Arterial Hemodynamics Flashcards by Julianna Small

What is pressure and what is it measured in?

The amount of force put on artery at any point in time.

Mm of mercury (mmHg)

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How does the pressure change from the heart to the ankles?

Systolic increases

Diastolic decreases

Mean decreases (creates gradient)

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What is kinetic energy and how much does it account for?

2 %

Energy created by the movement of blood

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When does KE increase?

During exercise or within a stenosis

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What is potential energy and how much does it account for?

98%

The main form of energy resulting from the pressure distending the vessels (stored within vessel walls).

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What is flow?

The amount of fluid travelling past a point in a given amount of time

Units = volume/time (L/min)

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What is the density of blood and does it change?

1.05 g/ml

No it is constant

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What is viscosity?

The resistance of a fluid in motion to flow, the amount of frictional forces as the molecules move against one another. (Thickness of a fluid).

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What is the most important factor affecting viscosity?

The concentration of RBC’s (hematocrit) and plasma protein.

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How does length effect resistance?

A longer length of tube contains more resistance due to increased friction

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How does radius effect resistance?

As radius decreases, resistance increases to the 4th power

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What is resistance?

The force that must be overcome for flow to happen that is created by the friction of blood against the wall.

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What is the most influential factor affecting resistance?

Radius

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What does poiseuille’s law define?

The relationship between pressure, volume flow and resistance through a cylinder.

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What is the equation for the Poiseille relationship?

Flow volume = (Pi x change in pressure) x r^4) divided by (8 x Length x viscosity)

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What is the abbreviated formula of Poiseuille’s law?

Flow volume = Pressure gradient divided by the radius

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What is the relationship between velocity and pressure?

Inverse

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What is stroke volume?

The amount of blood ejected from the heart during systole

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What dictates the stroke volume?

The arterial pressure and the peripheral resistance

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What is systolic pressure?

Due to increased pressure from increased volume the artery walls expand creating PE within them.

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What is the diastolic pressure?

As the volume and radius decreases during diastole, pressure decreases and blood flows due to its own momentum

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What allows blood to flow?

The pressure gradient between the LV 120 mmHg and the RA (2-6mmHg)

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What is hydrostatic pressure?

The force of gravity on a column of fluid

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Where is hydrostatic pressure the greatest?

In the lower portion of the body

Where is gravitational PE the highest?

In the upper portion of the body (right atrium).

How is velocity related to vessel diameter?

Inverse. Velocity up = diameter down

What type of flow is referred to as "parabolic" and why?

Laminar flow due to the velocity profile (normal spectral and clear window looks like a parabola).

How does mean velocity differ from max velocity i laminar flow?

Mean is half of the maximum peak

When does blunt flow occur?

During systole in larger vessels or arterial branch origins

What is flow separation?

A NORMAL flow variation when there is a sudden widening of a vessel causing fluid layers to separate and reverse flow along the wall

What is non-laminar flow?

Flow that can be both normal and abnormal where a normal velocity profile is not established for 3 cm after a disruption

What is the flow pattern of non-laminar flow?

Mixed w/forward and backward components

What is the transition zone?

The site of boundary layer spearation in non laminar flow where the lamina reach zero velocity while transitioning from forward to backward flow.

Where can the transition zone be seen?

Carotid bifurcation and distal to a stenosis.

What is turbulance?

Chaotic flow where fluid exits a tight spot and enters a wider area, fluid whirls and is much more disordered than disturbed flow.

What is the velocity pattern of turbulence?

Feathered appearance with spectral broadening.

What is does the Reynold's number predict? An how does velocity and viscosity affect?

A number that predicts when turbulence will occur. Risk of turb increases as velocity and viscosity increase

What is the reynolds number?

Turbulence occurs when the Reynolds meets or exceeds 2000

What is the flow pattern around bifurcations and branches?

Disturbed (larger vessel = greater disturbance)

What is the flow pattern most common in arteries with significant disease?

Disturbed

What happens to the pressure at bifurcations of normal vessels?

Small pressure drop

What type of flow patter occurs in curved vessels?

Helical flow

What is helical flow?

In a curved vessel the fluid flows faster near the walls and may reverse in the centre due to the fast flow moving outward as it enters the curve.

Match the flow profile to the region? (4)

Parabolic = laminar region Plug = laminar region Disturbed = transition zone Turbulent = turbulent region

List the 4 flow profiles from low to fast velocity?

1. Parabolic (lowest) 2. Plug (lower) 3. Disturbed (higher) 4. Turbulent (highest)

What does the Bernoulli principle explain?

The balance of energy in the movement of fluid, explains relationship between area, velocity and pressure at a stenosis.

What happens to the velocity and pressure within a stenosis?

Low pressure, high velocity (inversely related) to maintain the same total energy

What happens to the velocity and pressure distal to a stenosis?

Velocity decreases and pressure increases compared to IN stenosis but not proximal to it.

What is the profile proximal to a stenosis?

- Increased pulsatility (high resistance = peaks) - Narrow sharp peak - Low peak systolic velocity - Laminar flow - Thumping during systole

What happens to the peak systolic velocity and end diastolic velocity through a stenotic jet?

PSV increases to 80% of the diameter reduction and then DECREASES. EDV is markedly increased with greater than 70% stenosis

What happens distal to a stenosis?

- Post-stenotic turbulence - Dampened tardus parvus - Energy released as heat - Max flow disturbance is seen within 1 cm of stenosis -

How do tandem Lesions/stenosis differ from singular?

There is a greater loss of energy and volume than a single lesion.

In tandem lesions/stenosis how does the energy/velocity differ between the stenosis's?

The 1st stenosis will have a greater incoming energy and will produce higher velocities than the second

What are qualities of a low resistance waveform pattern?

Constant forward flow in systole and diastole with a diastolic component well above the baseline

What are the qualities of a high resistance waveform?

- Sharp upstroke - Low to absent diastolic flow - More pulsitile

What is low pulsatility?

Low resistance, has a broad systolic peak and forward flow through diastole

What is moderate pulsatility?

Tall sharp peak and little diastolic flow

What is high pulsatility?

High resistance, narrow systolic peak, flow reveral in early diastole and little/late diastolic flow.