Haemodynamics Flashcards
What is the difference between plasma and serum?
The fluid collected from unclotted blood is called plasma
The fluid collected from clotted blood is called serum.
Serum has plasma and clotting factors (in particular fibrinogen)
In what diseases does whole blood viscosity occur?
Multiple myeloma is the main cause of whole blood viscosity.
This is because the protein content increases.
Leukaemia -increase in white cells
polycythaemia -Increase in red blood cells
thrombocythaemia - Increase in platelets
can all also cause whole blood viscosity
What is the difference between plasma viscosity and whole blood viscosity?
Minor changes in plasma viscosity can result from raised levels of acute phase plasma proteins (eg fibrinogen, complement factors and C-reactive protein) which are released in response to inflammation.
Whereas, whole blood viscosity is a lot more serious.
What is used to ‘measure’ inflammation?
Minor changes in plasma viscosity can be used to ‘measure’ inflammation because the level of acute phase proteins in the blood rises with inflammation. In recent years, we have been able to measure the levels of CRP (C-Reactive Protein) to ‘measure’ inflammation.
What is the difference between laminar and tubiland flow?
Laminar - Blood flows in streamlines with each layer of blood, remaining the same distance form the wall.
When laminar flow occurs, the velocity of the blood in the centre of the vessel is greater than towards the other edge. This creates a parabolic effect.
Turbulent - blood flow in all directions and continually mixing within the vessel.
What causes turbulent flow?
Turbulent flow occurs when:
- The rate of blood flow becomes too great
- It passes an obstruction in a vessel
- It makes a sharp turn
- It passes over a rough surface
- Increased resistance to blood flow
How do you measure flow?
Volume per unit time
What is a rise in pressure called?
Anacrotic limb. This occurs during systole.
What is it called as pressure decreases?
Dicrotic limb. This occurs during diastole.
What causes the dicrotic notch?
The closing of the aortic valve
What is pulse pressure?
Pulse pressure = peak systolic pressure - end diastolic pressure
This is equal to
systole pressure - diastolic pressure because of the way we measure BP with a sphygmomanometer.
So, most commonly pulse pressure is 120mm/Hg - 80mm/Hg = 40mm/Hg
What is the mean arterial pressure?
It can be estimated as diastolic pressure + 1/3 of the pulse pressure.
Therefore, most commonly, mean arterial pressure is 80mm/Hg + 13mm/Hg = 93mm/Hg.
If the mean arterial pressure falls below 70mm Hg then organ perfusion is impaired.
What is a stenosis? What happens to velocity at this point?
A stenosis is the narrowing of the artery. Velocity will increase at the point of stenosis
What happens to velocity, pressure, energy and flow after a stenosis?
After stenosis, velocity will increase,
Flow will decrease,
Pressure will decrease,
energy will increase
What do we feel when were feeling a pulse?
We feel a shock wave that arrives slightly before the blood itself.
How is strength of pulse determined?
The strength (also called volume) of the pulse is determined by two things:
The force by which the left ventricle is able to eject blood into the arterial system. and thus develop a normal shock wave.
The pulse pressure. The greater the pulse pressure, the stronger the pulse.
What can cause reduced pulse volume?
Reduced pulse volume can result from left ventricular failure, aortic valve stenosis, hypovolaemia (severe dehydration, bleeding).
What is the term for weak pulse?
Thready
What is the term for a strong pulse?
Bounding
When do you get a bounding pulse?
Bradycardia such as a heart block widens pulse pressure and leads to a bounding pulse.
Low peripheral resistance (hot bath, exercise, pregnancy). This lowers the diastolic pressure so causes bounding pulse.
Why does aortic incompetence cause a bounding pulse?
LOOK IT UP!
What is the right size blood pressure cuff to use? Why is this important?
Bladder length should be at least 80% of arm circumference and the width should be 45% of arm circumference.
BP is often overestimated as hospital and GPs dont have enough large cuffs.
At what level should the arm be when measuring BP? Why?
Always measure BP with arm at level of heart as:
If above heart, BP wil be up to 60mm/Hg lower.
If lower, BP will be higher.
What is haemodynamics?
The study of the effect that pressure has on flow through blood vessels
What units do we use to measure flow?
Volume per unit of time eg ml/min l/hr
What is the measurement of pressure?
Pounds per square inch (PSI)
When is flow in blood vessels greater?
Flow is greater when blood vessels are not squeezed.
What is the term used to describe having one stenosis after another?
Critical ischaemia. This usually occurs in the lower limbs and can significantly reduce blood flow.
What happens to the artery distal to the stenosis?
Because of the increase energy and velocity of the blood, it will cause an aneurism (a post stenotic dilatation).
What is the effect of calcification of arteries?
As you age, your arteries calcify (eg the common femoral artery). This leads to lack of compliance which means that you cannot feel a pulse.
What is a thrill?
This is an artery at the point of a stenosis - when you can feel it vibrating.
What is a bruit?
This is when you can hear a stenosis in the peripheral artery. It sounds like an aircraft taking off.
What is a murmur?
When you can hear a druit across a heart valve
What is normal blood pressure?
120 mm Hg over 80 mmHg diastolic
What is hypertensive blood pressure?
larger than 140/90 mm Hg
What equipment do you need to measure blood pressure?
Stethoscope
Sphygmomanometer inc..
Blood pressure cuff, rubber bulb, adjustable valve, flexible tubing and manometer.
How do you measure blood pressure?
- Determine the pulse obliteration pressure.
- Inflate the cuff 20 - 30 mm Hg above the pulse-obliteration pressure.
- Deflate the cuff at a rate of 2 mm Hg /second
- Phase 1 sounds = systolic BP
- Phase 5 sounds = levels at which sounds disappear = diastolic BP
