S2 Control of Cardiac Output Flashcards
What is afterload?
The load the heart must eject blood against e.g. the aortic pressure
What is the preload?
The amount the ventricles are stretched/filled in diastole (linked to EDV and central venous pressure (CVP))
What is the total peripheral resistance?
Resistance to blood flow from all the systemic vasculature
Also known as systemic vascular resistance
What happens to pressure of fluid in a tube as it encounters resistance?
the pressure exerted drops as it flows through resistance
Which blood vessels give the largest resistance? What does this increased resistance mean for capillaries, arterial side and the venous side?
Constriction of arterioles
Causes pressure decrease in capillaries and venous side and the pressure to increase in the arterial side - pressure builds up prior to resistance and less gets through past resistance
If total peripheral resistance decreases and cardiac output stays the same, what happens to the arterial and venous pressures?
- arterial pressure decreases - as cardiac output not increased
- venous pressure increases
What happens to arterial pressure and venous pressure if total peripheral resistance increases and cardiac output stays the same?
- arterial pressure increases
* venous pressure decreases - blood can’t flow to venous side as easily
If cardiac output is increased and total peripheral resistance stays the same, what happens to the arterial and venous pressures?
- arterial pressure increases - heart is pumping out more
* venous pressure decreases
If cardiac output decreases and total peripheral resistance stays the same, what happens to the arterial and venous pressures?
- arterial pressure decreases
* venous pressure increases (only a small increase)
How do you calculate cardiac output?
Stroke volume x heart rate
How do you calculate stroke volume?
End diastolic volume - end systolic volume (SV = EDV - ESV)
How can you increase the stroke volume?
By increasing EDV or decreasing ESV
What is the stroke volume of a average 70kg man at rest?
About 70ml
When does the ventricle stop filling? What are the consequences for how much the heart fills and how high the pressure is?
What is this relationship called?
When the walls stretch enough to produce a intraventricular pressure equal to the venous pressure
The higher the venous pressure, the more the heart fills
And the more the heart fills, the higher the ventricular pressure
Ventricular compliance curve
When can compliance be increased or decreased?
In diseased states