Microvascular benefits of increasing plasma viscosity and maintaining blood viscosity: Counterintuitive experimental findings

Effects of acute normovolemic hemodilution and allogeneic blood transfusion on postoperative complications of oral and maxillofacial flap reconstruction: a retrospective study

OBJECTIVE

Patients undergoing oral and maxillofacial flap reconstruction often need blood transfusions due to massive blood loss. With the increasing limitations of allogeneic blood transfusion (ABT), doctors are considering acute normovolemic hemodilution (ANH) because of its advantages. By comparing the differences in the (Δ) blood indices and postoperative complications of patients receiving ABT or ANH during the reconstruction and repair of oral and maxillofacial tumor flaps, this study's purpose was to provide a reference for the clinical application of ANH.

METHODS

The clinical data of 276 patients who underwent oral and maxillofacial flap reconstruction from September 25, 2017, to October 11, 2021, in the Department of Oral and Maxillofacial Surgery, Sun Yat-sen Memorial Hospital, were retrospectively analyzed. According to the intraoperative blood transfusion mode, the patients were divided into two groups: ABT and ANH. The differences in the (Δ) blood indices and the incidence of postoperative complications between the groups were analyzed.

RESULTS

Among the 276 patients who had ANH (124/276) and ABT (152/276), there were no differences in (Δ) Hb, (Δ) PT, or (Δ) FIB (P > 0.05), while (Δ) WBC, (Δ) PLT, (Δ) APTT and (Δ) D-dimer were significantly different (P < 0.05). The blood transfusion method was not an independent factor for flap crisis (P > 0.05). The wound infection probability in patients with high post-PTs was 1.953 times greater than that in patients with low post-PTs (OR = 1.953, 95% CI: 1.232 ∼ 3.095, P = 0.004). A normal or overweight BMI was a protective factor for pulmonary infection, and the incidence of pulmonary infection in these patients was only 0.089 times that of patients with a low BMI (OR = 0.089, 95% CI: 0.017 ∼ 0.462). Moreover, a high ASA grade promoted the occurrence of pulmonary infection (OR = 6.373, 95% CI: 1.681 ∼ 24.163). The blood transfusion mode (B = 0.310, β = 0.360, P < 0.001; ANH: ln hospital stay = 2.20 ± 0.37; ABT: ln hospital stay = 2.54 ± 0.42) improved the length of hospital stay.

CONCLUSION

Preoperative and postoperative blood transfusion (Δ) Hb, (Δ) PT, and (Δ) FIB did not differ; (Δ) WBC, (Δ) PLT, (Δ) APTT, and (Δ) D-dimer did differ. There was no difference in the effects of the two blood transfusion methods on flap crisis, incision infection or lung infection after flap reconstruction, but ANH resulted in a 3.65 day shorter average hospital stay than did ABT.

Blood rheology and vascular function in sickle cell trait and sickle cell disease: From pathophysiological mechanisms to clinical usefulness

Sickle cell disease (SCD) is an autosomal recessive disorder. Although the molecular mechanisms at the origin of SCD have been well characterized, its clinical expression is highly variable. SCD is characterized by blood rheological abnormalities, increased inflammation and oxidative stress, and vascular dysfunction. Individuals with only one copy of the mutated β-globin gene have sickle cell trait (SCT) and are usually asymptomatic. The first part of this review focuses on the biological responses of SCT carriers during exercise and on the effects of combined SCT and diabetes on vascular function, several biomarkers and clinical complications. The second part of the review focuses on SCD and shows that the magnitude of red blood cell (RBC) rheological alterations is highly variable from one patient to another, and this variability reflects the clinical and hematological variability: patients with the less deformable RBCs have high hemolytic rate and severe anemia, and are prone to develop leg ulcers, priapism, cerebral vasculopathy, glomerulopathy or pulmonary hypertension. In contrast, SCD patients characterized by the presence of more deformable RBCs (but still rigid) are less anemic and may exhibit increased blood viscosity, which increases the risk for vaso-occlusive events. Several genetic and cellular factors may modulate RBC deformability in SCD: co-existence of α-thalassemia, fetal hemoglobin level, oxidative stress, the presence of residual mitochondria into mature RBCs, the activity of various non-selective cationic ion channels, etc. The last part of this review presents the effects of hydroxyurea and exercise training on RBC rheology and other biomarkers in SCD.

The unpredictable erythrocyte deformability alteration in some hematological disorders: How the classification of primary hyperviscosity syndromes could change

According to Wells classification, it is possible to distinguish the primary hyperviscosity syndromes in polycythemic, sclerocythemic and sieric and/or plasmatic. In polycythemia vera, multiple myeloma, Waldenström's macroglobulinemia, and monoclonal gammopathy of undetermined significance, we have observed an unexpected behaviour of the erythrocyte deformability. This data highlights that the hemorheological alteration present in polycythemia vera has not been related to the increase of RBC mass only, as well as that present in plasmacellular dyscrasias has not been attributable to the increase of plasma viscosity only.The aim of this paper is to suggest some starting points for an accurate reflection, emphasizing the need of a revision of the current classification of primary hyperviscosity syndromes.

Reflections on the unexpected laboratory finding of hemorheological alterations observed in some haematological disorders

Hyperviscosity syndrome is a clinical condition characterized by the slowing of blood flow through the vessels and it may be associated with several diseases. The nosographic classification of primary hyperviscosity conditions (Wells classification 1970) divided the primary hyperviscosity syndromes in polycythaemic, sclerocytemic and sieric. Recent and personal laboratory observations have highlighted an unexpected behaviour of the erythrocyte deformability observed in some haematological disorders such as polycythemia vera, multiple myeloma and monoclonal gammopathy of undetermined significance. The interest of this observation depends on the fact that up to now, according to the Wells classification, the hemorheological alteration present in PV was related to the increase of RBC mass while that present in MM and MGUS was attributable to the abnormality of plasma or serum viscosity only. Through an extensive research among the literature, using MEDLINE/PubMed to identify all published reports on the hyperviscosity syndromes, issues that until now have been dealt with separately will therefore be analyzed in a unique paper, allowing a global view. The aim of this paper is to provide some suggestions for reflection and emphasizing the need of a nosographic framework of hyperviscosity that, probably, deserves to be reviewed.

Hemorrhagic Shock and the Microvasculature

The microvasculature plays a central role in the pathophysiology of hemorrhagic shock and is also involved in arguably all therapeutic attempts to reverse or minimize the adverse consequences of shock. Microvascular studies specific to hemorrhagic shock were reviewed and broadly grouped depending on whether data were obtained on animal or human subjects. Dedicated sections were assigned to microcirculatory changes in specific organs, and major categories of pathophysiological alterations and mechanisms such as oxygen distribution, ischemia, inflammation, glycocalyx changes, vasomotion, endothelial dysfunction, and coagulopathy as well as biomarkers and some therapeutic strategies. Innovative experimental methods were also reviewed for quantitative microcirculatory assessment as it pertains to changes during hemorrhagic shock. The text and figures include representative quantitative microvascular data obtained in various organs and tissues such as skin, muscle, lung, liver, brain, heart, kidney, pancreas, intestines, and mesentery from various species including mice, rats, hamsters, sheep, swine, bats, and humans. Based on reviewed findings, a new integrative conceptual model is presented that includes about 100 systemic and local factors linked to microvessels in hemorrhagic shock. The combination of systemic measures with the understanding of these processes at the microvascular level is fundamental to further develop targeted and personalized interventions that will reduce tissue injury, organ dysfunction, and ultimately mortality due to hemorrhagic shock. Published 2018. Compr Physiol 8:61-101, 2018.

Effects of dance therapy on the selected hematological and rheological indicators in older women

OBJECTIVE

The aim of this study was to analyze the effects of dance therapy on selected hematological and rheological indicators in older women.

METHODS

The study included 30 women (aged 71.8±7.4), and the control group comprised of 10 women of corresponding age. Women from the experimental group were subjected to a five-month dance therapy program (three 45-minute sessions per week); women from the control group were not involved in any regular physical activity. Blood samples from all the women were examined for hematological, rheological, and biochemical parameters prior to the study and five months thereafter.

RESULTS

The dance therapy program was reflected by a significant improvement of erythrocyte count and hematocrit. Furthermore, the dance therapy resulted in a significant increase in the plasma viscosity, while no significant changes in glucose and fibrinogen levels were noted.

CONCLUSIONS

Dance therapy modulates selected hematological parameters of older women; it leads to increase in erythrocyte count and hematocrit level. Dance therapy is reflected by higher plasma viscosity. Concentrations of fibrinogen and glucose are not affected by the dance therapy in older women, suggesting maintenance of homeostasis. Those findings advocate implementation of dance therapy programs in older women.

Partitioning of red blood cell aggregates in bifurcating microscale flows

Microvascular flows are often considered to be free of red blood cell aggregates, however, recent studies have demonstrated that aggregates are present throughout the microvasculature, affecting cell distribution and blood perfusion. This work reports on the spatial distribution of red blood cell aggregates in a T-shaped bifurcation on the scale of a large microvessel. Non-aggregating and aggregating human red blood cell suspensions were studied for a range of flow splits in the daughter branches of the bifurcation. Aggregate sizes were determined using image processing. The mean aggregate size was marginally increased in the daughter branches for a range of flow rates, mainly due to the lower shear conditions and the close cell and aggregate proximity therein. A counterintuitive decrease in the mean aggregate size was apparent in the lower flow rate branches. This was attributed to the existence of regions depleted by aggregates of certain sizes in the parent branch, and to the change in the exact flow split location in the T-junction with flow ratio. The findings of the present investigation may have significant implications for microvascular flows and may help explain why the effects of physiological RBC aggregation are not deleterious in terms of in vivo vascular resistance.

Epoetin beta pegol ameliorates flow-mediated dilation with improving endothelial nitric oxide synthase coupling state in nonobese diabetic rats

Background/Aims

Patients with diabetic nephropathy have a high cardiovascular mortality. Epoetin beta pegol (continuous erythropoietin receptor activator, C.E.R.A.) is a drug for the treatment of renal anemia. In this study, we investigated the effect of C.E.R.A. on vascular endothelial function as evaluated by flow‐mediated dilation (FMD) and the relationship between hematopoiesis and FMD in diabetic nephropathy rats.

Methods

Male Spontaneously Diabetic Torii rats (SDT, 22 weeks old) were used. C.E.R.A. (0.6, 1.2 μg/kg) was administered subcutaneously once every 2 weeks for 8 weeks. At 1 week after last administration (31 weeks old), we assessed FMD in the femoral arteries of anesthetized rats using a high‐resolution ultrasound system. FMD was also measured 1 week after single C.E.R.A. treatment (5.0 μg/kg) to examine the influence of hematopoiesis.

Results

Flow‐mediated dilation was significantly decreased in SDT rats before the start of C.E.R.A. treatment (22 weeks old). Repeated administration of C.E.R.A. dose‐dependently improved FMD in SDT rats (31 weeks old) without changing blood glucose, nitroglycerin‐induced vasodilation, or kidney function. Long‐term administration of C.E.R.A. improved the state of endothelial nitric oxide synthase uncoupling in the femoral arteries of SDT rats, which showed a positive correlation with FMD. On the other hand, there was no correlation between FMD and Hb or Hct in SDT rats. Furthermore, at 1 week after single administration of C.E.R.A., FMD was not significantly improved although hemoglobin levels were comparable with levels following long‐term C.E.R.A. treatment.

Conclusion

Long‐term treatment with C.E.R.A. improved FMD in SDT rats even after onset of endothelial dysfunction.

The effect of red blood cell transfusion on the microcirculation of anemic children

Red blood cell transfusion can improve but also might temporarily reduce the microcirculation. The buccal microcirculation was visualized and total vessel density (TVD) determined with sidestream dark field imaging in 19 pediatric anemic (Hb 7.2 g/dL, 95 % CI 6.5-7.9) oncology or hematology patients receiving red blood cell transfusions (Tx) and in 18 age-matched healthy non-anemic controls. After transfusion, Hb (8.0 g/dL, 95 % CI 7.3-8.6) and TVD increased (14.7 ± 1.7 versus 16.6 ± 2.0 mm/mm(2)) significantly with a concomitant decrease in RBC velocity in medium-sized vessels (pre-Tx 711 ± 199 versus post-Tx 627 ± 163 μm/s). Compared to the controls, pre-Tx TVD (17.5 ± 1.3 mm/mm(2)) was lower and RBC velocity (476 ± 77 μm/s) was significantly higher. After transfusion, TVD and RBC velocity remained significantly lower and higher, respectively. In a subgroup, analysis of the transfused children with infection of TVD at baseline was lower with a larger increase after transfusion compared to anemic children without infection (ΔTVD 3.4 ± 2.6 versus ΔTVD 1.3 ± 1.5 mm/mm(2)).

CONCLUSION

With the rise of hemoglobin after transfusion, significant improvements of tissue perfusion were demonstrated but differences to non-anemic controls persisted. In particular, the microcirculation of anemic oncology patients with infection improved after transfusion.

WHAT IS KNOWN

• Transfusions can improve but also temporarily reduce the microcirculation. • In neonates, transfusion significantly increases total vessel density. What is New: • Pretransfusion, the microcirculation of the anemic children differed significantly from the controls. • After transfusion, the microcirculation improved but still differed from the controls. • These changes were most profound in anemic patients with concurrent infection, therefore transfusion threshholds might need to be higher.

Characterization and physiological effect of tapioca maltodextrin colloid plasma expander in hemorrhagic shock and resuscitation model

Plasma expanders (PEs) are administered fluids to replace blood volume when massive blood loss has occured. Maltodextrin from tapioca starch was selected as a study candidate to prepare a colloid PE due to an uncomplicated production process. The formulations of mixture between tapioca maltodextrin and 0.9 % sodium chloride solution were prepared and then characterized. This was to investigate the effects of a dextrose equivalent (DE) and the concentration on the physical properties. Storage stability of each formulation was also determined and compared with clinically used PE [6 % hydroxyethyl starch (HES), 130/0.4]. The effects on the circulatory system in hamsters with hemorrhagic shock and resuscitation using prepared PE were also investigated. The results showed that low DE value led to high retrogradation, turbidity and viscosity but low colloid osmotic pressure and poor solubility. Among the prepared solutions, tapioca maltodextrin with DE6 at 10 % w/v concentration had comparable properties with 6 % HES 130/0.4. Animals resuscitated with 10 % DE6 PE had improved mean arterial blood pressure similar to those resuscitated with 6 % HES 130/0.4. However, several parameters in animals resuscitated with 10 % DE6 PE were lower than those resuscitated with 6 % HES 130/0.4, i.e., heart rate, functional capillary density. Therefore, if using tapioca maltodextrin for PE, some properties have to be considered and efficiently optimized.

Detection of cellular prion protein in exosomes derived from ovine plasma

Prion protein (PrP) is present at extremely low levels in the blood of animals and its detection is complicated by the poor sensitivity of current standard methodologies. Interesting results have been obtained with recent advanced technologies that are able to detect minute amounts of the pathological PrP (PrPSc), but their efficiency is reduced by various factors present in blood. In this study, we were able to extract cellular PrP (PrPC) from plasma-derived exosomes by a simple, fast method without the use of differential ultracentrifugation and to visualize it by Western blotting, reducing the presence of most plasma proteins. This result confirms that blood is capable of releasing PrP in association with exosomes and could be useful to better study its role in the pathogenesis of transmissible spongiform encephalopathies.

NO supplementation for transfusion medicine and cardiovascular applications

Blood transfusions are used to treat reduced O₂-carrying capacity consequent to anemia. In many cases anemia is caused by a major blood loss, which also creates a state of hypovolemia. Whereas O₂ transport capacity is restored by increasing levels of circulating Hb, transfusion does not resolve the hypoperfusion, the hypoxia and the inflammatory cascades initiated during the anemia and hypovolemia. This explains why blood transfusion is not always an effective treatment and why transfusion of stored blood has been associated with increased morbidity and mortality, especially in patient populations receiving multiple transfusions. Epidemiologic data indicate that adverse events after transfusion are relatively common, having a great impact on the patients outcome and on the costs of public health. In this chapter, we explain why classical transfusion strategies target the reversal of hypoxia only, but do not address the inflammatory cascades initiated during anemic states and the importance of the flow and vascular endothelium interactions. We also establish the relation between red blood cells storage lesions, limited NO bioavailability and transfusion-associated adverse events. Lastly, we explain the potential use of long-lived sources of bioactive NO to reverse the hypoxic inflammatory cascades, promote a sustained increase in tissue perfusion and thereby allow transfusions to achieve their intended goal. The underlying premise is that adverse effects associated with transfusions are intimately linked to vascular dysfunction. Understanding of these mechanisms would lead to novel transfusion medicine strategies to preserve red cell function and to correct for functional changes induced by hemoglobinopathies that affect cell structure and function.

The distribution of whole blood viscosity, its determinants and relationship with arterial blood pressure in the community: cross-sectional analysis from the Gutenberg Health Study

Background:

Blood viscosity has a role in modulating cardiovascular homeostasis; changes in this parameter have been associated with cardiovascular mortality and morbidity. However, it remains unclear whether these changes are (1) involved in the pathophysiology of disease, (2) an epiphenomenon, or (3) the expression of counterregulatory mechanisms. We report data on the normal values of blood viscosity and its association with cardiovascular risk factors, prevalent cardiovascular disease, and blood pressure in a large population-based cohort study.

Methods and results:

Viscosity was calculated using validated formulae and its associations were explored in 15,010 participants (mean 55.0, min–max: 35–74 years old; 49.5% women) from the Gutenberg Health Study as well as in a subgroup of 3223 subjects (61.1% women, mean age 49.2, min–max 35–74 years old) without risk factors or self-reported cardiovascular disease. Age- and gender-adjusted mean values for viscosity were defined. Regression models showed a relationship between classical risk factors and blood viscosity measures; the overall R2 of the multiple linear regression model was however as low as 0.067 and 0.049 for high and low shear stress viscosity, respectively. After correction for cardiovascular risk factors, there was a very mild association between viscosity and prevalent coronary artery disease and heart failure. Systolic, mean and diastolic blood pressure increased with increasing blood viscosity after correction for age and gender.

Conclusions:

We provide reference values for viscosity in a population-based cohort. Blood viscosity decreases in older subjects and shows a very mild association with cardiovascular risk factors and prevalent disease in our cohort. There is a linear positive association between viscosity and blood pressure.

Environmental temperature impact on bone and cartilage growth

Environmental temperature can have a surprising impact on extremity growth in homeotherms, but the underlying mechanisms have remained elusive for over a century. Limbs of animals raised at warm ambient temperature are significantly and permanently longer than those of littermates housed at cooler temperature. These remarkably consistent lab results closely resemble the ecogeographical tenet described by Allen's "extremity size rule," that appendage length correlates with temperature and latitude. This phenotypic growth plasticity could have adaptive significance for thermal physiology. Shortened extremities help retain body heat in cold environments by decreasing surface area for potential heat loss. Homeotherms have evolved complex mechanisms to maintain tightly regulated internal temperatures in challenging environments, including "facultative extremity heterothermy" in which limb temperatures can parallel ambient. Environmental modulation of tissue temperature can have direct and immediate consequences on cell proliferation, metabolism, matrix production, and mineralization in cartilage. Temperature can also indirectly influence cartilage growth by modulating circulating levels and delivery routes of essential hormones and paracrine regulators. Using an integrated approach, this article synthesizes classic studies with new data that shed light on the basis and significance of this enigmatic growth phenomenon and its relevance for treating human bone elongation disorders. Discussion centers on the vasculature as a gateway to understanding the complex interconnection between direct (local) and indirect (systemic) mechanisms of temperature-enhanced bone lengthening. Recent advances in imaging modalities that enable the dynamic study of cartilage growth plates in vivo will be key to elucidating fundamental physiological mechanisms of long bone growth regulation.

Economic considerations on transfusion medicine and patient blood management

In times of escalating health-care cost, it is of great importance to carefully assess the cost-effectiveness and appropriateness of the most resource-consuming health interventions. A long-standing and common clinical practice that has been underestimated in cost and overestimated in effectiveness is the transfusion of allogeneic blood products. Studies show that this intervention comes with largely underestimated service cost and unacceptably high utilisation variability for matched patients, thus adding billions of unnecessary dollars to the health-care expenditure each year. Moreover, a large and increasing body of literature points to a dose-dependent increase of morbidity and mortality and adverse long-term outcomes associated with transfusion whereas published evidence for benefit is extremely limited. This means that transfusion may be a generator for increased hospital stay and possible re-admissions, resulting in additional billions in unnecessary expenditure for the health system. In contrast to this, there are evidence-based and cost-effective treatment options available to pre-empt and reduce allogeneic transfusions. The patient-specific rather than a product-centred application of these multiple modalities is termed patient blood management (PBM). From a health-economic perspective, the expeditious implementation of PBM programmes is clearly indicated. Both patients and payers could benefit from this concept that has recently been endorsed through the World Health Assembly resolution WHA63.12.

Comparative proteomics evaluation of plasma exosome isolation techniques and assessment of the stability of exosomes in normal human blood plasma

Exosomes are nanovesicles released by a variety of cells and are detected in body fluids including blood. Recent studies have highlighted the critical application of exosomes as personalized targeted drug delivery vehicles and as reservoirs of disease biomarkers. While these research applications have created significant interest and can be translated into practice, the stability of exosomes needs to be assessed and exosome isolation protocols from blood plasma need to be optimized. To optimize methods to isolate exosomes from blood plasma, we performed a comparative evaluation of three exosome isolation techniques (differential centrifugation coupled with ultracentrifugation, epithelial cell adhesion molecule immunoaffinity pull-down, and OptiPrep(TM) density gradient separation) using normal human plasma. Based on MS, Western blotting and microscopy results, we found that the OptiPrep(TM) density gradient method was superior in isolating pure exosomal populations, devoid of highly abundant plasma proteins. In addition, we assessed the stability of exosomes in plasma over 90 days under various storage conditions. Western blotting analysis using the exosomal marker, TSG101, revealed that exosomes are stable for 90 days. Interestingly, in the context of cellular uptake, the isolated exosomes were able to fuse with target cells revealing that they were indeed biologically active.

[Erythrocytes and microvascular tone during acute traumatic haemorrhagic shock]

Haemorrhagic shock remains a leading cause of death in trauma patients. The concept of haematologic damage control is gradually taking place in the management of traumatic haemorrhagic shock. It is based primarily on the early implementation of a quality blood transfusion involving erythrocytes, plasmas and platelets transfusion. Red blood cell transfusion is mainly supported by the oxygen carrier properties of erythrocytes. However, it appears that erythrocytes ability to modulate the bioavailability of nitric oxide (NO) plays a major role in capillary opening and perfusion. Erythrocytes are also actively involved in the processes of hemostasis and coagulation. In this context, it seems difficult to define a threshold of hemoglobin concentration to determine the implementation of a blood transfusion in traumatic haemorrhagic shock.

Preoperative anemia predicts thrombosis and free flap failure in microvascular reconstruction

Patients undergoing microvascular reconstruction are often anemic from a combination of iatrogenic hemodilution and acute blood losses. No major clinical study describes the impact of preoperative anemia on free flap morbidity. The plastic surgery service at a high-volume academic center performed 156 free flaps among 147 patients from December 2005 to December 2010. One hundred thirty-two had a preoperative hemoglobin (Hb) or hematocrit (Hct), with mean values of 11.8±2.4 g/dL and 35.2%±7.0%, respectively. The overall failure rate was 9% (12/132), primarily from vascular thrombosis (6/12). Through logistic regression analysis, Hb and Hct were significant predictors of flap failure (P<0.005) and vascular thrombosis (P<0.05). Fisher exact test revealed a significant increase in failure risk at Hct level less than 30% (Hb<10 g/dL) (relative risk, 4.76, P=0.006), and probit analysis demonstrated an exposure-response relationship to decreased Hct level (P<0.005). These findings support that preoperative anemia could significantly impact free flap morbidity.

Red blood cell volume and the capacity for exercise at moderate to high altitude

Hypoxia-stimulated erythropoiesis, such as that observed when red blood cell volume (RCV) increases in response to high-altitude exposure, is well understood while the physiological importance is not. Maximal exercise tests are often performed in hypoxic conditions following some form of RCV manipulation in an attempt to elucidate oxygen transport limitations at moderate to high altitudes. Such attempts, however, have not made clear the extent to which RCV is of benefit to exercise at such elevations. Changes in RCV at sea level clearly have a direct influence on maximal exercise capacity. Nonetheless, at elevations above 3000 m, the evidence is not that clear. Certain studies demonstrate either a direct benefit or decrement to exercise capacity in response to an increase or decrease, respectively, in RCV whereas other studies report negligible effects of RCV manipulation on exercise capacity. Adding to the uncertainty regarding the importance of RCV at high altitude is the observation that Andean and Tibetan high-altitude natives exhibit similar exercise capacities at high altitude (3900 m) even though Andean natives often present with a higher percent haematocrit (Hct) when compared with both lowland natives and Tibetans. The current review summarizes past literature that has examined the effect of RCV changes on maximal exercise capacity at moderate to high altitudes, and discusses the explanation elucidating these seemingly paradoxical observations.

Autoregulation and mechanotransduction control the arteriolar response to small changes in hematocrit

Here, we present an analytic model of arteriolar mechanics that accounts for key autoregulation mechanisms, including the myogenic response and the vasodilatory effects of nitric oxide (NO) in the vasculature. It couples the fluid mechanics of blood flow in arterioles with solid mechanics of the vessel wall and includes the effects of wall shear stress- and stretch-induced endothelial NO production. The model can be used to describe the regulation of blood flow and NO transport under small changes in hematocrit and to analyze the regulatory response of arterioles to small changes in hematocrit. Our analysis revealed that the experimentally observed paradoxical increase in cardiac output with small increases in hematocrit results from the combination of increased NO production and the effects of a strong myogenic response modulated by elevated levels of WSS. Our findings support the hypothesis that vascular resistance varies inversely with blood viscosity for small changes in hematocrit in a healthy circulation that responds to shear stress stimuli. They also suggest beneficial effects independent of changes in O(2) carrying capacity associated with the postsurgical transfusion of one or two units of blood.

The viscous behaviour of HES 130/0.4 (Voluven®) and HES 260/0.45 (Pentaspan®)

PURPOSE

Several fluids are available for volume therapy to address hypovolemia. We focus on two hydroxyethyl starches (HES) available for volume expansion in Canada, HES 130/0.4 (Voluven®) and HES 260/0.45 (Pentaspan®). Although information is available regarding their pharmacokinetic and risk/benefit profiles, this paper examines their viscous properties.

METHODS

Dynamic viscosities of HES 130/0.4 and HES 260/0.45 were measured through capillary viscometry at 21°C and 37°C. The viscosities of the solutions were then measured through a closed flow loop at room temperature across physiologically relevant flow rates that maintained a laminar flow regime.

RESULTS

Measured dynamic viscosity through capillary viscometry for HES 130/0.4 and HES 260/0.45 was 2.76 centipoises (cP) and 7.62 cP, respectively, at 21°C decreasing to 1.74 cP and 4.25 cP, respectively, at 37°C. Pipe flow analysis found that HES 130/0.4 (expiry 02/13) and HES 260/0.45 (expiry 10/10) displayed marginal variation in viscosity suggesting Newtonian behaviour. However, a sample of HES 130/0.4 (expiry 10/10) displayed an appreciable increase in viscosity (13%) at higher flow rates suggesting shear thickening behaviour.

CONCLUSION

This study represents an innovative characterization of not only the viscosity of two commonly utilized HES solutions but also their viscous behaviour across physiologically relevant flow rates. The shear thickening behaviour of a sample of HES 130/0.40 (expiry 10/10) at high flow rates was not expected, and the effect this result may have on endothelial cell function is unknown.

Reversal of anemia with allogenic RBC transfusion prevents post-cardiopulmonary bypass acute kidney injury in swine

Anemia during cardiopulmonary bypass (CPB) is strongly associated with acute kidney injury in clinical studies; however, reversal of anemia with red blood cell (RBC) transfusions is associated with further renal injury. To understand this paradox, we evaluated the effects of reversal of anemia during CPB with allogenic RBC transfusion in a novel large-animal model of post-cardiac surgery acute kidney injury with significant homology to that observed in cardiac surgery patients. Adult pigs undergoing general anesthesia were allocated to a Sham procedure, CPB alone, Sham+RBC transfusion, or CPB+RBC transfusion, with recovery and reassessment at 24 h. CPB was associated with dilutional anemia and caused acute kidney injury in swine characterized by renal endothelial dysfunction, loss of nitric oxide (NO) bioavailability, vasoconstriction, medullary hypoxia, cortical ATP depletion, glomerular sequestration of activated platelets and inflammatory cells, and proximal tubule epithelial cell stress. RBC transfusion in the absence of CPB also resulted in renal injury. This was characterized by endothelial injury, microvascular endothelial dysfunction, platelet activation, and equivalent cortical tubular epithelial phenotypic changes to those observed in CPB pigs, but occurred in the absence of severe intrarenal vasoconstriction, ATP depletion, or reductions in creatinine clearance. In contrast, reversal of anemia during CPB with RBC transfusion prevented the reductions in creatinine clearance, loss of NO bioavailability, platelet activation, inflammation, and epithelial cell injury attributable to CPB although it did not prevent the development of significant intrarenal vasoconstriction and endothelial dysfunction. In conclusion, contrary to the findings of observational studies in cardiac surgery, RBC transfusion during CPB protects pigs against acute kidney injury. Our study underlines the need for translational research into indications for transfusion and prevention strategies for acute kidney injury.

Exogenous nitric oxide prevents cardiovascular collapse during hemorrhagic shock

This study investigated the systemic and microvascular hemodynamic changes related to increased nitric oxide (NO) availability following significant hemorrhage, made available by administration of NO releasing nanoparticles (NO-nps). Hemodynamic responses to hemorrhagic shock were studied in the hamster window chamber. Acute hemorrhage was induced by arterial controlled bleeding of 50% of blood volume, and the resulting hemodynamic parameters were followed over 90 min. Exogenous NO was administered in the form of NO-nps (5mg/kg suspended in 50 μl saline) 10 min following induced hemorrhage. Control groups received equal dose of NO free nanoparticles (Control-nps) and Vehicle solution. Animals treated with NO-nps partially maintained systemic and microvascular function during hypovolemic shock compared to animals treated with Control-nps or the Vehicle (50 μl saline). The continuous NO released by the NO-nps reverted arteriolar vasoconstriction, partially recovered both functional capillary density and microvascular blood flows. Additionally, NO supplementation post hemorrhage prevented cardiac decompensation, and thereby maintained and stabilized the heart rate. Paradoxically, the peripheral vasodilation induced by the NO-nps did not decrease blood pressure, and combined with NO's effects on vascular resistance, NO-nps promoted intravascular pressure redistribution and blood flow, avoiding tissue ischemia. Therefore, by increasing NO availability with NO-nps during hypovolemic shock, it is possible that cardiac stability and microvascular perfusion can be preserved, ultimately increasing survivability and local tissue viability, and reducing hemorrhagic shock sequelae. The relevance, stability, and efficacy of exogenous NO therapy in the form of NO-nps will potentially facilitate the intended use in battlefield and trauma situations.