cas 1050 mod 8

definition of hemodynamics 

the study of blood flow and circulation.

What is the primary purpose of Doppler echocardiography in clinical practice?

It evaluates the hemodynamics and blood flow within the heart and vessels, which is especially important in cases of cardiac disease

Blood flow is determined by many factors, including:

• Volume

• Blood density and viscosity

• Vessel size and elasticity

• Resistance

• Systole versus diastole

• Systemic and pulmonary pressures (high vs. low pressures)

• The disease state present

• Loading conditions

• Heart rate

Define laminar blood flow 

represents normal blood flow, where all blood cells are traveling in the same direction within a narrow velocity range

fluid moves in layers

Flat profile:

The velocity of all layers is the same

Parabolic profile:

Velocity layers differ slightly. As blood flows through a long, straight vessel, the center moves faster than the outer layers due to friction against the vessel wall

How is "turbulent" blood flow defined?

It is abnormal flow where blood travels at different velocities and in different directions, becoming "chaotic

Under what three clinical conditions does turbulent flow typically occur?

It occurs with stenosis, regurgitation, and/or septal defects

What does the term "spectral" actually mean in this context?

refers to a spectrum, which is an array of frequency components of a wave separated and arranged by increasing frequency

What kind of information can be derived from a Spectral Doppler graph?

It provides a graphic representation of blood flow properties that allows for both quantitative (measurements) and qualitative information

What are the two types of audio signals described, and how do PW and CW pulses differ?

• Audio: Can be "loud and scratchy" or "soft and dull".

• PW (Pulsed Wave): Sends out short pulses and waits to analyze them before sending another.

• CW (Continuous Wave): Sends and analyzes pulses continuously

What is the most critical technical rule for accurate Doppler assessment?

The probe must be parallel to the direction of blood flow

Why is probe angle especially important when assessing stenotic valves?

Even a small deviation from the optimal angle will underestimate the flow velocity

What three technical settings must a sonographer manage for a clear trace?

Proper spectral gain settings, wall filters, and an appropriate scale to display the entire flow

On the Spectral Doppler display, what do the X and Y axes represent?

• X-axis: Timing in milliseconds (ms), showing the periods of systole and diastole.

• Y-axis: Direction and velocity in m/sec

What are calibration markers usually set to on the Y-axis?

They are usually set to 1 m/sec, though this depends on the scale setting

In terms of signal appearance, what does "intensity" represent?

It represents the amplitude or strength of the signal, appearing as brighter versus darker or "washed out" regions

What is "range resolution," and why is it an advantage for PW Doppler?

Range resolution means the system has a sample volume (SV) that can be adjusted to record flow velocities at one specific location

Aliasing is

an artifact that occurs when high-velocity blood flow exceeds the Nyquist limit (which is 1/2 the PRF).

This causes the waveform to "wrap around" from the top of the display to the bottom, similar to how a scale might wrap back to zero if a weight exceeds its maximum capacity

What is the primary limitation of PW Doppler, and what is its mathematical limit?

It can alias easily. This happens when blood flow exceeds the Nyquist Limit, which is equal to 1/2 of the Pulse Repetition Frequency (PRF)

What are the five "means of eliminating aliasing"

1. Image at a shallower depth (which increases PRF).

2. Increase the angle of insonation.

3. Use a low frequency transducer.

4. Manipulate the velocity scale and baseline.

5. Switch to continuous wave imaging

Spectral envelope:

The brighter white area forming the waveform

Spectral window:

the clear area under the envelope; a "window" appearance is typical for PW Doppler because it has less spectral broadening than CW

How many crystals does a CW Doppler probe use, and what are the two probe options?

It uses two crystals (one to send, one to receive). It can be done with a standard 2D imaging probe or a stand-alone blind probe called a Pedoff probe

What are the three main advantages of CW Doppler?

1. It has the best sensitivity and lowest frequency.

2. It can record high velocities without aliasing.

3. It allows you to obtain the highest possible velocity

What is the major limitation of CW Doppler compared to PW?

It has no range resolution. It continuously samples all blood along the entire beam rather than at one specific spot

Why does a CW trace look "filled-in" compared to a PW trace?

Because it samples along the whole beam, it records a larger range of velocities, resulting in more spectral broadening and the loss of the "spectral window

How does the Doppler Effect determine velocity and direction?

It detects the shift in frequency (the difference) between the transmitted frequency and the received frequency

Zero shift

No flow

Positive shift:

Blood flows towards the transducer; the trace is above the baseline.

Negative shift:

Blood flows away from the transducer; the trace is below the baseline