Flashcards in L1. Cardiac Function and its Control Deck (20):
What is the main purpose of the heart?
To pump oxygen around the body
Systolic pressure has a much higher resistance and a higher pressure. What does this mean for the left side of the heart?
The left ventricle has to pump the same amount of blood as the right ventricle (CO) but against a higher resistance and pressure.
Thus more work is done by the left ventricle leading to thicker walls.
Thicker walls however mean less compliance. And so filling of the left ventricle is also against greater work.
In what circumstances can the pericardium affect compliance of the heart?
It doesn't often occur but in some cases the normally frictionless glide can be affected by inflammation, fluid accumulation and cancer.
What are the two main determinants of mean arterial pressure? (Equation)
Mean arterial pressure depends on the amount of blood going through the arteries and at what rate (CO) and the resistance of the system.
MAP = CO x TPR
Where does most of the resistance lie in the systemic circulation?
In the arterioles, which regulate the amount of blood going to the tissues.
What does a reduction in TPR lead to for the systemic circulation? How?
Reduced TPR leads to an increase of blood going to the tissues, which requires a decrease of blood from the systemic circulation. This decreased blood leads to decrease pressure in the system.
What are the normal values for:
Early diastolic pressure
CO = 5 L
SV = 100 mL
ESV = 75 mL
EDV = 150 mL
Early diastolic pressure = 5 mmHg
Why is the volume of the heart not zero at the end of systole (ESV)?
Because there is a built in reduncdancy for the heart. This extra pool of blood is used in cases of needs to increase CO, without the reserve pool would take much longer.
Describe the differences in the pressure-volume curves for diastolic vs. systolic for the left ventricle (compliance curve)
During Diastole: higher volumes lead to higher pressures but the increase in pressure is not large. This reflects the low compliance of the ventricle to filling.
During Systole: higher volumes in the ventricle equate to much higher pressures as the ventricle generates higher pressures in order to generate higher forces to eject that increased volume.
What is stroke volume? And what do the following do the it..
Increased HR, Increased EDV, Increased ventricular contractility?
SV is the volume of blood ejected by the left ventricle in each beat.
Increased HR decreases SV because less time is available for the heart to eject blood out and has less time for filling
Increased EDV increases the SV because what goes in, comes out
Increased contractility also increases the SV because the forceful contraction forces more blood out (Eg. adrenergic receptors)
What does the Frank-Starling Relationship describe?
The Frank-Starling relationship explains that the more stretch of the wall (given by increased filling) generates more tension (pressure) in the wall to eject that volume.
What additional  factors (other than EDV) may affect contractility of the wall?
Acidosis reduces contractility
Sympathetic nerve innervation (increases): Adrenaline increases contractility
Caffeine increases contractility
Hypercapnia (increased CO2 may decrease)
Explain the cardiac cycle in terms of pressure and volume curves (Wigger's Diagram)
See lecture notes:
- When the valves close and open
- Isovolumetric phases
- Inclusion of the Aortic, LV and LA pressures and the LV volume
Explain the LV pressure-volume loop
See lecture notes
What is meant by the LV having a pressure reserve?
If superimpose the pressure-volume and the pressure-volume loop of the LV then you can see that the left ventricle works at much lower pressures than what is actually capable of the LV. This means that if needed, the LV has the capacity to increase the pressure generated per volume.
What does increasing LV contractility do to the curves?
Increased contractility means that the SV increases because more blood is able to be ejected. Thus the ESV decreases. However filling is not affected to EDV doesn't change.
What does reduced compliance do to the curves?
Reduced compliance means that the filling of the ventricle is less effective and the mitral valve closers sooner stopping filling sooner. Thus EDV is decreased and as a result SV is decreased. However the ESV doesn't change.
What happens to the parameters of the curve if the aortic pressure were to rise?
Increase in aortic pressure means that the pressure required to eject blood out of the heart needs to increase. It also means that the work required to eject blood out is higher meaning the SV decreases.
A decrease in SV means an increase in ESV. However, in mild/moderate cases EDV isn't affected.
What is afterload?
The load on the ventricle just after it begins contraction. Ie. what loads after the heart.
- Arterial hypertension, aortic stenosis
Thus the ventricle needs to generate higher forces to overcome them.