Week 16: (E) Control of Cardiovascular output

Question 1

What is cardiac output?

Answer 1

volume of blood pumped by each ventricle per minute

Question 2

Is the volume of blood flowing through the pulmonary circulation the same as the systemic circulation?

Answer 2

YES, at any point in time

Question 3

What ventricle does CO refer to?

Answer 3

CO from left ventricle, to body.

aorta

Question 4

What is the CO equation?

Answer 4

CO= HR X SV

Question 5

What is SV?

Answer 5

volume of blood (mL) ejected per contraction

SV= end diastolic volume - end systolic volume

Question 6

What is SV at rest?

Answer 6

~70 mL

Question 7

What is HR?

Answer 7

beats per min

Question 8

What is CO controlled by?

Answer 8

physiological requirememts

via control of HR and SV

Question 9

What regulates SV?

Answer 9

intrinsic & extrinsic control

Question 10

What is intrinsic control?

Answer 10

• Does not require any external impute i.e hormonal/ neural factors
• Related to the initial length of the cardiac muscle fibres, which in turn depend upon the end diastolic volume

Question 11

What is extrinsic control?

Answer 11

• Varying on extent of sympathetic stimulation

- Regulates contractility

Question 12

What does an increased EDV result in?

Answer 12

increased SV

Question 13

What does an increase in blood returned to the heart cause?

Answer 13

• Increase in contractility of cardiac muscle fibres

- Increase in SV and cardiac output

Question 14

Is it a simple relationship between EDV and SV?

Answer 14

No, heart does not eject all the blood it contains

Question 15

Is there blood left in the heart after systole? ESV

Answer 15

YES

~65 mL

Question 16

What does intrinsic control depend upon?

Answer 16

length-tension relationship of cardiac muscle

Question 17

What does SV relate to?

Answer 17

muscle tension

Question 18

What dies EDV relate to? (graph)

Answer 18

muscle fibre length

Question 19

does the normal resting length of cardiac muscle equal to the optimal length (lo)?

Answer 19

No, the length can ascend towards it

Question 20

What happens if length goes past lo?

Answer 20

it diminishes contractile strength

Question 21

What is preload?

Answer 21

The maximal blood volume in the ventricle before contraction

Question 22

What does increased length of heart cause?

Answer 22

increase contraction/tension

increase SV

Question 23

What are the 2 major advantages of matching SV with venous return? (intrinsic)

Answer 23

1) Equalises output between left and right sides of heart
- ->equally distributed between pulmonary and systemic circulations

i. e. increase output from aorta (left) increases the input to the pulmonary vein (right) and to pulmonary circulation. increase EDV on right side increases SV
2) When a larger CO is required, e.g. during exercise, venous return is increased through action of the sympathetic NS. The resulting increase in EDV automatically increases SV.

Question 24

What would happen if the left and right sides could not equalise one another?

Answer 24

blood would be damned up in the nous system, before the ventricle with the lower output

Question 25

What is increased in cardiac muscle during exercise?

Answer 25

HR and SV to increase CO, to supply more blood to exercising skeletal muscle

Question 26

What effect does increased initial length have on the cellular contractile mechanisms?

Answer 26

1) Greater initial length increases the sensitivity of contractile proteins in the myofibrils to Ca2+ 2) Increased initial fibre length may also increase Ca2+ release from the sarcoplasmic reticulum

Question 27

What does increased Ca2+ in cytosol do to cardiac muscle?

Answer 27

increase force of contraction increase SV increase blood preload

Question 28

What extrinsic factors enhance contractility of heart?

Answer 28

Adrenaline and sympathetic stimulation

Question 29

What does nor/adrenaline trigger?

Answer 29

- Increased ca2+ entry | - From intracellular Ca2+ store

Question 30

What phase of the AP of cardiac muscle does adrenaline act?

Answer 30

plateau phase

Question 31

What is Ca2+ required for in cardiac muscle cells?

Answer 31

E-C coupling

Question 32

How is systole shortened in sympathetic stimulation?

Answer 32

stimulating Ca2+ pumps- take up Ca2+ form cytoplasm more rapidly

Question 33

What is the collective term for the mechanism of contractility?

Answer 33

inotropic actions.

Question 34

What is the SV of sympathetic and sympathetic plus increased EDV?

Answer 34

100 ml | 140 ml

Question 35

What does increased BP do to the heart?

Answer 35

increase workload

Question 36

What must happen when ventricles contract?

Answer 36

- Must generate sufficient pressure to exceed the blood pressure in the major arteries. - To open semilunar valves and allow ejection

Question 37

What is the arterial blood pressure called?

Answer 37

afterload

Question 38

Why is it called afterload?

Answer 38

it is the workload imposed on the heart after the contraction has begun.

Question 39

How may the heart compensate for increased afterload?

Answer 39

enlarge (hypertrophy)

Question 40

What happens if you have a diseased of weakened heart and trying to compensate for increased after load?

Answer 40

may not be able to compensate completely = heart failure

Question 41

How many mm of Hg is at peak pressure resting?

Answer 41

120 mm

Question 42

How many mm of Hg is at peak pressure with Na (stimulation)?

Answer 42

180 mm | more rapid

Question 43

What is dP/dt?

Answer 43

change in pressure over time

Question 44

What can change in pressure over time be used for? | What can it determine?

Answer 44

estimate contractile state of myocardium | -->important in determining severity or progression of valve disfunction

Question 45

How do we get the simplest measurement of myocardial contractility?

Answer 45

Analysis of the pressure waveform during isometric contraction phase

Question 46

What is the advantage of using analysis of pressure waveform during isometric contraction phase?

Answer 46

independent of afterload

Question 47

What is the isometric contraction phase?

Answer 47

a brief moment when the AV and SL valves are closed