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PubMed2006

Capillary blood viscosity in microcirculation.

As known, at the arteriolar level there is the highest resistance to the flow due to the section and to the velocity with an average pressure fall of 50 mmHg (from 85 to 35 mmHg). This resistance is expressed in sec(-1) by the ratio W/2r. This ratio is very high with an average value of 332 sec(-1) and viscosity at this high shear-rate is negligible. At the capillary level the pressure fall is 11.5 mmHg but the vascular resistance W/2r is much lower, on average 32 sec(-1). We can say that if a resistance of 333 sec(-1) corresponds with a pressure fall of 50 mmHg, then a resistance of 32 sec(-1) should correspond with a pressure fall of 4.8 mmHg. The highest pressure fall is due to another kind of resistance which we can define as "Capillary Blood Viscosity" because it depends on the rheological and structural characteristics of the blood. Our instrument reproduces the structure of the capillary district in an experimental model and measures the General Blood Viscosity (GBV) and the Capillary Blood Viscosity (CBV) at the same shear-rate and in particular at the low shear-rate when in non-Newtonian fluids the highest increase in viscosity appears. Consequently, at the capillary, viscosity is dominant with respect to the other geometric and physical resistances. Moreover, the percentage ratio between the GBV and the CBV gives a physical measure of erythrocyte deformability. Knowing viscosity at shear-rate present in the circulatory system, we can obtain the size of RBCs aggregates in the different circulatory districts and their characteristics expressed like "aggregation bond". Changes in CBV are the only possibility in clinical practice to improve the circulatory flow in the capillary district because it is not sure that changes in the arteriolar section can improve the capillary flow or rather open arterio-venous anastomosis. Moreover, in the systemic circulation the aggregate size allows us to point out the phenomenon of cell adhesion because the presence of several receptors involves also the other blood cells. Finally the size and the stability of the RBCs aggregates can modify the endothelial thrombo-resistance.

Arthritis, Rheumatoid↗

PubMed1990

Effects of blood viscosity on renin secretion.

The effects of alterations in blood and plasma viscosities on plasma renin activity (PRA) were studied in dogs anesthetized with pentobarbital. Blood viscosity was altered by changing the hematocrit (Hct) level by isovolemic exchange using packed red blood cells or plasma. Plasma viscosity was elevated by isovolemic exchange using Hct-matched blood with high molecular weight dextran (Dx, mean m.w. approximately 450,000) dissolved in plasma. Following control measurements of plasma and blood viscosities, plasma [Dx], PRA, Hct and hemodynamic functions, the dog was subjected to isovolemic exchange transfusions to either alter the Hct or administer the Dx. Various measurements were repeated 40-60 min after each exchange. Arterial pressure and renal blood flow remained relatively constant after exchanges; increases in plasma and blood viscosities were accompanied by a decrease in renal vascular hindrance (vasodilation) to keep the renal flow resistance at control level. PRA rose with increases in plasma [Dx] and viscosity, and the rise in PRA was best correlated with the decrease in renal hindrance. The changes in PRA and renal hindrance have the same regression line whether blood viscosity was altered by Hct variation or Dx administration. The results indicate that increases in viscosity cause a compensatory vasodilation of renal vessels to cause renin secretion.

Animals↗

PubMed2006

Clinical laboratory measurement of serum, plasma, and blood viscosity.

This article discusses the fundamentals for measuring the viscosity of whole blood, serum, and plasma and its application to the diagnosis of hyperviscosity syndrome. We describe some of the terminology in the field, including relevant definitions, the different units of measure, and general principles of clinical laboratory viscosity measurement. The 3 main categories of instrumentation for viscosity measurement--capillary, falling-sphere, and rotational viscometers--are discussed. We compare the various types of instrumentation for their usefulness with various types of clinical specimens. Relevant features that may be important in selecting a viscometer are described. We describe our 1.5-year experience with the viscometer that we chose. We hope the information in this review will be useful to pathologists and clinical laboratory staff in explaining the available choices for measuring serum, plasma, and whole blood viscosity.

Blood Viscosity↗

PubMedDate not supplied

Blood viscosity in chronically hypoxic rats: an effect independent of packed cell volume.

We compared apparent blood viscosity, measured with a cone-plate viscometer, in normoxic and chronically hypoxic rats. All comparisons were made at equal packed cell volume (PCV) and shear rate conditions. Apparent viscosity of whole blood from the hypoxic rats was significantly lower than that from normoxic littermates and was similar to that of young rats. Apparent viscosity of red cells from hypoxic rats suspended in phosphate buffered saline remained lower than that from the normoxic rats. When blood cells from the hypoxic rats were suspended in plasma from normoxic rats, apparent viscosity was lower than when blood cells from normoxic animals were suspended in plasma from hypoxic rats. The lower viscosity of the blood from hypoxic rats appears to be associated with characteristics present in newly generated red cells. The reduced apparent viscosity of blood in hypoxic rats may partially compensate for the increase in PCV, at least during the early stages of hypoxia.

Aging↗

PubMed1991

The nature and reversibility of hypothermia-induced alterations of blood viscosity.

This study evaluates the nature and reversibility of the increase in whole blood viscosity known to be induced by hypothermia. Anticoagulated samples were obtained from normal volunteers and were assayed for cellular deformability by 4.7 microns membrane filtration of whole blood (n = 12) and washed RBCs (n = 10). Results were expressed as filtration rate. Specimens were evaluated for plasma (n = 10) and whole blood (n = 12) viscosity by cone plate viscometer. All assays were sequentially performed at 30 degrees, 34 degrees, and 37 degrees C and difference analyzed by paired t test. Hypothermia resulted in significant impairment of cellular deformability, which was reversed by rewarming: [table: see text] Hypothermia also resulted in a significant increase in plasma viscosity (mean difference = 0.5426 centipoise, p less than 0.02), which was likewise reduced on rewarming. The increase in whole blood viscosity associated with hypothermia is secondary to both diminished cellular deformability and increased plasma viscosity. Both of these alterations are reversible with appropriate rewarming.

Blood Viscosity↗

PubMed1976

Exercise fitness, cardiac work and blood viscosity factors in patients and normals.

A study of 41 cardiovascular patients and normals showed significant correlations between physical fitness (as expressed by a fitness index based on work output) and high shear rate blood viscosity (p less than 0.01); between the cardiac work expressed as double product (= myocardial oxygen demand) and aggregation of red cells (p less than 0.05); between the triple term of cardiac work (fitness index divided by double product) and high shear rate blood viscosity (p less than 0.005) or aggregation of red cells (p less than 0.05), in all cases correlations being negative i.e., higher cardiac work or higher fitness being related to low blood viscosity or lower aggregation of red cells. Significant differences were found between high-fitness and low-fitness groups, the high-fitness group showing from plasma viscosity (p less than 0.0005), lower fibrinogen level (p less than 0.05), and higher albumin/fibrinogen ratio (p less than 0.01).

Adult↗

PubMed1997

[Correlations between retinal fluorescein angiography and blood viscosity and other factors in patients with primary open angle glaucoma].

OBJECTIVE: To investigate the correlations between retinal fluorescein angiography and blood viscosity and other factors in patients with primary open angle glaucoma (POAG). METHODS: Multiple stepwise regression analysis was made to approach the correlation between each of the following blood vessel filling times: the arm-choroid (A-CT), arm-retinal artery (A-AT), and retinal artery-venous (A-VT) of the fundus fluorescein angiography (FFA) in 122 eyes with POAG and each of the following related factors in hemorheology: whole blood apparent viscosity at low, medium and high shear rates, plasma viscosity and hematocrit. Also, the same analysis was applied to investigate the correlation between each of the A-AT, A-VT of the FFA in 70 eyes with POAG and each of the following factors: systolic blood pressure, diastolic blood pressure, age and the whole blood apparent viscosity at low shear rate. RESULTS: The whole blood apparent viscosity at low shear rate was closely related to A-CT and A-AT, while hematocrit was closely related to A-VT of the FFA. The whole blood apparent viscosity at low shear rate and age, especially whole blood apparent viscosity, was closely related to A-AT, A-VT of the FFA. CONCLUSION: The blood viscosity can affect the filling times of the FFA in POAG.

Blood Viscosity↗

PubMedDate not supplied

Blood viscosity and uterine artery flow velocity waveforms in pregnancy: a longitudinal study.

In the course of pregnancy, whole blood viscosity (WBV) decreases, plasma viscosity (PV) increases and uteroplacental resistance to blood flow falls. According to the Hagen-Poiseuille law, viscosity influences resistance to blood flow. To investigate the contribution of these haemorheological changes to the decrease in resistance to blood flow in the uteroplacental circulation, a serial study was performed. Using blood viscosimetry and pulsed Doppler ultrasound recordings of the uterine arteries, 21 women with normal pregnancies were studied every 8 weeks from 12 weeks onwards. Statistical analysis revealed no significant relationship between WBV, PV and pulsatility index of the uterine arteries. It is concluded that the changes in blood viscosities are of minor influence on resistance to blood flow in the uteroplacental circulation throughout normal pregnancy. The vascular changes e.g. the considerable increase of the diameter of the spiral arteries have a much greater impact on resistance to blood flow.

Adult↗

PubMed1989

Endothelium dependent control of arterial diameter by blood viscosity.

The local control of arterial diameter by blood flow rate has been attributed to the ability of the endothelial cells to sense the shear stress exerted on them by flowing blood. Since shear stress is proportional to the product of flow rate and fluid viscosity, an increase in the latter will augment shear stress and lead to arterial dilatation as well. We therefore designed experiments to reveal the control of the arterial lumen by blood viscosity and to compare it with the control by blood flow rate. Changes in external diameter of a segment of feline femoral artery caused by variations in blood viscosity and/or flow rate were recorded during the perfusion in situ under stabilised transmural pressure. Decrease in blood viscosity evoked by haemodilution at a constant flow rate led to arterial constriction whereas an increase in viscosity due to haemoconcentration caused arterial dilatation. These viscosity induced changes in arterial diameter depended on intact endothelium. Responses to the changes in blood viscosity and flow rate of the same magnitude were practically identical. These results show that blood viscosity is a factor affecting vascular smooth muscle tone and confirm the suggestion that shear stress is the key signal in the endothelium dependent control of the arterial lumen by blood flow rate.

Animals↗

PubMed2002

Blood viscosity and platelet function in patients with obstructive sleep apnea syndrome treated with nasal continuous positive airway pressure.

Patients with obstructive sleep apnea syndrome (OSA) have a high incidence of cardiovascular events. We measured whole blood viscosity at high (94.5 s(-1)) and low (0.1 s(-1)) shear rate, hematocrit, fibrinogen, and platelet hemostatic function (PTA-100) at 7-8 p.m. and 7-8 a.m. in 8 controls and 13 patients, once with the established nasal continuous positive airway pressure (NCPAP) treatment and once without. OSA patients had a higher plasma viscosity (1.37+/-0.11 vs. 1.19+/-0.11 mPa.s in the evening, p<0.05) and fibrinogen (2.61+/-0.49 vs. 2.11+/-0.29 g/l, p<0.05) than controls, without diurnal difference, and similar values with or without NCPAP. Whole blood viscosity and hematocrit were similar in controls and patients before and after a night with or without NCPAP. Platelet activity was significantly higher in the morning than in the evening in controls and patients with or without NCPAP. We conclude that blood viscosity and platelet activity are similar in controls and patients with OSA on a long-term treatment with NCPAP, which is not worsened by a single night without NCPAP. The increase of plasma viscosity and fibrinogen in OSA patients as well as the general increase of platelet aggregation in the morning may contribute to the increased incidence of cardiovascular events.

Aged↗

PubMed1987

[Whole blood viscosity in patients with acral arterial occlusive diseases and their modification by rheologically active drugs].

Measurements of the whole-blood viscosity in patients with organic and functional disturbances of the acral blood supply were performed. In comparison with the whole-blood viscosity in normal persons patients with acral occlusive diseases showed a significantly increased viscosity. On the other hand, in patients with functional disturbances of the acral blood supply no differences could be established. In a therapy study the good efficacy of rheologically effective medicaments could be demonstrated particularly as combination therapy of pentoxifylline, acetylsalicylic acid and tolazoline in patients with acral occlusive diseases. These medicaments should by all means be used together with the basic therapy. In functional disturbances of the blood supply should predominantly be maintained physiotherapeutic methods of treatment.

Adult↗

PubMed1983

[Changes in blood viscosity after administration of vitamin E in the rabbit].

Vitamin E is an essential factor to maintain biological membranes stability and its lack may affect membranes structures and reduce erythrocyte life-span. Vitamin E also play a role in the maintenance of a normal platelet aggregation. A.A. studied the effects of a ten days supply of d-1-alpha tocopherol acetate (50 mg/Kg/die) on blood viscosity in 8 rabbits. Results obtained show a significant reduction of blood viscosity on 6th day of treatment in the male rabbits and a progressive reduction of values from the 6th till the 10th day in female rabbits. The most significant decrease of blood viscosity were obtained at the lowest shear-rates, due to an increased red cells deformability to the antioxidative action of vitamin E on the erythrocytes membrane and to a reduced red cells aggregation. Such modifications on the red blood cells caratheristics can be determined by vitamin E through different mechanism: a) inhibiting red cell membrane's polyunsaturable fatty acids oxidation; b) by removal of abnormal lipids from erythrocyte membrane; c) physical and chemical stabilization of membrane's surface.

Animals↗

PubMed1977

Blood viscosity, red-cell flexibility, haematocrit, and plasma-fibrinogen in patients with angina.

Whole-blood viscosity, haematocrit and plasma-fibrinogen concentration were measured in 22 patients with angina and 22 controls. All four variables were significantly higher in patients with angina. When the viscosity was corrected to a standard haematocrit (45%), however, there was no significant difference in the mean viscosity of the two groups, indicating that the higher viscosity in patients with angina is the result of the higher haematocrit. Increased red-cell flexibility tends to counteract the effect of increased plasma-fibrinogen concentration, which tends to increase blood-viscosity.

Adult↗

PubMed1978

The effects of intravenous isoxsuprine on blood viscosity in patients with occlusive peripheral arterial disease.

1 Blood viscosity is thought to be a major factor in disorders of the peripheral circulation. 2 Ten patients with obliterative arterial disease received an infusion of isoxsuprine of 20 micrograms kg-1 for 30 min. The infusion was followed by a highly significant and prolonged fall in blood, plasma and serum viscosity, in haematocrit and in plasma fibrinogen concentration. Blood lipid levels were also studied: total lipids and total cholesterol did not alter; triglyceride level was significantly lowered at the end of, and after, drug infusion. 3 There was no change in blood, plasma or serum viscosity in the four patients receiving a control infusion 2 days before the infusion of isoxsuprine. 4 The relationships between lowered viscosity and increasing peripheral tissue perfusion are discussed.

Aged↗

PubMed1975

Direct influence of blood viscosity on pulmonary vascular resistance.

When cardiac output is maintained constant in the intact animal, changes in blood viscosity exert a direct and rapid effect on pulmonary vascular resistance. The presence of intact cardiopulmonary reflex mechanisms does not alter the direct influence of blood viscosity on pulmonary vascular resistance.

Animals↗

PubMedDate not supplied

[Blood viscosity factor in persons with high and low risk of ischemic heart disease].

In the years 1986-1987, the blood viscosity factor, the content of haemoglobin in erythrocytes, the concentration of glucose in blood, the lipids and the blood coagulation system were examined in 180 subjects. They were divided into three groups according to the exposure to risk factors: group performing light manual work (L), group performing hard manual work (C) and group of engine drivers (M). No statistically significant differences in regard to age, employment period, number of cigarettes smoked, as well as arterial systolic and diastolic blood pressure were found between the subjects. Workers from group M had the highest body weight (P > 99%) and increased concentration in blood of triglycerides (P > 99% and Apo B (P > 99%. Subjects from group C had the lowest concentration of cholesterol in blood (P > 99%) and the smallest number of members with hypertensions (3.8%) and overweight (7.5%). Group L included the highest percentage of persons with arterial hypertension (17.5%), the highest, among all examined, blood viscosity factor determined at the coagulation rate of 18.6 s-1, and the lowest prothrombin factor (P > 99%).

Adult↗

PubMed1978

[The effect of operation, anaesthesia and blood viscosity on haemodynamic during aortofemoral bypass operation (author's transl)].

Cardiac index, total peripheral resistance, blood, plasma and serum viscosity in patients with peripheral vascular disease were measured pre-, intra- and postoperatively. Besides plasma and serum viscosity, most obviously blood viscosity decreased during anaesthesia and operation. The decrease of blood viscosity is caused mainly by the falling haematocrit. Red blood cell aggregation occuring under low-flow conditions is decreased. Thus blood viscosity additionally is diminished at least in the area of low shear rates. Corresponding haemodynamic measurements revealed that decreasing viscosity improves cardiac index and total pressure resistance if normovolaemia exists, but in general is masked by anaesthesia and operation.

Anesthesia↗

PubMed1988

Blood viscosity after a 1-h submaximal exercise with and without drinking.

Ten healthy subjects performed two exercise sessions similar to an endurance training session for average athletes (1 cycling exercise at 85% of the maximal heart rate on a Monark cycle ergometer). In the first session, the subjects were not allowed to drink during exercise. During the second session, the same subjects performed the same exercise as during the first session but they drank a beverage volume equal to the weight loss induced by the first exercise session to verify the hypothesis that the compensation of sweat loss by drinking could attenuate the exercise-induced blood viscosity increase. Both protocols (with and without drinking) induced a significant increase of hematocrit and plasma viscosity. The whole blood viscosity increased at all shear rates but this increase was significant only for the exercise protocol without drinking. Blood thixotropic property, erythrocyte deformability, and erythrocyte aggregability remained unchanged after both exercise protocols. Hemoconcentration explained the increase of hematocrit and plasma viscosity. Hemoconcentration was probably the consequence of a filtration process through capillary leakage in addition to sweat loss, which could explain the partial effect of drinking in our study.

Adult↗