Blood viscosity
Encyclopedia
Blood viscosity is a measure of the resistance
of blood
to flow, which is being deformed by either shear or extensional strain
.
Blood
is a liquid that consists of plasma
and particles, such as the red blood cell
s. The viscosity of blood thus depends on the viscosity
of the plasma, in combination with the hematocrit
. However, plasma can be considered a Newtonian fluid
, but blood cannot due to the red blood cells which add non-idealties to the fluid. The fluid must reach a shear rate of about 100 (1/sec) to be assumed Newtonian. Until this point is reached the term viscosity cannot be applied to blood. The viscosity of blood
after this shear rate is reached is about five times as great as the viscosity of water
. When the hematocrit
rises to 60 or 70, which it often does in polycythemia
, the blood viscosity can become as great as 10 times that of water, and its flow through blood vessels is greatly retarded because of increased resistance to flow. This will lead to decreased oxygen
delivery.
In pascal
-second
s (Pa·s), the viscosity
of blood at 37°C is normally 3*10-3 to 4*10-3. The analogous unit in the centimetre gram second system of units
is Poise
, and the viscosity of blood at 20°C is normally 10 centipoise (cP).
Plasma viscosity is determined by water-content and macromolecular components, so these factors that affect blood viscosity are the plasma protein concentration and types of proteins in the plasma, but these effects are so much less than the effect of hematocrit that they are not significant, and elevation of plasma viscosity correlates to the progression of coronary and peripheral vascular diseases. Anemia can lead to decrease blood viscosity, which may lead to heart failure.
Other factors influencing blood viscosity include temperature, where an increase in temperature results in a decrease in viscosity. This is particularly important in hypothermia, where an increase in blood viscosity will cause problems with blood circulation.
Vascular resistance
Vascular resistance is a term used to define the resistance to flow that must be overcome to push blood through the circulatory system. The resistance offered by the peripheral circulation is known as the systemic vascular resistance , while the resistance offered by the vasculature of the lungs...
of blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
to flow, which is being deformed by either shear or extensional strain
Strain
Strain can refer to:* Strain , variants of plants, viruses or bacteria; or an inbred animal used for experimental purposes* Strain , a chemical stress of a molecule...
.
Blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
is a liquid that consists of plasma
Blood plasma
Blood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...
and particles, such as the red blood cell
Red blood cell
Red blood cells are the most common type of blood cell and the vertebrate organism's principal means of delivering oxygen to the body tissues via the blood flow through the circulatory system...
s. The viscosity of blood thus depends on the viscosity
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
of the plasma, in combination with the hematocrit
Hematocrit
The hematocrit or packed cell volume or erythrocyte volume fraction is the percentage of the concentration of red blood cells in blood. It is normally about 45% for men and 40% for women...
. However, plasma can be considered a Newtonian fluid
Newtonian fluid
A Newtonian fluid is a fluid whose stress versus strain rate curve is linear and passes through the origin. The constant of proportionality is known as the viscosity.-Definition:...
, but blood cannot due to the red blood cells which add non-idealties to the fluid. The fluid must reach a shear rate of about 100 (1/sec) to be assumed Newtonian. Until this point is reached the term viscosity cannot be applied to blood. The viscosity of blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
after this shear rate is reached is about five times as great as the viscosity of water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
. When the hematocrit
Hematocrit
The hematocrit or packed cell volume or erythrocyte volume fraction is the percentage of the concentration of red blood cells in blood. It is normally about 45% for men and 40% for women...
rises to 60 or 70, which it often does in polycythemia
Polycythemia
Polycythemia is a disease state in which the proportion of blood volume that is occupied by red blood cells increases...
, the blood viscosity can become as great as 10 times that of water, and its flow through blood vessels is greatly retarded because of increased resistance to flow. This will lead to decreased oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
delivery.
In pascal
Pascal (unit)
The pascal is the SI derived unit of pressure, internal pressure, stress, Young's modulus and tensile strength, named after the French mathematician, physicist, inventor, writer, and philosopher Blaise Pascal. It is a measure of force per unit area, defined as one newton per square metre...
-second
Second
The second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock....
s (Pa·s), the viscosity
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
of blood at 37°C is normally 3*10-3 to 4*10-3. The analogous unit in the centimetre gram second system of units
Centimetre gram second system of units
The centimetre–gram–second system is a metric system of physical units based on centimetre as the unit of length, gram as a unit of mass, and second as a unit of time...
is Poise
Poise
The poise is the unit of dynamic viscosity in the centimetre gram second system of units. It is named after Jean Louis Marie Poiseuille ....
, and the viscosity of blood at 20°C is normally 10 centipoise (cP).
Plasma viscosity is determined by water-content and macromolecular components, so these factors that affect blood viscosity are the plasma protein concentration and types of proteins in the plasma, but these effects are so much less than the effect of hematocrit that they are not significant, and elevation of plasma viscosity correlates to the progression of coronary and peripheral vascular diseases. Anemia can lead to decrease blood viscosity, which may lead to heart failure.
Other factors influencing blood viscosity include temperature, where an increase in temperature results in a decrease in viscosity. This is particularly important in hypothermia, where an increase in blood viscosity will cause problems with blood circulation.