Flow through a blood vessel is determined by:
- 1. Pressure difference
- 2. Vascular resistance
Vessel diameter increase as _____ increases.
Veins or arteries, which are more distensible?
Veins are 6-10 x as distensible as arteries
- Transport blood to tissues
- High pressure
- Last, smallest branches of the arterial system
- Act as "control valves" for blood flow into capillaries
Exchange between blood and interstital spaces
Vasodilitation occurs when?
- During exercise
- After a meal
Vasoconstriction occurs when?
- In a resting state
- With fasting
Collect blood from capillaries and connect to larger veins
- Blood returned to heart
- Body contians many more veins than all other parts of the vascular system
Have the smallest cross-section area and therefore the highest velocity
Relationship of velocity to area
Velocity is inverse to area
Energy derived from the cardiac pump
- Pressure/stored energy
- Derived from the cardiac pump
- Distends vessels and stores energy
- Energy of motion
- KE < PE due to distensibility of vessels
Kinetic energy can increase due to:
- Increase in flow>> i.e. exercise
- Stenosis (increased velocity)
Movement of fluid between 2 points requires:
- Difference in energy
- Difference in pressure
Example of low resistance
- Low resistance = greater energy difference = greater flow
Example of high resistance
- Resting muscle
- High resistance = less flow
Defines relationship between pressure, volume flow, and resistance
The longer the vessel the _____ the resistance.
- High pressure is required to maintain flow
The shorter the vessel the ____ the flow volume.
What has the most significant impact on flow rate?
- Radius of the vessel
- Smaller the radius, the higher the resistance
Smaller the radius, the _____ the resistance.
Higher (and higher pressure)
- Flat profile
- Seen in stenotic area
- Same velocity throughout vessel (slower flow at wall)
- Most common flow pattern
- Seen during systole in smaller arteries
- Flow in center is highest and gradually tapers as it reaches the wall of the vessel
Disturbed flow is signified by?
Mathematical number to determine when flow turbulence will occur?
Reynolds number for when turbulance will occur
2000 Re or higher
Harmonic resonance produced by flow turbulence transmitted into vessel walls is known as
Where is normal disturbed flow visualized throughout the cardiac cycle?
Dampened wave forn distal to a stenosis
- Low resistance, continuous and steady throughout S and D
- Seen in normal arteries that supply low resistance vascular beds -liver, spleen, brain, kidneys
- Highest resistance to flow
- Antegrade/forward flow during systole
- Retrograde/reverse flow during diastole
- Seen in distal AO/iliac arteries
Cosine of the doppler angle is ______ly related to the doppler angle.
- Inversely related
- Angle of 0 = cosine 1.00
- Angle of 90 = cosine 0
Increase transmit frequency and _____ the size of the Doppler shift
Decrease velocity of flow and _____ the size of the Doppler shift.
Increase the Doppler angle and _____ the size of the Doppler shift.
Decrease the Doppler angle and ______ the size of the Doppler shift.
Cosine = 0
- 90 degree angle
- No Doppler shift
Cosine = 1.00
- 0 degree angle
- Largest Doppler shift
With spectral analysis the frequency is displayed on which axis?
Vertical y axis
What is displayed on the X axis of spectral analysis?
Amplitude or power is displayed as what on spectral analysis?
- Fast fourier time
- Current computer program for analyzing and displaying spectral representation
How can aliasing be eliminated?
- Increase PRF (increased nyquist limit)
- Shift baseline
- Increase size of angle
- Decrease transmit frequency
Main disadvantage of pulsed Doppler is?
- 1/2 the PRF
- Exceeding this produces aliasing
Changed the number of pulsed emitted per second
Primary advantage of CW Doppler
No velocity limit/ no aliasing
Main disadvantage of CW Doppler
- Large fixed sample volume
- POOR RANGE RESOLUTION
- Qualitative, NOT quantitative information
- Will produce aliasing
- Good range resolution
How to eliminate color aliasing
- Increase PRF (scale setting)
- Decrease sample volume depth
- Use larger Doppler angle
- Lower transmit frequency
- Go from triplex(color, image, spectra) to duplex (color, image)
- Encodes amplitude of blood cells
- Provides no info on direction of flow
- NO aliasing and less angle dependant
Components of pulsed Doppler instrumentation:
- Gated detector
- Spectral analysis
Length of pulses produced by pulser
The time period for acquisition of Doppler signal is determined by the _____.
Size of the gate
Phase shift means
Motion is present
Rhythmic cycles or beats produced when waves of different frequencies produce interference are added together and termed
Minimum number of cycles per pulse is?
Number of cycles required for fast flow
Number of cycles needed for gray scale
Number of cycles needed for slow flow
Typical sampling rate
25,600 times per second
High pass filter
- Rejects all frequencies below the threshold vaule
- Usually 100Hz
- Removes wall thump but not slow flow
Low pass filter
- Eliminates high frequency noise
- Improper adjustment can eliminate high frequency (fast) flow
One speed estimate has a _____ pulse minimum.
More than 3 pulses are required in order to:
- Improve accuracy of the estimate
- Determine the variance
- Improve detection of slow flow
Typical ensemble length range
Increasing ensemble length will ___ frame rate.
- AKA pulse packet size
- The number of pulses required to produce one color scan line