DMU 3313 Unit 6 Review

What states of matter are materials that flow/fluids

gases and liquids

What is viscosity

resistance to flow offered by a fluid in motion

What is the unit of viscosity?

poise

What is density?

mass per volume

What is pressure?

driving force behind fluid flow

What is required for flow to occur?

pressure difference

If pressure difference is greater, what happens to flow rate?

it increases

Pressure formula

pressure = force/area

What is resistance

the opposition of flow

What does flow resistance depend on?

kinematic viscosity, tube length, and tube radius

What factor has the largest effect on resistance?

radius of tube

Resistance equation

R = 8(tube length)(viscosity)/(pi)(r )^4

What is volumetric flow rate?

the volume of blood passing a point per unit of time

What unit is used for volumetric flow rate?

mL/s

volumetric flow rate equation

Q = pressure difference/resistance

Poiseuille’s equation with radius

Q = (pressure difference)(pi)(r^4) / (8)(L)(viscosity)

Poiseuille’s equation with diameter

Q = (pressure difference)(pi)(d^4) / (128)(L)(viscosity)

For steady flow in long straight tubes, if pressure difference or diameter of tube increases, flow rate will….

increase

For steady flow in long straight tubes, if viscosity or length of the tube increases, flow rate will…

decrease

What are the spatial categories for types of flow

plug, laminar, parabolic, disturbed, turbulent

What are the temporal categories for types of flow

steady and pulsatile

What is plug flow?

the speed of the fluid is essentially constant across the tube

What is laminar flow?

streamlines are parallel to each other and flow speed is maximum at the center of the tube and minimum or 0 at tube’s walls

What is parabolic flow?

a form of laminar flow where the average flow speed across the vessel is equal to ½ the maximum flow speed (center)

What is disturbed flow?

a form of laminar flow that occurs when the parallel streamlines are altered from their straight lines

When does disturbed flow occur?

in the region of a stenosis or at a bifurcation

What is turbulent flow?

nonlaminar flow with random and chaotic speeds and directions, but forward net flow is still maintained

What is steady flow?

pressures, flow speeds, and flow patterns do not change over time

What is pulsatile flow?

non-steady flow, with acceleration and deceleration over the cardiac cycle

What direction does flow move from?

high pressure to low pressure

How does inspiration affect flow?

increased flow from abdominal cavity into thoracic cavity and decreased flow from legs into abdominal cavity

How does expiration affect flow?

decreased flow from abdominal cavity into thoracic cavity and increased flow from legs into abdominal cavity

What is a stenosis?

abnormal narrowing of a passage in the body

What does the continuity rule state?

volumetric flow rate must be constant proximal, within, and distal to a stenosis

Continuity rule equation

Q = average velocity x area

What is the Bernoulli effect?

In order for blood to accelerate within a stenosis, there must be a drop in pressure (if flow speed increases, pressure decreases)

Where does the largest pressure drop occur in the cardiovascular system?

arterioles

Why does turbulence occur distal to stenoses?

increased velocity and vessel widening

What does post-stenotic turbulence result in?

bruit (sounds on auscultation from turbulence)

What does Doppler provide information about in DMU?

presence, direction, speed, and character of blood flow of motion

What is the Doppler effect?

the change in frequency caused by motion of a sound source, receiver, or reflector

Is wavelength effected by the Doppler effect?

not directly, but it is effected as a result of frequency being effected

What possible situations result in the Doppler effect?

moving source, receiver, reflector, or more than one of these moving

What is Doppler shift?

the difference between the frequency of the received sound wave and frequency of the emitted sound wave

What is the Doppler shift if the reflector is moving toward the source?

positive shift and ascending flow

What is the Doppler shift if a reflector is moving away from the source?

negative shift and descending flow

The amount of increase or decrease in frequency in Doppler shift depends on what?

speed of reflector, angle between wave motion and direction of reflector, and frequency of wave emitted from source

What is the Doppler equation? (Doppler shift)

fD = (2/c)(v)(fT)(cos(theta))

What is Doppler angle?

the angle between the direction of sound propagation and flow direction

Where does the Doppler gate indicator line need to be lined up on the image?

as close to parallel to the flow direction

As Doppler angle increases, the % of error in speed will…

increase

Doppler angles less than what are recommended to avoid error?

less than 60 degrees

If wave propagation is directly opposite of blood flow, what shift will be obtained?

maximum positive shift

If wave propagation is directly parallel moving with flow, what shift will be obtained?

maximum negative shift

If propagation direction is perpendicular to blood flow, what shift will be obtained?

no shift will be measured

What are the types of Doppler imaging?

pulsed wave, continuous wave, and power Doppler

What are the types of display in Doppler?

color flow, spectral, duplex, triplex, and audio

What does color Doppler show?

real time blood flow or tissue motion information

What type of display is color Doppler?

duplex

In color Doppler, what does red represent? What does blue represent?

red represents positive doppler shift, blue represents negative doppler shift

What is Nyquist limit?

the highest frequency in a sampled signal that can be displayed correctly or minimum number of samples to avoid aliasing

Nyquist limit equation

Nyquist limit (fD) = PRF/2

When does aliasing occur?

when the Doppler shift exceeds the Nyquist limit (PW only)

What is aliasing?

appearance of Doppler information on the wrong side of the baseline

What are the methods of reducing or eliminating aliasing?

shift baseline, increase PRF, increase doppler angle, use lower operating frequency, use a continuous wave device

What are advantages and limitations of color Doppler?

advantages: shows blood flow, direction of flow, and nonvascular motion

limitations: angle dependent, lower frame rates, lack of detailed spectral info

How to differentiate flow reversal and aliasing?

flow reversal has dark regions between opposite colors and aliasing has bright colors with no black

What is the power of Doppler shift determined by?

concentration of moving scatterers

What does power Doppler do?

presents 2D Doppler info by color encoding the strength of the Doppler shifts

What are advantages and disadvantages of power Doppler

advantages: angle independent, no aliasing, improved sensitivity

disadvantages: no directional info, no flow speed or character info

How does continuous wave spectral Doppler work?

detects the Doppler shift within the region of overlap between the beams of transmitting and receiving transducer elements

How does pulse wave spectral Doppler work?

emits ultrasound pulses and receives echoes using a single element transducer and array

What does the vertical axis of a spectral display represent?

Doppler shift frequency

What does the horizontal axis of a spectral display represent?

time

Where are positive shifts placed on a spectral display? Where are negative shifts placed?

positive shifts are above baseline, negative shifts below baseline

What is a spectral window?

the area within or under the waveform

What happens if all the cells are moving at the same speed?

there is a narrow range of velocities present, approximately plug flow, spectral trace is thin, and open spectral window

What is spectral broadening?

filling in of the spectral window

What are features of a low resistance waveform?

forward flow during systole and diastole, perfuse organs that need continuous blood flow, typically monophasic, and gentle upstroke

What are features of a high resistance waveform?

brief flow reversal during diastole, perfuse organs that do not need continuous flow, triphasic, and rapid upstroke

What type of waveform is shown in the image?

low resistance

What type of waveform is shown in the image?

high resistance