Erythrocyte sedimentation: Effect of aggregation energy on gel structure during collapse

Advances in Red Blood Cells Research

This Editorial 'Advances in Red Blood Cell Research' is the preface for the special issue with the same title which files 14 contributions listed in Table 1 [...].

Early stage of erythrocyte sedimentation rate test: Fracture of a high-volume-fraction gel

Erythrocyte sedimentation rate (ESR) is a clinical parameter used as a nonspecific marker for inflammation, and recent studies have shown that it is linked to the collapse of the gel formed by red blood cells (RBCs) at physiological hematocrits (i.e. RBC volume fraction). Previous research has suggested that the observation of a slower initial dynamics is related to the formation of fractures in the gel. Moreover, RBC gels present specific properties due to the anisotropic shape and flexibility of the RBCs. Namely, the onset of the collapse is reached earlier and the settling velocity of the gel increases with increasing attraction between the RBCs, while the gel of spherical particles shows the opposite trend. Here, we report experimental observations of the gel structure during the onset of the collapse. We suggest an equation modeling this initial process as fracturing of the gel. We demonstrate that this equation provides a model for the motion of the interface between blood plasma and the RBC gel, along the whole time span. We also observe that the increase in the attraction between the RBCs modifies the density of fractures in the gel, which explains why the gel displays an earlier onset when the aggregation energy between the RBCs increases. Our work uncovers the detailed physical mechanism underlying the ESR and provides insights into the fracture dynamics of an RBC gel. These results can improve the accuracy of clinical measurements.

The Impact of COVID-19 on Cellular Factors Influencing Red Blood Cell Aggregation Examined in Dextran: Possible Causes and Consequences

Several studies have indicated that COVID-19 can lead to alterations in blood rheology, including an increase in red blood cell aggregation. The precise mechanisms behind this phenomenon are not yet fully comprehended. The latest findings suggest that erythrocyte aggregation significantly influences microcirculation, causes the formation of blood clots in blood vessels, and even damages the endothelial glycocalyx, leading to endothelial dysfunction. The focus of this research lies in investigating the cellular factors influencing these changes in aggregation and discussing potential causes and implications in the context of COVID-19 pathophysiology. For this purpose, the aggregation of erythrocytes in a group of 52 patients with COVID-19 pneumonia was examined in a 70 kDa Dextran solution, which eliminates the influence of plasma factors. Using image analysis, the velocities and sizes of the formed aggregates were investigated, determining their porosity. This study showed that the process of erythrocyte aggregation in COVID-19 patients, independent of plasma factors, leads to the formation of more compact, denser, three-dimensional aggregates. These aggregates may be less likely to disperse under circulatory shear stress, increasing the risk of thrombotic events. This study also suggests that cellular aggregation factors can be responsible for the thrombotic disorders observed long after infection, even when plasma factors have normalized. The results and subsequent broad discussion presented in this study can contribute to a better understanding of the potential complications associated with increased erythrocyte aggregation.

Biomechanical Investigation of Red Cell Sedimentation Using Blood Shear Stress and Blood Flow Image in a Capillary Chip

Blood image intensity has been used to detect erythrocyte sedimentation rate (ESR). However, it does not give information on the biophysical properties of blood samples under continuous ESR. In this study, to quantify mechanical variations of blood under continuous ESR, blood shear stress and blood image intensity were obtained by analyzing blood flows in the capillary channel. A blood sample is loaded into a driving syringe to demonstrate the proposed method. The blood flow rate is set in a periodic on-off pattern. A blood sample is then supplied into a capillary chip, and microscopic blood images are captured at specific intervals. Blood shear stress is quantified from the interface of the bloodstream in the coflowing channel. τ0 is defined as the maximum shear stress obtained at the first period. Simultaneously, ESRτ is then obtained by analyzing temporal variations of blood shear stress for every on period. AII is evaluated by analyzing the temporal variation of blood image intensity for every off period. According to the experimental results, a shorter period of T = 4 min and no air cavity contributes to the high sensitivity of the two indices (ESRτ and AII). The τ0 exhibits substantial differences with respect to hematocrits (i.e., 30-50%) as well as diluents. The ESRτ and AII showed a reciprocal relationship with each other. Three suggested properties represented substantial differences for suspended blood samples (i.e., hardened red blood cells, different concentrations of dextran solution, and fibrinogen). In conclusion, the present method can detect variations in blood samples under continuous ESR effectively.

Red blood cell sedimentation rate measurements in a high aspect ratio microchannel

BACKGROUND

The erythrocyte sedimentation rate (ESR) test is commonly used in clinical practice for monitoring, screening and diagnosing pathological conditions and diseases related to the inflammatory response of the immune system. Several ESR techniques have been developed over the years improving the reliability, the precision and the duration of the measurement.

OBJECTIVE

In the present study a new low cost micro-ESR technique is described providing the major advantage of reducing the measurement time and the blood sample volume by multiple times compared to the commercial methods.

METHODS

Blood samples were obtained from healthy donors within the age group of 24-28 years and the haematocrit was adjusted to 30%, 40% and 50%. The ESR of the samples was measured utilizing a surface tension driven (STD) microfluidic chip and a monitoring device.

RESULTS

The evaluation of the method showed a high correlation (0.94, p < 10-5) at all haematocrit levels with the commercial instrument indicating the feasibility of the technique.

CONCLUSIONS

This micro-ESR technique provides the potential for a simple, low cost and fast tool for ESR measurement using low blood volume acquired by finger prick.

Red Blood Cell Sedimentation Index Using Shear Stress of Blood Flow in Microfluidic Channel

Red blood cell sedimentation has been used as a promising indicator of hematological diseases and disorders. However, to address several issues (i.e., syringe installation direction, blood on-off flow control, image-based quantification, and hemodilution) raised by the previous methods, it is necessary to devise a new method for the effective quantification of red blood cell sedimentation under a constant blood flow. In this study, the shear stress of a blood flow is estimated by analyzing an interface in a co-flowing channel to quantify the red blood cell sedimentation in blood syringes filled with blood (hematocrit = 50%). A red blood cell sedimentation index is newly suggested by analyzing the temporal variations in the shear stress. According to the experimental investigation, the sedimentation index tends to decrease at a higher flow rate. A higher level of hematocrit has a negative influence on the sedimentation index. As a performance demonstration of the present method, the red blood cell sedimentation processes of various test bloods were quantitatively compared in terms of the shear stress, image intensity, and sedimentation velocity. It was found that the proposed index provided a more than 10-fold increase in sensitivity over the previous method (i.e., image intensity). Additionally, it provided more consistent results than another conventional sedimentation method (sedimentation velocity). In conclusion, the present index can be effectively adopted to monitor the red blood cell sedimentation in a 10-min blood delivery.

Continuous Percoll Gradient Centrifugation of Erythrocytes-Explanation of Cellular Bands and Compromised Age Separation

(1) Background: When red blood cells are centrifuged in a continuous Percoll-based density gradient, they form discrete bands. While this is a popular approach for red blood cell age separation, the mechanisms involved in banding were unknown. (2) Methods: Percoll centrifugations of red blood cells were performed under various experimental conditions and the resulting distributions analyzed. The age of the red blood cells was measured by determining the protein band 4.1a to 4.1b ratio based on western blots. Red blood cell aggregates, so-called rouleaux, were monitored microscopically. A mathematical model for the centrifugation process was developed. (3) Results: The red blood cell band pattern is reproducible but re-centrifugation of sub-bands reveals a new set of bands. This is caused by red blood cell aggregation. Based on the aggregation, our mathematical model predicts the band formation. Suppression of red blood cell aggregation reduces the band formation. (4) Conclusions: The red blood cell band formation in continuous Percoll density gradients could be explained physically by red blood cell aggregate formation. This aggregate formation distorts the density-based red blood cell age separation. Suppressing aggregation by osmotic swelling has a more severe effect on compromising the RBC age separation to a higher degree.

Erythrocyte Sedimentation: Collapse of a High-Volume-Fraction Soft-Particle Gel

The erythrocyte sedimentation rate is one of the oldest medical diagnostic methods whose physical mechanisms remain debatable today. Using both light microscopy and mesoscale cell-level simulations, we show that erythrocytes form a soft-particle gel. Furthermore, the high volume fraction of erythrocytes, their deformability, and weak attraction lead to unusual properties of this gel. A theoretical model for the gravitational collapse is developed, whose predictions are in agreement with detailed macroscopic measurements of the interface velocity.

Cross-talk between red blood cells and plasma influences blood flow and omics phenotypes in severe COVID-19

Coronavirus disease 2019 (COVID-19) is caused by the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) and can affect multiple organs, among which is the circulatory system. Inflammation and mortality risk markers were previously detected in COVID-19 plasma and red blood cells (RBCs) metabolic and proteomic profiles. Additionally, biophysical properties, such as deformability, were found to be changed during the infection. Based on such data, we aim to better characterize RBC functions in COVID-19. We evaluate the flow properties of RBCs in severe COVID-19 patients admitted to the intensive care unit by using microfluidic techniques and automated methods, including artificial neural networks, for an unbiased RBC analysis. We find strong flow and RBC shape impairment in COVID-19 samples and demonstrate that such changes are reversible upon suspension of COVID-19 RBCs in healthy plasma. Vice versa, healthy RBCs resemble COVID-19 RBCs when suspended in COVID-19 plasma. Proteomics and metabolomics analyses allow us to detect the effect of plasma exchanges on both plasma and RBCs and demonstrate a new role of RBCs in maintaining plasma equilibria at the expense of their flow properties. Our findings provide a framework for further investigations of clinical relevance for therapies against COVID-19 and possibly other infectious diseases.