Lecture 03 Heart Physiology 2

Question 1

How is Cardiac Output measured?

Answer 1

litres per minute

Question 2

How is Cardiac Output calculated?

Answer 2

heart rate x stroke volume

Question 3

What is Cardiac Output?

Answer 3

how much blood is being delivered through the circulation per minute

Question 4

What is the blood volume?

Answer 4

5 litres

this is how much blood is pumped every minute at rest

Question 5

What is the maximal blood volume with exercise?

Answer 5

35 litres

Question 6

What is the Ejection Fraction (%)

Answer 6

refers to the percentage volume of blood ejected with each cardiac contraction
normally 55-60% at rest

Question 7

What factors affect heart rate?

Answer 7

sympathetic stimulation
parasympathetic stimulation
circulating catecholamines
drugs

Question 8

How does sympathetic regulation affect heart rate?

Answer 8

increases heart rate in response to NA

Question 9

How does parasympathetic regulation affect heart rate?

Answer 9

decreases heart rate in response to vagus nerve

Question 10

What is an example of a circulating catecholamine?

Answer 10

adrenaline

Question 11

When (medically) is sympathetic and parasympathetic regulation irrelevant?

Answer 11

individuals with a heart transplant

no autonomic control

Question 12

What factors affect stroke volume?

Answer 12

1. intrinsic contractility

2. extrinsic contractility

Question 13

What intrinsic factors affect stroke volume?

Answer 13

intracellular calcium 
oxygen 
free fatty acids
ATP 
muscle physiology

Question 14

What extrinsic factors affect stroke volume?

Answer 14

preload/filling pressure
afterload/resistance to ejection
sympathetic activity

Question 15

How would you increase a patient’s preload?

Answer 15

injection of saline increases their blood volume and therefore preload

Question 16

What does intracellular calcium activate? What does this lead to?

Answer 16

ryanodine receptors on the sarcoplasmic reticulum

cascade reaction leading to further activation of ryanodine receptors and release of calcium

Question 17

How would sympathetic activity affect the stroke volume?

Answer 17

preload and after load kept the same

increasing sympathetic activity increases cardiac output

Question 18

How does calcium initiate contraction?

Answer 18

calcium attaches to troponin
leads to myosin to be exposed
actin binds to myosin
contraction

Question 19

How does contraction occur?

Answer 19

1. myosin filaments have heads that form cross bridges when attached to actin filaments. ATP is hydrolysed when myosin head is unattached
2. ADP+P are bound to myosin as myosin head attaches to actin
3. ADP+P release causes head to change position and actin filament to move
4. binding ATP causes myosin head to return to resting position

Question 20

Why is it important that the wave of depolarisation moves through the heart quickly?

Answer 20

so that the whole cardiac muscle can contract together

Question 21

What does the Frank-Starling Mechanism compare?

Answer 21

cardiac output and end-diastolic pressure

Question 22

What is end diastolic pressure?

Answer 22

volume of blood in the ventricles at the end of diastole

Question 23

What is the principle of the Frank-Starling Mechanism?

Answer 23

the bigger the stretch of the myocardial fibres the larger the contraction, this increases the stroke volume and therefore the cardiac output

Question 24

How does changes in the venous return affect the LVEDP and stroke volume?

Answer 24

increased venous return increases the volume and therefore the LVEDP, this will increase the stroke volume
decreased venous return decreases the volume and therefore the LVEDP, this decreases the stroke volume

Question 25

Frank Starling Mechanism - what determines how the ventricle operates?

Answer 25

a family of curves determined by afterload and contractility

Question 26

Frank Starling Mechanism - what happens if the curve shifts up and left?

Answer 26

increased contractility, stroke volume and resistance
decreased afterload
overall increase in cardiac output

Question 27

Frank Starling Mechanism - what happens if the curve shits down and right?

Answer 27

decreased contractility and stroke volume
increased afterload
overall line is flatter

Question 28

Frank Starling Mechanism - what effect does the preload have?

Answer 28

curve defined by afterload

move up and down that curve defined by preload

Question 29

What is Isoprenaline?

Answer 29

synthetic catecholamine similar to NA

Question 30

What does Isoprenaline do?

Answer 30

enhances calcium influx, increased intracellular calcium causes enhanced contraction
shift Frank Starling curve left and up to a higher cardiac output

Question 31

Frank Starling Mechanism - what does the curve look like for a failing heart? What does this mean?

Answer 31

curve to the right and down, much flatter
doesn’t matter how much preload is increased, the stroke volume is limited
increasing pressure has little-to-no effect

Question 32

How is high LVEDP in heart failure patients treated? Why?

Answer 32

diuretics - decrease filling pressure decreases LVEDP

Question 33

What is a symptom of low cardiac output (medical shock)? What can this lead to if untreated?

Answer 33

breathlessness

heart failure

Question 34

How is low cardiac output treated?

Answer 34

ACE inhibitors - vasodilation

shift curve left and up increasing CO and decreasing afterload