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.

Laser Doppler flux measurement for the assessment of cutaneous microcirculatio--critical remarks.

Back scattered Laser Doppler (LD) signals are composed of two different individual signals. The number of the moving particles and the speed of the particles in the measured tissue volume determine the frequency shift and the band width of the Doppler signal. The dependence of the Laser Doppler flux on the number of scattering particles is highly nonlinear: at very low hematocrit and high speed the axial migration of the cells to the centre of the blood vessels is very strong, so that in these cases - because of the parabolic flow profile - the Doppler flux measurement overestimates the mean real blood flow (up to two- or three-fold).

Endothelial function and hemorheological parameters modulate coronary blood flow in patients without significant coronary artery disease.

Background: Coronary (micro)vascular resistance is regulated by the complex interplay of several factors. Two potentially important determinants include endothelial function and the rheological properties of blood. However, their impact on the control of the coronary resistance vasculature is poorly understood.

Parameters of blood viscosity do not correlate with the extent of coronary and carotid atherosclerosis and with endothelial function in patients undergoing coronary angiography.

While the role of physical forces on the control of atherogenesis and the modulation of endothelial function is well known, studies investigating the impact of shear stress on the extent of central atherosclerosis and flow-mediated dilation in humans produced controversial results. We investigated the relationship between viscosity, coronary atherosclerosis, carotid intima-media thickness and flow-mediated dilation in patients undergoing coronary angiography. 451 patients (306 males, mean age 66 ± 10) were enrolled.

Evidence of a weak correlation between peripheral endothelial function measures and carotid intima-media thickness.

Previous studies from our and other laboratories have demonstrated the existence of a clear relationship between different measures of endothelial function and the extent of coronary atherosclerosis. The relationship between endothelial function and carotid intima-media thickness has not been extensively investigated. Endothelial function using radial artery flow-mediated constriction (L-FMC) and dilation (FMD) was assessed in 513 consecutive patients undergoing diagnostic coronary angiography.

Endothelium and hemorheology.

A number of factors are involved in the regulation and maintenance of vascular homeostasis. The role of the vascular endothelium has been identified almost three decades ago, and a number of lines of evidence provide solid support to the role of this tissue in modulating not only vascular tone, but also phenomena such as platelet, red blood cell aggregation and deformability. In turn, hemorheological characteristics have been proven to impact on the endothelial release of mediators and therefore on vascular tone.

Endothelium and hyperviscosity.

The role of viscosity, and of interindividual variations in this parameter, in the pathophysiology of cardiovascular disease remain incompletely understood. Any speculation regarding the possible impact of "hemorheological" therapies is therefore even more complex. In the last years, the debate regarding the relationship between increased viscosity and atherogenesis has been opened again.

Chronic pharmacological preconditioning against ischemia.

Despite decades of research and thousands of experimental publications, acute preconditioning strategies have yet to be implemented in clinical practice. While some have attributed this to a failure of the experimental studies to mimic the clinical environment, others have suggested that acute preconditioning strategies themselves may possess physiological limitations. In particular, there is evidence to suggest a reduced efficacy of acute preconditioning in the aged heart and in disease states, such as diabetes, hypertension, hyperlipidemia, and atherosclerosis.

Peripheral hemorheological and vascular correlates of coronary blood flow.

The slow coronary flow phenomenon (SCF), a condition described by the presence of inappropriate delay in the progression of intracoronary contrast during angiography in the absence of stenoses, has been shown in some patients presenting with chest pain. While several conditions leading to "secondary" slow flow are known, there are no definitive conclusions regarding the exact pathogenesis of "primary" SCF. The present paper outlines the mechanisms that may lead to SCF, emphasizing the role of hemorheological and vascular factors in the pathogenesis of this phenomenon.

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

Decreasing blood viscosity has been proposed since the advent of hemodilution as a means for increasing perfusion in many pathological conditions, and increased plasma viscosity is associated with the presence of pathological conditions. However, experimental studies show that microvascular functions as represented by functional capillary density in conditions of significantly decreased viscosity is impaired, a problem corrected by increasing plasma and blood viscosity. Blood viscosity, primarily dependent on hematocrit (Hct) is a determinant of peripheral vascular resistance, and therefore blood pressure.

Different patterns of fundus autofluorescence related to ABCA4 gene mutations in Stargardt disease.

Background And Objective: Stargardt disease is a type of juvenile-onset macular dystrophy. The clinical presentation is characterized by macular atrophy and the presence of lipofuscin storage. The aim of this study was to investigate a possible correlation between different ABCA4 gene mutations and the autofluorescence pattern.

The mechanism of nitrate-induced preconditioning.

Nitroglycerin (GTN) has been shown, in both human and animal studies, to induce a protective phenotype that limits tissue damage after ischemia and reperfusion. This phenomenon is similar to ischemic preconditioning, and several reports suggest that also the molecular pathways involved in this protective effect of nitrates are the same that determine ischemic preconditioning. Our group conducted a series of studies aimed at investigating, using a human model of endothelial IR injury, the mechanism of nitrate-induced preconditioning and particularly the role of reactive oxygen species formation and of the opening of mitochondrial permeability transition pores.

Comparison of blood viscosity using a torsional oscillation viscometer and a rheometer.

The absence of a simple and clinically practical method to determine whole blood viscosity can partly justify why the medical community has been slow in realizing the significance of whole blood viscosity. For this reason, the availability of a technique able to evaluate blood viscosity in a rapid and direct manner is welcome. To evaluate the feasibility in hemorheological laboratory of a new torsional oscillation viscometer, it was compared with a conventional cone-plate system.

Nitroglycerine causes mitochondrial reactive oxygen species production: in vitro mechanistic insights.

Background: Nitroglycerine (GTN) is an organic nitrate that has been used for more than 100 years. Despite its widespread clinical use, several aspects of the pharmacology of GTN remain elusive. In a recent study, the authors of the present study showed that GTN causes opening of the mitochondrial permeability transition pore (mPTP) and mitochondrial production of reactive oxygen species (ROS).

Endothelium and haemorheology.

The vascular endothelium has been recognized to have a central importance in maintaining vascular homeostasis and in preventing cardiovascular disease. The mechanisms underlying the regulation of its function are extremely complex, and are principally determined by physical forces imposed on the endothelium by the flowing blood. In the present paper, we describe the interactions between the rheological properties of blood and the vascular endothelium.

Nitroglycerin protects the endothelium from ischaemia and reperfusion: human mechanistic insight.

Aims: Nitroglycerin (GTN) modulates tissue damage induced by ischaemia and reperfusion (IR) in a mechanism that is similar to ischaemic preconditioning. We set out to study, using a human model of endothelial IR injury, whether GTN-induced endothelial preconditioning is mediated by reactive oxygen species (ROS) formation and/or opening of mitochondrial permeability transition pores (mPTP).

Methods: In two double-blind, randomized, parallel studies, a total of 66 volunteers underwent measurement of radial artery endothelium-dependent, flow-mediated dilation (FMD) before and after local IR.

Correlation analysis between different parameters of conduit artery and microvascular vasodilation.

Impaired endothelial responsiveness to specific vasodilator stimuli has been used as a surrogate marker of cardiovascular risk. Multiple methods allow testing endothelial responses in both microvessels and conduit arteries, but it is still unclear whether there is a relationship in endothelial function between these two different vascular beds. Twenty-five healthy young non smoking male volunteers (age range 24-45) were enrolled.

Impact of hemorheological and endothelial factors on microcirculation.

Previous studies showed that endothelial alterations caused by physical stress worsened the hemorheological parameters mainly in patients affected by ischemic vascular diseases: major vascular alterations have been found in patients with very high endothelial dysfunction indexes: these indexes are given by the various substances produced by the endothelium, but it is very difficult to have a value which clearly identifies the real state of the endothelial alteration. The function of the NO, an endogenous vasodilator whose synthesis is catalyzed by NOs, can be determined by the Citrulline/Arginine ratio, which represents the level of activity of the enzyme. A very good index of the endothelial dysfunction is asymmetric dimethylarginine (ADMA), a powerful endogenous inhibitor of NOs; in fact several studies have demonstrated a strong relationship between ischemic vascular disease and high levels of plasmatic ADMA.

Postconditioning fails to prevent radial artery endothelial dysfunction induced by ischemia and reperfusion: evidence from a human in vivo study.

Animal studies have shown that, as compared with unrestricted reperfusion, exposure to brief periods of controlled ischemia (postconditioning) at the end of a prolonged ischemia reduces the extent of tissue damage. We set out to test whether postconditioning can prevent endothelial dysfunction induced by ischemia and reperfusion in a human in vivo model. Ten healthy young non-smoking volunteers were enrolled in this cross-over, controlled, investigator-blinded study.

Evaluation of a torsional-vibrating technique for the hemorheological characterization.

Clinical measurement of blood viscosity is an important parameter in the diagnosis of different diseases (e.g., diabetes, hypertension, cardiovascular diseases).