Chapter 2: Physiology and Hemodynamics Flashcards
each heart beat pumps about _____mLs of blood into the aorta
70
Cardiac Contraction stages:
pressure in lt ventricle rises lt ventricle pressure exceeds aortic pressure aortic valve opens blood is ejected BP rises
Increased heart rate delivers _____ blood volume
increased
The heart pump:
generates pressure to move the blood
results in pressure wave (energy wave) that travels through the system
blood flow through system
lt ventricle aorta large arteries arterioles capillaries venules large veins vena cava rt atrium
the pumping action of the heart results in
high volume of blood in arteries to maintain high pressure gradient between arteries and veins
cardiac output governs
the amount of blood that enters the arterial system
what determines the amount of blood that leaves the arterial system
arterial pressure and total peripheral resistance
pressure is greatest at
the heart
gradually decreases as blood moves further away
this pressure difference is necessary to maintain blood flood
movement of any fluid between two points requires two things:
a pathway along which the fluid can move
difference in energy levels (pressure difference/energy gradient)
the amount of flow depends on
energy difference
resistance opposing movement
lower resistance = _____ flow rate
higher
Higher resistance = ____ flow rate
lower
the total energy contained in moving fluid is the sum of
pressure (potential), kinetic and gravitational energy
Pressure
potential/stored energy
major form of energy for circulation of blood
pressure is expressed in
mmHg
Kinetic energy
velocity
small for circulating blood
kinetic energy is expressed in
fluid density and velocity measurements
gravitational energy
equivalent to weight of column of blood extending from the heart to the level where pressure is measured hydrostatic pressure (HP)
supine patient hydrostatic pressure
arteries and veins are at the same level as the heart
0mmHg against arteries and veins at ankle
standing patient hydrostatic pressure
at ankle pressure is about 100mmHg
a _____ is needed to move blood from one point to another
energy gradient
the greater the energy gradient the ____ the flow
greater
Inertia
tendency of fluid to resist chanegs in its velocity
as blood moves farther out to the periphery
energy is dissipated in the form of heat
energy is continually restored by the
pumping action of the heart
movement of fluid is dependent upon
physical properties of the fluid and
what is moving through
Resistance = 8 nl/r4pi
R= resistance n= viscosity of blood l= length of the blood vessel r^4= radius of blood vessel
Resistance is directly proportional to
viscosity and length
Resistance is inversely proportional to
radius of blood vessel
what has the most dramatic effect on resistance?
a change in vessel diameter
Internal friction within a fluid is measure by
it’s viscosity
Friction causes loss how
energy is lost in form of heat as rbcs rub together
elevated hematocrit _____ viscosity
increases
anemia ____ viscosity
decreases
Diminishing vessel size
increases frictional forces and heat energy loss
increase viscosity = _______ velocity
decreased
decrease viscosity = ____ velocity
increased
plug flow is seen at
vessel orgin
parabolic flow is usually seen
downstream
viscous energy loss is due to
increased friction between layer of blood
intertial losses occur
with deviations from laminar flow due to change in direction of velocity
what happens to the blood when deviations from laminar flow occur
parabolic flow profile becomes flattened
flow becomes disorganized
inertial energy loss typically occurs at
exit of a stenosis
Posieuille’s equation defines
relationship between pressure, volume flow, resistance
Poiseuille’s law helps answer the question
how much fluid moves through a vessel
Poiseuille’s equation:
Q = P / R
Q= volume flow P= Pressure R= resistance
Poiseuille’s equation and the relationship between contributors to flow itself
Q = (p1 - p2) pie r^4 / 8nL
Q= volume flow P1 - P2 = pressures at proximal / dst ends R = Radius of vessel L = Length of vessel n = viscosity of fluid
Radius of the vessel is
directly proportional to volume flow
the Law of Conservation of Mass explains what relationship
the relationship between velocity and area
Law of Conservation of Mass equation
Q = A x V
If area increases
velocity decreases
if area decreases
velocity increases
Bernoulli describes:
pressure and velocity relationship
The total energy contained in a moving fluid is the sum of
pressure, kinetic and gravitational energies
If there is a change in either kinetic, gravitational or pressure energies what happens
the other make up for the difference in order to maintain the original total fluid energy amount
if velocity increases, pressure
decreases
if velocity decreases, pressure
increases
pressure gradients are also known as
flow seperations
flow separation occur because
geometry change with or without intra-luminal disease, curves
in a flow separation velocity _____ and pressure ____
decreases
increases
flow separations result in regions of
stagnant flow or little movement
examples of flow separations include
bypass graft anastamosis site, valve cusp site
Reynolds Number (Re)
determines when fluid becomes unstable / disturbed
at which Reynolds number does laminar flow become turbulent
> 2000
Steady flow originates from
steady driving pressure, predictable behavior
in steady flow energy losses mainly occur from
viscous loss, can be described by poiseuille’s equation
pulsatile flow
changes in both driving pressure condition as as well as response to the system
Systole
forward flow throughout the periphery (fluid acceleration)
late systole/ early diastole
temporary flow reversal
late systole/early disatole is caused by
phase shifted negative pressure gradient and peripheral resistance
late systole/early diastole causes
reflection of the wave proximally
the dicrotic nothc is related to
closure of the aortic valve and influence of peripheral resistance
Late diastole
flow is foward again
relective wave hits proximal resistance of the oncoming next wave and reverses
low resistance flow
flow is continuous (steady) feeling a dilated vascular bed
examples of low resistance flow
ICA, vertbral, renal, celiac, splenic, hepatic
high resistance flow
pulsatile in nature
what happens in high resistance flow
between pulses, hydraulic reflections travel back up vessel from the periphery producing flow reversals
examples of high resistance flow vessels
ECA subclavian aorta iliac extremity arteries fasting sma
the reversal of flow in a high resistance vessel may disappear distal to a stenosis because
of decreased peripheral resistance, secondary to ischemia
doppler flow distal to a significant stenosis
lower resistance
more rounded in appearance
weaker in strength
what happens to a normally high resistant signal as it approaches a significant stenosis
normally biphasic or triphasic signal may become monophasic
doppler flow proximal to a significant stenosis is
higher resistant
could have no/minimal diastole
during vasoconstriction, pulsatile changes in medium/small sized arteries of the limbs are
increased and pulsatility changes in minute arteries are decreased
during vasodilation, pulsatile changes in medium/small sized arteries of the limbs are
decreased, lower resistant,
pulsatility changes are increased in minute arteries
as the inflow pressure falls as a result of stenosis, what does the periphery do?
vasodilate to maintain flow
at rest, total blood flow may be normal even in the presence of a stenosis/occluision.. why is this
development of a collateral network
compensatory decrease in peripheral resistance
Arterial obstruction can cause changes in collateral channels near the site of obstruction, these changes include:
increased flow
reversed flow direction
increased velocity
waveform pulsatility changes
location of collaterals can help provide information about what
location of stenosis or obstruction
exercise should induce:
vasofilation
vasodilation does what?
lowers distal peripheral resistance, increases blood flow
what also influences vasoconstriction and vasodilation of blood vessels
sympathetic innervation fibers which help regulate body temperature
what is the best single vasodilator of resistance vessels within skeletal muscles?
exercise
autoregulation
ability of most vascular beds to maintain a constant level of blood flow over a wide range of perfusion pressures
autoregulation is not present when
perfusion pressure drops below a critical level
BP rise:
constriction of resistance vessels
BP fall:
dilation of resistance vessels
exercise usually decreases what in the exercising extremity
decreases reflection, decreases resistance
what waveform is seen in extremity arteries after exercise
low resistant, monophasic caused by vasodilation
with proximal arterial obstructions what happens to the flow patterns distally
monophasic wave form due to peripheral dilatation
higher resistance signals may be seen when
vasoconstrction at the arteriolar level or distal arterial obstruction
flow to cool extremity
pulsatile
flow to warm extremity
continuous steady signal
a cross sectional area reduction of 75% = ____ diameter reduction
50%
effects of flow abnormality produced by a stenosis depends on 4 factors
length, diameter, shape of narrowing multiple obstructions (resistances are additive) obstructions in parallel vessels pressure gradient (peripheral resistance beyond stenosis)
Proximal to a stenosis
flow is dampened
at the stenosis entrance
increase in doppler shift frequencies
spectral broadening
elevated velocities
flow disturbance in a stenosis occurs
due to interrupted flow stability with high velocity and eddies currents
at the exit of a stenosis
flow reversals
flor separations
eddy currents
spectral broadening
