Reduced oxygen release from erythrocytes by the acceleration-induced flow shift, observed in an oxygen-permeable narrow tube

In vivo photoacoustic assessment of the oxygen saturation changes in the human radial artery: a preliminary study associated with age

SIGNIFICANCE

We demonstrate the potential of probing the sO2 change under blood flow in vivo using photoacoustic (PA) imaging and sheds light on the complex relationship between RBC aggregation and oxygen delivery.

AIM

To conduct in vivo assessments of the sO2 in the radial artery of healthy volunteers and simultaneously probe the relation between the sO2 and hemodynamic behavior such as red blood cell (RBC) aggregation.

APPROACH

The effects of PA-based measurements of blood hemodynamics were studied as a function of the subjects' age (20s, 30s, and 40s). The pulsatile blood flow in the human radial artery of 12 healthy subjects was imaged in the 700 to 900 nm optical wavelength range using a linear array-based PA system.

RESULTS

The PA power when blood velocity is minimum (Pamax) was larger than the one attained at maximum blood velocity (Pamin), consistent with predictions based on the cyclical variation of RBC aggregation during pulsatile flow. The difference between Pamin and Pamax at 800 nm (ΔPa800) increased with age (1.7, 2.2, and 2.6 dB for age group of 20s, 30s, and 40s, respectively). The sO2 computed from Pamax was larger than the one from Pamin.

CONCLUSIONS

The ΔPa800 increased with participant age. The ΔPa800 metric could be a surrogate of noninvasively monitoring the age-induced changes in RBC aggregation. The sO2 change during a cycle of pulsatile blood flow also increased with age, demonstrating that RBC aggregation can affect the sO2 change.

In vitro photoacoustic spectroscopy of pulsatile blood flow: Probing the interrelationship between red blood cell aggregation and oxygen saturation

We investigate the optical wavelength dependence in quantitative photoacoustic (QPA) assessment of red blood cell (RBC) aggregation and oxygen saturation (sO₂ ) during pulsatile blood flow. Experimentally, the pulsatile flow was imaged with a 700 to 900 nm laser using the VevoLAZR. Theoretically, the photoacoustic (PA) signals were computed based on a Green's function integrated with a Monte Carlo simulation of radiant fluence. The pulsatile flow created periodic conditions of RBC aggregation/nonaggregation, altering the aggregate size, and, in turn, the sO₂ . The dynamic range, DR (a metric of change in PA power) from 700 to 900 nm for nonaggregated RBCs, was 5 dB for both experiment and theory. A significant difference in the DR for aggregated RBCs was 1.5 dB between experiment and theory. Comparing the DR at different wavelengths, the DR from nonaggregated to aggregated RBCs at 700 nm was significantly smaller than that at 900 nm for both experiment (4.0 dB < 7.1 dB) and theory (5.3 dB < 9.0 dB). These results demonstrate that RBC aggregation simultaneously affects the absorber size and the absorption coefficient in photoacoustic imaging (PAI) of pulsatile blood flow. This investigation elucidates how QPA spectroscopy can be used for probing hemodynamics and oxygen transport by PAI of blood flow.

Simultaneous assessment of red blood cell aggregation and oxygen saturation under pulsatile flow using high-frequency photoacoustics

We investigate the feasibility of photoacoustic (PA) imaging for assessing the correlation between red blood cell (RBC) aggregation and the oxygen saturation (sO2) in a simulated pulsatile blood flow system. For the 750 and 850 nm illuminations, the PA amplitude (PAA) increased and decreased as the mean blood flow velocity decreased and increased, respectively, at all beat rates (60, 120 and 180 bpm). The sO2 also cyclically varied, in phase with the PAA for all beat rates. However, the linear correlation between the sO2 and the PAA at 850 nm was stronger than that at 750 nm. These results suggest that the sO2 can be correlated with RBC aggregation induced by decreased mean shear rate in pulsatile flow, and that the correlation is dependent on the optical wavelength. The hemodynamic properties of blood flow assessed by PA imaging may be used to provide a new biomarker for simultaneous monitoring blood viscosity related to RBC aggregation, oxygen delivery related to the sO2 and their clinical correlation.

Effects of synthetic colloid and crystalloid solutions on hemorheology in vitro and in hemorrhagic shock

Background

Plasma expanders are commonly used in the management of critically ill patients, which may exhibit altered hemorheology. We evaluated the effects of various synthetic colloids and Lactated Ringer’s (LR) solution on hemorheological parameters in vitro and in a rodent hemorrhagic shock model.

Methods

For the in vitro experiments, rat blood was incubated with hydroxyethyl starch (HES) 130/0.4, HES 200/0.5, succinylated gelatine (GEL), or LR at various ratios. The control consisted of blood without dilution. The hemorheological parameters were measured after a 15-min incubation. For the in vivo study, rats were subjected to a severe volume-controlled hemorrhage and were resuscitated using a colloid solution (HES 130/0.4, HES 200/0.5, or GEL) or LR. The hemorheological parameters were measured 2 h after resuscitation.

Results

The GEL significantly elevated the plasma viscosity compared to the other groups. In the in vitro study, GEL and LR accelerated the erythrocyte aggregation. There was no significant difference between HES 130/0.4, HES 200/0.5, and control groups regarding the aggregation amplitude and index. In the in vivo study, the aggregation amplitude increased significantly in the GEL group compared to the HES 130/0.4, HES 200/0.5, LR, and sham groups. There was no significant difference between the groups with respect to the elongation index in vivo.

Conclusions

Hydroxyethyl starch did not change the erythrocyte aggregation compared to the control. GEL significantly accelerates the erythrocyte aggregation and elevates the plasma viscosity compared to hydroxyethyl starch. The in vitro hemorheological measurements most likely provide hints for the in vivo study.

Erythrocyte aggregation as a cause of slow flow in patients of acute coronary syndromes

BACKGROUND

There are multiple lines of evidence to suggest the role of erythrocyte aggregation (EA) in microcirculatory dysfunction during conditions of very slow flow. Such conditions might develop in the myocardium of patients with acute coronary syndromes (ACS).

METHODS

EA as a function of shear stress was evaluated by using a cell flow properties analyzer (CFA) in a cohort of 91 ACS patients and in 36 patients with non specific chest pain or heart failure at the time of cardiac catheterization.

RESULTS

The ACS group included 34 patients with acute myocardial infarction and 57 patients with unstable angina. In addition, we examined 36 patients who underwent angiography for non specific chest pain or heart failure. A significant (r=0.44, p<0.0005) correlation was found between the concentration of fibrinogen and the average aggregate size (AAS) only when using conditions of very slow flow and applying relatively low (0.15 dyn/cm(2)) shear stress in the ACS group. This correlation decreased and became insignificant when applying shear stress forces of 1 dyn/cm(2) and more. This correlation was nonsignificant for all the 5 shear stress forces (between 0.15 and 4 dyn/cm(2)) in the samples obtained from the non-ACS group.

CONCLUSION

Erythrocytes that are suspended in autologous plasma obtained from patients with ACS tend to aggregate in conditions of very slow flow. These findings might be detrimental in terms of microcirculatory flow in ACS patients and might open new therapeutic options such as the use of low dose thrombolysis following PCI.

Blood rheological properties in patients with atopic dermatitis (AD)

Inflammatory processes and psychological states may mutually enhance each other as well as contribute to haemorheological alterations. The objective of the recent study was to determine blood rheological profile in patients with AD at different clinical stages. Blood rheology, as estimated by blood viscosity as well as deformability (elongation index-EI) and aggregation of erythrocytes (aggregation half time (AT1/2)--expressing the kinetic aspects and syllectogram amplitude (AMP)--representing total aggregation extent) were measured in 25 female AD patients, who showed clinical features of mild to severe AD and in 14 healthy subjects. There were no significant differences in blood rheological properties between patients with mild AD and the controls. A significant decrease in erythrocytes AT1/2 and AMP as well as EI were observed in severe AD patients as compared to other groups. Whole blood and plasma viscosity were similar in all groups. Both erythrocytes deformability and aggregation may be affected by pathophysiological processes associated with AD. Only AD patients with severe skin changes showed increased aggregability and decreased deformability of erythrocytes, suggesting that the phenomenon might be related to the disease activity.

Increased strength of erythrocyte aggregates in blood of patients with inflammatory bowel disease

BACKGROUND

Increased strength of red blood cell (RBC) aggregates are present during the acute inflammatory response and contribute to erythrocyte aggregation and may lead to microvascular dysfunction. Inflammatory bowel diseases (IBDs) are characterized by damage to the bowel wall. This damage may be at least partially attributed to microvascular ischemia caused by enhanced erythrocyte aggregation. The aim of this study was to evaluate the strength of RBC aggregates in the blood of patients with IBD.

METHODS

The strengths of RBC aggregates were characterized by integrative RBC aggregation parameters, determined by measuring of RBC aggregation as a function of shear stress. The results are represented as the area under the curve (AUC) of aggregate size plotted against shear stress. For each patient, dynamic aggregation and disaggregation of RBC were recorded and analyzed according to the RBC aggregate size distribution at the different shear stresses. Aggregation indices were correlated with disease activity and inflammatory biomarkers.

RESULTS

We examined 53 IBD patients and 63 controls. IBD patients had significantly elevated concentrations of inflammation-sensitive proteins and aggregation parameters. The strength of large aggregates, represented by AUC for large fraction aggregates, among patients (15.2 +/- 18.6) was double that of controls (7 +/- 10.9) (P = 0.006). The strength of large aggregates correlated with disease activity (r = 0.340; P < 0.001) with concentration of fibrinogen (r = 0.575; P < 0.001) and with concentration of high sensitivity C-reactive protein (r = 0.386; P < 0.001).

CONCLUSIONS

The strength of RBC aggregates is increased in patients with IBD and correlates with the intensity of the acute phase response. This could contribute to bowel damage in these diseases.

A Hemodynamic Study on a Marginal Cell Depletion Layer of Blood Flow Inside a Microchannel

Biological flows, especially blood flow, have attracted a great deal of attention from fluid engineering and hemodynamic investigation fields with advances in bio-technology. The flow of blood carries dissolved gases, nutrients, hormones, and metabolic waste through the circulatory system in the human body. In the present study, the characteristics of blood flow inside a microchannel are investigated by using a micro-particle image velocimetry (micro-PIV) and an optical image processing technique. The motion of red blood cells (RBCs) was visualized with a high-speed CCD camera. The microchannel is made of polydimethylsiloxane (PDMS) material and a slide-glass is attached to the top. The thickness of the margin cell depletion layer is calculated from an acquired raw image through the image processing method, with variations in microchannel width.

Association of metabolic syndrome with white blood cell subtype and red blood cells

Inflammation and thrombogenesis have been suggested as possible causes for cardiovascular events in patients suffering from metabolic syndrome (MS). The primary objective of this study was to determine the relationship between red blood cell (RBC) or white blood cell (WBC) subtypes and MS. The secondary objective was to reveal any gender differences inherent to this association. Body mass index (BMI), blood pressure, serum high-density lipoprotein cholesterol, triglycerides, and glucose were measured. The numbers of WBC subtypes and RBCs were determined in healthy adults. In male subjects, the numbers of total leukocytes, neutrophils, and lymphocytes was elevated in the MS patients (P<0.05). In the male subjects, the numbers of total leukocytes, neutrophils, and lymphocytes were elevated in accordance with the metabolic component count (P<0.05). RBC, monocyte, eosinophil, and basophil counts did not differ in accordance with metabolic component counts (r = 0.406, r = 0.304, r = 0.366; P<0.05). In the female subjects, we determined there to be no differences in the numbers of RBC and WBC subtypes in the MS patients, in accordance with metabolic component counts. The numbers of total leukocytes, neutrophils, and lymphocytes were elevated in the male MS subjects in this study, and these counts increased in accordance with the metabolic component counts. In the female subjects in this study, we determined there to be no association between RBC and WBC subtype counts with MS.

Plasma dependent reduction in red blood cell aggregation after dextran sulfate low-density lipoprotein apheresis--implications for rheological studies

Red blood cell (RBC) aggregation is increased in familial hypercholesterolemia, and is reduced significantly after low density lipoprotein (LDL) apheresis. The purpose of the present study was to clarify whether this reduction depends on changes in plasma composition, RBC membrane properties, or both. RBC aggregation was determined in a computerized cell flow-properties analyzer, before and after LDL apheresis. We compared RBC aggregation in autologous plasma with aggregation in a plasma-free standard solution (0.5% of dextran 500 kDa) to define the separate contributions of plasma and cellular properties to the observed RBC aggregation. RBC aggregation in autologous plasma was reduced by 35.5% after LDL apheresis (P=0.01) but was not significantly affected when measured in dextran 500. This suggests that LDL apheresis attenuated RBC aggregation by altering plasma composition rather than RBC membrane properties. These results are relevant to the understanding of hemorheological changes which follow therapeutic apheresis in hypercholesterolemic patients.

Inflammation-sensitive proteins and erythrocyte aggregation in atherothrombosis

OBJECTIVE

To find the relative contribution of various inflammation-sensitive proteins including fibrinogen, immunoglobulins (IgG, IgM and IgA), ceruloplasmin and high sensitivity C-reactive protein (hs-CRP) to the induction and/or maintenance of enhanced erythrocyte adhesiveness/aggregation in the peripheral blood of individuals with atherothrombotic risk factors.

METHODS

The degree of erythrocyte adhesiveness/aggregation was determined by a simple slide test and image analysis. In addition, we measured various inflammation-sensitive protein levels including fibrinogen, ceruloplasmin, immunoglobulins and hs-CRP in a group of 234 individuals with atherothrombotic risk factors and healthy ones. Pearson partial correlations and multiple linear regression analysis were performed.

RESULTS

Fibrinogen was found to be the major protein contributing to the enhanced erythrocyte adhesiveness/aggregation, explaining 30% of the model. Fibrinogen and IgG together explained 32.4% of the model. Other inflammation-sensitive proteins did not reach statistical significance and were excluded from the model.

CONCLUSIONS

Among inflammation-sensitive proteins measured in our cohort, fibrinogen is the dominant contributor to erythrocyte adhesiveness/aggregation in the peripheral blood of individuals with atherothrombotic risk factors and healthy ones. These findings may pave the way for the development of therapeutic strategies directed at the attenuation of erythrocyte aggregability in individuals with atherothrombosis.

Inflammation-related erythrocyte aggregation in patients with inflammatory bowel disease

Chronic inflammation is associated with increased erythrocyte adhesiveness/aggregation. This might have deleterious effects on the microcirculatory flow and tissue oxygenation. We aimed to determine the degree of erythrocyte adhesiveness/aggregation in the peripheral blood of individuals with inflammatory bowel disease (IBD). Fifty-two patients (24 women and 28 men) with ulcerative colitis (UC) at a mean age of 44.0+/-16.8 years and 96 patients (44 women and 52 men) with Crohn's disease (CD) at a mean age of 38.0+/-15.5 years, with various degrees of disease activity, were matched to normal controls. A simple slide test and image analysis were used to determine the degree of erythrocyte adhesiveness/aggregation. CD activity index (CDAI) was determined in patients with CD, while clinical colitis activity index was applied for patients with UC. A significant (P < 0.0005) increment in the degree of erythrocyte adhesiveness/aggregation was noted in both groups of IBD patients compared with matched control groups. This increment was evident even in individuals with a low index of disease activity and during remission. The highly significant correlation with the concentrations of fibrinogen suggests that the degree of erythrocyte adhesiveness/aggregation is an inflammation-related phenomenon. An enhanced state of erythrocyte adhesiveness/aggregation was noted in the peripheral blood of patients with IBD. This might have a deleterious effect on intestinal microcirculatory flow and tissue oxygenation.

Association of components of the metabolic syndrome with the appearance of aggregated red blood cells in the peripheral blood. An unfavorable hemorheological finding

BACKGROUND

Components of the metabolic syndrome are associated with low-grade inflammation. This can be accompanied by the synthesis of sticky proteins and erythrocyte aggregation.

METHODS

The degree of erythrocyte aggregation was evaluated by a simple slide test and image analysis along with other markers of the acute-phase response, including the white blood cell count (WBCC), erythrocyte sedimentation rate (ESR), fibrinogen and high sensitivity C-reactive protein (hs-CRP) concentrations. Patients were categorized in four groups according to the absence or presence of 1, 2 and 3 or more components of the metabolic syndrome.

RESULTS

We examined a total of 1447 individuals (576 women and 871 men) who gave their informed consent for participation. A significant cardiovascular risk factors, age and hemoglobin adjusted correlation was noted between the degree of erythrocyte aggregation and the number of components of the metabolic syndrome (r = 0.17, p < 0.0005). This correlation was better than that observed for clottable fibrinogen (r = 0.13 p < 0.0005), for ESR (r = 0.11 p < 0.0005) or WBCC (r = 0.13 p < 0.0005). A somewhat better correlation was noted for hs-CRP (r = 0.26 p < 0.0005).

CONCLUSIONS

The multiplicity of components of the metabolic syndrome is associated with enhanced erythrocyte aggregation, probably related to the presence of multiple adhesive macromolecules in the peripheral blood. The enhanced aggregation might contribute to capillary slow flow, tissue deoxygenation as well as vasomotor tone changes in the presence of multiple components of this syndrome.

The degree of red blood cell aggregation on peripheral blood glass slides corresponds to inter-erythrocyte cohesive forces in laminar flow

OBJECTIVE

To determine the degree of correlation between red blood cell (RBC) aggregation on peripheral blood glass slides (PBGS) as determined by image analysis and the inter-erythrocytic cohesive forces as determined in a computerized cell flow properties analyzer (CFA).

STUDY DESIGN

RBC aggregation was assessed using both systems simultaneously in healthy volunteers, obese patients and hypercholesterolemic individuals before and following LDL apheresis.

RESULTS

A significant (r = 0.5, p < 0.001) correlation was noted between the flow-dependent average aggregate size (AAS) obtained in the CFA and the degree of RBC aggregation on peripheral blood glass slides. Moreover, the enhanced RBC aggregation on the slides was positively associated with the appearance of larger aggregates in the CFA (r = 0.5, p < 0.001) and inversely with the formation of smaller aggregates (r = -0.27, p < 0.04). A similar reduction in RBC aggregation following LDL apheresis was noted in both systems.

CONCLUSIONS

The phenomenon of RBC aggregation on peripheral blood glass slides is governed by significant inter-erythrocytic cohesive forces and is not a result of a mere coincidental superimposition of cells. The slide test offers a rapid and simple method of evaluating rheologically significant RBC aggregation, and may allow stratification of patients at risk for atherothrombosis.

O2 release from Hb vesicles evaluated using an artificial, narrow O2-permeable tube: comparison with RBCs and acellular Hbs

A phospholipid vesicle that encapsulates a concentrated hemoglobin (Hb) solution and pyridoxal 5'-phosphate as an allosteric effector [Hb vesicle (HbV) diameter, 250 nm] has been developed to provide an O2 carrying ability to plasma expanders. The O2 release from flowing HbVs was examined using an O2-permeable, fluorinated ethylenepropylene copolymer tube (inner diameter, 28 microm) exposed to a deoxygenated environment. Measurement of O2 release was performed using an apparatus that consisted of an inverted microscope and a scanning-grating spectrophotometer with a photon-count detector, and the rate of O2 release was determined based on the visible absorption spectrum in the Q band of Hb. HbVs and fresh human red blood cells (RBCs) were mixed in various volume ratios at a Hb concentration of 10 g/dl in isotonic saline that contained 5 g/dl albumin, and the suspension was perfused at the centerline flow velocity of 1 mm/s through the narrow tube. The mixtures of acellular Hb solution and RBCs were also tested. Because HbVs were homogeneously dispersed in the albumin solution, increasing the volume of the HbV suspension resulted in a thicker marginal RBC-free layer. Irrespective of the mixing ratio, the rate of O2 release from the HbV/RBC mixtures was similar to that of RBCs alone. On the other hand, the addition of 50 vol% of acellular Hb solution to RBCs significantly enhanced the rate of deoxygenation. This outstanding difference in the rate of O2 release between the HbV suspension and the acellular Hb solution should mainly be due to the difference in the particle size (250 vs. 7 nm) that affects their diffusion for the facilitated O2 transport.

Changes of RBC aggregation in oxygenation-deoxygenation: pH dependency and cell morphology

The effects of the oxygenation-deoxygenation process on red blood cell (RBC) aggregation were examined in relation to morphological changes in RBCs and the contribution of CO(2). A low-shear rheoscope was used to measure the rate of rouleaux (one-dimensional aggregate) formation in diluted autologous plasma exposed to gas mixtures with different Po(2) and Pco(2). RBC indexes and RBC suspension pH were measured for the oxygenated or the deoxygenated condition, and the cell shape was observed with a scanning electron microscope. In the oxygenation-deoxygenation process, the rate of rouleaux formation increased with rising pH of the RBC suspension, which was lowered in the presence of CO(2). The rate increased with increasing mean corpuscular hemoglobin concentration (thus the cells shrank), which increased with rising pH and decreased in the presence of CO(2). With rising pH, cell diameter increased and cell thickness decreased (thus the cell flattened). In addition, slight echinocytosis was induced in the presence of CO(2), and the aggregation was reduced by the morphological change. In conclusion, RBC aggregation in the oxygenation-deoxygenation process is mainly influenced by the pH-dependent change in the surface area-to-volume ratio of the cells, and the aggregation is modified by CO(2)-induced acidification and the accompanying changes in mean corpuscular hemoglobin concentration and cell shape.