Haemodynamics 2 Flashcards
What is pulse pressure?
Peak systolic pressure - end diastolic pressure
(the difference between the systolic blood pressure and diastolic blood pressure)
What is the mean arterial pressure?
How do you work out mean arterial pressure?
What is the mean arterial pressure NOT?
It is the average blood pressure throughout the cardiac cycle
Diastolic blood pressure + 1/3(pulse pressure)
NOT the arithmetic mean of SBP and DBP
What is critical point of mean arterial pressure?
Below 70mmHg = organ perfusion becomes impaired
In this equation (Darcy’s law), what does each variable represent?
What is cardiac output? Units? Formula?
The amount of blood/flow that is leaving the heart at a given time
Volume/min ie ml/min
Stroke volume x heart rate
What governs pulse pressure?
What will cause an increase in pulse pressure?
What else may impact pulse pressure?
1) Volume of blood ejected and compliance of arterial system
2) Increased stroke volume during exercise with relative compliance of vessels = increased pulse pressure
3)
Haemorrage - decrease in PP
Age - with age, a lot of people develop atherosclerosis , decrease in compliance
What is the formula for mean arterial pressure and explain how it gets deduced?
MAP = CO X TPR
What is a pulse?
Shock wave that arrives slightly before the blood itself
What is a bounding pulse?
A pulse that is abnormally strong
What is an increase in pulse pressure described as?
What is actually happening when pulse pressure is increasing?
- A bounding pulse
- There is a larger gap between systolic and diastolic pressures
Describe 3 situations that could lead to/influence increasing pulse pressure
1) Heart block (conduction in the heart is compromised) so you become bradycardic (slow heart rate)
2) Vasodilatation due to hot bath or pregnancy ie, leads to decrease in peripheral resistance
3) Elite athlete like swimmers or track cyclists, as they train harder, you get increase in systolic pressure and decrease in diastolic
DOTTED line shows these things
What causes pathological turbulence in blood flow?
Describe what is occurring in this case
Caused in a stenosed vessel through atheroma or stenotic heart valve or if a vessel is occluded in a particular way
Velocity increases through the stenosis and turbulence occurs beyond the stenosis
How does measuring blood pressure work?
- Normally, blood flow is laminar so it’s silent
- Increase the cuff pressure to completely occlude brachial artery
- You get silence because you have occluded the brachial artery, so there’s no blood flow
- Gradually reduce cuff pressure
- Korotkoff sounds are produced
- Initial Korotkoff sound = systolic pressure/start of systole is indicated
- There’s some blood flow but it’s TURUBLENT FLOW
- Reduce cuff pressure further until cuff pressure < artery pressure
- When sound stops = diastolic pressure/start of diastole is indicated here
- Sound has stopped because there is now normal blood flow
Describe how to manually measure blood pressure (5 marks)
- Inflate cuff around upper arm whilst palpating the brachial pulse [1 mark]
- Inflate to 30mmHg above the point where the pulse disappears [1 mark]
- Release pressure slowly, listening with stethoscope over brachial artery [1 mark]
- First Korotkoff sound = systolic pressure [1 mark]
- Fifth Korotkoff sound (where sounds disappear) = diastolic pressure [1 mark]
What can be felt and heard when pathological turbulent flow occurs?
Thrill can be felt
Bruit (bro-eee) can be heard
(Velocity increases through stenosis, turbulence occurs beyond)
What sounds do you hear when measuring BP?
What are these?
- Korotkoff sounds
- These are sounds that occur due to changes from laminar to turbulent blood flow which can be used to estimate blood pressure
What is important when measuring blood pressure? (7)
1) Cuff size
- too small = will overestimate bp
- too big = will underestimate bp
2) Positioning of cuff - over brachial artery
3) Measure in both arms, often a difference, use the higher as reference arm
4) Sat comfortably, upright with legs uncrossed and flat on the ground
5) Supported arm on table
6) Repeat several times - take arithmetic mean of 2 values
7) MEASURE AT THE LEVEL OF THE HEART and at rest
Gravity effects on BP
- In order for blood to flow, it needs to move from an area of high pressure to an area of low pressure
- Pressure below the level of the heart is higher than pressure above
- But blood is still able to move from the heart to the feet while standing
- Gravity enables this
Describe how gravity enables blood to move from the heart to the feet while standing
- Gravity acts
- and maintains a pressure gradient,
- so the pressure above is now higher than the pressure below,
- allowing blood to move from the heart to feet whilst standing.
Describe the concept of blood pooling an the effects
- Pooling of blood at the feet in the venous system when you stand up
- Less blood being returned to the heart initially
- Smaller stroke volume
- Lower stroke volume=less blood able to get to vital systems ie cerebral circulation.
What is postural hypotension?
Dizziness upon standing from a decrease in stroke volume and transient arterial hypotension
How do you calculate Mean arterial pressure with cardiac output?
MAP = CO x total peripheral resistance
What is the slight raise on blood pressure graph after peak systolic?
What is happening here?
Dicrotic notch
Aortic valve closing = short increase in pressure
