Cell-free layer development and spatial organization of healthy and rigid red blood cells in a microfluidic bifurcation

Bifurcations and branches in the microcirculation dramatically affect blood flow as they determine the spatiotemporal organization of red blood cells (RBCs). Such changes in vessel geometries can further influence the formation of a cell-free layer (CFL) close to the vessel walls. Biophysical cell properties, such as their deformability, which is impaired in various diseases, are often thought to impact blood flow and affect the distribution of flowing RBCs. This study investigates the flow behavior of healthy and artificially hardened RBCs in a bifurcating microfluidic T-junction. We determine the RBC distribution across the channel width at multiple positions before and after the bifurcation. Thus, we reveal distinct focusing profiles in the feeding mother channel for rigid and healthy RBCs that dramatically impact the cell organization in the successive daughter channels. Moreover, we experimentally show how the characteristic asymmetric CFLs in the daughter vessels develop along their flow direction. Complimentary numerical simulations indicate that the buildup of the CFL is faster for healthy than for rigid RBCs. Our results provide fundamental knowledge to understand the partitioning of rigid RBC as a model of cells with pathologically impaired deformability in complex in vitro networks

Red blood cell lingering modulates hematocrit distribution in the microcirculation

The distribution of red blood cells (RBCs) in the microcirculation determines the oxygen delivery and solute transport to tissues. This process relies on the partitioning of RBCs at successive bifurcations throughout the microvascular network, and it has been known since the last century that RBCs partition disproportionately to the fractional blood flow rate, therefore leading to heterogeneity of the hematocrit (i.e., volume fraction of RBCs in blood) in microvessels. Usually, downstream of a microvascular bifurcation, the vessel branch with a higher fraction of blood flow receives an even higher fraction of RBC flux. However, both temporal and time-average deviations from this phase-separation law have been observed in recent studies. Here, we quantify how the microscopic behavior of RBC lingering (i.e., RBCs temporarily residing near the bifurcation apex with diminished velocity) influences their partitioning, through combined in vivo experiments and in silico simulations. We developed an approach to quantify the cell lingering at highly confined capillary-level bifurcations and demonstrate that it correlates with deviations of the phase-separation process from established empirical predictions by Pries et al. Furthermore, we shed light on how the bifurcation geometry and cell membrane rigidity can affect the lingering behavior of RBCs; e.g., rigid cells tend to linger less than softer ones. Taken together, RBC lingering is an important mechanism that should be considered when studying how abnormal RBC rigidity in diseases such as malaria and sickle-cell disease could hinder the microcirculatory blood flow or how the vascular networks are altered under pathological conditions (e.g., thrombosis, tumors, aneurysm)

Red blood cell flow in in-vivo and in-vitro network

The precise partitioning of red blood cells (RBCs) in the complex network of our circulatory system plays a crucial role in delivering oxygen to various organs and tissues. This phenomenon, crucial for overall health, is particularly significant in the context of diseases that impair blood flow, such as diabetes and malaria. The classical Zweifach- Fung effect has provided a foundational model, explaining that daughter branches with higher flow rates collect a greater number of RBCs. However, it has been demonstrated that deviations from this model occur in small capillaries. In the first part of this thesis, through in vivo experiments, we illuminate the phenomenon of lingering RBCs at bifurcations. Notably, we reveal that as the lingering effect increases, deviations from the Zweifach-Fung model become more pronounced. Crucially, a linear correlation emerges between the lingering effect and the deviation from Zweifach-Fung model. Our investigation also investigated the differnces characteristics of bifurcations to pinpoint the origins of this intriguing lingering effect. The second part of our study employs in vitro experiments to analyze the development of the cell-free layer (CFL) after bifurcations, where asymmetrical CFLs manifest in the daughter branches. To facilitate these experiments, we employ a method of RBC rigidification using glutaraldehyde. Our findings paint a distinct picture: the CFL develops at a markedly higher velocity for healthy RBCs compared to rigid RBCs. In sum, this comprehensive exploration of RBC partitioning and CFL development in microvascular bifurcations sheds new light on the intricacies of hemodynamics. Our results offer insights that extend beyond the confines of laboratory experiments, potentially impacting our understanding of blood flow in both health and disease.Die präzise Aufteilung der roten Blutzellen (engl. red blood cells, RBCs) im komplexen Netzwerk unseres Kreislaufsystems spielt eine entscheidende Rolle bei der Sauerstoffversorgung zu den Organen und zum Gewebe. Dieses Phänomen, das für die allgemeine Gesundheit entscheidend ist, hat besonders in Zusammenhang mit Krankheiten, die den Blutfluss beeinträchtigen, wie Diabetes und Malaria, eine hohe Bedeutung. Der so genannte klassische Zweifach-Fung-Effekt hat ein grundlegendes Modell geliefert, das erklärt, dass Gefäße mit höheren Durchflussraten eine größere Anzahl von RBCs aufweisen. Es wurde jedoch gezeigt, dass Abweichungen von diesem Modell in kleinen Kapillaren auftreten. Im ersten Teil dieser Arbeit beleuchten wir durch in-vivo-Experimente ein Phänomen, bei dem RBCs an Verzweigungen verweilen, dem so genannten ”lingering” Effekt. Beachtenswert ist, dass mit zunehmendem Verweilen (engl. lingering) an der Bifurkation die Abweichungen vom Zweifach-Fung-Modell deutlicher werden. Hiebei zeigt sich eine lineare Korrelation zwischen dem Verweileffekt und der Abweichung vom Zweifach-Fung- Modell. Wir untersuchen auch die unterschiedlichen Eigenschaften von Verzweigungen, um die Ursprünge dieses faszinierenden Verweileffekts zu ermitteln. Der zweite Teil unserer Studie verwendet in-vitro-Experimente, um die Entwicklung der zellfreien Schicht (engl. cell-free layer, CFL) nach Verzweigungen zu analysieren, wobei asymmetrische CFLs in den Tochterzweigen auftreten. Zur Durchführung dieser Experimente verwenden wir eine Methode zur Versteifung der RBCs unter Verwendung von Glutaraldehyd. Unsere Ergebnisse zeichnen ein deutliches Bild: die CFL entwickelt sich bei gesunden RBCs im Vergleich zu versteiften RBCs mit einer deutlich höheren Geschwindigkeit. Zusammenfassend liefert diese umfassende Untersuchung der Aufteilung der RBCs und der Entwicklung der CFL in mikrovaskulären Verzweigungen neue Erkenntnisse im Bereich der Hämodynamik. Unsere Ergebnisse bieten Einblicke, die über die Grenzen von Laborexperimenten hinausgehen und möglicherweise unser Verständnis des Blutflusses sowohl in der Gesundheit als auch bei Krankheiten beeinflussen können

Prevalence of depression in rheumatoid arthritis patients and its relationship with disease activity: A cross-sectional study

Background. Depression is a common disorder in rheumatoid arthritis (RA) patients and can affect clinical outcomes. This study was conducted to determine the prevalence of depression and its relationship with disease activity in RA patients. Methods. In this cross-sectional study, 144 patients with RA were recruited from the Rheumatology Outpatients Clinic, Mostafa Khomeini Hospital Ilam, and were examined for disease activity and depression symptoms. Disease activity was assessed by DAS28 using laboratory tests and physical examination. The Beck self-report questionnaire was used for measuring depression disorder. Data were analyzed using the linear regression models in STATA 14 software. Results. The prevalence of depression in the sample was 61%. Multivariate analyses showed that patients with severe disease activity faced a significantly greater risk of depression compared to those with mild disease activity. Average levels increased by about 12.43 points in depression for patients with severe disease activity compared to those with mild disease activity. This association was statistically significant after adjusting for the model's other predictors (P<0.001). Furthermore, predicted models showed that the probability of depression increased with age and disease duration in patients with severe activity. Conclusion. Considering the relationship between depression and severe RA disease activity, the need to screen RA patients in terms of depression disorder and pay attention to comprehensive mental and physical care and cure for better clinical outcomes seems necessary. Practical Implications. Severe disease activity in RA may have been influenced by a psychological phenomenon such as depression; therefore, it was suggested that depression, as one of the diseases worsening the RA symptoms, should be screened and evaluated. It was also recommended that a comprehensive and multidisciplinary approach should be adopted by seeking assistance from psychiatric and psychological specialists in RA disease management

Cell-free layer development and spatial organization of healthy and rigid red blood cells in a microfluidic bifurcation

peer reviewedBifurcations and branches in the microcirculation dramatically affect blood flow as they determine the spatiotemporal organization of red blood cells (RBCs). Such changes in vessel geometries can further influence the formation of a cell-free layer (CFL) close to the vessel walls. Biophysical cell properties, such as their deformability, which is impaired in various diseases, are often thought to impact blood flow and affect the distribution of flowing RBCs. This study investigates the flow behavior of healthy and artificially hardened RBCs in a bifurcating microfluidic T-junction. We determine the RBC distribution across the channel width at multiple positions before and after the bifurcation. Thus, we reveal distinct focusing profiles in the feeding mother channel for rigid and healthy RBCs that dramatically impact the cell organization in the successive daughter channels. Moreover, we experimentally show how the characteristic asymmetric CFLs in the daughter vessels develop along their flow direction. Complimentary numerical simulations indicate that the buildup of the CFL is faster for healthy than for rigid RBCs. Our results provide fundamental knowledge to understand the partitioning of rigid RBC as a model of cells with pathologically impaired deformability in complex in vitro networks

Cell-Free Layer of Red Blood Cells in a Constricted Microfluidic Channel under Steady and Time-Dependent Flow Conditions

peer reviewedConstricted blood vessels in the circulatory system can severely impact the spatiotemporal organization of red blood cells (RBCs) causing various physiological complications. In laboratory-on-a-chip applications, constrictions are commonly used for cell sorting and plasma separation based on the formation of a cell-free layer (CFL) at the channel boundary. However, such devices usually employ a steady flow, although time-dependent and pulsatile flow conditions enhance many microfluidic operations and possess significant relevance for in vitro studies under physiologically relevant flow conditions. In this study we examine the CFL dynamics in a constricted microchannel under steady and time-dependent flow. Therefore, we develop an image-processing routine that allows us to resolve the spatiotemporal evolution of the CFL under time-dependent driving of the flow with arbitrary waveform. First, we perform a characterization of the CFL and the cell-free area (CFA) before and after the constriction under steady flow conditions. Second, we employ our method to study the effect of the hematocrit and the parameters of the flow modulations on the CFL and CFA using a sinusoidal pressure profile. Our results highlight the dominant effects of the RBC concentration and the amplitude of the applied pressure signal predominantly on the CFA dynamics. Moreover, we observe a dampening of the CFA amplitude with increasing hematocrit or decreasing pressure amplitude, and a peculiar phase shift of the CFA oscillations pre- and postconstriction. Complementary numerical simulations reveal how the time-dependent CFA dynamics are coupled with the dynamically changing flow field at the constriction. Due to the increasing demand for investigations and applications under time-dependent flow conditions, our study provides crucial insight into the flow behavior of complex fluids in unsteady microscale flows

Effects of cannabinoid receptor type 2 in respiratory syncytial virus infection in human subjects and mice

An accumulating body of evidence suggests that the endocannabinoid system plays a significant role in pathophysiological processes and impacts disease severity. Here we investigate the possible role of a cannabinoid receptor type 2 (CB2) functional variant in determining disease severity and the potential pharmacological therapeutic effects of CB2 activation in viral respiratory infection. The common missense variant (CAA/CGG; Q63R) of the gene-encoding CB2 receptor (CNR2) was evaluated in 90 inpatient and 90 outpatient children with acute respiratory tract infection (ARTI). The frequency distribution of respiratory syncytial virus (RSV)-the main cause of severe cases of bronchiolitis and pneumonia in children-was studied in all collected samples. The mechanism through which CB2 affects clinical outcomes in case of RSV infection was studied in Balb/c mice model using AM630 as a CB2 antagonist. The potential therapeutic effect of CB2 activation during RSV infection was studied using a selective agonist, JWH133. The CB2 Q63R variation was associated with increased risk of hospitalization in children with ARTI. Children carrying the QQ genotype were more prone to developing severe ARTI (OR = 3.275, 95% CI: 1.221–8.705; p = 0.019). Of all the children enrolled in the study, 83 patients (46.1%) were found positive for RSV infection. The associated risk of developing severe ARTI following RSV infection increased more than two-fold in children carrying the Q allele (OR = 2.148, 95% CI: 1.092–4.224; p = 0.026). In mice, the blockade of CB2 by AM630 during RSV infection enhanced the influx of BAL cells and production of cytokines/ chemokines while exaggerating lung pathology. CB2 activation by JWH133 reduces the influx of BAL cells and production of cytokines/chemokines while alleviating lung pathology. Collectively, CB2 is associated with RSV severity during infancy and may serve as a therapeutic target in RSV infection through the alleviation of virus-associated immunopathology