Blood flow

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Blood flow

Blood flow is the flow of blood

Blood

Blood is a specialized bodily fluid that delivers necessary substances to the body's Cell s ? such as nutrients and oxygen ? and transports waste products away from those same cells....
in the cardiovascular system.

It can be calculated by dividing the vascular resistance

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 is known as the pulmonary vascular re...
into the pressure gradient

Pressure gradient

In atmospheric sciences , the pressure gradient is a physical quantity that describes in which direction and at what rate the pressure changes the most rapidly around a particular location....
.

ematically, blood flow is described by Darcy's law

Darcy's law

In fluid dynamics and hydrology, Darcy's law is a Phenomenology derived constitutive equation that describes the flow of a fluid through a porous medium....
(which can be viewed as the fluid equivalent of Ohm's law

Ohm's law

Ohm's law applies to electrical circuits; it states that the electric current through a conductor between two points is directly Proportionality to the potential difference or voltage across the two points, and inversely proportional to the Electrical resistance between them....
) and approximately by Hagen-Poiseuille equation

Hagen-Poiseuille equation

The Hagen-Poiseuille equation is a physical law that describes slow viscousincompressible flow through a constant circular cross-section. It is also known as the Hagen-Poiseuille law, Poiseuille law and Poiseuille equation....
.

Blood is a heterogeneous medium consisting mainly of plasma
Blood plasma

Blood plasma is the liquid component of blood, in which the blood cells are suspended. It makes up about 55% of total blood volume. It is composed of mostly water , and contains dissolved proteins, glucose, clotting factors, mineral ions, Hormone and carbon dioxide ....
and a suspension of red blood cell
Red blood cell

Red blood cells are the most common type of blood cell and the vertebrate body's principal means of delivering oxygen to the body tissues via the blood....
s. Red cells tend to coagulate when the flow shear rate
Shear rate

Shear rate is the rate at which a shear is applied....
s are low, while increasing shear rates break these formations apart, thus reducing blood viscosity
Viscosity

Viscosity is a measure of the Drag of a fluid which is being deformed by either shear stress or extensional stress. In everyday terms , viscosity is "thickness"....
.

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Encyclopedia

Blood flow is the flow of blood
Blood

Blood is a specialized bodily fluid that delivers necessary substances to the body's Cell s ? such as nutrients and oxygen ? and transports waste products away from those same cells....
in the cardiovascular system.

It can be calculated by dividing the vascular resistance
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 is known as the pulmonary vascular re...
into the pressure gradient
Pressure gradient

In atmospheric sciences , the pressure gradient is a physical quantity that describes in which direction and at what rate the pressure changes the most rapidly around a particular location....
.

Physics
Mathematically, blood flow is described by Darcy's law
Darcy's law

In fluid dynamics and hydrology, Darcy's law is a Phenomenology derived constitutive equation that describes the flow of a fluid through a porous medium....
(which can be viewed as the fluid equivalent of Ohm's law
Ohm's law

Ohm's law applies to electrical circuits; it states that the electric current through a conductor between two points is directly Proportionality to the potential difference or voltage across the two points, and inversely proportional to the Electrical resistance between them....
) and approximately by Hagen-Poiseuille equation
Hagen-Poiseuille equation

The Hagen-Poiseuille equation is a physical law that describes slow viscousincompressible flow through a constant circular cross-section. It is also known as the Hagen-Poiseuille law, Poiseuille law and Poiseuille equation....
.

Blood is a heterogeneous medium consisting mainly of plasma
Blood plasma

Blood plasma is the liquid component of blood, in which the blood cells are suspended. It makes up about 55% of total blood volume. It is composed of mostly water , and contains dissolved proteins, glucose, clotting factors, mineral ions, Hormone and carbon dioxide ....
and a suspension of red blood cell
Red blood cell

Red blood cells are the most common type of blood cell and the vertebrate body's principal means of delivering oxygen to the body tissues via the blood....
s. Red cells tend to coagulate when the flow shear rate
Shear rate

Shear rate is the rate at which a shear is applied....
s are low, while increasing shear rates break these formations apart, thus reducing blood viscosity
Viscosity

Viscosity is a measure of the Drag of a fluid which is being deformed by either shear stress or extensional stress. In everyday terms , viscosity is "thickness"....
. This results in two non-Newtonian blood properties, shear thinning
Shear thinning

A pseudoplastic material is one in which viscosity decreases with increasing rate of shear stress . This property is found in certain complex solutions, such as ketchup, whipped cream, blood, paint, and nail polish....
and yield stress
Yield (engineering)

The yield strength or yield point of a material is defined in engineering and materials science as the Stress at which a material begins to Plasticity ....
. In healthy large arteries blood can be successfully approximated as a homogeneous, Newtonian fluid
Newtonian fluid

A Newtonian fluid is a fluid whose shear stress versus rate of strain curve is linear and passes through the Origin . The constant of proportionality is known as the viscosity....
since the vessel size is much greater than the size of particles and shear rates are sufficiently high that particle interactions may have a negligible effect on the flow. In smaller vessels, however, non-Newtonian blood behavior should be taken into account.

The flow in healthy vessels is generally laminar
Laminar flow

Laminar flow, sometimes known as Streamlines, streaklines and pathlines flow, occurs when a fluid flows in parallel layers, with no disruption between the layers....
, however in diseased (e.g. atherosclerotic
Atherosclerosis

Atherosclerosis is a syndrome affecting artery blood vessels. It is a chronic inflammatory response in the walls of arteries, in large part due to the accumulation of macrophage white blood cells and promoted by low density lipoproteins without adequate removal of fats and cholesterol from the macrophages by functional high density lipoprot...
) arteries the flow may be transitional or turbulent
Turbulence

In fluid dynamics, turbulence or turbulent flow is a fluid regime characterized by chaotic, stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time....
.

Equations
The first equation below is Darcy's law, the second is the Hagen-Poiseuille equation:

where:

F = blood flow
P = pressure
R = resistance
? = fluid viscosity

L = length of tube
r = radius of tube

In the last equation it is important to note that resistance to flow changes dramatically with respect to the radius of the tube. This is important in angioplasty
Angioplasty

Angioplasty is the technique of mechanically widening a narrowed or obstructed blood vessel; typically as a result of atherosclerosis. Tightly folded balloons are passed into the narrowed locations and then inflated to a fixed size using water pressures some 75 to 500 times normal blood pressure ....
, as it enables the increase of blood flow with balloon catheter
Balloon catheter

A balloon catheter is a type of "soft" catheter with an inflatable "balloon" at its tip which is used during a catheterization procedure to enlarge a narrow opening or passage within the body....
to the deprived organ significantly with only a small increase in radius of a vessel.

Disturbed blood flow
Disturbed blood flow may cause ischemia
Ischemia

In medicine, ischemia is a restriction in blood supply, generally due to factors in the blood vessels, with resultant damage or dysfunction of tissue....
and even infarction
Infarction

In medicine, an infarction results in the death of a macroscopic area of tissue in an organ due to loss of adequate blood supply. This dead tissue is then known as necrosis....
of the dependent tissue supplied by the struck vessels.

Causes include:
Thrombosis
Thrombosis

Thrombosis is the formation of a blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel is injured, the body uses platelets and fibrin to form a blood clot, because the first step in repairing it is to prevent loss of blood....
Atherosclerosis
Atherosclerosis

Atherosclerosis is a syndrome affecting artery blood vessels. It is a chronic inflammatory response in the walls of arteries, in large part due to the accumulation of macrophage white blood cells and promoted by low density lipoproteins without adequate removal of fats and cholesterol from the macrophages by functional high density lipoprot...
Prolonged bedrest
Bedrest

Bedrest as a medicine treatment refers to staying in bed day and night as a treatment for an illness or medical condition, especially when prescribed or chosen rather than resulting from severe prostration or imminent death....
or immobilization
Immobilization

Immobilization in soil science, is when organic matter decomposes and is absorbed by micro-organisms, therefore preventing it being accessible to plants....
Myocardial infarction
Myocardial infarction

Myocardial infarction , commonly known as a heart attack, occurs when the Blood flow to part of the heart is interrupted. This is most commonly due to occlusion of a coronary artery following the rupture of a Vulnerable plaque, which is an unstable collection of lipids and white blood cells in the wall of an artery....
Atrial fibrillation
Atrial fibrillation

Atrial fibrillation is a cardiac arrhythmia that involves the two upper chambers of the heart. It can often be identified by taking a pulse and observing that the heartbeats don't occur at regular intervals, but a conclusive indication of AF is the absence of P waves on an electrocardiogram ....
Prosthetic cardiac valves

Disturbed blood flow is a factor in Virchow's triad
Virchow's triad

Virchow's triad encompasses the three broad categories of factors that are thought to contribute to thrombosis.It is named for Germany physician Rudolf Virchow ....
for thrombosis.

See also

Heart rate
Heart rate

Heart rate is a measure of the number of heart beats per minute . The average resting human heart rate is about 70 bpm for adult males and 75 bpm for adult females....