3. Control of Cardiac Output

Question 1

What is meant by the term cardiac output?

Answer 1

Cardiac output is the volume of blood pumped by the left ventricle in one minute

Question 2

How is cardiac output calculated?

Answer 2

Calculated by multiplying heart rate by stroke volume

Question 3

What alters the heart rate?

Answer 3

Sympathetic and parasympathetic nervous systems

Question 4

What effect does the sympathetic nervous system have on the heart?

Answer 4

Speeds up the heart

+ve chronotropic efffect

Question 5

How does the sympathetic nervous system speed up?

Answer 5

Beta 1 receptor opens Ca++ L channels
Increases slope of prepotential, making it reach firing level quicker, more rapid SA firing.
Speeds AV conduction
R symps to SA node, L to AV node

Question 6

What effect does the parasympathetic nervous system have on the heart?

Answer 6

Slows down heart (-ve chronotropic effect)

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Question 7

How does the parasympathetic nervous system speed up?

Answer 7

M2 receptor opens K+ channels, slows opening of Ca++ channels
Hyperpolarises cell, decreases slope of prepotential, making it reach firing level more slowly, slower SA firing.
Slow AV conduction
R vagus to SA node, L vagus to AV node

Question 8

How is cardiac output influenced?

Answer 8

Altercations in stroke volume

Question 9

What do changes in the altercations in stroke volume depend on?

Answer 9

These changes may depend on the intrinsic properties of cardiac muscle, on autonomic stimulation and on hormones

Question 10

What is meant by heterometric regulation?

Answer 10

Changes in C.O. dependent on initial length of cardiac muscle fibre

Question 11

What is meant by homeometric regulation?

Answer 11

Changes in C.O. independent of such changes

Question 12

What are the features of a frank-starling relationship?

Answer 12

Stroke volume (and CO) is dependent on the degree of stretch on ventricular walls
Increases in End-diastolic volume stretch ventricular walls increasing stroke volume
More in = more out, elegant!
Preload and afterload
Decompensation
Mechanism now debated
Overlap? Ca++ sensitivity or influx?

Question 13

What happens in sympathetic stimulation?

Answer 13

Shifts Starling up and to the left (see previous)
Affect on Beta 1 adrenergic receptors
Positive inotropic effect of sympathetic stimulation

Question 14

What is meant by parasympathetic stimulation?

Answer 14

Negative inotropic effect on atria but no effect on ventricles

Question 15

What other factors affect contractility?

Answer 15

Catecholamines

Force-frequency relation

Question 16

What are examples of catecholamines and what do they do?

Answer 16

Noradrenaline and adrenaline

Amplify beta effects

Question 17

What are examples of force frequency relations?

Answer 17

Post-extrasystolic potentiation
Paired stimuli
Fast heart rates

Question 18

What is the fick principle?

Answer 18

Amount of a substance taken up per unit time by an organ (or the whole body) equals arterial content – venous content (A – V difference) times the blood flow through the organ (or body).

Question 19

What is the indicator dye method?

Answer 19

look at slide 18

Question 20

What is cardiac failure?

Answer 20

insufficient peripheral perfusion despite normal blood volume, a sufficient filling pressure and intact intrinsic and extrinsic compensatory mechanisms

Question 21

What are some of the causes of cardiac failure?

Answer 21

Common causes - Coronary artery disease

Cardiac tamponade and valvular problems