Chapter 18 Flashcards
Flow
indicates the volume of blood moving at a particular time
units: volume/time ex. liters/mm “how much?”
Velocity
indicates the speed of a fluid moving from one location to another
units: distance/time ex. 200cm/sec
3 Basic Forms of Blood Flow
pulsatile
phasic
steady
Pulsatile Flow
occurs when blood moves with variable velocities, accelerates and decelerates from cardiac contraction and appears in the arterial circulation
Phasic Flow
occurs when blood moves with variable velocities, accelerates and decelerates from respiration and appears in venous circulation
Steady Flow
occurs when blood moves at a constant velocity, steady flow is present in the venous circulation when individuals stop breathing for a moment
ex. of steady flow, water running through a garden hose
Laminar Flow
when the flow streamlines and is parallel, layers of blood travel at individual speeds, commonly found in normal physiological states
2 Forms of Laminar Flow
plug flow
parabolic flow
Plug Flow
when all the layers of blood cells travel at the same velocity (center of river)
Parabolic Flow
velocities are highest in the center and gradually decrease to the minimum at the vessel wall (has a bullet-shaped profile)
Plug and Parabolic Flow are…
Laminar and associated with normal physiology. Laminar flow is silent.
Reynolds number
predicts whether flow is laminar or turbulent
laminar flow is less than 1,500
turbulent flow is more than 2,000
Turbulent Flow
chaotic flow patterns in many different directions and at many different speeds
hurricane-like, also called an eddy current or vortex
Turbulent Pathology
associated with cardiovascular pathology and elevated blood velocities
may be seen downstream from stenosis in a vessel
Turbulent Flow converts flow energy into..
sound and vibrations
Turbulence associated with sound
is called murmur or a bruit
Turbulence associated with vibrations
is called a thrill, also described as a palpable murmur, you can feel it with your fingertips
Where can turbulent flow be detected?
1 cm after the stenosis
Energy Gradient
blood moves from regions of higher energy to lower energy
What event provides energy to the circulating blood?
energy is imparted to blood by the contraction of the heart during systole
Forms of energy associated with blood
kinetic
pressure
gravitational
the total energy at a specific location with the circulation is the sum of all 3 energy forms
Kinetic Energy
is associated with a moving object
determined by 2 factors: object’s mass and the speed at which it moves
Pressure Energy
stored or potential energy, has the ability to perform work
pressure is a major form of energy in the circulation system, creates flow by over coming resistance
Gravitational Energy
stored or potential energy (like pressure energy), associated with any elevated object (use of gravity)
identical objects at the same height have the same gravitational energy
Energy is lost 3 ways during circulation
viscous loss
frictional loss
inertial loss
Viscous loss
associated with thickness of the blood, energy is lost by overcoming its internal thickness
Viscosity is measured in units called…
Poise
Viscous energy loss in blood is determined by the.. .
Hematocrit, % of blood made up of red blood cells.
Frictional Energy loss
energy is lost when flow energy is converted to heat
blood sliding across the vessel walls
Inertial Energy loss
energy is lost when the speed of the fluid changes, regardless is the fluid accelerates or decelerates
Inertia
relates to the tendency of a fluid to resist changes in its velocity
Inertial Energy loss occurs during 3 events
pulsatile flow
phasic flow
velocity changes at a stenosis
velocity increases…
when the vessel is at its narrowest
velocity decreases…
when the blood flows out of a stenosis into the normal vessel diameter
Stenosis
is a narrowing in the lumen of a vessel
5 affects of a Stenosis
change in flow direction increased velocity as vessel narrows turbulence downstream from the stenosis pressure graident across the stenosis loss of pulsatility
Bernoulli’s Principle
describes the relationship between velocity and pressure in a moving fluid
principle of conservation of energy- with a steady flow, the sum of all energy is the same everywhere
The relationship between flow resistance and pressure gradient is defined by what equation?
flow X resistance = pressure gradient
Pressure gradient increases when..
flow increases
resistance increases
Flow increases when…
pressure gradient increases
resistance decreases
Ohm’s Law
current X resistance = voltage
Ohm’s is…
electrical resistance
Fluids
pressure
flow
resistance
Electricity
voltage
current
resistance (ohms)
What is the typical resistance of veins?
low resistance
How do veins adapt to increased inflow during periods of exercise?
the cross section shape of the vein changes from hourglass to oval and then to round
Hydrostatic Pressure
pressure related to the weight of blood pressing on a vessel measured at a height above or below the heart level
Units of Hydrostatic Pressure
mmHg
What is the hydrostatic pressure when an individual is supine?
Zero, all parts of the body are at the same level as the heart
Respiration affects venous flow for 2 reasons
the venous system is low pressure
muscles responsible for respiration alter pressures in the thorax and the abdomen
Breathing affects 2 venous flows
venous flows in the legs
venous return to the heart, which comprises venous flow from the head, arms and flow from the inferior vena cava to the heart
Venous flow in the legs correlates with movement of the…
diaphragm
Downward movement of the diaphragm…
decreases venous flow in the legs
downward-decrease
Upward movement of the diaphragm…
increase venous flow in the legs
upward-increase
When venous flow in the leg decreases…
venous return to the heart increases
When venous flow in the leg increases…
venous return to the heart decreases
