Control Of Cardiac Output

Question 1

Define afterload

Answer 1

The load the heart must eject blood against (~aortic pressure)

Question 2

Define preload

Answer 2

The amount the ventricles are stretched (filled) in diastole

Related to end diastolic volume or central venous pressure

Question 3

Define total peripheral resistance (TPR)

Answer 3

Resistance to blood flow offered by all systemic vasculature

a.k.a. Systemic vasculature resistance

Question 4

What happens to blood pressure as it flows through a resistance?

Answer 4

Blood pressure drops

Question 5

Which vasculature offers the greatest resistance?

Answer 5

Arterioles

Question 6

What happens to arterial pressure and venous pressure when TPR DECREASES, CARDIAC OUTPUT STAYS THE SAME?

Answer 6

Arterial pressure = decrease

Venous pressure = increase

Question 7

What happens to arterial pressure and venous pressure when TPR INCREASES, CARDIAC OUTPUT STAYS THE SAME?

Answer 7

Arterial pressure = increases

Venous pressure = decreases

Question 8

What happens to arterial pressure and venous pressure when CARDIAC OUTUT INCREASES, TPR STAYS THE SAME?

Answer 8

Arterial pressure = increase

Venous pressure = decrease (heart emptied more)

Question 9

What happens to arterial pressure and venous pressure when CARDIAC OUTPUT DECREASE, TPR STAYS THE SAME?

Answer 9

Arterial pressure = decreases

Venous pressure = increases (heart not emptied as much)

Question 10

What happens if tissues need more blood?

Answer 10

Arterioles + precapillary sphincters will dilate

• peripheral resistance falls
• heart pumps more so arterial pressure doesn’t fall or venous to rise

Question 11

What is stroke volume?

Answer 11

The volume of blood pumped out of the left ventricle of the heart during each systolic cardiac contraction.
SV = EDV(end diastolic volume) - ESV (end systolic volume)
~70ml

Question 12

Define cardiac output

Answer 12

The amount of blood the heart pumps through the circulatory system in a minute.
CO = STROKE VOLUME X HEART RATE

Question 13

During ventricular filling, how far does the ventricle walls stretch?

Answer 13

Ventricle walls stretch to the point where IV pressure equals venous pressure.
The higher venous pressure, the more the heart gets filled.

Question 14

What is the Frank-Starling law

Answer 14

The more the heart stretches/fills, the header it contacts

• bigger stroke volume
• from an increase in venous pressure

Question 15

How is Starling’s law an example of intrinsic control mechanism?

Answer 15

Ensures both sides maintain same output

Pulmonary and systemic circulations operate in series = same volume to body as to the lungs

Question 16

Define contractility

Answer 16

The force of contraction for a given fibre length

Question 17

How is contractility an extrinsic mechanism and how does changes affect the starling curve?

Answer 17

Under sympathetic stimulation or use of adrenaline.
Increased contractility = steeper slope
Decreased contractility = less steep of a slope

Question 18

How is the jugular venous pulse (JVP) measured?

Answer 18

In the right internal jugular vein or use a central line inserted into jugular vein

Question 19

What is the JVP used for?

Answer 19

Estimating central venous pressure (filling pressure of the heart that determines preload)