BACKGROUND: Great deformability allows red blood cells (RBCs) to flow through narrow capillaries in tissues. A number of microfluidic devices with capillary-like microchannels have been developed to monitor storagerelated impairment of RBC deformability during blood banking operations. This proof-of-concept study describes a new method to standardize and improve reproducibility of the RBC deformability measurements using one of these devices.STUDY DESIGN AND METHODS: The rate of RBC flow through the microfluidic capillary network of the microvascular analyzer (MVA) device made of polydimethylsiloxane was measured to assess RBC deformability. A suspension of microbeads in a solution of glycerol in phosphate-buffered saline was developed to be used as an internal flow rate reference alongside RBC samples in the same device. RBC deformability and other in vitro quality markers were assessed weekly in six leukoreduced RBC concentrates (RCCs) dispersed in saline-adenine-glucose-mannitol additive solution and stored over 42 days at 4°C. RESULTS:The use of flow reference reduced deviceto-device measurement variability from 10% to 2%. Repeated-measure analysis using the generalized estimating equation (GEE) method showed a significant monotonic decrease in relative RBC flow rate with storage from Week 0. By the end of storage, relative RBC flow rate decreased by 22 AE 6% on average. CONCLUSIONS:The suspension of microbeads was successfully used as a flow reference to increase reproducibility of RBC deformability measurements using the MVA. Deformability results suggest an early and late aging phase for stored RCCs, with significant decreases between successive weeks suggesting a highly sensitive measurement method.R ed blood cells (RBCs) are responsible for O 2 and CO 2 transport through blood vessels. 1 The deformability of healthy discoidal RBCs allows their passage through much narrower blood capillaries. 2,3 Over their 120-day lifespan, aging RBCs are prone to various alterations that are countered by beneficial enzymatic activity and shedding of damaged cell components via microvesiculation. RBCs with impaired deformability are trapped in the spleen and liver, and senescent markers are recognized by macrophages, leading to RBCs engulfment and degradation. The senescent RBCs are removed daily resulting in a heterogeneous age distribution of the RBCs in the bloodstream.In blood banking operations, RBCs are separated from other blood components before being dispersed in an additive solution and stored at temperature (T) = 2-6°C, allowing preservation of RBC concentrates (RCCs) for up to 42 days prior to transfusion. 4 During storage, RBCs undergo many changes, which include intracellular [K + ] and [Na + ] imbalance, ATP and 2,3-DPG depletion, cytoskeleton and membrane component alteration, decrease of cellular antioxidant capability, and exposure of markers of senescence. 5 These changes (collectively labeled "storage lesions") result in generation of microvesicles, impairment of deformability and hemolysis, 5-7 and a...

Ocular oximetry, in which blood oxygen saturation is evaluated in retinal tissues, is a promising technique for the prevention, diagnosis and management of many diseases and conditions. However, the development of new tools for evaluating oxygen saturation in the eye fundus has often been limited by the lack of reference tools or techniques for such measurements. In this study, we describe a two-step validation method. The impact of scattering, blood volume fraction and lens yellowing on the oximetry model is investigated using a tissue phantom, while a Monte Carlo model of the light propagation in the eye fundus is used to study the effect of the fundus layered-structure. With this method, we were able to assess the performance of an ocular oximetry technique in the presence of confounding factors and to quantify the impact of the choroidal circulation on the accuracy of the measurements. The presented strategy will be useful to anyone involved in studies based on the eye fundus diffuse reflectance.

No abstract