Control of Cardiac Output

Question 1

What is the equation for Cardiac output?

Answer 1

CO= stroke volume x heart rate

Question 2

How is stroke volume increased?

Answer 2

increasing contractility of the heart forces more blood out per ejection

Question 3

How is heart rate increased to increase CO?

Answer 3

increase sympathetic innervation

Question 4

Why is there a limited level to which CO can be increased to?

Answer 4

heart needs cycled through contraction and relaxation at an efficient speed to allow it to refill

Question 5

What are EDV and ESV?

Answer 5

• end diastolic volume, volume of blood in ventricle after it has fully relaxed
• end systolic volume, volume left in ventricle after it has contracted

Question 6

What does an increase in EDV mean?

Answer 6

increased volume in blood in ventricle, more blood pumped out, greater SV hence greater CO

Question 7

What sort of mechanism is increasing EDV?

Answer 7

intrinsic mechanism

Question 8

How is EDV increased?

Answer 8

increase the venous return to the heart which will increase amount of blood in the ventricles therefore increasing the end diastolic pressure

Question 9

What is preload?

Answer 9

the venous pressure and the venous return to the heart

Question 10

what is afterload?

Answer 10

• the force the blood is pushing against

- pressure the L ventricle is working against

Question 11

What is the length/tension relationship?

Answer 11

increasing the length of the sarcomere increases the force of tension generated to an optimal level then increasing sarcomere length above that will decrease the force of tension produced

Question 12

What length are the sarcomeres of cardiac muscle at normally?

Answer 12

length of cardiac sarcomeres are held at a level so that they produce sub-optimal force of tension

Question 13

What effect does increasing venous return to heart have on sarcomeres of cardiac muscle? Explain how force of contraction is increased as a result.

Answer 13

Since cardiac sarcomeres are eld at a length which produces sub-optimal force of tension when venous return to heart is increased this increases the volume of blood in the ventricle and hence stretches the ventricle wall = stretching the sarcomeres of cardiac muscle to length which produces optimal force of tension = total force your heart can generate is increased hence the force of contraction is increased

Question 14

What is the effect on the force of contraction by overfilling the ventricle with venous blood?

Answer 14

overfilling will over-stretch the sarcomeres of cardiac muscle above the length which produces optimal tension and beyond to a level where the sarcomeres are too long and begin to produce sub optimal forces of tension = force heart generates is reduced hence contractility is decreased

Question 15

What is the difference in pressures of the systemic and pulmonary circulations?

Answer 15

the overall operating pressure in the pulmonary circulation is lower

Question 16

What sort of flow do you want through capillaries in the systemic circulation? What is the purpose of this?

Answer 16

• smooth, laminar, slow flow

- to allow exchange of materials an nutrients between blood and tissues

Question 17

How is pressure in capillaries in systemic circulation so low despite the huge pressure in the aorta?

Answer 17

masses of capillaries branched round body tissues hence pressure from the aorta is evenly spread out amongst all the branches

Question 18

Since pressure decreases in vessels from large conducting arteries down to same capillaries what is the effect on the structure an properties of these vessels?

Answer 18

• there is a change in the amount of fibrous tissue, elastic tissue and smooth muscle in vessels
• change in conductance and dampening of oscillation from large conducting arteries down to arterioles and capillaries

Question 19

What adds to form the total pressure in the aorta?

Answer 19

flow cardiac output and the sum of the resistance of all the downstream arteries

Question 20

Define vascular compliance.

Answer 20

how likely a vessel will change to accommodate a volume and how the pressure changes in that vessel as a result

Question 21

Describe the compliance of the aorta.

Answer 21

Large volume of blood pushed through the aorta will increase the pressure within and it will swell to accommodate the increased pressure as a result of the large volume of blood

Question 22

How compliant are capillaries?

Answer 22

can increase the pressure of blood through the capillaries however the volume of the vessels will not change

Question 23

What is the relationship for mean arterial blood pressure?

Answer 23

MABP= diastolic blood pressure+ 1/3 of pulse pressure

Question 24

How is pulse pressure calculated?

Answer 24

pulse pressure= systolic pressure - diastolic pressure

Question 25

How does viscosity of blood affect blood flow?

Answer 25

increase in viscosity of blood as a result of increasing haematocrit there is a reduction in the flow of blood

Question 26

What is the most important factor in resistance to blood flow?

Answer 26

radius of blood vessel

Question 27

What is Poiseulle’s equation? What is the equation of flow you can obtain from Pioseulle’s relationship?

Answer 27

• flow varies directly with change in pressure x radius of vessel4 and inversely with viscosity x length

flow=change in pressure/resistance

Question 28

How is arterial pressure calculated?

Answer 28

AP= CO x total peripheral resistance

Question 29

What is arterial pressure?

Answer 29

mean arterial pressure generated in the aorta that drives blood around the system

Question 30

How is the CO in the pulmonary and systemic circulations the same if the operating pressure of the pulmonary circulation is lower than that of the systemic circulation?

Answer 30

the resistances of the two circulations are also different hence when factored in with the different operating pressures the CO remain equal

Question 31

what extrinsic mechanisms affect SV?

Answer 31

effects of contractility mediated by sympathetic innervation

Question 32

What 2 things decrease arterial compliance?

Answer 32

• age

- atherosclerosis