Cardiovascular benefits in moderate increases of blood and plasma viscosity surpass those associated with lowering viscosity: Experimental and clinical evidence

Novel roles of cardiac-derived erythropoietin in cardiac development and function

The role of erythropoietin (EPO) has extended beyond hematopoiesis to include cytoprotection, inotropy, and neurogenesis. Extra-renal EPO has been reported for multiple tissue/cell types, but the physiological relevance remains unknown. Although the EPO receptor is expressed by multiple cardiac cell types and human recombinant EPO increases contractility and confers cytoprotection against injury, whether the heart produces physiologically meaningful amounts of EPO in vivo is unclear. We show a distinct circadian rhythm of cardiac EPO mRNA expression in adult mice and increased mRNA expression during embryogenesis, suggesting physiological relevance to cardiac EPO production throughout life. We then generated constitutive, cardiomyocyte-specific EPO knockout mice driven by the Mlc2v promoter (EPOfl/fl:Mlc2v-cre+/-; EPOΔ/Δ-CM). During cardiogenesis, cardiac EPO mRNA expression and cellular proliferation were reduced in EPOΔ/Δ-CM hearts. However, in adult EPOΔ/Δ- CM mice, total heart weight was preserved through increased cardiomyocyte cross-sectional area, indicating the reduced cellular proliferation was compensated for by cellular hypertrophy. Echocardiography revealed no changes in cardiac dimensions, with modest reductions in ejection fraction, stroke volume, and tachycardia, whereas invasive hemodynamics showed increased cardiac contractility and lusitropy. Paradoxically, EPO mRNA expression in the heart was elevated in adult EPOΔ/Δ-CM, along with increased serum EPO protein content and hematocrit. Using RNA fluorescent in situ hybridization, we found that Epo RNA colocalized with endothelial cells in the hearts of adult EPOΔ/Δ-CM mice, identifying the endothelial cells as a cell responsible for the EPO hyper-expression. Collectively, these data identify the first physiological roles for cardiomyocyte-derived EPO. We have established cardiac EPO mRNA expression is a complex interplay of multiple cell types, where loss of embryonic cardiomyocyte EPO production results in hyper-expression from other cells within the adult heart.

Influence of a Decrease in Blood Viscosity on Arterial Pressure in Normotensive and Spontaneously Hypertensive Rats

We investigated the effect of a decrease in blood viscosity on the mean BP during isovolumic hemodilution and vasodilating activity of the endothelium in normotensive Wistar rats and spontaneously hypertensive rats (SHR). Blood viscosity was reduced by isovolumic hemodilution (replacement of 10% of circulating blood with an equal volume of plasma). Hemodilution caused the same reduction in blood viscosity by 16% in both groups of rats. In Wistar rats, a decrease in blood viscosity did not significantly change in the mean BP; no significant correlations between blood viscosity and mean BP were observed before and after hemodilution. In SHR, a decrease in blood viscosity led to a significant decrease in the mean BP by 18%. Correlations were found between the mean BP and blood viscosity in SHR before (r=0.63; p=0.028) and after (r=0.71; p=0.009) isovolumic hemodilution. In SHR, a decrease in the index of vasodilating activity of the endothelium due to a decrease in the vasodilatory response to intravenous administration of the endothelium-dependent vasodilator acetylcholine was revealed. In SHR, BP passively follows the change, in this case, the decrease in blood viscosity, which attests to impaired BP regulation in response to changes in shear stress on the vascular endothelium caused by the development of endothelial dysfunction in hypertensive animals.

Investigating Causal Effects of Hematologic Traits on Lung Cancer: A Mendelian Randomization Study

BACKGROUND

Observational studies have suggested blood cell counts may act as predictors of cancer. It is not known whether these hematologic traits are causally associated with lung cancer.

METHODS

Two-sample bidirectional univariable Mendelian randomization (MR) and multivariable MR (MVMR) were performed to investigate the causal association between hematologic traits and the overall risk of lung cancer and three histologic subtypes [lung adenocarcinoma, squamous cell lung cancer, and small cell lung cancer (SCLC)]. The instrumental variables of 23 hematologic traits were strictly selected from large-scale genome-wide association studies. Inverse-variance weighted method and five extra methods were used to obtain robust causal estimates.

RESULTS

We found evidence that genetically influenced higher hematocrit [OR, 0.845; 95% confidence interval (CI), 0.783-0.913; P = 1.68 × 10-5] and hemoglobin concentration (OR, 0.868; 95% CI, 0.804-0.938; P = 3.20 × 10-4) and reticulocyte count (OR, 0.923; 95% CI, 0.872-0.976; P = 5.19 × 10-3) decreased lung carcinoma risk, especially in ever smokers. MVMR further identified hematocrit independently of smoking as an independent predictor. Subgroup analysis showed that a higher plateletcrit level increased the risk of small cell lung carcinoma (OR, 1.288; 95% CI, 1.126-1.474; P = 2.25 × 10-4).

CONCLUSIONS

Genetically driven higher levels of reticulocyte count and hematocrit decreased lung cancer risk. Higher plateletcrit had an adverse effect on SCLC. Hematologic traits may act as low-cost factors for lung cancer risk stratification.

IMPACT

Further studies are required to elucidate the potential mechanisms underlying the dysregulation of homeostasis related to hematologic traits, such as subclinical inflammation.

Hypoxia and the Aging Cardiovascular System

Older individuals represent a growing population, in industrialized countries, particularly those with cardiovascular diseases, which remain the leading cause of death in western societies. Aging constitutes one of the largest risks for cardiovascular diseases. On the other hand, oxygen consumption is the foundation of cardiorespiratory fitness, which in turn is linearly related to mortality, quality of life and numerous morbidities. Therefore, hypoxia is a stressor that induces beneficial or harmful adaptations, depending on the dose. While severe hypoxia can exert detrimental effects, such as high-altitude illnesses, moderate and controlled oxygen exposure can potentially be used therapeutically. It can improve numerous pathological conditions, including vascular abnormalities, and potentially slows down the progression of various age-related disorders. Hypoxia can exert beneficial effects on inflammation, oxidative stress, mitochondrial functions, and cell survival, which are all increased with age and have been discussed as main promotors of aging. This narrative review discusses specificities of the aging cardiovascular system in hypoxia. It draws upon an extensive literature search on the effects of hypoxia/altitude interventions (acute, prolonged, or intermittent exposure) on the cardiovascular system in older individuals (over 50 years old). Special attention is directed toward the use of hypoxia exposure to improve cardiovascular health in older individuals.

Comparative Study of Complete Blood Count Between High-Altitude and Sea-Level Residents in West Saudi Arabia

The reduction in oxygen partial pressure at high altitudes leads to diminished oxygen saturation in the arteries, stimulating erythropoietin production and erythropoiesis to restore appropriate oxygenation. While many studies have explored acclimatization to high altitude and its effects on complete blood count (CBC) parameters, our research uniquely examined both male and female healthy individuals, emphasizing the novelty of gender-specific observations. We analyzed 1,160 individuals in Taif (Al Hada), east Saudi Arabia, a high-altitude region, and compared them to 1,044 counterparts in Jeddah, at sea level. Our results revealed significant variations in CBC parameters, including white blood count, red blood count, hemoglobin, hematocrit, platelets, neutrophils, lymphocytes, monocytes, eosinophils, and basophils, reflecting the body's hypoxic response. These variations were observed in both genders, with specific differences noted between males and females. For example, NEU (neutrophils), representing the absolute count of a type of white blood cell essential in the immune system's defense, showed significant variations for males. The male results show that the variation in males between the sea level and high altitudes indicated significant p-values for all CBC parameters except NEU between at sea level (Jeddah city), whose p-value was 0.8696, and at high altitude (Taif city, Al Hada). In contrast, MONO (monocytes), another type of white blood cell involved in immune response, and RBC (red blood cells), responsible for oxygen transport, were mentioned but did not show significant variations for females. The full results for females showed significant results (P<0.0001) for BASO, HCT, HGB, MCH, MCHC, MPV, PLT, RDW, and WBC between the sea-level altitude and high altitude for females. Also, EOS and LYM showed significant P-values of 0.0002 and 0.0001, respectively, while MONO, NEU, and RBC indicated no significance between the sea-level altitude and high altitude for females. The p-values of MONO, NEU, and RBC, respectively, were 0.1907, 0.1259, and 0.0677. The results for both genders combined showed significant variations of all CBC parameters (P<0.0001) between the sea-level altitude and high altitude except for MONO, NEU, and RBC, which were not significant for both males and females, with p-values of 0.1589, 0.2911, and 0.0595, respectively. All unhealthy individuals were excluded from the study with any condition that would cause significant changes in CBC parameters and would skew the results, ensuring a focus on physiological adaptations in healthy subjects. By comparing healthy individuals and examining each gender separately, this study contributes valuable insights into high-altitude acclimatization, enhancing our understanding of physiological adaptations and potentially guiding health management in such environments within the normal range.

Effects of a Maximal Exercise Followed by a Submaximal Exercise Performed in Normobaric Hypoxia (2500 m), on Blood Rheology, Red Blood Cell Senescence, and Coagulation in Well-Trained Cyclists

Acute normoxic exercise impacts the rheological properties of red blood cells (RBC) and their senescence state; however, there is a lack of data on the effects of exercise performed in hypoxia on RBC properties. This crossover study compared the effects of acute hypoxia vs. normoxia on blood rheology, RBC senescence, and coagulation during exercise. Nine trained male cyclists completed both a session in normoxia (FiO₂ = 21%) and hypoxia (FiO₂ = 15.3% ≈ 2500 m). The two sessions were randomly performed, separated by one week, and consisted of an incremental and maximal exercise followed by a 20 min exercise at the first ventilatory threshold (VT1) on a home-trainer. Blood samples were taken before and after exercise to analyze hematological parameters, blood rheology (hematocrit, blood viscosity, RBC deformability and aggregation), RBC senescence markers (phosphatidylserine (PS) and CD47 exposure, intraerythrocyte reactive oxygen species (ROS), and calcium content), and blood clot viscoelastic properties. Hemoglobin oxygen saturation (SpO₂) and blood lactate were also measured. In both conditions, exercise induced an increase in blood viscosity, hematocrit, intraerythrocyte calcium and ROS content, and blood lactate concentration. We also observed an increase in blood clot amplitude, and a significant drop in SpO₂ during exercise in the two conditions. RBC aggregation and CD47 exposure were not modified. Exercise in hypoxia induced a slight decrease in RBC deformability which could be related to the slight increase in mean corpuscular hemoglobin concentration (MCHC). However, the values of RBC deformability and MCHC after the exercise performed in hypoxia remained in the normal range of values. In conclusion, acute hypoxia does not amplify the RBC and coagulation changes induced by an exercise bout.

Another possible determinant for ischemic stroke with nonvalvular atrial fibrillation other than conventional oral anticoagulant treatment: The relationship between whole blood viscosity and stroke☆

OBJECTIVES

Patients with nonvalvular atrial fibrillation (NVAF) still experience ischemic stroke despite recommended medications and this could be the consequence of increased whole blood viscosity (WBV). We evaluated the predictive value of WBV for stroke in patients with NVFA despite receiving oral anticoagulant (OAC) therapy.

METHODS

One thousand and forty-three NVAF patients on OAC medication were followed up for median 36.13 ± 18.31 months. WBV was calculated according to the validated de Simone's formula.

RESULTS

WBV was significantly higher in stroke group when compared to non-stroke group at both low shear rate (LSR) and high shear rate (HSR). Multiple regression analysis demonstrated an independent association between WBV and stroke when adjusted for other risk factors.

CONCLUSIONS

WBV appears to be a profitable predictor of ischemic stroke in patients with NVAF receiving OAC.

Hypoxia and hemorheological properties in older individuals

Hypoxia is caused by insufficient oxygen availability for the organism leading to reduced oxygen delivery to tissues and cells. It has been regarded as a severe threat to human health and it is indeed implicated in pathophysiological mechanisms involved in the development and progression of many diseases. Nevertheless, the potential of controlled hypoxia interventions (i.e. hypoxia conditioning) for improving cardio-vascular health is gaining increased attention. However, blood rheology is often a forgotten factor for vascular health while aging and hypoxia exposure are both suspected to alter hemorheological properties. These changes in blood rheology may influence the benefits-risks balance of hypoxia exposure in older individuals. The benefits of hypoxia exposure for vascular health are mainly reported for healthy populations and the combined impact of aging and hypoxia on blood rheology could therefore be deleterious in older individuals. This review discusses evidence of hypoxia-related and aging-related changes in blood viscosity and its determinants. It draws upon an extensive literature search on the effects of hypoxia/altitude and aging on blood rheology. Aging increases blood viscosity mainly through a rise in plasma viscosity, red blood cell (RBC) aggregation and a decrease in RBC deformability. Hypoxia also causes an increase in RBC aggregation and plasma viscosity. In addition, hypoxia exposure may increase hematocrit and modulate RBC deformability, depending on the hypoxic dose, i.e, beneficial effect of intermittent hypoxia with moderate dose vs deleterious effect of chronic continuous or intermittent hypoxia or if the hypoxic dose is too high. Special attention is directed toward the risks vs. benefits of hemorheological changes during hypoxia exposure in older individuals, and its clinical relevance for vascular disorders.

The effect of whole blood viscosity on contrast-induced nephropathy development in patients undergoing percutaneous coronary intervention

OBJECTIVE

In our study, we aimed to investigate how whole blood viscosity (WBV) affects the development of contrast-induced nephropathy (CIN) in patients undergoing percutaneous coronary intervention (PCI).

METHODS

In our study, 500 patients who applied to the cardiology clinic and underwent PCI for elective procedure, ST segment elevation myocardial infarction (STEMI), and non-STEMI were prospectively included. Before the procedure, we calculated WBV using the formula [(0.12× hematocrit) + (0.17×(total protein - 2.07)]. We defined CIN as the absolute (≥0.5 mg/dl) or relative increase (≥25%) in serum creatinine 48-72 h after exposure to a contrast agent compared with baseline serum creatinine values.

RESULTS

CIN was developed in 69 (13.6%) of the 500 patients in the study. PCI was performed in 206 patients (41.2%) electively, 175 (35%) due to non-STEMI, and 119 (23%) due to STEMI. CIN was observed in 20.2% of the STEMI group, 13.7% of the non-STEMI group, and 10.2% of the elective PCI group. Multivariate logistic regression analysis results show that the independent predictors of CIN are low ejection fraction [OR:0.95 (95% CI:0.92-0.97); p < 0.001], low glomerular filtration rate [OR:0.96 (95% CI:0.95-0.98); p < 0.001], and increased amount of contrast agent [OR:1.008 (95% CI:1.004-1.01); p < 0.001]. When all patients were examined, no significant relationship was found between WBV and CIN. However, in the subgroup evaluation, it was concluded that low WBV was an independent predictor in elective PCI patients [OR:0.60 (95% CI:0.36-0.99); p = 0.04] for CIN.

CONCLUSION

We found that low WBV was an independent predictor of CIN in patients undergoing elective PCI(NCT04703049).

Associations of urinary sodium excretion with central hemodynamics and changes in vascular structure and function at high altitude

Research reports on associations of urinary sodium excretion with central hemodynamic parameters and vascular changes are quite limited in general or non‐hypertensive population. The purpose of the current study was to explore such associations in Chinese general Tibetans living at high altitude. This cross‐sectional study was conducted in Luhuo County, Ganzi Tibetan Autonomous Prefecture with average elevation of 3800 meters from December 2018 to January 2019. A total of 294 Tibetans were included in the current study. Twenty‐four hour urinary sodium excretion was estimated by second fasting spot urine in the morning using Kawasaki formula. Central hemodynamic parameters, including central systolic blood pressure (CSBP), central diastolic blood pressure (CDBP), central pulse pressure (CPP), central mean arterial pressure (CMAP), augmentation pressure (AP), and augmentation index standardized for heart rate of 75 (AIx₇₅), were evaluated using the SphygmoCor system. Vascular structures and functions were assessed by carotid intima media thickness (CIMT) test and brachial ankle pulse wave velocity (baPWV), respectively. Estimated mean 24h urinary sodium excretion of Tibetans in Luhuo County was 5.26±1.61 g. After adjustment, estimated 24h urinary sodium was positively associated with CSBP (β = 1.15, p = .008) and CPP (β = 0.87, p = .013). Line graph of means across urinary sodium quartiles showed that associations of 24 h urinary sodium excretion with AIx₇₅ and baPWV presented approximate “J” shape after controlling for confounders. Estimated 24 h sodium excretion was independently and positively associated with CSBP and CPP. Moreover, association between urinary sodium excretion and arterial elasticity, as evaluated by baPWV and AIx₇₅, presented “J” shape. Further studies are needed to verify J‐shaped association and “safe” zone of sodium intake.

Implication of Blood Rheology and Pulmonary Hemodynamics on Exercise-Induced Hypoxemia at Sea Level and Altitude in Athletes

This study aimed to investigate the changes in blood viscosity, pulmonary hemodynamics, nitric oxide (NO) production, and maximal oxygen uptake (V˙O2max) during a maximal incremental test conducted in normoxia and during exposure to moderate altitude (2,400 m) in athletes exhibiting exercise-induced hypoxemia at sea level (EIH). Nine endurance athletes with EIH and eight without EIH (NEIH) performed a maximal incremental test under three conditions: sea level, 1 day after arrival in hypoxia, and 5 days after arrival in hypoxia (H5) at 2,400 m. Gas exchange and oxygen peripheral saturation (SpO2) were continuously monitored. Cardiac output, pulmonary arterial pressure, and total pulmonary vascular resistance were assessed by echocardiography. Venous blood was sampled before and 3 min after exercise cessation to analyze blood viscosity and NO end-products. At sea level, athletes with EIH exhibited an increase in blood viscosity and NO levels during exercise while NEIH athletes showed no change. Pulmonary hemodynamics and aerobic performance were not different between the two groups. No between-group differences in blood viscosity, pulmonary hemodynamics, and V˙O2max were found at 1 day after arrival in hypoxia. At H5, lower total pulmonary vascular resistance and greater NO concentration were reported in response to exercise in EIH compared with NEIH athletes. EIH athletes had greater cardiac output and lower SpO2 at maximal exercise in H5, but no between-group differences occurred regarding blood viscosity and V˙O2max. The pulmonary vascular response observed at H5 in EIH athletes may be involved in the greater cardiac output of EIH group and counterbalanced the drop in SpO2 in order to achieve similar V˙O2max than NEIH athletes.

The association between thrombotic and inflammatory biomarkers and lower-extremity peripheral artery disease

Lower-extremity peripheral artery disease (LEAD) is associated with increased rates of mortality and morbidity. The aim of this study was to evaluate the associations among inflammatory and thrombotic markers and lower-extremity peripheral disease. A total of 280 patients were enrolled in this study. Of these patients, 152 patients had LEAD on peripheral angiography that was performed because of suspected lower-extremity peripheral disease based on history, physical examination, and non-invasive tests. The control group consisted of 128 patients without LEAD on peripheral angiography. Patients with LEAD were classified according to trans-atlantic inter-society consensus (TASC) II classification. Subsequently, patients in TASC A to B were defined as having mild to moderate peripheral artery disease, and those in TASC C to D were defined as having advanced peripheral artery disease. Thrombotic and inflammatory markers, such as the neutrophil-to-lymphocyte ratio (NLR), the high-sensitivity C (hs-C) reactive protein level, the monocyte-to-high-density lipoprotein-cholesterol ratio, the fibrinogen to albumin ratio (FAR), and whole-blood viscosity at high shear rate (HSR) and low shear rate (LSR), were evaluated in this population. The NLR, the monocyte-to-high-density lipoprotein-cholesterol ratio, the FAR, and whole-blood viscosity, both at a LSR and a HSR, were significantly higher in patients with lower-extremity peripheral disease compared with patients without lower-extremity peripheral disease. We determined that lower-extremity peripheral disease severity was correlated with the NLR, monocyte-to-high-density lipoprotein-cholesterol ratio, FAR, whole-blood viscosity at LSR, and whole-blood viscosity at HSR (r = 0.719, P = .004; r = 0.25, P = .008; r = 0.691, P = .002; r = 0.546, P < .001; and r = 0.448, P = .001, respectively). However hs-C reactive protein levels were similar between patients with or without LEAD (2.47 ± 1.32 1.61 ± 0.91 P = .685). In addition, there was no correlation between the severity of LEAD and hs-C reactive levels. In this study, we determined that the levels of inflammatory and thrombotic biomarkers are elevated in peripheral artery disease, and these levels predict disease severity.

The impact of hypoxaemia on vascular function in lowlanders and high altitude indigenous populations

Exposure to hypoxia elicits widespread physiological responses that are critical for successful acclimatization; however, these responses may induce apparent maladaptive consequences. For example, recent studies conducted in both the laboratory and the field (e.g. at high altitude) have demonstrated that endothelial function is reduced in hypoxia. Herein, we review the several proposed mechanism(s) pertaining to the observed reduction in endothelial function in hypoxia including: (i) changes in blood flow patterns (i.e. shear stress), (ii) increased inflammation and production of reactive oxygen species (i.e. oxidative stress), (iii) heightened sympathetic nerve activity, and (iv) increased red blood cell concentration and mass leading to elevated nitric oxide scavenging. Although some of these mechanism(s) have been examined in lowlanders, less in known about endothelial function in indigenous populations that have chronically adapted to environmental hypoxia for millennia (e.g. the Peruvian, Tibetan and Ethiopian highlanders). There is some evidence indicating that healthy Tibetan and Peruvian (i.e. Andean) highlanders have preserved endothelial function at high altitude, but less is known about the Ethiopian highlanders. However, Andean highlanders suffering from chronic mountain sickness, which is characterized by an excessive production of red blood cells, have markedly reduced endothelial function. This review will provide a framework and mechanistic model for vascular endothelial adaptation to hypoxia in lowlanders and highlanders. Elucidating the pathways responsible for vascular adaption/maladaptation to hypoxia has potential clinical implications for disease featuring low oxygen delivery (e.g. heart failure, pulmonary disease). In addition, a greater understanding of vascular function at high altitude will clinically benefit the global estimated 85 million high altitude residents.

Global REACH 2018: High Blood Viscosity and Hemoglobin Concentration Contribute to Reduced Flow-Mediated Dilation in High-Altitude Excessive Erythrocytosis

Excessive erythrocytosis (EE; hemoglobin concentration [Hb] ≥21 g/dL in adult males) is associated with increased cardiovascular risk in highlander Andeans. We sought to quantify shear stress and assess endothelial function via flow-mediated dilation (FMD) in male Andeans with and without EE. We hypothesized that FMD would be impaired in Andeans with EE after accounting for shear stress and that FMD would improve after isovolemic hemodilution. Brachial artery shear stress and FMD were assessed in 23 male Andeans without EE (age: 40±15 years [mean±SD]; Hb<21 g/dL) and 19 male Andeans with EE (age: 43±14 years; Hb≥21 g/dL) in Cerro de Pasco, Peru (4330 m). Shear stress was quantified from Duplex ultrasound measures of shear rate and blood viscosity. In a subset of participants (n=8), FMD was performed before and after isovolemic hemodilution with blood volume replaced by an equal volume of human serum albumin. Blood viscosity and Hb were 48% and 23% higher (both P<0.001) and FMD was 28% lower after adjusting for the shear stress stimulus ( P=0.013) in Andeans with EE compared to those without. FMD was inversely correlated with blood viscosity ( r²=0.303; P<0.001) and Hb ( r²=0.230; P=0.001). Isovolemic hemodilution decreased blood viscosity by 30±10% and Hb by 14±5% (both P<0.001) and improved shear stress stimulus-adjusted FMD from 2.7±1.9% to 4.3±1.9% ( P=0.022). Hyperviscosity, high Hb, or both, actively contribute to acutely reversible impairments in FMD in EE, suggesting that this plays a pathogenic role in the increased cardiovascular risk.

Relation of Preprocedural Hemoglobin Level to Outcomes After Percutaneous Coronary Intervention

Adverse effects have been reported in patients with preprocedural anemia after percutaneous coronary intervention (PCI), but data regarding the relation between elevated hemoglobin (Hb) level and post-PCI prognosis remain limited. This study assessed the impact of elevated Hb on major adverse cardiac and cerebrovascular event (MACCE) at 12 months, a composite of all-cause mortality, nonfatal myocardial infarction, and ischemic stroke after PCI. We pooled patient-level data from four Korean multicenter drug-eluting stent registries from 2010 to 2016. In total, 5,107 patients were divided into 5 categories according to the baseline Hb level (<10, 10 to 12.9, 13 to 14.9, 15 to 16.9 and ≥17 g/dl). Patients with higher Hb levels were significantly younger, predominantly male, current smokers with higher body mass index, and more frequent dyslipidemia. Hypertension, diabetes, chronic kidney disease, and cerebrovascular accident were more prevalent in lower Hb groups. Categorically, a U-shaped curvilinear relation was observed between baseline Hb and clinical outcomes showing significantly higher MACCE rate in <10g/dl (hazard ratio [HR], 4.62 [2.81 to 7.68]) and ≥17 g/dl (HR, 4.06 [1.57 to 10.5]) groups compared with the reference group (13 to 14.9 g/dl), especially in men. In nonanemic patients (Hb ≥13 g/dl), adjusted HRs of MACCE, mortality, and stroke were significantly higher in ≥17 g/dl group than in the reference group. Furthermore, ≥17 g/dl was an independent predictor for MACCE and all-cause mortality after PCI. In conclusion, not only low Hb but also elevated Hb of ≥17 g/dl was significantly associated with higher MACCE rates and all-cause mortality after PCI. An appropriate treatment strategy for patients with high Hb level should be identified through future studies.

Global Reach 2018: reduced flow-mediated dilation stimulated by sustained increases in shear stress in high-altitude excessive erythrocytosis

Excessive erythrocytosis [EE; hemoglobin concentration (Hb) ≥ 21 g/dL in adult men] is a maladaptive high-altitude pathology associated with increased cardiovascular risk and reduced reactive hyperemia flow-mediated dilation (FMD); however, whether a similar impairment occurs in response to more commonly encountered sustained increases in shear stress [sustained stimulus (SS)-FMD] over a range of overlapping stimuli is unknown. We characterized SS-FMD in response to handgrip exercise in Andeans with and without EE in Cerro de Pasco, Peru (4,330 m). Andean highlanders with EE (n = 17, Hb = 23.2 ± 1.2 g/dL) and without EE (n = 23, Hb = 18.7 ± 1.9 g/dL) performed 3 min of rhythmic handgrip exercise at 20, 35, and 50% of maximum voluntary contraction (MVC). Duplex ultrasound was used to continuously record blood velocity and diameter in the brachial artery, and blood viscosity was measured to accurately calculate shear stress. Although baseline shear stress did not differ, Andeans with EE had 22% lower shear stress than Andeans without at 50% MVC (P = 0.004). At 35 and 50% MVC, SS-FMD was 2.1 ± 2.0 and 2.8 ± 2.7% in Andeans with EE compared with 4.1 ± 3.4 and 7.5 ± 4.5% in those without (P = 0.048 and P < 0.001). The stimulus-response slope (∆shear stress vs. ∆diameter) was lower in Andeans with EE compared with Andeans without (P = 0.028). This slope was inversely related to Hb in Andeans with EE (r² = 0.396, P = 0.007). A reduced SS-FMD in response to small muscle mass exercise in Andeans with EE indicates a generalized reduction in endothelial sensitivity to shear stress, which may contribute to increased cardiovascular risk in this population.NEW & NOTEWORTHY High-altitude excessive erythrocytosis (EE; hemoglobin concentration ≥ 21 g/dL) is a maladaptation to chronic hypoxia exposure and is associated with increased cardiovascular risk. We examined flow-mediated dilation (FMD) in response to sustained elevations in shear stress achieved using progressive handgrip exercise [sustained stimulus (SS)-FMD] in Andean highlanders with and without EE at 4,330 m. Andeans with EE demonstrated lower SS-FMD compared with those without. Heightened hemoglobin concentration was related to lower SS-FMD in Andeans with EE.

Biomechanical Forces and Atherosclerosis: From Mechanism to Diagnosis and Treatment

The article provides an overview of current views on the role of biomechanical forces in the pathogenesis of atherosclerosis. The importance of biomechanical forces in maintaining vascular homeostasis is considered. We provide descriptions of mechanosensing and mechanotransduction. The roles of wall shear stress and circumferential wall stress in the initiation, progression and destabilization of atherosclerotic plaque are described. The data on the possibilities of assessing biomechanical factors in clinical practice and the clinical significance of this approach are presented. The article concludes with a discussion on current therapeutic approaches based on the modulation of biomechanical forces.

The association of estimated whole blood viscosity with hemodynamic parameters and prognosis in patients with heart failure

AIM

We aimed to investigate the association of estimated whole blood viscosity (WBV) with hemodynamic parameters and prognosis in patients with heart failure with reduced ejection fraction.

MATERIALS & METHODS

Total of 542 patients were included and followed-up for median 13 months.

RESULTS

The WBV parameters had negative relationship with right atrium pressure and positive correlation with cardiac index. The WBV parameters were found to be independent predictors of composite end point (CEP) and all-cause mortality. Every one cP increases of WBV(h) and WBV(l) were associated with 17 and 1% reductions of CEP. In Kaplan-Meier analysis, patients with low WBV quartiles were found to have significantly more CEP.

CONCLUSION

Being an easily accessible and costless prognosticator, WBV seems to be a novel marker for determining prognosis and an emerging tool to individualize heart failure with reduced ejection fraction management.

Echocardiography Differentiates Lethally Irradiated Whole-Body From Partial-Body Exposed Rats

Background: Acute radiation syndrome (ARS) affects morbidity and mortality dependent on the amount of body exposed. We propose the use of echocardiography (EC) to differentiate between survivors and non-survivors by measuring changes in cardiac function (CF) and pulmonary arterial function (PAF). We also investigate the role of rheology in our observed changes. Methods and Results: Rats were irradiated to the whole body (WB) or partial body with two-legs shielded (2LS) at a lethal dose of 7.5Gy. EC and magnetic resonance imaging were performed, and rheological measurements conducted. Only 2LS survived past 12-days post-exposure and their CF and PAR were not significantly different from baseline. WB was significantly different from both baseline and 2LS in stroke volume (P < 0.05), velocity time integral (VTI; P < 0.05) and pulmonary artery acceleration time (PAAT; P < 0.05). Differences were identified as early as six-days post-exposure, where VTI and PAAT were significantly (P < 0.05) decreased in WB versus baseline but only PAAT was different from 2LS. Blood viscosity was significantly lower in the WB versus baseline and 2LS (P < 0.0001). WB exhibited a significant rise in dense red blood cells versus baseline (P < 0.01) and 2LS (P < 0.01). Cell-free hemoglobin, a contributor to pulmonary artery hypertension and vasculopathy, was significantly elevated in WB vs. sham. Conclusions: Non-invasive and readily available imaging can be used to identify critically affected victims. Our findings point to heart failure as one possible cause of death in WB exposed animals, potentially exacerbated by rheological, hemolytic, and pulmonary factors, and the importance of developing radiomitigators against cardiac ARS mortality.

Hemolysis During Pediatric Extracorporeal Membrane Oxygenation: Associations With Circuitry, Complications, and Mortality

OBJECTIVES

To describe factors associated with hemolysis during pediatric extracorporeal membrane oxygenation and the relationships between hemolysis, complications, and mortality.

DESIGN

Secondary analysis of data collected prospectively by the Collaborative Pediatric Critical Care Research Network between December 2012 and September 2014.

SETTING

Three Collaborative Pediatric Critical Care Research Network-affiliated hospitals.

PATIENTS

Age less than 19 years and treated with extracorporeal membrane oxygenation.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Hemolysis was defined based on peak plasma free hemoglobin levels during extracorporeal membrane oxygenation and categorized as none (< 0.001 g/L), mild (0.001 to < 0.5 g/L), moderate (0.5 to < 1.0 g/L), or severe (≥ 1.0 g/L). Of 216 patients, four (1.9%) had no hemolysis, 67 (31.0%) had mild, 51 (23.6%) had moderate, and 94 (43.5%) had severe. On multivariable analysis, variables independently associated with higher daily plasma free hemoglobin concentration included the use of in-line hemofiltration or other continuous renal replacement therapy, higher hemoglobin concentration, higher total bilirubin concentration, lower mean heparin infusion dose, lower body weight, and lower platelet count. Using multivariable Cox modeling, daily plasma free hemoglobin was independently associated with development of renal failure during extracorporeal membrane oxygenation (defined as creatinine > 2 mg/dL [> 176.8 μmol/L] or use of in-line hemofiltration or continuous renal replacement therapy) (hazard ratio, 1.04; 95% CI, 1.02-1.06; p < 0.001), but not mortality (hazard ratio, 1.01; 95% CI, 0.99-1.04; p = 0.389).

CONCLUSIONS

Hemolysis is common during pediatric extracorporeal membrane oxygenation. Hemolysis may contribute to the development of renal failure, and therapies used to manage renal failure such as in-line hemofiltration and other forms of continuous renal replacement therapy may contribute to hemolysis. Hemolysis was not associated with mortality after controlling for other factors. Monitoring for hemolysis should be a routine part of extracorporeal membrane oxygenation practice, and efforts to reduce hemolysis may improve patient care.

Microcirculatory changes in children undergoing cardiac surgery: a prospective observational study

BACKGROUND

The effects of cardiac surgery on the microcirculation of children are unknown. The aim of this study was to assess the microcirculatory changes in children undergoing surgery for correction of congenital heart disease.

METHODS

We used a videomicroscope (Sidestream Dark Field, SDF) in a convenience sample of 24 children <five yr old. Total vascular density (TVD, vessels mm(-2)), microvascular flow index (MFI, arbitrary units), proportion of perfused small vessels (PPV, percentage), and perfused vessel density (PVD) were obtained after induction of anaesthesia (T1), at the end of the surgical procedure (T2), after intensive care unit (ICU) admission (T3), and at six h (T4) and 12h (T5) after ICU admission.

RESULTS

Microcirculatory variables did not significantly change over time. Haemodynamic parameters and microcirculatory variables were not correlated. In a subanalysis conducted for cyanotic (n=7) and acyanotic (n=17) children, repeated measures ANOVA showed a significant interaction between time and the presence of cyanosis for PPV (P=0.03), TVD (P=0.03), and PVD (P=0.03). Weak inverse correlations were found between storage time of transfused red blood cell (RBCs) and MFI at T3 (r=-0.63, P=0.01) and T4 (r=-0.53, P=0.03).

CONCLUSIONS

Microcirculatory variables have a different time-related trend in cyanotic and acyanotic children undergoing cardiac surgery. The storage time of transfused RBCs seems to negatively impact the microcirculation. Further and larger studies are warranted to prove the potential implications of this study.

Serum nitric oxide level correlates with serum brain natriuretic peptide and whole blood viscosity in hemodialysis patients

BACKGROUND

Nitric oxide (NO) is tonically synthesized by the vascular endothelium and known as a marker of vasodilatation and blood flow. As NO has a critical role in hemodynamics, NO may be associated with other hemodynamics-related factors including atrial natriuretic peptide (ANP), B-type natriuretic peptide (BNP) and whole blood viscosity (WBV). It has been reported that serum NO level increased in patients undergoing hemodialysis. However, there are few reports about the relationship between NO and hemodynamic parameters in hemodialysis patients.

OBJECTIVE

We investigated the associations between serum levels of NO and other hemodynamics-related factors such as ANP, BNP and WBV in patients with hemodialysis.

METHODS

NO, ANP, and BNP levels before hemodialysis were measured using ELISA method. We measured WBV in pre- and post-dialysis.

RESULTS

Mean serum levels of NO, ANP, and BNP were 13.97 ± 10.34 μg/mL, 198.85 ± 61.56 pg/mL, and 1233.32 ± 280.81 pg/mL, respectively in patients with hemodialysis. The mean WBV values at shear rates of 1, 5, and 300 s^-1 for pre-dialyses were 168.5 ± 62.5, 76.9 ± 20.6, and 33.3 ± 3.8 mP, respectively. Serum NO level was positively correlated with WBV at shear rates of 1, 5, and 300 s^-1 at pre- and post-hemodialysis. There is a correlation between serum nitrite levels and the change of SBV during hemodialysis. Serum nitrite levels correlated with the serum BNP levels. ANP levels have a negative correlation with pre-dialytic WBV. However, BNP levels did not correlate with WBV during hemodialysis.

CONCLUSIONS

WBV is linked to an imbalance in serum vasoactive substances in hemodialysis patients and can cause significant hemodynamic disturbance.

No effect on the short-term of a decrease in blood viscosity on insulin resistance

BACKGROUND

Blood viscosity (BV) might influence glucose delivery to peripheral tissues and play an important role in insulin resistance and diabetes mellitus. However, the exact relationship between BV and insulin resistance is not yet clear.

OBJECTIVES

Aim of the present study is to evaluate the effects of the acute reduction in BV on insulin resistance, in healthy male subjects.

METHODS

Fifteen healthy male blood donors have been studied before and 48 hours after blood donation. Blood and plasma viscosity have been measured at 37°C with a cone-plate viscometer. Insulin resistance has been evaluated by euglycemic/hyperinsulinemic clamp in eight subjects, and by iHOMA2 Index in further seven subjects.

RESULTS

Blood viscosity was markedly reduced after blood donation (BV225 (cP) 4.53 ± 0.59 vs. 4.18 ± 0.31, p < 0.05). Insulin resistance was unchanged: MFFM clamp: 5.6 ± 4.5vs. 4.4 ± 2.2 and iHOMA2 Index 1.2 ± 0.6 vs. 1.2 ± 0.5, before vs. after respectively, p = NS. Blood pressure and lipids were unchanged after blood donation.

CONCLUSIONS

The present results demonstrate that acute reduction of BV in healthy male subjects does not change the insulin resistance, measured using both euglycemic/hyperinsulinemic clamp and iHOMA2 Index. Further intervention studies are needed to assess the effect that the reduction in BV can have in subjects with insulin resistance.

Empagliflozin influences blood viscosity and wall shear stress in subjects with type 2 diabetes mellitus compared with incretin-based therapy

Background

Cardiovascular protection following empagliflozin therapy is not entirely attributable to the glucose lowering effect. Increased hematocrit might influence the shear stress that is the main force acting on the endothelium, regulating its anti-atherogenic function.

Objective

We designed the study with the aim of investigating the effect of empagliflozin on blood viscosity and shear stress in the carotid arteries. A secondary endpoint was the effect of empagliflozin on carotid artery wall thickness.

Methods

The study was a non-randomized, open, prospective cohort study including 35 type 2 diabetic outpatients who were offered empagliflozin or incretin-based therapy (7 liraglutide, 8 sitagliptin) in combination with insulin and metformin. Blood viscosity, shear stress and carotid wall thickness were measured at baseline and at 1 and 3 months of treatment. Blood viscosity was measured with a viscometer, and shear stress was calculated using a validated formula. Intima-media thickness (IMT) of the carotid artery was detected by ultrasound and was measured with dedicated software.

Results

Blood viscosity (4.87 ± 0.57 vs 5.32 ± 0.66 cP, p < 0.02) and shear stress significantly increased in the Empagliflozin group while no change was detected in the Control group (4.66 ± 0.56 vs 4.98 ± 0.73 cP, p = NS). IMT significantly decreased in the Empagliflozin group after 1 and 3 months (baseline: 831 ± 156, 1-month 793 ± 150, 3-month 766 ± 127 μm; p < 0.0001), while in the liraglutide group, IMT significantly decreased only after 3 months (baseline 879 ± 120; 1-month 861 ± 163; 3-month 802 ± 114 μm; p < 0.001). In the sitagliptin group, IMT remained almost unchanged (baseline 901 ± 135; 1-month 902 ± 129; 3-month 880 ± 140 μm; p = NS).

Conclusions

This study is the first to describe a direct effect of empagliflozin on blood viscosity and wall shear stress. Furthermore, IMT was markedly reduced early on in the Empagliflozin group.

Reduced amputation rate with isovolemic hemodilution in critical limb ischemia patients

AIMS

Critical limb ischemia (CLI) patients are characterized by intractable pain in spite of medication, non-healing ulcers, and gangrene. The objective of this study was to investigate whether or not isovolemic hemodilution treatment can reduce the rate of major amputations in CLI.

METHODS

28 patients were studied who had tissue loss on Rutherford Grade III, Category 5 or 6. The subjects were divided into two arms: standard-of-care, conventional therapy (CT) (n = 15) as a control group and hemodilution therapy (HT) (n = 13) as a study group. For the HT group, weekly isovolemic hemodilution was performed over 4 consecutive weeks, removing 250 ml of whole blood with the infusion of hydroxyl-ethyl starch solution. Blood viscosity, hematocrit, hemoglobin, ankle-brachial index, VA pain scale, time-to-amputation from admission, and survival time were measured.

RESULTS

The mean Hct gradually decreased from 36.6 to 35.1, whereas the WBV at a shear rate of 1 s-1 significantly decreased from 18.2 to 10.5 during the same period. Subsequently, tissue oxygen delivery index, defined as the ratio of Hct to WBV at a shear rate of 1 s-1, increased from 24.4 to 37.0 by 51.7%, suggesting improvements in oxygen delivery in the patients. The average rate of lower limb major amputation in the control group was 93% (14/15), whereas that in the study group was 31% (4/13) (p = 0.001). Amputation-free median survival time and amputation-free 5-year survival rate in the control group were 1.2 months and 7%, while those in the study group were 30.2 months and 44% (p = 0.001). There were no adverse effects from repetitive hemodilution in the study group.

CONCLUSIONS

Isovolemic hemodilution treatment of CLI patients was found to be well-tolerated and reduced the rate of major amputation resulting from the deterioration of CLI.

Eryptosis and hemorheological responses to maximal exercise in athletes: Comparison between running and cycling

We compared the effects of cycling and running exercise on hemorheological and hematological properties, as well as eryptosis markers. Seven endurance-trained subjects randomly performed a progressive and maximal exercise test on a cycle ergometer and a treadmill. Blood was sampled at rest and at the end of the exercise to analyze hematological and blood rheological parameters including hematocrit (Hct), red blood cell (RBC) deformability, aggregation, and blood viscosity. Hemoglobin saturation (SpO2), blood lactate, and glucose levels were also monitored. Red blood cell oxidative stress, calcium content, and phosphatidylserine exposure were determined by flow cytometry to assess eryptosis level. Cycling exercise increased blood viscosity and RBC aggregation whereas it had no significant effect on RBC deformability. In contrast, blood viscosity remained unchanged and RBC deformability increased with running. The increase in Hct, lactate, and glucose concentrations and the loss of weight at the end of exercise were not different between running and cycling. Eryptosis markers were not affected by exercise. A significant drop in SpO2 was noted during running but not during cycling. Our study showed that a progressive and maximal exercise test conducted on a cycle ergometer increased blood viscosity while the same test conducted on a treadmill did not change this parameter because of different RBC rheological behavior between the 2 tests. We also demonstrated that a short maximal exercise does not alter RBC physiology in trained athletes. We suspect that exercise-induced hypoxemia occurring during running could be at the origin of the RBC rheological behavior differences with cycling.

Posttransfusion Increase of Hematocrit per se Does Not Improve Circulatory Oxygen Delivery due to Increased Blood Viscosity

BACKGROUND

Blood transfusion is used to treat acute anemia with the goal of increasing blood oxygen-carrying capacity as determined by hematocrit (Hct) and oxygen delivery (DO2). However, increasing Hct also increases blood viscosity, which may thus lower DO2 if the arterial circulation is a rigid hydraulic system as the resistance to blood flow will increase. The net effect of transfusion on DO2 in this system can be analyzed by using the relationship between Hct and systemic blood viscosity of circulating blood at the posttransfusion Hct to calculate DO2 and comparing this value with pretransfusion DO2. We hypothesized that increasing Hct would increase DO2 and tested our hypothesis by mathematically modeling DO2 in the circulation.

METHODS

Calculations were made assuming a normal cardiac output (5 L/min) with degrees of anemia ranging from 5% to 80% Hct deficit. We analyzed the effects of transfusing 0.5 or more units of 300 cc of packed red blood cells (PRBCs) at an Hct of 65% and calculated microcirculatory DO2 after accounting for increased blood viscosity and assuming no change in blood pressure. Our model accounts for O2 diffusion out of the circulation before blood arriving to the nutritional circulation and for changes in blood flow velocity. The immediate posttransfusion DO2 was also compared with DO2 after the transient increase in volume due to transfusion has subsided.

RESULTS

Blood transfusion of up to 3 units of PRBCs increased DO2 when Hct (or hemoglobin) was 60% lower than normal, but did not increase DO2 when administered before this threshold.

CONCLUSIONS

After accounting for the effect of increasing blood viscosity on blood flow owing to increasing Hct, we found in a mathematical simulation of DO2 that transfusion of up to 3 units of PRBCs does not increase DO2, unless anemia is the result of an Hct deficit greater than 60%. Observations that transfusions occasionally result in clinical improvement suggest that other mechanisms possibly related to increased blood viscosity may compensate for the absence of increase in DO2.

Effects of pentoxifylline on hemodynamic, hemorheological, and microcirculatory parameters in young SHRs during arterial hypertension development

The most common form of hypertension in young adults is isolated diastolic hypertension. Diastolic arterial pressure is determined by the total peripheral resistance and depends on both vascular hindrance and blood viscosity. The aim of our work was to study the efficiency of pentoxifylline (PTX) in young spontaneously hypertensive rats (SHRs) during the development of arterial hypertension. The effects of a treatment course with PTX (100 mg/kg/day p.o. for 6 weeks, from 5 to 11 weeks old) on the mean, systolic, and diastolic blood pressure (BP); stroke volume; cardiac output; total peripheral resistance (TPR); whole blood viscosity (BV); plasma viscosity; hematocrit; RBC aggregation and deformability; local cerebral blood flow (lCBF); and microvascularization of the visual cortex were studied in SHRs in comparison with control SHRs and Wistar Kyoto rats. PTX-treated SHRs had significantly lower systolic, diastolic, and mean BP (by 24%, 26%, and 15%, respectively) and BV (by 5-9%) and a higher erythrocyte deformability index (by 1.5-2%), lCBF (by 42%), average diameter of capillaries (by 11%), density of the capillary network (by 23%), and percentage of capillaries with a diameter of 3-7 µm in comparison with control SHRs. In conclusion, PTX exerted positive effects on the hemodynamic, hemorheological, and microcirculatory parameters in SHRs during the development of arterial hypertension.

Comparison of endothelin and nitric oxide synthase blockers on hemorheological parameters in endotoxemic rats

BACKGROUND/AIM

Septic shock is an important health problem that vastly alters cardiovascular and hemodynamic status. Increased production of nitric oxide (NO) and endothelin is a counterpart of this endotoxemic state. This study was conducted to test the hypothesis that nonselective NO synthesis blocker (L-NAME), inducible NO synthesis blocker (L-canavanine), or endothelin receptor antagonist (bosentan) will reverse the effects of sepsis on hemorheological parameters.

MATERIALS AND METHODS

Forty-eight male Sprague-Dawley rats were used in 8 groups: saline (control), endotoxin, bosentan, L-NAME, L-canavanine, endotoxin + bosentan, endotoxin + L-NAME, and endotoxin + L-canavanine. Blood was withdrawn at the 4th hour of endotoxemic state. Erythrocyte deformability and erythrocyte aggregation were determined by laser-assisted optical rotational cell analyzer at 37 °C. Plasma viscosity (mPa.s) was measured by a cone-plate viscometer with 0.5 mL of plasma.

RESULTS

Endotoxin administration significantly increased aggregation half-time and lowered erythrocyte aggregation amplitude and aggregation index compared to the control, indicating a slower and weaker aggregation pattern. L-NAME and L-canavanine alleviated the effects of endotoxin on erythrocyte aggregation without altering the values in the control animals. However, bosentan did not perform such a restoration.

CONCLUSION

This finding suggests that these restoration effects of the blockers occur via their modulation of nitric oxide synthesis rather than through the endothelin pathway.

A dramatic blood plasticity in hibernating and 14-day hindlimb unloading Daurian ground squirrels (Spermophilus dauricus)

We compared the effects of hibernation inactivity and 14-day hindlimb unloading in non-hibernating period on biochemical, rheological, and hematological parameters of blood in Daurian ground squirrels (Spermophilus dauricus). Twenty-four squirrels were randomly divided into four groups: control (CON), hibernation (HIB), post-hibernation (POST), and 14-day hindlimb unloading (HU). The results showed that serum enzymes (L-lactate dehydrogenase, alanine aminotransferase, and aspartate aminotransferase) activities decreased in HIB, POST, and HU squirrels compared with CON. Total protein (including albumin and globulin) maintained in HIB but decreased in HU compared with CON. Total cholesterol and high-density lipoprotein-cholesterol increased in HIB but maintained in HU and POST compared with CON. Meanwhile, serum creatinine decreased and urea increased in HU compared with CON. All blood ions concentrations were unchanged in HIB, POST, and HU squirrels compared with CON except calcium which increased in HIB compared with CON, and phosphorus which increased in HIB and POST compared with CON. Most of detected serum biochemical analytes in POST recovered to the CON level. Blood viscosity, which was unchanged in all shear rates in HU, increased in HIB and recovered in POST in lower shear rates compared with CON. Erythrocyte and corpuscular volume decreased in HIB and HU but maintained in POST compared with CON. All the routine hematological parameters recovered in POST as compared with CON except platelet, which decreased in HIB and POST but maintained in HU compared with CON. In conclusion, our results suggested a remarkable ability to maintain blood homeostasis in hibernating squirrels.

Impaired blood rheology is associated with endothelial dysfunction in patients with coronary risk factors

To investigate the relationship between blood rheology and endothelial function in patients with coronary risk factors, brachial arterial flow-mediated vasodilatation (FMD), an index of endothelial function and blood passage time (BPT), an index of blood rheology, and fasting blood cell count, glucose metabolism, and plasma fibrinogen, lipid, C-reactive protein, and whole blood viscosity levels were measured in 95 patients with coronary risk factors and 37 healthy controls. Brachial arterial FMD after reactive hyperemia was assessed by ultrasonography. BPT was assessed using the microchannel method. In healthy controls, BPT significantly correlated with FMD (r = - 0.325, p <  0.05), HDL cholesterol (r = - 0.393, p <  0.05), body mass index (BMI; r = 0.530, p <  0.01), and plasma fibrinogen concentration (r = 0.335, p <  0.05). In a multivariate regression analysis adjusted for all clinical variables, BPT remained significantly associated with BMI and fibrinogen, but not with FMD, in healthy controls. In patients with coronary risk factors, BPT significantly correlated with FMD (r = - 0.331, p <  0.01), HDL cholesterol (r = - 0.241, p <  0.05), BMI (r = 0.290, p <  0.01), hematocrit (r = 0.422, p <  0.001), white blood cell count (r = 0.295, p <  0.01), platelet count (r = 0.204, p <  0.05), and insulin (r = 0.210, p <  0.05). In a multivariate regression analysis adjusted for all clinical variables, BPT remained strongly associated with FMD and hematocrit in patients with coronary risk factors. These data indicate that BPT is closely associated with FMD in patients with coronary risk factors and suggest that the measurement of blood rheology using the microchannel method may be useful in evaluating brachial arterial endothelial function as a marker of atherosclerosis in these patients.

Prognostic significance of whole blood viscosity estimated by de Simone’s formula in ST-elevation myocardial infarction

Background: We assessed the predictive value of estimated whole blood viscosity (WBV) in-hospital and long-term cardiovascular outcomes in patients with ST-elevation myocardial infarction (STEMI). Materials & methods: One thousand eight hundred and thirty-five STEMI patients were followed up for median 34.6 months. WBV was calculated consistent with the de Simone’s formula. Results: In-hospital and long-term major adverse cardiovascular events (MACE) demonstrated an incremental trend in ascending order of WBV tertiles at low and high shear rate. Kaplan–Meier analysis showed a higher occurrence of long-term MACE in third WBV tertiles compared with other tertiles. Conclusion: WBV seems to be a feasible prognostic indicator of short- and long-term cardiovascular adverse events in patients with STEMI. As an easily available parameter, WBV may be utilized in identifying high-risk patients for subsequent MACE.

Asymmetric dimethylarginine and whole blood viscosity in renal failure

BACKGROUND

Renal failure is a disease with accelerated atherosclerosis beginning with endothelial cell dysfunction. Factors affecting endothelial cell dysfunction include whole blood viscosity (WBV) and asymmetric dimethylarginine (ADMA). The relationship in controls and renal failure was determined.

METHODS

51 subjects, 20 controls, 11 renal transplant recipients, 10 chronic kidney disease and 10 end-stage renal disease patients had blood samples drawn for WBV, Hematocrit, and ADMA. WBV was measured at various shear rates from 10 s(-1) to 780 s(-1) at 37 °C. Hematocrit using CritSpin, and ADMA was assayed using an ELISA method. The significance between groups was compared by boxplots and analysis of variance. Linear relationships were shown by regression lines and correlation coefficients.

RESULTS

ADMA was elevated in all groups with renal failure when compared to controls (p < 0.05). Control subjects showed a positive correlation between ADMA and WBV, while those who received a renal transplant had a negative correlation (p < 0.05). The difference in ADMA comparing pre-dialysis to post-dialysis conditions was positive (p < 0.05).

CONCLUSIONS

The positive relationship between WBV and ADMA in controls is a novel finding and allows for comparison with other groups. This relationship is dramatically altered in renal failure.

An overlooked parameter in coronary slow flow phenomenon: whole blood viscosity

Aims: We aimed to assess the relationship between coronary slow flow phenomenon (CSFP) and whole blood viscosity (WBV). Materials & methods: Two hundred patients with CSFP and 200 subjects with normal coronary arteries as control group were enrolled. WBV was calculated from hematocrit and plasma protein concentration at low shear rate (LSR) (0.5 s-1) and high shear rate (HSR) (208 s-1) by a validated equation. Results: CSFP patients had significantly higher WBV for LSR and HSR. The mean corrected TIMI frame count was highest in the highest tertile group for both shear rates. Corrected TIMI frame count revealed a significant relationship with WBV for LSR (r = 0.562) and HSR (r = 0.611). At multivariate analysis, WBV at LSR and HSR were independent predictors of CSFP. Conclusion: WBV seemed to have a significant and an independent predictor of CSFP.

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.

Vinpocetine and pyritinol: a new model for blood rheological modulation in cerebrovascular disorders—a randomized controlled clinical study

Blood and plasma viscosity are the major factors affecting blood flow and normal circulation. Whole blood viscosity is mainly affected by plasma viscosity, red blood cell deformability/aggregation and hematocrit, and other physiological factors. Thirty patients (twenty males + ten females) with age range 50-65 years, normotensive with history of cerebrovascular disorders, were selected according to the American Heart Stroke Association. Blood viscosity and other rheological parameters were measured after two-day abstinence from any medications. Dual effects of vinpocetine and pyritinol exhibit significant effects on all hemorheological parameters (P < 0.05), especially on low shear whole blood viscosity (P < 0.01), but they produced insignificant effects on total serum protein and high shear whole blood viscosity (P > 0.05). Therefore, joint effects of vinpocetine and pyritinol improve blood and plasma viscosity in patients with cerebrovascular disorders.

Replacing the Transfusion of 1-2 Units of Blood with Plasma Expanders that Increase Oxygen Delivery Capacity: Evidence from Experimental Studies

At least a third of the blood supply in the world is used to transfuse 1–2 units of packed red blood cells for each intervention and most clinical trials of blood substitutes have been carried out at this level of oxygen carrying capacity (OCC) restoration. However, the increase of oxygenation achieved is marginal or none at all for molecular hemoglobin (Hb) products, due to their lingering vasoactivity. This has provided the impetus for the development of “oxygen therapeutics” using Hb-based molecules that have high oxygen affinity and target delivery of oxygen to anoxic areas. However it is still unclear how these oxygen carriers counteract or mitigate the functional effects of anemia due to obstruction, vasoconstriction and under-perfusion. Indeed, they are administered as a low dosage/low volume therapeutic Hb (subsequently further diluted in the circulatory pool) and hence induce extremely small OCC changes. Hyperviscous plasma expanders provide an alternative to oxygen therapeutics by increasing the oxygen delivery capacity (ODC); in anemia they induce supra-perfusion and increase tissue perfusion (flow) by as much as 50%. Polyethylene glycol conjugate albumin (PEG-Alb) accomplishes this by enhancing the shear thinning behavior of diluted blood, which increases microvascular endothelial shear stress, causes vasodilation and lowering peripheral vascular resistance thus facilitating cardiac function. Induction of supra-perfusion takes advantage of the fact that ODC is the product of OCC and blood flow and hence can be maintained by increasing either or both. Animal studies suggest that this approach may save a considerable fraction of the blood supply. It has an additional benefit of enhancing tissue clearance of toxic metabolites.

Relationship Between Hematocrit Level and Cardiovascular Risk Factors in a Community-Based Population

BACKGROUND

This study aimed to determine the relationship between hematocrit (HCT) levels and cardiovascular risk factors in a community-based population of middle-aged adults.

METHODS

From April 2011 to February 2012, a total of 1,884 middle-aged adults were selected from a community-based population in China. Blood and urine samples were collected for routine blood and urine tests, and measurement of plasma glucose and lipid levels. Baseline information including traditional cardiovascular risk factors was obtained by standard questionnaire to analyze. We evaluated the distribution of the HCT values for middle-aged adults with or without cardiovascular risk factors. There were 548 males and 1,336 females in this study. The mean age of all subjects was 54.7 ± 6.7 years. There were 1,209 subjects with risk factors and 675 without risk factors.

RESULTS

The HCT levels in subjects with risk factors were higher than those without risk factors (P = 0.005). According to a simplified tool for evaluation of the 10-year risk of ischemic cardiovascular diseases (CVDs) in Chinese populations, all subjects were divided into four groups: the ultralow-risk group (1,367, 72.6%), low-risk group (232, 12.3%), intermediate-risk group (201, 10.7%), and high-risk/ultrahigh-risk group (84, 4.4%). Compared with HCT levels in the ultralow-risk group, significant differences were found in the low-risk, intermediate-risk, and high-risk/ultrahigh-risk groups (all P < 0.05).

CONCLUSION

Our results indicate that elevated HCT levels may be positively associated with cardiovascular risk factors. Thus, the combination of HCT values and cardiovascular risk factors may enable early diagnosis of CVDs.

Impact of closed minimal extracorporeal circulation on microvascular tissue perfusion during surgical aortic valve replacement: intravital imaging in a prospective randomized study

OBJECTIVES

Closed minimal extracorporeal circulation (MECC) systems currently do not represent the standard of surgical care for open-heart surgery. Yet, considering the beneficial results reported for coronary artery bypass graft (CABG) surgery, we used an MECC system in aortic valve replacement (AVR) and analysed the effects on intraoperative microvascular perfusion in comparison with conventional open extracorporeal circulation (CECC).

METHODS

In the current study, we analysed alterations in microvascular perfusion at 4 predefined time points (T1-T4) during surgical AVR utilizing orthogonal polarization spectral (OPS) imaging. Twenty patients were randomized for being operated on utilizing either MECC or CECC. Changes in functional capillary density (FCD, cm/cm(2)), mircovascular blood flow velocity (mm/s) and vessel diameter (μm) were analysed by a blinded investigator.

RESULTS

After the start of extracorporeal circulation and aortic cross-clamping (T2), both groups showed a significant drop in FCD, but with a significantly higher FCD in the MECC group (153.1 ± 15.0 cm/cm² in the CECC group vs 160.8 ± 12.2 cm/cm² in the MECC group, P = 0.034). During the late phase of the cardiopulmonary bypass (CPB) (T3), the FCD was still significantly depressed in both treatment groups (153.5 ± 14.6 cm/cm² in the CECC group, P <0.05 vs 'T1'; 159.5 ± 12.4 cm/cm² in the MECC group, P <0.05 versus 'T1'). After termination of CPB (T4), the FCD recovered in both groups to baseline values. Microvascular blood flow velocity tended to remain at a higher level in the MECC group, whereas haemodilution during CPB was significantly reduced in the MECC group.

CONCLUSIONS

The use of MECC in AVR did not affect procedural safety and, resulted in beneficial preservation of microvascular blood flow velocity and significantly reduced haemodilution during CPB. In contrast to CABG surgery, the use of MECC did not improve FCD during surgical AVR. Clinical advantages possibly resulting from attenuated haemodilution and preservation of microvascular blood flow velocity require further validation in larger patient cohorts.

Cardiovascular benefits of phlebotomy: relationship to changes in hemorheological variables

Renewed interest in the age-old concept of “bloodletting”, a therapeutic approach practiced until as recently as the 19th century, has been stimulated by the knowledge that blood loss, such as following regular donation, is associated with significant reductions in key hemorheological variables, including whole blood viscosity (WBV), plasma viscosity, hematocrit and fibrinogen. An elevated WBV appears to be both a strong predictor of cardiovascular disease and an important factor in the development of atherosclerosis. Elevated WBV through wall shear stress is the most direct physiological parameter that influences the rupture and erosion of vulnerable plaques. In addition to WBV reduction, phlebotomy may reduce an individual’s cardiovascular risk through reductions in excessive iron, oxidative stress and inflammation. Reflecting these findings, blood donation in males has shown significant drops in the incidence of cardiovascular events, as well as in procedures such as percutaneous transluminal coronary angioplasty and coronary artery bypass grafting. Collectively, the available data on the benefits of therapeutic phlebotomy point to the importance of monitoring WBV as part of a cardiovascular risk factor, along with other risk-modifying measures, whenever an increased cardiovascular risk is detected. The development of a scanning capillary tube viscometer allows the measurement of WBV in a clinical setting, which can prove to be valuable in providing an early warning sign of an increased risk of cardiovascular disease.

Peak and time-integrated shear rates independently predict flow-mediated dilation

BACKGROUND

To determine whether peak and time-integrated shear rates independently predict flow-mediated dilation (FMD).

METHODS

Eleven physically active (25 ± 5 years old) male subjects were tested. FMD was defined as the shear rate-diameter relationship. Hierarchical linear modeling was used to estimate brachial artery diameter change with repeated measures of shear rate nested within each subject. Two models were tested: 1) FMD was induced using ischemia-induced hyperemia (2, 4, 6, and 10 minutes); and 2) FMD was induced following transient (ischemia) and steady-state (forearm heating and handgrip exercise) increases in shear rate. For both models we determined whether peak, in addition to time-integrated shear rates, explained a significant portion of variation for diameter change.

RESULTS

Model 1: Time integrated shear rates explained most of the variation for diameter change. However, peak shear rate explained an additional significant portion of variation. Model 2: The transient condition resulted in significantly (p = 0.012) smaller diameter change per shear rate change than the steady-state condition. However, when specifying peak shear rate as a covariate, the difference between conditions became nonsignificant (p = 0.138).

CONCLUSIONS

Peak and time-integrated shear rates independently predict FMD. Future studies using the FMD test should consider both parameters.