Control Of Cardiac Output

Question 1

What is afterload?

Answer 1

The pressure the heart must pump/eject blood against

Question 2

What is preload?

Answer 2

The amount the ventricles stretch in diastole

Question 3

What determines preload?

Answer 3

End diastolic volume
Central venous pressure

Question 4

What is Central venous pressure?

Answer 4

Pressure in the large veins draining into the heart

Question 5

What is arterial pressure and where is it normally measured?

Answer 5

Pressure in the large arteries
Measured at Brachial arteries

Question 6

What is Total peripheral resistance? (TPR)

Answer 6

Resistance to blood flow offered by all the systemic vasculature

Question 7

Which blood vessels offer the greatest resistance?

Answer 7

Arterioles

Question 8

How/why do arterioles have the greatest resistance?

Answer 8

Narrow lumen
Lumen can constrict narrowing it increasing resistance

Question 9

What is the affect of constricting arterioles on arterial pressure and venous pressure?

Answer 9

LOWERS VENOUS PRESSURE
INCREASES ARTERIAL PRESSURE

Question 10

What happens in terms of Central Venous Pressure and Arterial pressure if Total Peripheral Resistance (TPR) is reduced (Arterioles dilate) but Cardiac output remains the same?

Answer 10

Blood flows easier so arterial pressure decrease
Central venous pressure increases

Question 11

What happens in terms of Central Venous Pressure and Arterial pressure if Total Peripheral Resistance (TPR) is increased (arterioles constrict) but Cardiac output remains the same?

Answer 11

Arterial pressure INCREASED
Central venous pressure DECREASED

Question 12

What happens in terms of Central Venous Pressure and Arterial pressure if Total Peripheral Resistance (TPR) stays the same but Cardiac output increases?

Answer 12

Arterial pressure INCREASES
(So heart fills easier with blood since it is emptied more)
Central venous pressure DECREASES

Question 13

What happens in terms of Central Venous Pressure and Arterial pressure if Total Peripheral Resistance (TPR) stays the same but Cardiac output decreases?

Answer 13

Arterial pressure DECREASES (Heart doesn’t empty as much)
Heart doesn’t as readily fill with blood
Central venous pressure must INCREASE

Question 14

What feature is usually changed to allow for increased demands of blood to be met?

Answer 14

Reduce peripheral resistance
(Arterioles dilate)

Question 15

When arterioles dilate what affect does this have on arterial pressure and venous pressure?

Answer 15

Decreases arterial pressure
Increases venous pressure

Question 16

How does the heart ensure that arterial pressure and venous pressure dont change when there’s an increased demand for blood?

Answer 16

Pumps more

Question 17

What is cardiac output?

Answer 17

Volume of blood ejected from the left ventricle per min (or per unit time)

Question 18

What is the equation for cardiac output

Answer 18

Cardiac output = Stroke vol x Heart rate

Question 19

What is the equation for Stroke volume?

Answer 19

SV = End diastolic volume - end systolic volume

SV = EDV - ESV

Question 20

What is the average Cardiac output for the average man?

Answer 20

5L/min

Question 21

What is the average stroke volume for the 70kg man at rest?

Answer 21

70ml

Question 22

How can stroke volume be increased? (Think about the equation)

Answer 22

Increase EDV (End Diastolic Volume)
Decrease ESV (End systolic volume)

Question 23

During diastole what valves are open and closed?

Answer 23

Tricuspid and Mitral valve is open
Pulmonary and aortic valve are closed

Question 24

How does venous pressure affect end diastolic volume?

Answer 24

Higher the venous pressure the larger the end diastolic volume (the more the heart fills)

Question 25

What is Frank-Starling law?

Answer 25

The more the heart fills (the more the fibres of the heart stretch) the harder it contracts up to a limit

Question 26

How does strength of contraction affect stroke volume?

Answer 26

Harder contraction = higher stroke volume

Question 27

What is the type of relationship between left ventricular end-diastolic pressure and stroke volume?

Answer 27

Linear relationship (up until a point)

Question 28

How does an increased amount of stretching of the heart fibres increase contraction strength?

Answer 28

More stretch = Inc Ca2+ sensitivity = more contraction ALSO More cross bridges can occur

Question 29

How are both sides of the heart balanced?

Answer 29

If 1 side of the heart has to pump more blood, the other side must match it

Question 30

What is an example of an intrinsic mechanism which ensures both sides of the heart are balanced?

Answer 30

Increasing stroke volume as heart fills up with more blood

Question 31

What is meant by contractility?

Answer 31

Force of contraction for a given fibre length

Question 32

What EXTRINSIC factors affect contractility?

Answer 32

Sympathetic stimulation Circulating adrenaline

Question 33

What is afterload? (Aortic impedance)

Answer 33

The pressure the heart has to pump against

Question 34

How does increased TPR affect venous pressure and therefore the filling of the heart?

Answer 34

Reduces venous pressure Reduces filling of the heart

Question 35

What is the effect of hyper tension (increased arterial pressure) on the heart?

Answer 35

Heart works harder due to a larger afterload Hypertrophy likely to follow

Question 36

What receptors are important in controlling cardiac output?

Answer 36

Baroreceptors

Question 37

What do baroreceptors detect and where are they found?

Answer 37

Stretch receptors found in the aorta and carotid arteries

Question 38

How does the nervous system act when arterial blood pressure drops?

Answer 38

Stimulate sympathetic nervous system Reduce parasympathetic nervous system

Question 39

How is cardiac output determined?

Answer 39

Strength of contraction (EDV and contractility) How hard it is to eject blood (aortic impedance)

Question 40

How does TPR change when theres an increased demand for blood?

Answer 40

Decreases

Question 41

How does the heart need to respond when TPR has decreased to increase blood supply?

Answer 41

When TPR decreases venous pressure INCREASES This means heart fills more Frank-starling law states heart will contract harder

Question 42

How does increased cardiac output affect arterial and venous pressure?

Answer 42

Inc arterial Dec venous

Question 43

How is venous pressure and arterial pressure affected pooling of blood in the feet when you’re sitting down then you stand up?

Answer 43

Venous and arterial pressure both drop since pressure is higher at the feet due to gravity

Question 44

What is the baroreceptor reflex?

Answer 44

Detecting drop in arterial pressure, ANS increases sympathetic activity and decreases parasympathetic activity INCREASED HR AND CONTRACTILITY

Question 45

What happens if the baroreceptor reflex fails when you stand up?

Answer 45

Postural hypotension

Question 46

What happens in response to exercise?

Answer 46

Decreased TPR (Inc venous pressure) Inc HR Inc contractility

Question 47

Where is the jugular vein generally located?

Answer 47

Neck

Question 48

What muscle is the internal jugular vein posterior to?

Answer 48

Sternocleidomastoid muscle

Question 49

What other blood vessel is the internal jugular vein directly in contact with?

Answer 49

Superior vena cava

Question 50

What can the internal jugular be used to estimate?

Answer 50

Central venous pressure

Question 51

How can the internal jugular vein be used to estimate the central venous pressure?

Answer 51

Patient lies at 45º Head turned to left Height of pulsations estimated against sternal angle

Question 52

What is the estimated normal highest visible pulsation of the Jugular vein?

Answer 52

5 to 8cm

Question 53

How does ESV affect venous pressure?

Answer 53

More blood that remains in heart the harder it is to fill with blood This means venous pressure must increase