Principles of haemodynamics Flashcards by Syed Kamran

What is flow determined by?

Determined by arterial blood pressure and resistance

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What are the 3 different flow patterns?

Patterns – laminar, turbulent and bolus

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What are the 2 types of arterial pressure?

Systolic

Diastolic

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What is haemodynamics?

Haemodynamics is the relationship between blood flow, blood pressure and resistance to flow

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What type of system is the CVS?

Closed system

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Where is majority of the blood in the CVS?

Venous system

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Comment on the venous system

A low pressure reservoir system

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What can the reservoir of venous blood be used to do?

Can be used to increase cardiac output

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What can reduced blood flow in one area of the CVS cause?

Reduced blood flow to one area increases pressure upstream and alters flow to
other areas.

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Darcy’s law

Flow(Q)=Pressure difference/R

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Bernoulli’s law

Role of pressure, kinetic and potential energies in flow
 Kinetic Energy: Momentum of Blood
 Potential energy: effect of gravity
 p = fluid mass
 P = pressure
 V = velocity
 h = height
 g = acceleration due to gravity

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What is blood flow?

Volume of blood flowing in a given time (ml/min)

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What is perfusion?

Blood flow per given mass of tissue (ml/min/g)

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What is the velocity of blood flow?

Blood flow divided by the CSA through which the blood flows (cm/s)

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Where is the velocity of blood flow the highest?

Velocity of blood flow in the aorta is high

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What does branching of the arteries do?

Branching of the arteries slows velocity

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What happens as cross sectional area increases?

Greater the CSA, slower the flow, slowest in capillaries

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When does velocity increase?

Velocity increases with the veins come together

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Equation for volume flow

Volume flow(Q)=Velocity(V)xArea(A)

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What are the three patterns of blood flow?

Laminar
Turbulent
Bolus

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Where is laminar blood flow patterns mostly occuring?

Most arteries, arterioles, venules veins

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How is the laminar pattern said to be as?

Concentric shells

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What is the velocity at walls in laminar pattern?

Zero velocity at walls (molecular interactions)

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Where is the maximum velocity in a laminar pattern?

Study These Flashcards

Maximum velocity at centre

Where does the laminar pattern move RBC to ?

Moves RBC's towards centre

What does the laminar pattern do to blood flow through narrow vessels?

Speeds up blood flow through narrow vessels

How is turbulent pattern blood flow?

``` Blood does not flow linearly and smoothly in adjacent layers (whirlpools, eddies, vortices) due to increased pressure & velocity ```

Where does the bolus pattern of blood flow found?

Capillaries

How do the RBC's move through capillaries and why?

RBCs have a larger diameter of capillaries so | move in a single file

What are trapped between RBC's in bolus pattern blood flow?

Plasma columns are trapped between RBC

Comment on velocity in bolus pattern blood flow

Uniform velocity

What does the reynolds number describe?

Describes what determines change from laminar to turbulent flow

When does turbulence occur and give examples when this can ouccur?

Turbulence occurs when Reynold’s number exceeds a critical value (>2000) o E.g. bruits, ejection murmur, increased blood velocity

Equation for blood flow

Blood flow=Arterial blood pressure/TPR

Where is blood pressure the highest?

Highest in aorta

Pressures in aorta during sytole and diastole

 120 mmHg during systole |  80 mmHg during diastole

What happens to arterial pressure in systemic circulation?

Arterial pressure falls steadily in systemic circulation with distance from the left ventricle

What are the factors that affect arterial blood pressure?

o Cardiac output (SV, HR) o Properties of arteries o Peripheral resistance o Blood viscosity

What four key relation ships interact and involved in arterial blood pressure?

``` o Systolic Pressure  Pressure when ejecting o Diastolic Pressure  Pressure when relaxing o Pulse pressure  Difference between diastolic and systolic pressure o Mean blood pressure  Average pressure ```

What does the recoil of elastic fibers of aorta and large arteries help to do?

Recoil of elastic fibers of the aorta and large arteries helps to propel the blood into the circulation

During LV ejection, what percentage of stroke volume is stored in aorta and arteries and why?

60-80% of stroke volume is stored in the aorta and arteries as these structures expand

Where is energy stored in during LV ejection?

Energy stored in stretched elastin

During LV diastole, what happens to the energy which is stored in stretched elastin?

Energy is returned to the blood as the walls of the aorta and arteries contract

What does return of energy to blood sustatin?

This sustains diastolic blood pressure and blood flow when the heart is relaxed

What is pulse pressure and an example?

- Pulse pressure is that the finger senses | o E.g. at the wrist (radial artery)

What does pulse pressure tell us?

Tells you about stroke volume and arterial compliance (stretchiness)

Pulse pressure equation

Pulse pressure=Stroke volume/Compliance

During exercise what happens to the compliance curve as the SV increases and what does this lead to?

``` During exercise, as the SV increases, the compliance curve gets very steep leading to a very high pulse pressure ```

What happens as more blood is ejected and what does this cause and causes what to increase?

``` There is a greater stretch of the arteries as more blood is ejected o This causes less compliance and less recoil and the difference between systole and diastole increases  So, the pulse pressure increases ```

Arterial compliance

Decreased compliance

What does SV now do as there's decreased compliance?

o Decreased compliance (steeper curve) | o Stroke volume now increases systolic and pulse pressure disproportionally

What does age do to stifness of vessels and what does this mean?

Age increases stiffness of the vessels – particularly the aorta o This means that large pulse pressure is present throughout the arterial tree

What happens as you move away from the aorta?

As you move away from the aorta, the pulse pressure increases

What also happens as age increases to vessels?

You also get tapering of the vessels

What happens to pulse pressure at arterioles?

At arterioles, the pulse pressure disappears due to a drop in velocity

What is pulse pressure at aorta and what happens to this pulse pressure further down the arterial tree and why?

- Pulse pressure at the aorta is relatively small but further down the arterial tree it increases slightly. o This is because the vessels become less compliant

Why is the increase not significant?

However, you are still getting the effects of the aorta so the increase is not too significant

What controls mean blood pressure?

- Age - Disease - Distance along the arterial tree - Blood volume – SV, CO - Exercise – SV, CO - Emotion – stress, anger, fear, apprehension, pain

Mean BP equation

Mean BP=diastolic pressure +(1/3)pulse pressure

Principles of haemodynamics Flashcards

(59 cards)