Principles of haemodynamics Flashcards
What is flow determined by?
Determined by arterial blood pressure and resistance
What are the 3 different flow patterns?
Patterns – laminar, turbulent and bolus
What are the 2 types of arterial pressure?
Systolic
Diastolic
What is haemodynamics?
Haemodynamics is the relationship between blood flow, blood pressure and resistance to flow
What type of system is the CVS?
Closed system
Where is majority of the blood in the CVS?
Venous system
Comment on the venous system
A low pressure reservoir system
What can the reservoir of venous blood be used to do?
Can be used to increase cardiac output
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.
Darcy’s law
Flow(Q)=Pressure difference/R
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
What is blood flow?
Volume of blood flowing in a given time (ml/min)
What is perfusion?
Blood flow per given mass of tissue (ml/min/g)
What is the velocity of blood flow?
Blood flow divided by the CSA through which the blood flows (cm/s)
Where is the velocity of blood flow the highest?
Velocity of blood flow in the aorta is high
What does branching of the arteries do?
Branching of the arteries slows velocity
What happens as cross sectional area increases?
Greater the CSA, slower the flow, slowest in capillaries
When does velocity increase?
Velocity increases with the veins come together
Equation for volume flow
Volume flow(Q)=Velocity(V)xArea(A)
What are the three patterns of blood flow?
Laminar
Turbulent
Bolus
Where is laminar blood flow patterns mostly occuring?
Most arteries, arterioles, venules veins
How is the laminar pattern said to be as?
Concentric shells
What is the velocity at walls in laminar pattern?
Zero velocity at walls (molecular interactions)
Where is the maximum velocity in a laminar pattern?
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
