Physics Ch 4 Hemodynamics & Doppler

what is hemodynamics

study of blood flow through vessels of body

what provides potential/pressure energy at beginnin gof cycle

pumping of heart (left ventricle)

when does it turn to kinetic energy

flowing blood (velocity) within blood vessels

what does hydrostatic pressure describe

relationship between gravity, diensity of blood, and distance between an arbitrary reference point (usually heart)

what is formula for kinetic energy

equal to one half of the product of the density and velocity of blood squared (1/2) of [density x (velocity of blood squared)]

what determines kinetic energy

mass and speed of which it moves

formula for hydrostatic pressure

equal to product of height of colum of blood, density of the blood, and gravity P=densityxgravityxheight

how does blood lose energy through a vessel

viscous energy (viscosity), inertia

will higher viscocity have more or less energy loss

more

what unit of measurement is used for viscocity

poise

what is continuity equation (volume flow)

Q=VA (volume flow = velocity x area)

what does Reynold’s number indicate

amount of turbulence in blood vessel

how does viscous energy create energy loss

when kinetic energy is converted to heat as a result of friction

how does inertia cause energy loss

it is resistance to the acceleration (object at rest stays at rest…) from changing pressure waves during contraction and relaxing of ventricles

potential/pressure energy from the heart contracting is equivalent to

blood pressure

kinetic energy is equivalent to

velocity (kinetic energy minus friction energy loss)

what is hydrostatic pressure

energy from gravity

what is viscous energy

energy loss from friction, creating heat

what is inertial losses

energy lost because of acceleration in pulsatile system

kinetic energy plus heat energy is equal to

potential energy found at beginning of system

what is flow (Q)

volume of blood moving through a vessel per unit time

what is pressure difference

P1 minus P2

what kind of relationship are amount of flow and pressure difference

directly proportional - bigger pressure difference, more flow

what vessels are responsible for vasoconstriction & vasodilation

arterioles

what allows veins to store blood

capacitance (up to 2/3 of blood stored here)

which layer of vessel is much thicker in arteries

tunica media

what layer has vasa vesorum

tunica adventitia/external

what type of flow is plug flow

usually at entrance to large vessels, blunt, flow at same velocity (least frictional loss)

what is parabolic/laminar flow

most common type of blood flow in arteries, contains boundary layer near vessel wall, fastet flow in center, shape of flow profile as it travels and has frictional loss due to vessel walls (bullet) (subcategory is disturbed flow)

what Reynods number is considered turbulant flow

>2000 (under 1500 is laminar)

what is Bernoulli’s principle about

relationship between velocity and pressure in a moving fluid

formula for Bernoulli’s principle

change in pressure (P1-P2) = 4v²

what is Poiseuille’s law

relationship of volume to resistance

what is Poiseuille’s law formula

Q = change in pressure divided by resistance (assumes straight, rigid, non pulsatile similar to Ohm’s law)

what type of relationship is velocity and pressure

inverse (garden hose)

what angle does the highest, most accurate, frequency shift and accurate velocity, come from

0 degree

what frequency shift is obtained at 90 deg

cosine of 90 is 0, so no frequency shift

what is cosine of 0 deg angle

1

what is cosine of 45 deg angle

0.71

what is cosine of 60 deg angle

0.50

what is cosine of 90 deg angle

0.00

what is cosine of 180 deg angle

-1

increased scatter has more or less attenuation

more

what is the duty factor of CW transducer

100% or 1 (100% transmit time)

with CW transducers, the oscillating voltage is equal to what?

operating frequency

what is FFT/Fast Fourier Transform

what is used to break down signal and produce a spectral waveform (spectral analysis), produces a dot for EVERY RBC

what is displayed on x axis of spectral display

time

what changes the time scale on doppler instrument

sweep speed

what is presented on the y axis of spectral display

velocity

what does the resistive index quantify

resistance at distal bed

what is pulsatile index used for

quantify how pulsatile a vessel is over time

what is represented on z azix of spectral display

amplitude (brightness=# RBC’s)

what is the envelope of spectral waveform

how many RBCs are traveling at that velocity at a specifice time (the actual line)

what is the spectral window

the area under the envelope

what is spectral broadening

a filling in of the window when flow is turbulant or use of a wide sample window

PW doppler devices typically transmit ___ - ___ cycles per pulse

5 - 30

what is duplex imaging

PW doppler device that allows B mode image and Doppler signal on display at same time

what is duplex imaging good for

allows real time adjustment of doppler curser while observing grayscale image

what is negative about duplex imaging

affects frame rate which decreases temporal resolution

what is triplex imaging

combined grayscale, spectral, and color Doppler

what is aliasing

wrap-around of Doppler signal (positive shifts displayed as negative shifts)

what is the highest frequency shift that can be meaured

half of PRF

what is Nyquist limit

the highest frequency shift (1/2 PRF)

what is PRF

number of pulses per second

if PRF is 2500 HZ, what frequency shift will cause aliasing

>1250

what will correct aliasing

increase PRF (scale), lower the frequency (shift needs to decrease), decrease sample depth, use CW, change baseline (just a visual fix)

what is range gate

specific depth selection of PW doppler (placed inside vessel)

does CW doppler alias

no

what is RI formula

systole-diastole/systole

what is PI formula

systole-diastole/mean

what is Doppler shift equation

(2 x v x f x cosine of theta)/prop speed

will high frequency transducers create more or less aliasing

more, higher doppler shifts = more likely to exceed Nyquist limit

what does angle correct do

helps distinguish between velocity and frequency shifts

deeper the vessel, the higher or lower the PRF

lower

what is the wall filter

erases low frequency signals from vessel walls or heart motion (best in cardiac imaging)

what will increasing wall filter do

increase amount of signals eliminated

other names for wall filter

high pass or wall thump filter

how do you angle correct in PW

steering control or heal/toe

spectral doppler is specific to every RBC (measures peak), color doppler is an average

what is autocorrelation

processing technqiue used to obtain color flow, faster than FFT but not as accurate as FFT since it’s using mean/average

what is ensemble length/packet size

number of pulses per scan line within a color box

benefit and draw back of large packet size

more sampling points=higher sensitivity and helps pick up slow flow; bad due to low frame rate

how can you determine flow direction with a steered gate

draw line “the transducer” from overhanging corner of dopper gate, flow is moving away or toward the line based on color scale

how can you determine flow direction in non steered gate

using color scale

what will increasing the color persistence help with

reduces noise and makes easier to follow small vessels, drawback is decreased frame rate

what mode is color scale most commonly represented

velocity mode, vertically oriented

what is variance mode

distinguishes laminar from turbulent flow - Laminar flow on Left, turbulent on right

how can you determine color aliasing from flow reversal

if colors that touch each other in image go through the map’s middle, it is flow reversal; if colors go around outside of color map, it is aliasing

what is tissue doppler imaging used for

cardiac

what is power doppler (also color doppler energy, amplitude doppler and color power angio)

one color, no directtion, ignores frequency shift and focuses on amplitude or strength of shift (just proves if there’s flow)

good and bad of Power doppler

angle doesn’t matter, sensitive good for slow flow, bad for movement, no aliasing

what is strain and strain rate

used in cardiac, evaluates stretch and deformity of muscle

if RBC’s travel at 2 m/s at 60 degrees, what is velocity

1 m/s (60 deg cosine = 0.5)

what is ghosting/clutter

very low doppler shifts from moving anatomy (heart)

how can you fix ghosting/clutter

wall filter (rejects low doppler shifts)

what is biggest influence on resistance

radius of vessel

slide 157

what is biggest influence on flow control

arterials

if radius doubles, flow increases by a factor of

16

what are inertial losses caused by

branching