Ch 18 Book Flashcards
Hemodynamic
study of blood moving through the circulatory system
Flow indicates
Units
volume of blood moving during a particular time
liters/min, L/min
Velocity indicates
Units
speed or swiftness of a fluid moving from one location to another
cm/s
Pulsatile Flow
occurs when blood moves with a variable velocity
Pulsatile Flow: Blood accelerates and decelerates b/c
cardiac contraction
Pulsatile Flow: Present in
arterial circulation
Phasic flow
occurs when blood moves with a variable velocity
Phasic flow: Blood accelerates and decelerates b/c
respiration
Phasic flow: Present in
venous circulation
Steady Flow
Ex:
occurs when a fluid moves at a constant speed or velocity
water flowing through a hose
Steady Flow: Present in
venous circulation when individual stop breathing for a brief moment
Laminar flow
when the flow streamlines are aligned and parallel
Characterized by layer of blood that travels at individual speeds
Commonly found in normal physiologic status
Silent flow
Laminar flow forms: Plug flow
occurs when all of the layers and blood cells travel at same velocity
Laminae flow forms: Parabolic flow
has a bullet-shaped profile.
Velocity is highest in the center
Gradually decreases to its minimum at the vessel wall
Turbulent flow
characterized as chaotic flow patterns in many different directions and at many speeds
Associated with cardiovascular pathology and elevated blood velocities
Found downstream from stenosis
Converts flow energy into other forms such as sound and vibration
Vortex
Small, hurricane like, swirling, rotational patterns appear
Murmur or Bruit
Sound associated with turbulence
Thrill
associated with turbulence
Described as a palpable murmur
Reynolds number
predicts whether flow is laminar or turbulent
2,000 = turbulent
Energy Gradient
Blood moves from regions of higher energy to lower energy
Energy is imparted to blood by the contraction of the heart during systole
Kinetic Energy
Associated with a moving object
Heavy moving objects have lots of kinetic energy as slow moving objects have little
Kinetic Energy:
Determined by two factors:
An object’s mass
The speed at which it moves
Pressure Energy
A form of stored or potential energy
Potential energy has the ability to perform work
major form of energy for circulating blood and creates flow by overcoming resistance
Gravitation Energy
Associated with
A form of stored or potential energy
elevated object
All elevated objects have stored energy (gravitation energy) that can perform work.
Viscous Energy Loss
Describes the thickness of a fluid
More energy is lost with movement of high viscosity
Loss is associated with blood overcoming its internal stickiness and determined by the hematocrit
Viscous Energy Loss: Hematocrit
percentage of blood made up of red blood cells
Normal value is 45%
Anemia, hematocrit reduced and blood has a reduced viscosity
Units: Poise
Frictional Energy Loss
Occur when flow energy is converted to heat as one object rubs against another
Blood sliding across vessel walls creates heart
Inertial Energy Loss
“Objects at rest tend to stay at rest and objects in motion tend to stay in motion” – Sir Isaac Newton
Energy is lost when the speed of a fluid changes, regardless of whether the fluid speeds up or slows down
Inertial Energy Loss: Inertia relates to
tendency of a fluid to resist changes in its velocity
Inertial energy loss occurs during three events
Pulsatile flow (arterial)
Phasic Flow (venous)
Velocity changes at a stenosis
Inertial Energy Loss: Velocity
Velocity increases as the vessel narrows
Maximum velocity exists where the vessel is narrowest
Velocity decreases as blood flows out of the stenosis into a vessel segment of normal diameter
Stenosis
Narrowing in the lumen of a vessel
Stenosis Effects
change in flow direction increased velocity as vessel narrows turbulence downstream from the stenosis pressure gradient across the stenosis loss of pulsatility
Stenosis Effects: increased velocity within the stenosis
highest where vessel is narrowest
Stenosis Effect: turbulence downstream from stenosis
post stenotic turbulence
Lumen expands more dramatically than the streamlines of blood flow are able to fill it
Streamlines are destroyed and turbulence appears
Converted to sound (bruit) or vibrations (thrill) or both
Stenosis Effect: Pressure gradient across the stenosis
the pressure downstream from the stenosis is lower than the pressure upstream
decreases the results from the loss of energy as blood moves through the stenosis
Bernoulli’s Principle describes
relationship between velocity and pressure in a moving fluid
Bernoulli’s Principle derived from
the principle of conservation of energy
Bernoulli’s Principle states
with a steady flow, the sum of all forms of energy is same everywhere
The sum of kinetic energy and pressure energy remains constant
Bernoulli’s Principle: The Law of Conservation of Energy
states that energy is neither created nor destroyed, it is converted from one form to another
Arterioles
resistance vessels
Pressure gradient =
flow x resistance
Pressure gradient increase when either
Flow increases
Resistance increases
Flow increases when either
Pressure gradient increases
Resistance decreases
Fluids vs Electricity
Fluids: Pressure
Electricity: ______
Voltage
Fluids vs Electricity
Fluids: Flow
Electricity: ______
Current
Fluids vs Electricity
Fluids: Resistance
Electricity: ______
Resistance
Ohm’s Law
Units
Voltage = current x resistance
Ohms
Veins
thin-walled collapsible
low pressure: partially filled with blood, partially expanded
low resistance vessels
Veins during exercise
increases
changes from hourglass to oval than round
allows veins to accommodate a large volume increases with a very small increase in pressure
more round, resistance decreases, increasing outflow toward heart
Hydrostatic Pressure
Unit
pressure related to the weight of blood pressing on a vessel measured at a height above or below heart level
mmHg
Hydrostatic Pressure accuracy measured at
level of the heart
too high, below the heart
too low, above the heart
Hydrostatic Pressure- Supine
flat on your back
All parts of the body are at the same level as the heart and the pressure is zero everywhere
Hydrostatic Pressure - Standing
Upright at heart level
pressure 0
measured pressure accurately represents true circulatory pressure
Hydrostatic Pressure - Standing
below heart level
positive
measured pressure will be higher than the true circulatory pressure
Hydrostatic Pressure - Standing
above heart level
negative
measured pressure will be lower than the true circulatory pressure
Respiration affects venous flow for two reasons
Venous system is low pressure
Muscles responsible for respiration alter pressures in the thorax and the abdomen
Breathing affects two venous flows
Venous flow to legs
Venous returns to heart, which comprises venous flow from the head, arms, and flow from the IVC to heart
Diaphragm
Responsible for breathing
moves up and down, alternating the pressure in thorax and abdomen
Inspiration
Diaphragm moves downward towards the abdomen
Thoracic pressure decreases
Adnominal pressure increases
Venous return to the hear increases
Venous flow in legs decreases
Expiration
Diaphragm moves upward into thorax
Thoracic pressure increases
Abdominal pressure decreases
Venous return to the heart decreases
Venous flow in legs increases
