through a network of microfluidic capillaries could provide a more sensitive assessment of the progressive impairment of RBC deformability during hypothermic storage than ektacytometry. RBC units (n = 9) were split in half, with one half stored under standard (normoxic) conditions and the other half stored hypoxically, for up to 6 weeks. RBC deformability was measured weekly using two microfluidic devices, an artificial microvascular network (AMVN) and a multiplexed microcapillary network (MMCN), and two commercially available ektacytometers (RheoScan-D and LORRCA). By week 6, the elongation indexes measured with RheoScan-D and LORRCA decreased by 5.8–7.1% (5.4–6.9% for hypoxic storage). Over the same storage duration, the AMVN perfusion rate declined by 27.5% (24.5% for hypoxic) and the MMCN perfusion rate declined by 49.0% (42.4% for hypoxic). Unlike ektacytometry, both AMVN and MMCN measurements showed statistically significant differences between the two conditions after 1 week of storage. RBC morphology deteriorated continuously with the fraction of irreversibly-damaged (spherical) cells increasing significantly faster for normoxic than for hypoxic storage. Consequently, the number of MMCN capillary plugging events and the time MMCN capillaries spent plugged was consistently lower for hypoxic than for normoxic storage. These data suggest that capillary networks are significantly more sensitive to both the overall storage-induced decline of RBC deformability, and to the differences between the two storage conditions, than ektacytometry.
Highlights
Ektacytometry has been the primary method for evaluating deformability of red blood cells (RBCs) in both research and clinical settings
We showed that small subpopulations of irreparably damaged, poorly deformable RBCs significantly decrease the ability of entire populations of stored RBCs to traverse microfluidic networks and significantly increase the occurrence and duration of RBCs plugging events
This was because flow through the artificial microvascular network (AMVN) and multiplexed microcapillary network (MMCN) microfluidic networks was dependent on the ability of individual RBCs to deform and pass through narrow constrictions smaller than the resting diameter of the RBCs
Summary
Ektacytometry has been the primary method for evaluating deformability of red blood cells (RBCs) in both research and clinical settings. The number of MMCN capillary plugging events and the time MMCN capillaries spent plugged was consistently lower for hypoxic than for normoxic storage These data suggest that capillary networks are significantly more sensitive to both the overall storageinduced decline of RBC deformability, and to the differences between the two storage conditions, than ektacytometry. The multiplexed microcapillary network (MMCN) device comprises a network of narrowing microcapillaries arranged in a parallel array, and in addition to measuring the network perfusion rate evaluates the frequency of intermittent plugging of its individual microcapillaries by poorly preserved RBCs that cannot deform sufficiently to traverse the 3 μm constriction, as well as the fraction of time the microcapillaries remain in a plugged state[17,27]. MMCN devices challenge individual RBCs to deform and pass through narrow constrictions enabling detection of poorly deformable cells within a population of otherwise normal RBCs, and AMVN devices enable quantification of the impact of these subpopulations of poorly deformable cells on overall perfusion rate under physiologically inspired c onditions[17,25]
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