Control of Cardiac Output

Question 1

What type of system is the cardiovascular system + what is the sig of this?

Answer 1

• closed
• amount of blood leaving the heart (CO) must = amount entering it (venous return) so blood isn’t building up in parts of body

Question 2

What situations does CO =/= VR?

Answer 2

• transient events
• e.g. when you stand up CO > VR as ~ 500ml of blood pools in the extremities - quickly reg by body to balance once again

Question 3

What type of circ are systemic + pul circ?

Answer 3

series

Question 4

What must the outputs of LV + RV be?

Answer 4

• equal

- both sides need to pump same amount

Question 5

What mech exist to ensure LV CO = RV CO?

Answer 5

Starling mech

Question 6

Which heart is adjusted to cope with inc/dec VR?

Answer 6

R

Question 7

Which 4 things directly influence CO?

Answer 7

1. Preload
2. Afterload
3. HR
4. Contractility

Question 8

What is preload?

Answer 8

• degree of stretch of heart immediately before it contracts (at end of diastole just before systole)
• P filling R vent
• blood flowing back to heart

Question 9

What is afterload?

Answer 9

• P against heart must pump to eject blood into aorta (due to aortic P)
• R to outflow from LV due to aortic/arterial P

Question 10

Which factors inc CO?

Answer 10

• inc contractility
• inc HR
• inc preload

Question 11

Which factor dec CO?

Answer 11

afterload

Question 12

What is contractility + HR controlled by?

Answer 12

ANS

Question 13

What is contractility?

Answer 13

heart beat more/less strongly

Question 14

Why is CVP = R vent EDP?

Answer 14

no valves sep venous circ from R vent as R vent filling

Question 15

Which factors that influence CO are intrinsic mech?

Answer 15

• preload

- afterload

Question 16

What causes the degree of stretch in preload?

Answer 16

blood coming in from the veins

Question 17

How is preload related to EDV?

Answer 17

• as P inc due to more blood filling vent

- EDV inc due to higher P - stretches heart + cardiac cells

Question 18

What is EDV related to?

Answer 18

filling P aka R atrial P of heart

Question 19

What is preload closely affected by?

Answer 19

• CVP

- EDP of R atrium

Question 20

What is afterload mainly due to + why?

Answer 20

• aortic P bc as it inc e.g. hypertension - more diff for heart to pump blood into aorta - has to work harder which inc afterload

Question 21

What is afterload influenced by + why?

Answer 21

• TPR: inc peripheral R where small arteries + arterioles constricted - inc aortic P
• aortic stiffness: as get older, aorta gets more fibrous - less blood expelled into heart as its less expandable - inc work to get blood into aorta so inc afterload

Question 22

Describe the Starling curve

Answer 22

• as inc P going into vent, tension dev during systole inc

- inc P inc P the vent could gen + amount of blood it could have pumped

Question 23

What relationship does the Starling curve have + why?

Answer 23

• sigmoidal
• ability of vent to pump (gen P) v. sensitive to filling P
• degree of stretch had big effect on vent work
• but reaches sat point where inc filling P no longer has effect on vent P

Question 24

What is the sig of phys range of F-S relationship of vent function curve?

Answer 24

• Physiologically, we operate in range where inc in vent stretch would not get sat which is at low levels so small in vent stretch have large effect on SV and CO

Question 25

What does the F-S relationship/cardic/vent function curve show?

Answer 25

• cardiac myocytes gen more force (SV/vent work) when stretched (vent stretch/EDV)

Question 26

Why is EDP plotted instead of EDV on the vent function curve?

Answer 26

easier to measure

Question 27

Are EDP + EDV linearly related?

Answer 27

• normally are but not in certain cases
• e.g. in case of stiffness of vent in heart failure
• harder to expand heart as in P doesn’t cause in in vol - curve shifts slightly