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Biorheology is an international interdisciplinary journal that publishes research on the deformation and flow properties of biological systems or materials. It is the aim of the editors and publishers of
Biorheology to bring together contributions from those working in various fields of biorheological research from all over the world. A diverse editorial board with broad international representation provides guidance and expertise in wide-ranging applications of rheological methods to biological systems and materials.
The aim of biorheological research is to determine and characterize the dynamics of physiological processes at all levels of organization. Manuscripts should report original theoretical and/or experimental research promoting the scientific and technological advances in a broad field that ranges from the rheology of macromolecules and macromolecular arrays to cell, tissue and organ rheology. In all these areas, the interrelationships of rheological properties of the systems or materials investigated and their structural and functional aspects are stressed.
The scope of papers solicited by
Biorheology extends to systems at different levels of organization that have never been studied before, or, if studied previously, have either never been analyzed in terms of their rheological properties or have not been studied from the point of view of the rheological matching between their structural and functional properties. This biorheological approach applies in particular to molecular studies where changes of physical properties and conformation are investigated without reference to how the process actually takes place, how the forces generated are matched to the properties of the structures and environment concerned, proper time scales, or what structures or strength of structures are required.
Biorheology invites papers in which such 'molecular biorheological' aspects, whether in animal or plant systems, are examined and discussed. While we emphasize the biorheology of physiological function in organs and systems, the biorheology of disease is of equal interest. Biorheological analyses of pathological processes and their clinical implications are encouraged, including basic clinical research on hemodynamics and hemorheology.
In keeping with the rapidly developing fields of mechanobiology and regenerative medicine,
Biorheology aims to include studies of the rheological aspects of these fields by focusing on the dynamics of mechanical stress formation and the response of biological materials at the molecular and cellular level resulting from fluid-solid interactions. With increasing focus on new applications of nanotechnology to biological systems, rheological studies of the behavior of biological materials in therapeutic or diagnostic medical devices operating at the micro and nano scales are most welcome.
Abstract: To obtain insights into transmural myocardial perfusion during coronary artery stenosis, we evaluated the characteristics of septal arterial blood flow velocity using a 20 MHz multichannel pulsed Doppler velocimeter. Septal arterial blood flow velocity was characterized by the presence of a retrograde blood velocity component. Thus, a substantial amount of blood that entered the myocardium during diastole flows backward to the proximal coronary arteries. This is evidence of the coronary slosh phenomenon. With coronary artery stenosis, the systolic retrograde flow was enhanced, and was augmented further by coronary vasodilation. Since the component of blood moving backward in systole does…not contribute to the perfusion of the myocardial bed, an augmented coronary slosh phenomenon plays an important role in disturbing myocardial inflow in addition to the stenotic impeding effects on diastolic flow.
Abstract: Nonlinear mathematical techniques now make it possible to quantify the complexity of an irregular time series through calculation of a parameter known as fractal dimension. In the present study, we use such an analysis to provide evidence that histamine-induced pressure oscillations in an isolated rabbit ear resistance artery are generated by deterministic rather than stochastic mechanisms, and that a minimum of 3 independent control variables is necessary to account for the complexity of the dynamics of these oscillations. The fractal dimension of the responses was independent both of the concentration of histamine used to induce rhythmic behavior, and the level…of activity of the endogeneous nitrovasodilator, EDRF. While both superficially influenced the form of the oscillations, it follows that neither are key control variables involved in their genesis. Nonlinear analysis of data obtained in the presence of NG -nitro-L-arginine methyl ester (L-NAME), which blocks EDRF synthesis, provided insights into the intrinsic smooth muscle control mechanisms responsible for generating rhythmic activity. The oscillations exhibited distinct “fast” and “slow” components (periods of 5–20 secs and 1–5 min. respectively). The former involved ion movements at the cell membrane and was inhibited by low [Ca2+ ]o, verapamil (which blocks voltage-dependent Ca2+ influx) and tetraethylammonium (which blocks Ca2+ -activated outward K+ channels), whereas the latter involved Ca2+ -induced Ca2+ release from intracellular stores and was inhibited by ryanodine. All such interventions decreased the overall fractal dimension of the responses to a value <2, thus removing one degree of complexity (and hence control variable) from the dynamics. We conclude that the nonlinear interaction between a fast membrane oscillator and a slow intracellular oscillator generates chaos in vascular smooth muscle and that exogeneous constrictor agonists and EDRF may be regarded as permissive and modulatory influences, respectively.
Abstract: Myocardial contrast echocardiography was used to characterize changes in the regional and transmural myocardial blood flow distribution that were provoked by rapid atrial pacing stress in patients with coronary artery diseases. In patients with coronary organic stenosis, a decrease in the myocardial contrast-enhancement in the subendocardial half after rapid atrial pacing was associated with stress-induced chest pain and electrocardiographic ST-T changes. The decrease in the myocardial contrast-enhancement in the subendocardial half after rapid atrial pacing was not observed in patients without coronary stenosis or after coronary angioplasty. Thus, the finding was considered to reflect myocardial ischemia. Pacing-induced decreases in myocardial…contrast-enhancement were observed in some patients with old myocardial infarction and significant resting coronary collaterals. In these patients, myocardial ischemia was considered to have developed at rapid pacing because collateral function was good enough to perfuse the infarct myocardium at rest, but was not good enough to prevent myocardial ischemia at stress. Thus, myocardial contrast echocardiography seems to be particularly useful in assessing myocardial ischemia at stress due to coronary stenosis in patients with angina pectoris and due to poor dynamic collateral function in patients with old myocardial infarction.
Abstract: Oxygen-derived free radicals are thought to inactivate ectosolic enzymes that regulate myocardial cellular functions. One such enzyme is ecto-5’-nucleotidase, which is responsible for adenosine production during coronary hyperemic flow. In the present study, we measured both reactive and hyperemic flow and adenosine release during reperfusion with and without superoxide dismutase. In 10 open chest dogs, the left anterior descending coronary artery was perfused through an extracorporeal bypass tube from the carotid artery. In the control hearts, a five-minute occlusion of the coronary artery caused the hyperemic flow with increased release of adenosine. In the superoxide dismutase-treated hearts, although administration of…superoxide dismutase altered neither adenosine release nor coronary blood flow in the baseline, it augmented both peak coronary blood flow and repayment, and adenosine release during reperfusion. Therefore, we hypothesized that superoxide dismutase reduces generation of oxygen-derived free radicals during ischemia and reperfusion and attenuates the degradation of ecto-5’-nucleotidase. The administration of superoxide dismutase enhanced the increase in ecto-5’-nucleotidase activity at 10 minutes after reperfusion over the untreated group. Thus, we conclude that super oxide dismutase enhances reactive hyperemic flow and adenosine release during reperfusion following ischemia, which may be attributable to the protection of ecto-5’-nucleotidase by superoxide dismutase during ischemia and reperfusion.
Abstract: The ATP-sensitive potassium channel (K+ ATP channel) is known to exist in blood vessels and to regulate vascular tone. We examined the role of this channel in coronary arteriolar vasomotion during coronary autoregulation, ischemia, reactive hyperemia and endothelium-dependent response by acetylcholine in vivo . Experiments were performed with anesthetized open-chest dogs. Coronary arterioles were directly observed in situ by means of a floating objective system or a stroboscropic epi-illumination system synchronized with cardiac motion. Small arterioles less than 100 μ m in internal diameter dilated in response to reduction in perfusion pressure (perfusion pressure: 60, 40, 25 mm…Hg). Glibenclamide, a selective blocker of the K+ ATP channel, reversed the dilation. Reactive hyperemia produced by 20-second occlusion of the left anterior descending coronary artery resulted in arteriolar dilation, the magnitude of which was greater in smaller arterioles than in larger ones. Glibenclamide significantly inhibited the dilation in both large and small arterioles. Acetylcholine (ACh) produced dilation in arterioles of all sizes. NG-monomethyl L-arginine, a competitive inhibitor of nitric oxide synthesis, abolished the dilation of large arterioles, but failed to abolish the dilation in small arterioles. Glibenclamide, however, did not have any additional inhibitory effect on ACh-induced arteriolar dilation. Thus, we conclude that the K+ ATP channel plays an important role in coronary microvascular vasomotion during autoregulation, ischemia and reactive hyperemia, but not during endothelium-dependent vasodilation induced by ACh in vivo .
Abstract: Perfusion of the heart takes place mainly in diastole. It is therefore important to study the factors that affect coronary diastolic flow. One of the factors that may limit coronary artery vasoactive responses is the surrounding cardiac tissue. We have therefore studied the intramyocardial septal artery, both when still embedded in the diastolic, unstretched myocardial tissue and after complete dissection (n = 6). In situ , the average external diameter was 351 ± 21 μ m; after dissection, it was 362 ± 21 μ m. These values were not significantly different. The average response of the vessel to KCl (125…mM, receptor-independent constriction) reduced the diameter to 56.1 ± 5.0% and 69.4 ± 3.7% of the maximal diameter for in situ and dissected vessels, respectively. The reduction in diameter after dissection was significantly less than the reduction in situ . The response to vasopressin (1,000 μ U/ml, a receptor-dependent constrictor) was a reduction to 62.6 ± 4.7% and 70.4 ± 4.5%, respectively. The reduction in diameter of the dissected vessel is significantly smaller than that of the in situ vessel. The average values of the ratios of the diameter reductions for vasopressin and KCl were 0.85 ± 0.06 in the in situ condition and 0.95 ± 0.08 after dissection and were not significantly different (paired t-test). The results show that the dilated diameter and the diameter responses of intramyocardial conduit arteries are not affected by the surrounding diastolic cardiac tissue.
Abstract: Intramyocardial stresses appear to be an important factor in the degree of compression of the coronary vasculature, directly influencing the peripheral impedance of the coronary hemodynamic network. A method is presented for predicting variation in the luminal area of small vessels embedded in myocardial tissue, due to changes in surrounding stresses. Such stresses and strains were calculated as those generated in the wall of a cylindrical structure, a model of the cardiac ventricular wall. Based on the classical theory of linear elasticity and assumptions of superposition of strains generated within the medium by the cyclic variation of tissue pressure and…fiber stress, changes in the inner cross-section area of microvessels were computed. Applied to coronary microvasculature, it was shown for the range of tested parameters that these microvessels are not likely to be subjected to instability phenomena and subsequent collapses, but rather show a small change in area. These results are in agreement with physiological observations concerning the degree of area reduction in arterioles and venules localized within the endocardial portion of the left ventricular wall. Based on this theory, analysis of variations in distensibility, compliance and resistance of microvessels, such as arterioles and venules, vs . internal pressure, and different cardiac states and locations within the myocardial wall is possible.
Abstract: Although the stability and viscoelasticity of the red cell membrane are undoubtedly governed by the membrane’s underlying protein skeleton, the mechanism by which this network controls elasticity is uncertain. The structural constraints, that impose end-to-end spacing on the spectrin molecules well below that in free solution, may impart rubbery (entropic) elasticity to the system. However, other enthalpic and entropic contributions due to interactions between spectrin chains or between spectrin and other proteins, the lipid bilayer or the solvent must also prevail. To relate structural features to elasticity, explicit measurements of membrane rigidity are required. The most widely used measurement is…that of the membrane shear elastic modulus by micropipette aspiration. Analysis of genetic variants of membrane structure have shown that the density of spectrin is directly correlated with membrane rigidity. Although cross-linking of the skeleton increases rigidity, interruption of the continuity of the network by dissociating spectrin tetramers into dimers does not reduce rigidity as might be expected. On the other hand, external ligands that cause new interactions between integral proteins and the skeletal network do increase rigidity. Moreover, hereditary ovalocytes, which have a deletion of 9 amino acids from band 3 at the first point of entry into the membrane, are extremely rigid. This mutation is associated with decreased translational and rotational mobility of the band 3, and may impair flexural freedom of its cytoplasmic domain. It thus appears that elasticity may be regulated not only by the structure of the spectrin network, but also by its interactions with and freedom of motion relative to the lipid bilayer.
Keywords: Erythrocyte, membrane, elasticity, protein skeleton, rheology
vol. 30, no. 5-6, pp. 397-407, 1993
Abstract: Rheological and compositional properties of pathological synovial fluids were measured and compared in order to reveal differences between disease states. The cases include degenerative joint disease, rheumatoid arthritis, mixed connective tissue disease, and pseudo gout. Using an oscillatory flow capillary instrument, measurements were made of both the frequency and shear rate dependence of the complex viscoelasticity. The fluid types differ most in their elasticity, with the degenerative joint disease fluids having the greatest average viscosity, elasticity and intrinsic viscosity, followed by the rheumatoid arthritis fluids, and the fluids from cases of mixed connective tissue disease. Differences in the hyaluronate and…protein concentrations are not as great as those between rheological variables. The viscoelasticity of synovial fluid appears more strongly dependent on the degree of polymerization of hyaluronate than on its concentration. These synovial fluids conform well to a model of relaxation process truncation. Distinct types of elastic stres train behavior reveal the nature of the dynamic fluid structure.
Abstract: The effect of supravalvular aortic stenosis on cardiac left ventricular ejection was determined from a realistic left ventricle (LV) model built from the profile of a diastolic dog LV. The ejection fraction was considered to be 75% of the diastolic volume. The maximum blood ejection velocities and ventricular pressure occurred at the start of the diastolic flow since the ventricular walls moved the fastest at this point. Going from a healthy non-stenotic LV to one with 64% stenosis increased the maximum ejection velocity from 117 cm/sec to 269 cm/sec, and the maximum relative pressure increased from 10,420 dynes/cm2 to…33,550 dynes/cm2 (7.82 to 25.16 mm Hg). The supravalvular stenotic aorta showed major flow disturbances as the degree of stenosis increased. The computational technique using a realistic model gives predictions in general agreement with observed experimental results, and allows a complex determination of the three-dimensional flow patterns.
Abstract: Rheological properties and fractal structure of the polyion complex between chitosan and alginate have been studied using IR spectra, dynamic viscoelasticity and SAXS measurements. The complexation seems to occur between a carboxyl anion of the alginate and an amino group of the chitosan. The complex develops most markedly at a mixing ratio in weight of the chitosan/alginate from ca . 1/1 to 1/2 (in molar ratio), at which the dynamic viscoelastic functions of the systems manifest a plateau region due to a heterogeneous structure at a low frequency range. The heterogeneous structure shows a surface fractal structure having a fractal…dimension of ca . 2.4.
Abstract: Human red cell aggregability and disaggregability represent important hemorheological parameters of blood. Several techniques have been proposed to evaluate the tendency of red cells to form aggregates and to disrupt in the presence of shear stress. One of the most recent approaches is based on the characterization of the intensity of ultrasonic scattered signals. A pulsatile flow loop model is used in the present study to demonstrate the potential applicability of Doppler ultrasound to detect and characterize the hemodynamic behavior of red cell aggregates. Porcine whole blood specimens collected from 20 different pigs were circulated in the flow model (tube…diameter of 0.476 cm) at different mean velocities and pulsation rates. At a pulsation of 70 beats/min for mean velocities of 13 cm/sec and 63 cm/sec, no cyclic variation of the Doppler power was observed, suggesting the absence of rouleaux build-up and rouleaux disruption. At a pulsation of 20 beats/min and mean velocities of 11 cm/sec and 38 cm/sec, statistically significant cyclic variations (p < 0.01) were measured. It is suggested that aggregate size enlargement, rouleaux orientation with the flow field and the effect of shear stress on rouleaux disruption are possible causes for the observed cyclic variation of the Doppler power within the flow cycle at a pulsation of 20 beats/min. A discussion of the potential application of this technique for in vivo study in large vessels is given.
Keywords: Erythrocyte aggregation, biorheology in large vessels, rouleaux orientation, ultrasonics, Doppler ultrasound, power spectrum
vol. 30, no. 5-6, pp. 443-461, 1993
Abstract: Human erythrocytes were transformed to advanced stages of echinocytes by means of an increase of the pH, by addition of 2,4-dinitrophenol or by an increase in temperature. Scanning electron microscopy pictures were taken and the lateral distribution of the spicula was analyzed. Regardless of the method of the production of the echinocytes, no correlation of the spatial distribution of the spicula was detected. Except for the exclusion due to the finite size of the spicula basis, the distribution was random. The conclusion was drawn that the generation of spicula is a local process. No long-range ordering interaction between the spicula…could be detected.
Keywords: Human erythrocytes, echinocytes, spicula distribution, shape transformation
vol. 30, no. 5-6, pp. 463-470, 1993