Control of Cardiac Output

Question 1

What are the intrinsic mechanisms for control of stroke volume?

Answer 1

• self regulation
• Frank- Starling mechanism
• increasing EDV to increase force of contraction

Question 2

Explain the Frank-Starling mechanism

Answer 2

• increasing the filling pressure of the heart stretches the muscle and increases its force of contraction
• increasing the force of contraction expels more blood from the left ventricle
• cardiac output increases when preload increases

Question 3

What is preload?

Answer 3

• venous pressure and volume inside the ventricle before it contracts
• increasing EDV increases preload

Question 4

What is afterload?

Answer 4

aortic/pulmonary pressure

Question 5

Explain the extrinsic mechanism of control of stroke volume

Answer 5

• sympathetic stimulation effect
• bigger force of contraction (due to increased contractility)
• bigger stroke volume (more blood ejected from ventricle)
• overall volume still the same

Question 6

What is the benefit of the Frank-Starling law of the heart?

Answer 6

it allows for automatic adjustment for the small imbalances between the left ventricle and right ventricle

Question 7

Explain how the Frank-Starling law can be paired with a positive ionotropic effect

Answer 7

• independent mechanisms that can work together
• sympathetic NS stimulates the heart to increase contractility
• occurs while there is an increase in venous return to the heart
• causes more blood in ventricle increasing EDV
• potentiates tension

Question 8

What is a reason for pressures within the CVS varying between vessels?

Answer 8

• to comply with the physiological properties of the different vessels
• high pressures through vessels such as capillaries which are only one cell thick would be very damaging

Question 9

What is total peripheral resistance/systemic vascular resistance?

Answer 9

measure of how much resistance to flow around CV tree caused by muscled arteries

Question 10

Explain non-compliance and examples of vessels

Answer 10

• rigid tubes that resist expansion when internal pressure rises
• huge increases in pressure for small increases in volume
• eg. capillaries, arterioles

Question 11

Explain compliance and examples of vessels

Answer 11

• tubes with elastic walls that swell when internal pressure rises
• easily distend to accumulate huge volumes with small pressure changes
• eg. arteries and veins

Question 12

How do you calculate mean arterial blood pressure (MABP)?

Answer 12

MABP = diastolic pressure + 1/3 pulse pressure

Question 13

How do you calculate pulse pressure?

Answer 13

systolic pressure - diastolic pressure

Question 14

What are the factors determining the magnitude of pulse pressure?

Answer 14

• stroke volume
• speed of ejection of stroke volume
• arterial compliance

Question 15

What is flow directly proportional to?

Answer 15

• radius of vessel

- pressure gradient along the vessel

Question 16

What is flow inversely proportional to?

Answer 16

• length of vessel

- thickness of fluid

Question 17

How do you calculate arterial pressure and what is this derived from?

Answer 17

• arterial pressure = cardiac output x total peripheral resistance
• derived from Poiseuille equation of flow = change in pressure/resistance