lecture 5 module 1 Flashcards
Mean arterial pressure =
Cardiac output x total peripheral resistance
Why is it important that we maintain mean arterial blood pressure?
so that all the organs are perfused
Define total peripheral resistance
this is the resistance to blood flow through the blood vessels
Cardiac output =
heart rate x stroke volume
We control cardiac output by controlling what?
heart rate and stroke volume
We can control cardiac output by controlling heart rate and stroke volume from both intrinsic factors and from extrinsic factors. What are the extrinsic factors that control the heart rate and stroke volume?
hormones and nervous control
The whole control of MAP is a ________ loop. What does this mean?
closed
this means if you change anything in the cycle, it is going to have consequences for everything else
you never just switch on to increase your heart rate or switch on to decrease your heart rate, it is always a balance
Define stroke volume
the volume of blood ejected from either ventricle
What is the intrinsic control of the heart rate?
this is very limited
What is the extrinsic control of the heart rate?
parasympathetic and sympathetic control
Although we don’t change heart rate intrinsically, if we change heart rate, that has an intrinsic effect on stroke volume. True or false?
true
If we develop an action potential, it is going to generate some _______ and there will be a _________. If the action potentials are spaced out, they will generate the same amount of ________. If you increase the frequency of action potential, the force generation _________. What is this known as?
force
contraction
force
increases
this is known as the force/frequency relationship/ Treppe effect or Bowditch effect
What does the force/frequency relationship/ Treppe effect of Bowditch effect say?
that the myocardial contraction increases as frequency increases
Why does the myocardial contraction increase as frequency increases?
because there is an increase in the Ca2+ per unit time
with every action potential, not all Ca2+ will be cleared so the Ca2+ builds up over time so more force is generated
What is heart failure?
when the heart cannot generate enough cardiac output to perfuse your body sufficiently
What is the negative force-frequency relation and why is this a hallmark of heart failure? Why is this bad for the heart?
Normally, as the action potential increases, the force increases. If this is not the case then the heart is failing.
This is bad for the heart because if you are trying to increases cardiac output, you don’t want the stroke volume to go down so if heart rate goes up and stroke volume goes down cardiac output will not change
In a healthy heart, as heart rate goes up, when happens to stroke volume and cardiac output?
Due to the increase in heart rate, stroke volume increases and therefore cardiac output increases
How can stroke volume be controlled intrinsically?
By changing preload, afterload and contractility
What is afterload?
this is the load on the heart when it is trying to eject (how much resistance was there to blood output)
Define contractility
this is a measure of the quality of the pump
What is Pre-load also called?
the Frank-Starling mechanism
How does increases in preload affect the stroke volume?
increases in preload produces larger stroke volumes
How can you increase pre-load? Why is this?
by increasing venous return
Just prior to contraction (after atrial top-up), we have the largest volume of blood in the heart (the end-diastolic volume). If the ventricles are more filled with blood, they will be stretched. This means that each of the cardiac cells and sarcomere inside the muscle cell are stretched too. This increases contraction and therefore increases stroke volume
How does increasing pre-load increase stroke volume?
Just prior to contraction (after atrial top-up), we have the largest filling of blood in the heart (the end-diastolic volume). If the ventricles are more filled with blood, they will be stretched. This means that each of the cardiac cells and sarcomere inside the muscle cell are stretched too. This increases contraction and therefore increases stroke volume
What measurements need to be on each axis in order to show the Frank-Starling Mechanism (increasing preload increases stroke volume)?
What does this graph look like?
On the x axis there is ventricular end-diastolic volume (in mLs) and on the y axis, there is stroke volume (also in mLs). The graph shows that as you increase ventricular EDV, stroke volume also increases
Describe the pressure volume loop - what are the axis?
on the x axis there is volume of blood (mLs)
on the y axis, there is left ventricular pressure