Blood viscosity at different shear rates in capillary tubes

Bate, H

doi:10.3233/bir-1977-145-607

Cited by 17 publications

(9 citation statements)

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“…Of note, as a non-Newtonian fluid, blood increases its viscosity with decreased shear stress. 38 Therefore, regulation of blood viscosity appears to be an at least as important mechanism as vasodilatation. The simplest way to maintain the blood viscosity as low as possible despite the elevated hematocrit is to keep the erythrocyte population as young as possible.…”

Section: Discussionmentioning

confidence: 99%

Enhanced erythro-phagocytosis in polycythemic mice overexpressing erythropoietin

Bogdanova

Mihov

Lutz

et al. 2007

Blood

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Adaptive mechanisms to hematocrit levels of 0.9 in our erythropoietin-overexpressing mice (tg6) include increased plasma nitric oxide levels and erythrocyte flexibility. Doubled reticulocyte counts in tg6 suggest an increased erythrocyte turnover. Here we show that compared with wild-type (wt) animals, erythrocyte lifespan in tg6 is 70% lower in tg6 mice. Transgenic mice have a younger erythrocyte population as indicated by higher intercellular water and potassium content, higher flexibility, decreased density, increased surface to volume ratio, and decreased osmotic fragility. Interestingly, despite being younger, the tg6 erythrocyte population also harbors characteristics of accelerated aging such as an increased band 4.1a to 4.1b ratio, signs of oxidative stress, or decreased surface CD47 and sialic acids. In tg6, in vivo tracking of PKH26-labeled erythrocytes revealed dramatically increased erythrocyte incorporation by their liver macrophages. In vitro experiments showed that tg6 macrophages are more active than wt macrophages and that tg6 erythrocytes are more attractive for macrophages than wt ones. In conclusion, in tg6 mice erythrocyte aging is accelerated, which results, together with an increased number and activity of their macrophages, in enhanced erythrocyte clearance. Our data points toward a new mechanism downregulating red cell mass in excessive erythrocytosis in mice. IntroductionDuring aging, the erythrocytes considerably change the internal ion and protein composition, and the biomechanical and biochemical properties of their cell membrane, as well as size, shape, and surface to volume ratio. In humans, these changes finally result in selective elimination of senescent erythrocytes from the circulation. 1 The clearance of erythrocytes in mice and rabbits is in part age dependent and in part random. 2 Nevertheless, the agedependent erythrocyte clearance in these mammals is well controlled, involving oxidative damage, phosphatidylserine exposure, 3,4 desialylation, 5 and immunoglobulins. 6 The involvement of immunoglobulins in clearance of senescent erythrocytes in mice must, however, differ from that in humans, because naturally occurring antibodies in mice are exclusively of the IgM class. Under pathological conditions such as sickle cell anemia the phosphatidylserine exposure to the outer leaflet of the red cell membrane presumably plays a predominant role since in this disease the percentage of phosphatidylserine-expressing red cells is increased 2-to 10-fold. 4 Our transgenic (tg6) mice that constitutively overexpress human Epo in an oxygen-independent manner have a 12-fold elevated Epo plasma level 7 leading to hematocrit values of up to 0.9. As to the question how tg6 mice cope with excessive erythrocytosis, we reported earlier that they show chronic vasodilatation due to excessive NO production 7 and regulate blood viscosity by elevating erythrocyte flexibility. 8 Here we were especially interested to define the process of erythrocyte turnover in tg6 animals by focusing on mechanisms of...

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Section: Discussionmentioning

confidence: 99%

Enhanced erythro-phagocytosis in polycythemic mice overexpressing erythropoietin

Bogdanova

Mihov

Lutz

et al. 2007

Blood

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“…The plasma was never coloured with haemoglobin after centrifugation, which gave assurance that the red cells had not been haemolysed by their repeated passage through the perfusion pump. In several animals measurements of blood viscosity were made by Dr Hilary Bate at the end of the experiment using a capillary viscometer (Bate, 1977) at 22 IC.…”

Section: Methodsmentioning

confidence: 99%

The response of the hind‐limb vascular bed of the rabbit to sympathetic stimulation and its modification by pregnancy.

Humphreys¹,

Joels²

1982

The Journal of Physiology

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SUMMARY1. Pressure-flow relationships in the hind limb, perfused with blood at a series of constant flows, have been compared in primigravid and virgin rabbits following section of the lumbar sympathetic chain.2. In the absence of sympathetic stimulation perfusion pressure was lower (P < 0 05) in the pregnant rabbits at all levels of flow to the leg.3. It is concluded that pregnancy leads to a reduction in the vascular resistance of the acutely sympathectomized hind limb.4. The pressure-flow curves of hind limbs from pregnant and non-pregnant rabbits in which the cutaneous circulation had been excluded by skinning the leg and ligating the ankle were also compared. Again, perfusion pressure at each flow level was lower in the limbs from the pregnant animals (P < 0 05).5. The sympathetic supply was stimulated at frequencies of 0 3, 1, 3, 7, 15 and 30 Hz. Irrespective of whether the cutaneous circulation was excluded, the pressureflow curves for the hind limbs of pregnant and non-pregnant rabbits were different at the lower frequencies. As stimulus frequency rose this difference became smaller, and at a stimulus frequency of 7-15 Hz or more there was little difference in the position of the curves in pregnant and non-pregnant rabbits.6. Examination of the pressure-flow curves suggests that when, as in these experiments, flow is held constant, the ability of sympathetic stimulation to increase the resistance to blood flow is reduced in pregnancy. However, if these pressure-flow curves are used to predict the change of flow that would occur at a constant perfusion pressure, the response to sympathetic stimulation appears to be greater in pregnancy.7. Futher analysis of the findings, based on certain assumptions, suggests that differences between the pressure-flow curves of pregnant and non-pregnant animals during sympathetic stimulation are due in the main to either a differing size of the unstimulated vascular beds or a differing compliance of their vessel walls, rather than to any intrinsic alteration in their response to sympathetic stimulation.

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“…[24] reported that the rheological properties of human blood at a shear rate ranging from 0.1 to 1.0s −1 are consistent with the Casson model, but they deviate to some extent in the range of 1 − 40s −1 . Bate [25] believed that the blood flow through tubes is best described by the Casson model in the shear rate range of 15 − 6400s −1 . Therefore, for large-diameter vessels, like arteries, a modified and more-general Casson model was formulated by Gonzalez and Moraga [26]:…”

Section: Modified Casson Modelmentioning

confidence: 99%