Physiology and Hemodynamics Flashcards
Multi-branched elastic conduit is set into oscillation by what?
each beat of the heart
Each beat of the heart pumps about how much blood into the aorta causing a blood pressure pulse?
70 milliliters
What are the 3 actions of a cardiac contraction?
- Pressure in the left ventricle rises rapidly
- Left ventricle pressure exceeds that in the aorta
- Aortic valve opens, blood is ejected, BP arises
Increased hear rate delivers what?
An increased blood volume
The heart pump generates what?
the pressure to move the blood
The heart pump results in what?
A pressure wave (energy wave) that travels rapidly throughout the system, demonstrating transformation as it travels distally.
Pumping action the heart results in what?
High volume of blood in arteries to maintain a high pressure gradient between the arteries and veins
Cardiac output governs the amount of:
The blood that enters the arterial system: arterial pressure and total peripheral resistance, determines the amount that leaves it.
Pressure is greatest where?
The heart
Movement of any fluid medium between two points require two things:
- A pathway along which the fluid can flow
- Difference in energy levels (pressure difference)
The amount of flow depends on:
- Energy difference: includes losses resulting from fluid movement
2.Any resistance which tends to oppose such movement
lower resistance =
higher flow rate
higher resistance =
lower flow rate
The total energy contained in moving fluid is the sum of what?
Pressure (potential)
Kinetic and gravitational energies
Describe pressure energy:
Sideways flow*
- Stored energy
- Major form of E for circulation of blood
- Expressed in mmHg
Describe kinetic energy (velocity):
Forward flow*
- Small for circulating blood
- Expressed in terms of fluid density and its velocity measurements
What happens at the same time of heart contractions?
Pressure and Kinetic energy (velocity)
What is gravitational energy also called?
Hydrostatic pressure (HP)
Gravitational energy is equivalent to what?
The weight of the column of blood extending from the heart to level where pressure is measured
When standing, HP increases, adding about
When standing, HP increases, adding about:
100 mmHg against ankle vessels
What is needed to move blood from one point to another?
Energy gradiant
The greater the gradient:
greater the flow!
_____________ : relates to the tendency of a fluid to resist changes in its velocity.
Inertia
As the blood moves farther out of periphery, what happens to the energy?
it dissipates largely in the form of heat
Energy is continually restored by what?
Pumping action of the heart
Movement of a fluid (blood) is dependent on:
physical properties of the fluid and what its moving through
R =
n =
r =
L =
R = Resistance
n = viscosity
r = radius
L = vessel length
R =
R = 8nL / pie r^4
What has the most dramatic effect on resistance?
vessel diameter
Internal friction within a fluid is measured by:
viscosity
Elevated hematocrit increases blood ________.
viscosity
Severe anemia decreases blood __________.
viscosity
May use hematocrit instead of ___________.
viscosity
Diminishing vessel size leads to:
increases frictional forces and heat energy losses
increased viscosity =
low velocity
Laminar flow consists of:
layers of fluid particles moving against one another
Laminal flow looks like:
fast flow in the center and stationary flow at the wall
What flow is considered stable?
Laminar
Where is plug flow seen?
At vessels origin
Parabolic profile of laminar flow is seen?
usually downstream
Viscous is also known as:
Thickness
Viscous energy loss is due to:
Increased friction between molecules and layers which ultimately causes energy loss
Inertial losses occur with what:
Deviations from laminal low, due to changes in direction and/or velocity
has biggest change
What 3 things happen with energy losses?
- The parabolic flow profile becomes flattened
- Flow moves in a disorganized fashion
3.This type of energy loss occurs at the exit of a stenosis
Poiseuille’s equation defines relationships between what?
pressure
volume flow
resistance
What helps answer the question of “how much fluid moves through vessel”?
Poiseuille’s equation
What is Poiseuille’s equation?
Q = P / R
Q = volume
P = pressure
R = resistance
Poiseuille’s equation:
Increase in P =
Increase in R =
Increase in P = Increase in Q
Increase in R = Decrease in Q
Q = (P1 - P2) pie R^4 / 8 n L
Q = Volume Flow
P1 - P2 = Pressure at proximal/distal ends
r = Radius of the tube
L - Length of the tube
n = viscosity of the fluid
What has the most dramatic effect on resistance?
Diameter change
Radius (r^4) of vessel is directly proportional to what?
Volume flow
Small changes in radius may result in;
large changes in volume flow
The Law of Conservation of Mass explains the relationship between:
velocity and area
(Q = A x V)
Total energy contained in moving fluid is the sum of what?
Pressure, kinetic and gravitational energies
Why do pressure gradients (slow separations) occur?
Because of a geometry change with or without intra-luminal disease and because of curves
Flow separations result in what?
Regions with stagnant or little movement
What does Reynolds Number (RE) predict?
when fluid becomes unstable/disturbed
What is reynolds number?
> 2000, means laminar flow tends to become disturbed
In a rigid tube, energy losses are mainly:
Viscous
What flow changes both the driving pressure condition as well as the response of the system?
Pulsatile flow
___________: forward flow throughout the periphery (fluid acceleration).
Systole
______________________: temporary flow reversal, due to a phase shifted negative pressure gradient and peripheral resistance, causing reflection of the wave proximally.
Late systole/Early diastole
The dicrotic notch is related to what?
the closure of the aortic valve and the influence of peripheral resistance
_______________: flow is forward again, as reflective wave hits the proximal resistance of the next oncoming wave, and reverses.
Late diastole
_______________ : flow of a continuous (steady_ nature feeding a dilated vascular bed
Low resistance
What type of flow is seen in organs?
Low resistance
Example arteries of low resistance flow:
ICA
Vertebral
Renal
Celiac
Splenic
Hepatic
______________: flow of a pulsatile nature. Between incident pulses, hydraulic reflections travel back up the vessel from the periphery producing flow reversals in the vascular compartment
High resistance flow
Example arteries of high resistance flow:
ECA
Subclavian
Aorta
Iliac
Extremity arteries
Fasting SMA
The reversal component of a high resistant signal may disappear distal to a stenosis because:
decreased peripheral resistance, secondary to ischemia
Doppler flow distal to a significant stenosis is ___________.
lower resistance
- more rounded in appearance and is weaker in strength
A normally high resistant (biphasic or triphasic) signal may become monophasic as it approaches what?
the significant stenosis and/or aterial obstruction
Doppler flow proximal to a significant stenosis has what kind of resistance?
higher resistance in quality
What happens with vasoconstrictions?
Pulsatile changes in medium/small sized arteries of the limbs are increased. When this occurs, pulsatility changes are usually decreased in the minute arteries.
What happens with vasodilatation?
Pulsatile changes in medium/small sized arteries of the limbs are decreased (lower resistance). When this occurs, pulsatility changes are increased in minute arteries.
What is the natural response in the periphery as the inflow pressure falls as a result in stenosis?
vasodilate to maintain flow
Arterial obstruction may alter flow in collateral channels nearby or further away from site of obstruction. Changes include:
- Increased volume flow
- Reversed flow direction
- Increased velocity
- Waveform pulsatility changes
What induces peripheral vasodilatation and lowers the distal peripheral resistance, increasing blood flow?
Exercise
Vasoconstriction and vasodilation of blood vessels within skeletal muscles also influenced by sympathetic innervation fibers functioning primary for _________.
Regulation of body temperature
What is the ability of most vascular beds to maintain constant level of blood flow over a wide range or perfusion pressures?
Autoregulation
BP rise = ________________ of resistance vessels
constrictions
Flow to a cool extremity (vasoconstriction) will have what type of signal?
pulsatile
Flow to a warm extremity (vasodilation) will have what type of signal?
continuous and steady
Distal effects of obstructive disease may only be detectable following:
stress
A hemodynamically significant stenosis causes a notable reduction in what?
volume flow and pressure
Cross sectional area reduction of 75% = diameter reduction of __________.
50%
Effects of flow abnormality produced by a stenosis depends on factors such as:
- Length, diameter, shape, degree of narrowing
- Multiple obstruction in the same vessel: resistance to flow is additively it results in a higher resistance than in each individual narrowing
- Obstructions in different vessels that are parallel: resistance to flow is less than the resistance in each individual narrowing because only part of the blood flow is going through each narrowing
- Pressure gradient; peripheral resistance beyond stenosis
Where are flow frequencies usually dampened, with or without disturbance?
Proximal to a stenosis
Entrance into the stenosis produces an increase in Doppler shift frequencies (DSF), resulting in what?
Spectral broadening and elevated velocities
Flow disturbance occurs due to what?
Interrupted flow stability with high velocities and eddy currents
Where is post-stenotic turbulence seen?
At stenosis exit, flow reversals, flow separations, vortices / eddy currents occur near edge of flow pattern.
Post-stenotic turbulence flow quality is compromised of what?
multiple changes in direction and spectral broadening as displayed by the spectral pattern
