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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: Blood flow, normally laminar, can exhibit high frequency fluctuations suggesting turbulence, which has important implications for the pathophysiology of vascular diseases and the design of blood-bearing devices. According to the classical model of turbulence in a homogeneous fluid, these fluctuations can be attributed to the cascade of eddies down to the Kolmogorov length scale, which, for apparent turbulence in blood, is reported to be on the order of tens of microns. On the other hand, blood is a suspension of mostly red blood cells (RBC), the size and concentration of which would seem to preclude the formation of eddies down…to these scales. Assuming dissipation occurs instead via cell–cell interactions mediated by the plasma, here we show how turbulent velocity fluctuations, normally ascribed to turbulent (Reynolds) stresses, could give rise to viscous shear stresses. This may help to resolve fundamental inconsistencies in the understanding of mechanical hemolysis, and it provides a physical basis for the forces actually experienced by formed elements in the blood under nominally turbulent flow. In summary, RBC must be acknowledged as equal players if a satisfactory definition of turbulence in blood is to be achieved.
Abstract: Blood flow characteristics in an axis-deviated artery bypass model were studied numerically and compared with those in a conventional bypass model. The numerical results revealed that a pronounced swirl flow was created in the host artery by the geometrical configuration of the axis-deviated bypass. The swirl flow created in the axis-deviated bypass model altered the overall flow pattern and eliminated the slow recirculation zone with low wall shear stress existing in the conventional model on the host artery floor where there is disturbed flow known to be associated with the development of intimal thickening and hyperplasia. The numerical study therefore…suggests that by intentionally introducing swirl flows into the bypassed arteries, the adverse effects along the host artery floor can be suppressed.
Abstract: The structure of stress fibers, contractile actin bundles, differs between motile and non-motile cells, though the same term “stress fiber” is used to refer to the structurally as well as functionally different actin bundles. Stress fibers in non-motile cells run between separate focal adhesions, producing isometric tension due to actomyosin contraction. The stress fiber contraction is maintained through dynamic molecular exchanges between preformed and cytoplasmic components. This isometric contraction has been recognized as being essential for extracellular matrix assembly and resultant wound healing. In addition, there have recently been increasing data suggesting that stress fibers under contraction by themselves work…as a mechanosensitive element. In this review we discuss, from molecular and physical viewpoints, biomechanical properties of the stress fiber of non-motile cells such as contraction force, resistance to stretching, and their roles in keeping a mechanical homeostasis, which play vital roles in the mechanosensing process.
Abstract: Nitric oxide (NO) is a potent regulator of vascular tone and hemorheology. The signaling function of NO was largely unappreciated until approximately 30 years ago, when the endothelium-derived relaxing factor (EDRF) was identified as NO. Since then, NO from the endothelium has been considered the major source of NO in the vasculature and a contributor to the paracrine regulation of blood hemodynamics. Because NO is highly reactive, and its half-life in vivo is only a few seconds (even less in the bloodstream), any NO bioactivity derived from the intraluminal region has traditionally been considered insignificant. However, the availability and significance…of NO signaling molecules derived from intraluminal sources, particularly erythrocytes, have gained attention in recent years. Multiple potential sources of NO bioactivity have been identified in the blood, but unresolved questions remain concerning these proposed sources and how the NO released via these pathways actually interacts with intravascular and extravascular targets. Here we review the hypotheses that have been put forward concerning blood-borne NO and its contribution to hemorheological properties and the regulation of vascular tone, with an emphasis on the quantitative aspects of these processes.
Abstract: It has been previously demonstrated that red blood cells (RBC) possess functional nitric oxide (NO) synthesizing mechanisms. RBC are also equipped with variety of intracellular control mechanisms, and respond to mechanical forces and to various biological stimuli by increased release of ATP. Nitric oxide has also been demonstrated to be released from RBC under certain circumstances, and it has been hypothesized that NO synthase (NOS), which is located in both the RBC membrane and cytoplasm, might be activated by mechanical factors. The present study aimed at investigating NOS activation and NO export induced by mechanical stress applied to RBC in…suspension. Heparinized venous blood samples were obtained from healthy, adult volunteers and their hematocrit adjusted to 0.4 l/l. The RBC suspensions were equilibrated at room temperature (22±2°C) with either room air or made hypoxic (36 mmHg, ~70% saturation) using moisturized 100% nitrogen. The samples were then continuously pumped through a glass tube (diameter = 0.06 cm; length = 33 cm) for 30 min using a dual syringe pump to maintain a wall shear stress of 0.5–2 Pa with NO concentrations in the RBC suspensions measured electrochemically. NO concentration significantly increased under the influence of 2 Pa in hypoxic RBC suspensions: 105.0±14.2 nM to 127.1±12.0 nM as the peak value at 20 min of perfusion. No increase was observed at lower levels of shear stress. Plasma nitrite/nitrate concentrations were measured in samples obtained at five minute intervals. Application of fluid shear stress to hypoxic RBC suspensions resulted in a significant, time-dependent increase of plasma nitrite/nitrate levels, reaching to 14.7±1.5 μM from a control value of 11.2±1.3 μM. The presence of the non-specific NOS inhibitor L-NAME (10−3 M) prevented this increment. Additionally, both eNOS and serine 1177 phosphorylated eNOS immuno-fluorescence staining in RBC cytoplasm were shown to increase in response to applied shear stress. Our results support the hypothesis that RBC NO synthase is activated and that export of NO from RBC is enhanced by mechanical stress.
Keywords: Shear stress, red blood cell NOS, nitric oxide, L-NAME, NOS activation
vol. 46, no. 2, pp. 121-132, 2009
Abstract: Aerobic performance is dependent on both cardio-respiratory and peripheral factors with hemodynamic parameters playing a major role. However, whether blood rheology might affect aerobic performance through an effect on hemodynamic factors is not known. The aim of the present study was to assess the relationships between hemodynamic, hemorheological and metabolic parameters in response to a sub-maximal cycling exercise protocol consisting of three successive levels of nine min duration (50, 100 and 150 W). Ten young sportsmen participated in the present study. Mean arterial pressure (MAP) was measured manually, with thoracic impedance used to monitor cardiac output (Qc ): systemic vascular…resistance (SVR) was then calculated. Whole blood viscosity (ηb ) was measured and used to calculate systemic vascular hindrance. Hematocrit (Hct) was determined by micro-centrifugation and red blood cell (RBC) deformability (EI) was determined by ecktacytometry. A breath-by-breath gas analyzer was used to measure oxygen uptake (VO2 ); the Fick equation was used to calculate arterio-venous oxygen difference [(a-v)O2 ] from VO2 and Qc . All measurements were performed at rest, during exercise and during recovery. Compared to baseline, Qc , MAP, Hct, EI, VO2 , and (a-v)O2 increased during exercise. ηb increased above baseline only at 150 W and remained elevated during recovery; the increase in ηb during the last level of exercise was associated with a decrease of SVR and systemic vascular hindrance. There was a significant negative correlation between EI and SVR (r=−0.35, p<0.01) and a significant positive relationship between EI and (a-v)O2 (r=0.35, p<0.01) and between EI and VO2 (r=0.37, p<0.01) across all exercise workloads, thus suggesting a potential role for RBC deformability as a factor affecting aerobic performance via oxygen delivery to tissues. These data lend support to the concept that hemorheological parameters may contribute to hemodynamic and cardio-respiratory adaptations in response to exercise in moderately trained sportsmen.
Abstract: Shear stress is considered an important stimulus for vascular adaptations with exercise training, yet the shear rate response to exercise has not been carefully examined in women or in healthy older adults. Therefore, the purpose of this study was to determine if age or sex differences are present in common femoral artery (CFA) shear rates during leg exercise. Diameter and mean blood velocity were measured in the CFA using Doppler ultrasound in young (20–30 yr) and older (60–79 yr) men and women at rest and during single-leg knee extensor exercise. Shear rate was calculated. Resting shear rate was lower in…older compared to young adults (33.9±3.7 vs. 58.3±3.6 s−1 , respectively; p<0.05) and lower in men than women (36.8±3.8 vs. 55.4±3.5 s−1 , respectively; p<0.05). During exercise, older adults had overall lower shear rates compared to young adults (within-sex comparison, p<0.05). The rise in shear rate with work rate showed no age difference but was lower in men than women (4.6±0.4 vs. 8.6±0.4 s−1 per W, p<0.05). These results suggest that age and sex differences are present in CFA shear rates during exercise which could have implications for vascular adaptability with exercise training.
Keywords: Shear stress, aging, vascular conductance, sex differences
vol. 46, no. 2, pp. 145-154, 2009
Abstract: Hematocrit (Hct) is the major determinant of whole blood viscosity and of its oxygen binding capacity: with increasing Hct, viscosity increases exponentially and oxygen capacity increases linearly. Thus, the theoretical oxygen transport potential of blood, as indexed by the ratio of Hct to viscosity (Hct/viscosity), generally yields a curve concave to the Hct axis with a maximum at an “optimal hematocrit” value. This study analyzed relations between Hct, blood viscosity and shear rate for rats and dogs to explore whether different optima exist for Hct or Hct/viscosity. Our results reveal differences depending on both shear rate and species: at equal…Hct, rats had higher blood viscosity and thus lower Hct/viscosity levels. Optimum values for Hct/viscosity were markedly different between the two species at shear rates of 90 and 200 s−1 . Conversely, Hct/viscosity data at 10 s−1 did not exhibit an optimum but rather a linear decrease of the ratio with increasing hematocrit. Relations between Hct and blood viscosity thus differ among animal species. Inasmuch as animal studies are often utilized as an aid to understanding hemorheological aspects of clinical conditions and/or therapy, evaluating Hct/viscosity ratios may be a useful supplementary tool for research focused on various physiological and patho-physiological processes.
Keywords: Optimal hematocrit, blood viscosity, dog, inter-species differences, rat
vol. 46, no. 2, pp. 155-165, 2009