Control Of Cardiac Output

Question 1

What is the definition of Cardiac Output?

Answer 1

Volume of blood ejected by each ventricle per minute

Cardiac Output (CO) is calculated as CO = HR x SV, where HR is heart rate and SV is stroke volume.

Question 2

What is the formula to calculate Cardiac Output?

Answer 2

CO = HR x SV

CO is measured in liters per minute (L/min), HR is in beats per minute (bpm), and SV is in milliliters (ml).

Question 3

What are typical values for Cardiac Output at rest?

Answer 3

CO ~5 L/min, HR ~70 bpm, SV ~70 ml

These values can vary based on individual fitness and health conditions.

Question 4

How does Cardiac Output change during exercise?

Answer 4

CO increases from ~5 L/min to ~20 L/min

During exercise, HR can increase up to 190 bpm and SV can increase to 105 ml.

Question 5

What factors affect Heart Rate?

Answer 5

• Autonomic Innervation
• Hormones
• Chronotropic Effects
• Neural and Hormonal Regulation

The heart rate is influenced by both sympathetic and parasympathetic nervous systems.

Question 6

What is Stroke Volume?

Answer 6

Volume of blood ejected by each ventricle per beat

Stroke Volume (SV) is a key component in calculating Cardiac Output.

Question 7

What are the determinants of Stroke Volume?

Answer 7

• End Diastolic Volume (EDV)
• End Systolic Volume (ESV)
• Preload
• Contractility
• Afterload

Each determinant influences how much blood the heart can pump with each beat.

Question 8

What is Preload?

Answer 8

The degree to which ventricular muscle cells are stretched at the end of diastole

Preload is directly related to the volume of blood returning to the heart (venous return) and the available filling time

Question 9

What is Contractility?

Answer 9

The force produced by ventricular muscle cells during systole at a given preload

This is affected by inotropic effects

Increased contractility leads to increased stroke volume.

Question 10

What is Afterload?

Answer 10

The force the ventricle needs to overcome to open the semilunar valve and eject blood

Increased afterload can reduce stroke volume and cardiac output.

Question 11

What is the effect of sympathetic stimulation on heart rate?

Answer 11

Increases heart rate

Sympathetic stimulation involves neurotransmitters like norepinephrine and epinephrine.

Question 12

What is the effect of parasympathetic stimulation on heart rate?

Answer 12

Lowers heart rate

Parasympathetic stimulation primarily uses acetylcholine.

Question 13

Fill in the blank: The SA Node has an inherent rate of ______ bpm.

Answer 13

> 100 bpm

This intrinsic rate is modified by autonomic influences.

Question 14

What is the Frank-Starling Law?

Answer 14

The force developed in a muscle fibre is dependent on the extent it is stretched

This law explains the relationship between preload and stroke volume.

Question 15

What are the effects of increased afterload on cardiac output?

Answer 15

Reduces stroke volume and cardiac output

Increased afterload can lead to longer isovolumic contraction and potential heart failure.

Question 16

True or False: Bradycardia refers to a pathologically fast heart rate.

Answer 16

False

Bradycardia refers to a pathologically low heart rate.

Question 17

What role does the Vagus Nerve play in heart rate regulation?

Answer 17

It is involved in parasympathetic control, reducing heart rate

Increased vagal tone results in a lower heart rate.

Question 18

What is the role of the skeletal muscle pump in venous return?

Answer 18

Movement of skeletal muscles constricts veins, aiding venous return

Valves in veins prevent backflow, enhancing venous return to the heart.

Question 19

What is the effect of venous capacitance on venous return?

Answer 19

SNS activity reduces compliance and increases central venous pressure

This effect ultimately aids in increasing venous return.

Question 20

What are the parasympathetic effects on heart rate and cardiac output?

Answer 20

Hormone = ACh
Has a negative chronotropic effect
Lowers HR
Reduces CO

Question 21

What are the sympathetic effects on heart rate and cardiac output?

Answer 21

Hormone = Noradrenaline (NA)/ adrenaline
Positive chronotropic effect
Increases HR
Increases CO

Question 22

What is bradycardia?

Answer 22

Pathologically low HR
(Less than 50/60)

Question 23

What is tachycardia?

Answer 23

Pathologically fast HR
(Around 100bpm)

Question 24

What are chronotropic effects?

Answer 24

Factors affecting HR

Question 25

What is the parasympathetic effects on ionic control at the SA node?

Answer 25

Sensitive to ACh at repolarisation
So more negative resting potential
So takes longer to reach threshold

Question 26

What is the sympathetic effects on ionic control at the SA node?

Answer 26

Increases entry of Na+ and K+
So more depolarisation

Question 27

What factors affect venous return?

Answer 27

• Posture = decreases venous return (blood pools in leg veins when standing due to gravity)
• Skeletal muscle pump = increases venous return (constricts veins so aids venous return, valves prevent backflow)
• Respiratory pump = increases venous return (inspiration reduces intrathoracic pressure whilst increasing intraabdominal pressure)
• Venous capacitance (stretchiness of veins) = increases venous return (SNS activity reduces compliance and increases central venous pressure)

Question 28

What are the SNS effects on contractility?

Answer 28

Increases force of contraction and velocity of conduction

Maximises diastolic time = increased filling