UNIT 18 BLOOD FLOW

Which condition will MOST directly reduce blood flow if pressure remains constant?

Decreased vessel radius

According to Poiseuille’s principle, reducing vessel radius by half will result in blood flow that is approximately:

One-sixteenth the original flow

In a patient with a focal arterial stenosis, which change occurs immediately distal to the stenosis?

Decreased pressure and increased velocity

If vascular resistance increases while blood flow must be maintained, which compensatory change is required?

Increased pressure gradient

An increase in Reynolds number indicates an increased likelihood of:

Turbulent flow

Which factor contributes MOST to the development of turbulent flow?

High velocity through a narrowing

According to Bernoulli’s principle, velocity acceleration within a stenosis results in:

Conversion of pressure energy to kinetic energy

Hydrostatic pressure in the lower extremities is greatest when the patient is:

Standing upright

During inspiration, venous flow in the lower extremities decreases primarily due to:

Compression of abdominal veins by the diaphragm

During inspiration, venous flow in the upper extremities increases because of

Decreased intrathoracic pressure

Which statement BEST describes the relationship between pressure gradient and flow?

Flow increases as pressure gradient increases

According to Ohm’s Law, if resistance doubles and pressure remains constant, blood flow will:

Decrease by half

Which vessel characteristics Most contributes to arterial compliance?

Elastic fibers

Large elastic arteries primarily function to:

Dampen pulsatile blood flow

With aging and atherosclerosis, decreased arterial compliance results in:

Increased systolic pressure

Which waveform change is MOST likely in a vessel with decreased compliance?

Increased pulsatility

Which factor will increase resistance according to Poiseuille’s principle?

Increased blood viscosity

In which situation would laminar flow MOST likely be preserved?

Low velocity in a straight vessel

Spectral broadening on Doppler is MOST associated with:

Turbulent or disturbed flow

Which concepts BEST explains why venous flow changes with patient position?

Hydrostatic pressure

Hemodynamics is the study of:

Blood flow characteristics

Blood flow is best defined as:

Volume of blood moving per unit time

If vessel diameter decreases and flow remains constant, velocity will:

Increase

Blood velocity is highest:

At the center of the vessel

Laminar flow is characterized by:

Highest velocity at the center

Turbulent flow is MOST likely to occur:

Distal to stenosis

Turbulent flow results in:

Spectral broadening

Reynolds number predicts:

Likelihood of turbulence

Turbulence is MORE likely when Reynolds number:

Increases

Reynolds number increases with:

Increased vessel diameter

According to Bernoulli’s principle, when velocity increases:

Pressure decreases

Pressure is lowest:

Within stenosis

A stenosis will cause:

Increased velocity

Turbulence associated with stenosis occurs:

Distal to stenosis

Post-stenotic flow is typically:

Turbulent

Which factor has the GREATEST effect on resistance?

Vessel radius

If vessel radius is reduced by half, resistance will:

Increase 16 times

Resistance is directly proportional to:

Length

Resistance is inversely proportional to:

Radius⁴

Increased viscosity will:

Increase resistance

In laminar flow, blood velocity at the vessel wall is:

Zero

Which vessel is MOST likely to have laminar flow?

Long, straight artery

Steady flow is best described as:

Blood flow that remains constant with time

Non-steady flow is characterized by:

Changing velocity with time

Blood flow in the human body is MOST accurately described as:

Non-steady

Pulsatile flow is defined as:

Flow with cardiac cyclic changes in velocity

Pulsatile flow is a type of:

Non-steady flow

Phasic flow is characterized by:

velocity changes due to respiration

Plug flow is best described as:

Equal velocities across most of the vessel

Parabolic flow is associated with:

Laminar flow

Blood flows primarily due to:

Pressure gradient

Blood flows from:

High pressure to low pressure

Increasing the pressure gradient will:

Increase flow

Bernoulli’s principle BEST explains:

Pressure drop in stenosis

Ohm’s law for blood flow states:

Flow = pressure ÷ resistance

If resistance increases and pressure remains constant, flow will:

Decrease

Reynolds number LESS than 2000 indicates:

Laminar flow

Reynolds number GREATER than 4000 indicates:

Turbulent flow

Small changes in vessel radius cause:

Large changes in resistance

Compliance is defined as:

Ability of a vessel to expand

Which vessel has the GREATEST compliance?

Aorta

High compliance vessels:

Expand easily with pressure

Which condition DECREASES vessel compliance?

Atherosclerosis

Decreased compliance results in:

Increased pulsatility

Compliance is mathematically expressed as:

ΔV / ΔP

A vessel with HIGH compliance will show:

Large volume change for small pressure change

Aging affects compliance by:

Decreasing arterial compliance

Hydrostatic pressure is caused by:

Gravity acting on blood

Hydrostatic pressure:

Increases with distance below the heart

In the standing position, venous pressure is HIGHEST in the:

Feet

In the supine position, hydrostatic pressure:

Is evenly distributed

Venous return is GREATEST when a patient is:

Supine

Standing position DECREASES venous return because:

Hydrostatic pressure increases in the legs

During inspiration:

Venous return to the heart increases

Inspiration increases venous return because:

Thoracic pressure decreases

During expiration:

Venous return decreases

Which condition will MOST increase venous return?

Deep inspiration

Hemodynamics is the study of:

Blood flow and forces affecting it

If velocity of fluid in a pipe is doubled, Reynolds number will:

Double

Reynolds number increases when:

Velocity increases

If fluid viscosity doubles while all other variables remain constant, Reynolds number will:

Become half

If pipe diameter is reduced to half, Reynolds number will:

Become half

Which change will most likely convert laminar flow to turbulent flow?

Increasing diameter

Which parameter is inversely proportional to Reynolds number?

Viscosity

During normal inspiration, intra-abdominal pressure:

Increases

During inspiration, venous flow in lower extremity veins typically:

Decreases

During inspiration, venous flow in the inferior vena cava (IVC) typically:

Increases

During expiration, lower extremity venous flow generally:

Increases

The main reason lower extremity venous flow decreases during inspiration is:

Increased abdominal pressure

During inspiration, thoracic pressure:

Decreases

Which Doppler finding suggests increased distal resistance?

Reduced diastolic flow

High velocity without proportional flow increase indicates:

Nonlinear pressure-flow relationship

Mean arterial pressure is best described as:

The average arterial pressure during one cardiac cycle

MAP is weighted closer to diastolic pressure because:

Diastole occupies more of the cardiac cycle

MAP is primarily determined by:

Cardiac output × peripheral resistance

Turbulent flow on spectral Doppler shows:

Spectral broadening and filled-in window

In a stenotic artery, spectral Doppler is likely to show:

Laminar flow pre-stenosis, turbulent flow post-stenosis

Reduced diastolic flow on Doppler indicates:

Increased distal resistance

Laminar flow produces which Doppler spectral pattern?

Narrow spectral tracing

Which statement BEST describes pressure-flow relationships in normal vessels?

Linear