Control Of Cardiac Output 2

Question 1

What type of control is changing stoke volume to match LVEDP

Answer 1

Intrinsic control

Question 2

Contractility

Answer 2

Force of contraction for given fibre length

Causes change in slope of starling curve

Question 3

Increase in contractility

Answer 3

Increase force of contraction = increase stroke volume

Question 4

What factors influence contractility?

Answer 4

Extrinsic - sympathetic nervous stimulation

Adrenaline

Question 5

What effect does reducing sympathetic stimulation have?

Answer 5

Reduce contractility

Question 6

What effect does increasing arterial pressure have on stroke volume?

Answer 6

Increased when peripheral resistance is increased
Harder for heart to pump out blood

Also if resistance increases, venous pressure decreases so harder for heart to fill

DECREASED STROKE VOLUME

Question 7

Factors determining cardiac output

Answer 7

Ventricular emptying: (stroke volume)

• hard it contracts (end diastolic volume - more full = more empty and contractility)
• how hard it is to eject blood (aortic impedance/arterial pressure)

Autonomic nervous system:
Contractility
Heart rate

Question 8

What does a decrease in BP cause?

Answer 8

Sensed by baroreceptors in aorta and carotid artery
Reduce parasympathetic activity
Stimulate sympathetic = increase HR and contractility

Question 9

Demand led pumping

Answer 9

If metabolism increases
TPR falls to supply more blood
Arterial blood pressure decreases
Venous pressure increases
Heart pumps more

Question 10

Eating a meal changes

Answer 10

Vasodilation of gut 
Lower TPR
Lower arterial pressure
Increase venous pressure 
Soooo —> increase HR and stroke volume

= Increase in cardiac output
Arterial pressure rises, venous pressure falls

BALANCE

Question 11

Standing up effects

Answer 11

Pooling of blood in legs
Decrease venous pressure
Decrease cardiac output
Decrease arterial pressure

Question 12

How does body respond to standing up?

Answer 12

NOT by intrinsic (both low)
Baroreceptor reflex and autonomic nervous system
Increase HR, contractility and TPR

Question 13

What happens if baroreceptor reflex doesn’t work when you stand?

Answer 13

Postural hypotension
Dizzy
Lack of blood to brain = faint

Question 14

Exercise effects

Answer 14

Initially Venoconstriction returns more blood to heart
Decrease in TPR = increase venous pressure
Increased HR
Increased contractility
= increased cardiac output

Question 15

Jugular vein pulse

Answer 15

Biphasic
Measured on the right
Pulse seen behind sternocleidomastoid muscle

Question 16

How to measure jugular venous pressure

Answer 16

45 degree angle
Right side
From sternum measure highest height of pulsations then add 4cm
Measured in cm H20

Normal 5-8cm H20

Question 17

Other ways to measure jugular venous pulse

Answer 17

Central line

Question 18

Why can jugular venous pressure be used

Answer 18

Direct column of blood connected to right atrium

No valves

Question 19

Pulse wave form of venous pressure (ACXVY)

Answer 19

A - atrial systole (pressure increases, pulsation)
Atrial diastole (pressure decreases)

C - tricuspid valve closes (brief raise in pressure)

X - ventricle contracts so downward movement = low pressure

V - blood filling right atrium

Y - tricuspid valve opens

Question 20

Conditions that increase JVP

Answer 20

If right side of heart doesn’t pump blood out properly
Volume overload - IV (too much blood)
Impairment of filling (stab wound, pericarditis)