Hemodynamics of Vascular Disease Flashcards
What is blood flow influenced by
- Heart influences the strength and amount of ejected blood
- Elastic arteries store energy during systole and maintain blood flow during diastole
- Muscular arteries maintain tone
- Arterioles, capillaries and venules supply blood to different organs
- veins ensure adequate return of blood to the heart
what must be present for blood flow to occur between any two points in the circulatory system
Energy difference between these two points
what is the difference in energy levels usually caused by?
Blood pressure
what is continually lost because of friction between the layers of flowing blood
energy
Both ______ and ______decrease as the red blood cells transit from the arterial to the venous system
Pressure and kinetic energy
What does generated arterial pressure do?
Forces blood to move from the arterial system into the venous system and maintains the arterial pressure and the energy difference needed for blood to keep flowing
where is a balance of blood mainatined
Arterial reservoir
blood flow to all the body tissues is adjudged
According to the tissues particular needs at a given time
Achieved by vasoconstriction
what is the main form of blood stored in flowing blood
Potential energy due to the pressure of distending the vessels
Some energy stored in blood is also____
Kinetic energy
Kinetic energy of blood is proportional to what?
its density (stable in normal circumstances)
Kinetic energy is proportional to the square of
Its velocity
As artery lumen increases
Kinetic energy is converted back into pressure (potential energy) as velocity decreases
Narrowed artery lumen
Potential energy is converted back into kinetic energy
blood flow is said to be what?
Laminar
Loss of energy is due to
Friction
Amount of friction and energy loss
Largely determined by the dimensions of the vessels
Decrease in radius by 10%
Decrease the volume flow in a rube by about 35%
Poiseuille’s law
Applies to constant laminar flow of a simple fluid in a rigid tube of a uniform diameter
Vessels in a series
overall resistance is equal to the sum of the resistances of the individual vessels
where do alterations in blood flow profiles occur?
Curves, bifurcations, any branch point and at stenic lesions
Site of boundary layer seperation
Transition zone where the lamina has zero velocity, classically at the carotid artery bifurcation
what does the vascular system consist of?
Heart, arteries, arterioles, capillaries, venules, veins
what occurs across the capillary walls
exchange of gases, nutrients and waste products
pulmonary circulation
right side of the heart pumps blood through pulmonary vessels, through the lungs for oxygenation and back to the left side of the heart
Systemic circulation
Pumps blood from the left side of the heart through vessels supplying either the head and arms or the lower body and back to the right side of the heart
Heart
Propels blood through the system
Arteries
Series of vessels efferent from the heart that become smaller and smaller as they branch into various organs
Capillaires
Smallest vessels, site of exchange between blood and tissue
Microvasculature bed
complex network of thin, anastomosing tubules formed by capillaries
Veins
Convergence of venules into a system of larger channels that continue enlarging as they approach the heart
what occurs in pulmonary circulation
blood is oxygenated by the lungs
what occurs in systemic circulation
Blood brings nutrients and removes waste in tissues throughout the body
What are organs with high metabolic rates
Liver
Spleen
Kidneys
what kind of vascular beds do high metabolic rate organs have?
Low resistance vascular beds
what are organs with low metabolic rates
Stomach
Small intestine
Muscle
what kind of vascular beds do low metabolic rate organs have?
High resistance vascular beds
what are the three layers of vessel walls?
Tunica intima
Tunica media
Tunica adventitia
Tunica Intima
Innermost layer
Consists of endothelial cell lining with connective tissue beneath
Tunica Media
Middle layer
Thickest component
Composed mainly of smooth muscle
Varies in the amounts of elastic fibers and collagen
Tunica Adventitia
Outermost layer
Composed of connective tissue, nerve fibers, and small vessel capillaries
In contact with surrounding tissue
what is the size of large conducting arteries
2.5-1cm
what are large arteries composed of?
Elastic arteries with less smooth muscle
Aorta and its largest branches
what are medium and small sized arteries composed of?
Well developed smooth muscle layers
Includes all arteries except aorta and major branches
what is the size of medium and small-sized arteries
Approximately 1 -0.3mm in diameter
What is the size of arterioles
03.mm - 10 µm
what do arterioles do?
Stopcocks“ of the vascular system
Circular smooth muscle layers control contraction and resistance
what is minute by minute flow into the capillary bed determined by?
arteriole diameter
are veins more or less muscular?
less muscular
are veins more or less thick then arteries
Walls are thinner than arteries
what are the walls of venules composed of?
Connective tissue
size of venules
8 - 100 µm
Size of medium veins
Diameters from 1 to 10 mm
what do medium veins include
Includes all veins except portal vein and vena cava and main branches
Have a thin tunica media
what are large veins
Include portal vein, superior and inferior vena cava (IVC), and main branches
Thick adventitial layer with fibrous and elastic tissues
what do venous valves prevent?
Retrograde movement of blood
what are venous valves
Bicuspid inward projections of tunica intima
What is the sinus
Enlarged area behind leaflets
where are valves most numerus
Lower extremities
Where are valves absent?
thorax and abdomen
what is the smallest vessel in the body?
Capillaries
what is the wall of the capillary composed of?
Walls composed primarily of a layer of endothelial cells with small amount of basement membrane
Primary place where nutrient exchange occurs
total energy remains what?
Constant-conserved over time
Energy….
can be neither created nor destroyed; rather transforms from one form to another
what is total fluid energy made up of?
Potential and kinetic energy
Potential energy
Stored or resting energy
Represented by the intravascular pressure
Supplied by the contraction of the heart
what stores potential energy
Contraction of the heart
Kinetic energy
Energy of work or motion
Represented by the velocity of moving blood
how does blood move
Moves from an area of high energy (pressure) to an area of lower energy (pressure)
Circulatory system is what kind of system?
Closed system
what must there be for blood to move
Energy gradient
what is the driving force behind fluid flow?
Pressure
The greater the pressure difference
The greater the flow rate (Directly proportional)
Equal pressure
No flow
Korotkoff sounds
soft ticking while measuring blood pressure
Continuity Rule
Blood is neither created nor destroyed as it flows through a vessel
What goes in must come out
Volumetric flow rate must be what?
Constant proximal, within and distal to a change in vessel diameter
what does the continuity rule mean?
Same volume proximally moves distally to a narrower area and therefore will necessitate a fast velocity to get through the vessel.
Velcoity
rate of movement with respect to time (centimeters per second)
Volume Flow
the volume of something moved per unit time (milliliters per second)
what is the velocity formula?
v=Q/A
V=Velocity, Q=Volume, A=Area
what occurs with stenosis (Narrowing)
VELOCITY must increase to maintain volume flow
Area is _______to velocity
Indirectly Proportional
As total cross sectional area increases
Blood velocity decreases
what does Poiseuille’s Law define
Defines the pressure/flow relationships in the vascular system
Poiseuille’s law: pressure difference
If pressure difference or the diameter of the tube increases, flow rate increases
Poiseuille’s law: Viscoity
If viscosity or the length of the tube increases, flow rate decreases
what is viscosity
Property of a fluid that resists the force tending to cause fluid to flow
The friction that exists between bordering layers of fluid
Creates energy “losses” in the vascular system (conversion of friction to heat)
what is resistance equal to?
Resistance is equal to the pressure drop divided by flow
How can resistance be expressed?
In the circulatory system, blood vessel length is virtually constant as is blood viscosity
Changes in resistance are due to changes in vessel radius
what causes changes in resistance
Due to changes in vessel radius
Series resistance
The total resistance of the entire system equals the sum of the individual resistances
what will multiple stenosis’s do?
Multiple stenosis’ along the same blood vessel will increase the total resistance
Parallel resistance
The reciprocal of the total resistance is equal to the sum of the reciprocals of the individual resistances
what occurs with more parallel elements in a network
the lower the overall resistance of the network
Plug Flow
The speed of the fluid is essentially constant across the tube
As flow enters a vessel, streamlines move in approximately the same velocity
Laminar flow
Streamlines are straight and parallel to each other
Flow speed is maximum at the center of the tube and minimum or zero at the tube’s walls
what occurs with laminar flow
Successive layers of fluid slide on each other with relative motion.
what is blood flow
Laminar
Parabolic flow
A form of laminar flow
The average flow speed across the vessel is equal to one half the maximum flow speed (center)
where is parabolic flow often seen?
Thoracic and abdominal aorta
Disturbed flow
A form of laminar flow
Occurs when the parallel streamlines are altered from their straight line form
Occurs in the region of a stenosis or at a bifurcation
Turbulent Flow
Non-laminar flow with random and chaotic speeds and directions
Forward net flow is still maintained
Greater pressure is required to move fluid under turbulent conditions
Turbulence can be defined by “Reynolds number”
when can turbulence occur
Transition from high flow speed in a narrow channel to slow flow in a broad stream
Inertia
Is the tendency of a body at rest to stay at rest or a body in motion to stay in motion unless acted upon by an outside force.
what is Reynolds number
likelihood of turbulence
What is Reynolds number directly proportional to?
- velocity of blood
- density of blood
- radius of blood vessel
what is Reynolds inversely proportional to?
-viscosity of blood
when is turbulence likely to develop?
Reynolds number above 2000
what does turbulence mainly depend on?
velocity and vessel radius
as blood flows through a stenosis, what occurs?
velocity increases
what occurs after a stenosis
Turbulence
