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How does the micro and nanostrure of blood influence its rheology

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1 How does the micro and nanostrure of blood influence its rheology
Anna Kucaba-Piętal (Rzeszów)

2 Contents I. II. Blood as suspension Plasma Red Blood Cells
White Blood Cells Platelets II. Rheological parameters of blood Problems with theoretical modelling Blood viscosity Hematocrits’ effect on blood rheology Blood viscoelasticity Fahraeus–Lindquist Effect Perspectives

3 Microscopic view of blood
Blood is a liquid tissue. Suspended in the plasma are seven types of cells and cell fragments The microcirculation is the business end of the vascular system and with its 60,000 miles of capillaries in the human body is responsible for the transport of nutrients and metabolites to the body's many tissues. Microscopic view of blood

4 Blood - functions Blood performs two major functions: 1) transports through the body: oxygen and carbon dioxide food molecules (glucose, lipids, amino acids) ions (e.g., Na+, Ca2+, HCO3−) wastes (e.g., urea) hormones heat 2) defends the body against infections and other foreign materials. All the WBCs participate in these defenses.

5 Blood - characteristics
Adult ♂ contains 5-6L Adult ♀ contains 4-5L T is about 100.4 F 5 times as viscous as water pH ranges from 7.35 – 7.45 (slightly alkaline) Color ranges from scarlet (oxygenated blood) to deep red (deoxygenated blood).

6 Blood - components Blood is made of four components: Plasma (55%)
Platelets (0,17%) White BC (0,1%) Red BC (45%)

7 Blood as suspension Whole Blood Plasma (46-63%) Formed Elements
(37-54%) Water (92%) Plasma Proteins (7%) Other Solutes (1%) Red Blood Cells (99.9%) Platelets White BC (0,1%)

8 Composition of blood plasma:
Plasma is the straw-colored liquid in which the blood cells are suspended. Composition of blood plasma: Component Percent Water ~92 Proteins 6–8 Salts 0.8 Lipids 0.6 Glucose (blood sugar) 0.1

9 Plasma - functions Plasma transports materials needed by cells and materials that must be removed from cells: various ions (Na+, Ca2+, HCO3−, etc. ) glucose and traces of other sugars amino acids other organic acids cholesterol and other lipids hormones urea and other wastes

10 The serum proteins can be separated by electrophoresis.
Plasma - components Serum Proteins Proteins make up 6–8% of the blood. They are about equally divided between serum albumin and a great variety of serum globulins. After blood is withdrawn from a vein and allowed to clot, the clot slowly shrinks. As it does so, a clear fluid called serum is squeezed out. Thus: Serum is blood plasma without fibrinogen and other clotting factors.   The serum proteins can be separated by electrophoresis.

11 Red Blood Cells (Erythrocytes)

12 Red Blood Cells - characteristics
Most abundant blood cells In ♂, 1µL of blood contains million RBCs In ♀, 1µL of blood contains million RBCs Contains the red pigment hemoglobin which binds and transports O2 and CO2 Each RBC is a biconcave disc however while moving it deforms itself adapting like a liquid-filled baloon to the shape of capilaries.

13 Red Blood Cells Red blood cells is a membrane filled with a solution of hemoglobin and various salts. They manufacture hemoglobin until it accounts for some 90% of the dry weight of the cell. The viscosity of the RBC interior fluid is five to ten times greater than of exterior fluid. RBC in quiescent plasma tend to form aggregates known as rouleax

14 Hemoglobine Gas transporting protein molecule that makes up 95% of a red cell Each chain contains a single molecule of heme, an iron-containing pigment Each red cell has about 270,000,000 iron-rich hemoglobin molecules Note the 2  chains and 2 β chains. Notice how each has an associated heme molecule with an iron atom.

15 Red Blood Cells - functions
RBCs transport oxygen from the lungs to all of living tissues of the body and carry away carbon dioxide. The RBC values can vary depending on such factors as health and altitude. Peruvians living at 18,000 feet may have as many as 8.3 x 106 RBCs per µl. People who are anemic have deficency in red cells. RBC precursors mature in the bone marrow closely attached to a macrophage. The nucleus is squeezed out of the cell and is ingested by the macrophage.

16 Hematocrit Percentage of whole blood occupied by packed red blood cells Average in a ♂ is 46 (range of 40-54) Average in a ♀ is 42 (range of 37-47) Determined by centrifuging a blood sample so that all formed elements come out of suspension Low Hct values may indicate anemia whereas high values may indicate polycythemia

17 Lifecycle of an RBC Are produced continously in our bone marrow from stem cells They can never divide After ≈120d, the RBC cell membrane ruptures, or the damage is detected by phagocytic cells in the liver and spleen Most of the iron in their hemoglobin is reclaimed for reuse macrophage phagocytizing multiple RBCs RBC flow through capilaries

18 White Blood Cells White blood cells are clear round cells that are bigger than red blood cells. White blood cells produce proteins called antibodies that help our bodies fight infections caused by bacteria, viruses, and foreign proteins.

19 White Blood Cells Leukocytes (leuko=white, cyte=cell)
All contain nuclei and organelles Help defend the body against invasion by pathogens, and they remove toxins, wastes, and abnormal/damaged cells A typical µL of blood contains WBCs (1% volume) Most of the WBCs in the body at a given moment are in the connective tissue proper or in organs of the lymphatic system Remain viable only last hours before they also are removed

20 Types of WBC 1 Can be classified based on the appearance of granules when viewed under the light microscope. Granulocytes_protect body from infection: Basophils Eosinophils Neutrophils Agranulocytes are a part of immune system Lymphocytes Monocytes 2

21 Types of WBC Neutrophil Eosinophil Monocyte Basophil Lymphocyte
60% neutrophils % lymphocytes 6% monocytes % eosinophils % basophils Neutrophil Eosinophil Monocyte Basophil Lymphocyte

22 Platelets Platelets aren't really cells at all; they are just fragments of cells. When we are injured, platelets gather at the site of the injury and stick to the edges of the wound. They release chemicals that help start the process of blood clotting so that bleeding will stop.

23 Platelets Flattened disk-like cell fragments that are about 1µm by 4µm (1/3 size of RBC). Continuously being replaced. Each platelet circulates for 9-12 days before being removed by splenic phagocytes. On average there are 350,000 platelets/µL of blood. Produced in the bone marrow. Large cells called megakaryocytes release fragments (platelets) into the circulation.

24 Platelets - functions Act as a participant in the vascular clotting system. Platelets are sometimes referred to as thrombocytes (thrombus=clot) When blood vessels are cut or damaged, the loss of blood from the system must be stopped before shock and possible death occur. This is accomplished by solidification of the blood, a process called coagulation or clotting. A blood clot consists of a plug of platelets enmeshed in a network of insoluble fibrin molecules.

25 Part Two

26 Why is it important to predict rheological
parameters of blood? To use it in diagnostics of clinical disorders To maintain nonbiological fluids that has rheological properties comparble to blood Due to formulation blood flow equations Starting from a mean value of about 3,51 cP (with share rate = 100 sec.-1), the viscosity grows (for share rates up to 0,1 sec.-1) until 57,09 cP [5]. Therefore the knowledge of the viscosity, including its variations, is extremely important in the study of the blood rheology.

27 Rheological parameters
The viscosity and elasticity determine the pressure required to produce blood flow. The heart pumps energy into the blood with each beat. Portions of this energy are either dissipated or stored as the blood cells rearrange, orient and deform. Viscosity is an assessment of the rate of energy dissipation due to cell deformation and sliding. Elasticity is an assessment of the elastic storage of energy primarily in the kinetic deformability of the red blood cells.

28 Blood viscosity I The blood viscosity is a function of the protein concentration of the haematocrit (Ht), of the pH of plasma, and of the temperature (this dependence is negligible in physiological condition). Blood is considered as a Newtonian fluid for high values of the gradient dv/dn (for the arterial flow) and non-Newtonian for low values, because in these circumstances the development of groups of  7-10 erythrocytes (rouleaux) is common; in this last case the viscosity is no longer constant. Among the main factors from which the blood viscosity depends, the haematocrit is quite effective. The erythrocytes tend to reduce the speed gradient dv/dn. This is the reason why the viscous term rises. Such increase is reduced by the deformability of the erythrocytes (that reduces the effect between the speeds of adjacent fluid threads)

29 Blood viscosity II for Ht=45% the viscosity of blood is:
 at 20ºC   µ=3,45 cP  at 37ºC   µ=2,72 cP and that is it decreases with the temperature, even if in the physiological field of variation of the temperature it can be considered constant: The viscosity of the plasma is µ=1,2 cP. cP = 4 * 10-3 Pa * s Plasma is a Newtonian fluid.

30 Results

31 Blood – viscosity

32 Problems Blood is a concentrated suspension of Red Blood Cells; outside the range of dilute suspension Particles change their shape in response to the fluid forces The nature of RBC membrane and its deformation stress/strain is much less established RBC tends to form agregates known as rouleaux


34 Blood – Casson model . g mapp = t

35 Results

36 Hematocrit in blood circulation
Hmicro-microvessel hematocrit Hsys- large blood vessels hematocrit

37 Hematocrit’s effect on blood rheology
The influence of blood cell concentration (hematocrit H) on viscosity and viscoelasticity of blood

38 Viscoelasticity The tendency of materials to respond to stress as if they were a combination of elastic solids and viscous fluids This property, possessed by all plastics to some degree, dictates that while plastics have solid-like characteristics such as elasticity, strength and form stability they also have liquid-like characteristics such as flow depending on time, temperature, rate and amount of loading

39 Blood Viscoelasticity I
When the red cells are at rest they tend to aggregate In order for blood to flow freely, the size of these aggregates must be reduced The forces that disaggregate the cells also produce elastic deformation and orientation of the cells, causing elastic energy to be stored in the cellular microstructure of the blood. The most common method of determining the consistency of a flowing liquid uses the relation between shear stress and time rate of shear strain (or shear rate). If the flow is constant in time, then the ratio of shear stress to shear rate is the viscosity. When flows are changing with time, such as blood flow in the human circulation, the liquid generally demonstrates both a viscous and an elastic effect, both of which determine the stress-to-strain rate relationship. Such liquids are called viscoelastic. Blood plasma normally shows viscosity only[8], while whole blood is both viscous and elastic. Parameters of human blood measured at a frequency near that of the human pulse.

40 Blood Viscoelasticity II
Modification of plasma such as changes in osmotic pressure, pH, concentration of fibrinogen and other plasma proteins, and clinically introduced blood volume expanders, can have major effects on blood viscoelasticity The viscoelasticity of blood is traceable to the elastic red blood cells, which occupy about half the volume. When the red cells are at rest they tend to aggregate and stack together in a space efficient manner. In order for blood to flow freely, the size of these aggregates must be reduced, which in turn provides some freedom of internal motion. The forces that disaggregate the cells also produce elastic deformation and orientation of the cells, causing elastic energy to be stored in the cellular microstructure of the blood. As flow proceeds, the sliding of the internal cellular structure requires a continuous input of energy, which is dissipated through viscous friction. These effects make blood a viscoelastic fluid, exhibiting both viscous and elastic properties. The viscoelasticity for normal 0.46 H blood diluted to 0.31 H by the addition of Dextran 40 (D), autogenous plasma (P), and lactated Ringer's solution (L). Measurements were made at 2 Hz and 22 °C.

41 Blood Viscoelasticity III
Variation in blood viscoelasticity among normals is very small. So it can be treated as a useful clinical parameter. viscoelasticity of an individual's blood changes significantly as the result of disease or surgical intervention Cardiopulmonary bypass surgery

42 The Fahraeus Effect In blood vessels with diameters less than 500 mm both the hematocrit and viscosity decrease with diameter. The hematocrit in the capillary is greatly reduced because the red cells speed up relative to the plasma as they squeeze through the capillary. Since they must travel faster than the plasma, there must be fewer of them present to maintain the same proportions of cells and plasma as blood exits the capillary. This is the so-called Fahraeus-Lindquist Effect. d Viscosity (µ) of blood versus the diameter (d) of the vessel (µm)

43 Perspectives: Develop an understanding of how the micro- and nano-structure of blood influences its rheology Explore to use of rheological parameters in diagnostics and menagement of clinical disorders and inoptimisation of blood processing

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