ch 18, 19, 20 ut physics

What is hemodynamics?

Study of blood flow.

What is flow rate?

The volume of blood moving through a vessel over time.

What is a pressure gradient?

The difference in pressure between two locations.

How does blood normally flow through the body?

From high pressure to low pressure.

What is resistance?

Opposition to blood flow.

What factors increase resistance?

Smaller vessel diameter, increased viscosity, and increased vessel length.

How does vessel diameter affect resistance?

Smaller diameter increases resistance. Larger diameter decreases resistance.

How does vessel diameter affect velocity?

As vessel diameter decreases, velocity increases.

Why does blood move faster through a smaller vessel?

The same volume of blood is squeezed through a smaller area.

What is the Continuity Principle?

Flow rate remains constant throughout the system.

How does cross-sectional area affect velocity?

Smaller area increases velocity. Larger area decreases velocity.

What is the Bernoulli Principle?

Velocity and pressure have an inverse relationship.

How does velocity affect pressure?

As velocity increases, pressure decreases.

What is laminar flow?

Normal layered blood flow.

Where is blood flow fastest during laminar flow?

In the center of the vessel.

Where is blood flow slowest during laminar flow?

Near the vessel wall.

What is turbulent flow?

Chaotic, disturbed blood flow.

What conditions commonly cause turbulent flow?

Stenosis, vessel narrowing, and high velocities.

What is Reynolds Number used for?

Predicting the likelihood of turbulence.

What factors increase the likelihood of turbulence?

High velocity, large diameter, and low viscosity.

What is Poiseuille's Law?

A principle showing that blood flow is strongly affected by vessel radius.

What is the most important factor affecting flow according to Poiseuille's Law?

Vessel radius.

What is the Doppler Effect?

A change in frequency caused by moving blood cells.

What is a Doppler Shift?

The difference between transmitted and received frequency.

How does blood velocity affect Doppler shift?

Higher velocity produces a larger Doppler shift.

What happens to Doppler frequency when blood moves toward the transducer?

The frequency increases, producing a positive shift.

What happens to Doppler frequency when blood moves away from the transducer?

The frequency decreases, producing a negative shift.

What Doppler angle provides the most accurate measurements?

0°–60°.

Why should Doppler angles near 90° be avoided?

A 90° angle produces no Doppler shift.

How does Doppler angle affect Doppler shift?

As Doppler angle increases, Doppler shift decreases.

What is Continuous Wave (CW) Doppler?

A Doppler mode that continuously transmits and receives sound.

What is the main advantage of CW Doppler?

It measures very high velocities.

What is the main disadvantage of CW Doppler?

It has no depth resolution.

Does CW Doppler experience aliasing?

No.

What is Pulsed Wave (PW) Doppler?

A Doppler mode that uses pulses and a sample volume.

What is the main advantage of PW Doppler?

It provides range specificity and depth resolution.

What is the main disadvantage of PW Doppler?

It can experience aliasing.

Does PW Doppler experience aliasing?

Yes.

What is Color Doppler used for?

Displaying blood flow direction.

What is Power Doppler used for?

Displaying Doppler signal strength.

What information does Power Doppler NOT provide?

Velocity and direction.

What is the main advantage of Power Doppler?

It is very sensitive to weak flow.

What is aliasing?

An incorrect display of Doppler velocities.

What causes aliasing?

The Doppler shift exceeds the Nyquist Limit.

What is the Nyquist Limit?

The maximum Doppler shift that can be measured accurately.

How is the Nyquist Limit calculated?

PRF ÷ 2.

How does PRF affect aliasing?

Increasing PRF decreases aliasing.

How does imaging depth affect PRF?

Increasing depth decreases PRF.

How does imaging depth affect aliasing?

Increasing depth increases aliasing.

What adjustments can reduce aliasing?

Increasing PRF, decreasing depth, lowering frequency, using CW Doppler, or shifting the baseline.