Lecture 6 - Cardiac Output

Question 1

define End-systolic volume

Answer 1

The volume of blood in a ventricle at the end of contraction

Question 2

Define End-diastolic volume

Answer 2

The amount of blood in the ventricles just before systole

Question 3

Define pre-load

Answer 3

The amount of blood that enters the ventricles before the ventricles contract

Question 4

Define After-load

Answer 4

The amount of resistance that the heart must overcome to open aortic valve and push blood volume out into systemic circulation

Question 5

Define stroke volume

Answer 5

The amount of blood pumped by the left ventricle of the heart in one contraction

Question 6

What are factors that affect preload

Answer 6

Decrease in heart rate 
Increase in aortic pressure 
Increase in central venous pressure 
Increase ventricular compliance 
Increase atrial contractility

Question 7

Decrease in heart rate

Answer 7

Slower heart rate means there is more time for blood to flow in and ventricles to fill
Increase ventricular filling time

Question 8

Increase in aortic pressure

Answer 8

Reduce stroke volume by increasing end systolic volume

Question 9

Increase in central venous pressure

Answer 9

Result from decreased venous compliance or thoracic blood volume
Increase total blood volume/ venous return

Question 10

Increase ventricular compliance

Answer 10

Greater expansion of chamber
Inverse of stiffness
Ventricles will have certain stiffness

Question 11

Increase atrial contractility

Answer 11

Sympathetic stimulation of atria

Increase in blood as atrium squeeze harder

Question 12

What does the Frank-Starling mechanism represent

Answer 12

Relationship between stroke volume and end diastole volume

Question 13

Frank-Starling Mechanism

Answer 13

The ability of the heart to change its force of contraction and therefore stroke volume in response to changes in venous return

Question 14

What does Frank-Starling mechanism show?

Answer 14

Changes in pre-load lead to changes in stroke volume

Question 15

What does law state (Frank-Starling mechanism)?

Answer 15

Stroke volume of the heart increases in response to increase in volume of blood in ventricles, before contraction

Question 16

What happens when a larger volume of blood flows into ventricles?

Answer 16

The blood stretches the cardiac muscle fibres
Increase in force of contraction
Increase preload = increase stroke volume

Question 17

What is the Frank-Starling law of heart?

Answer 17

The greater be diastolic filling - the larger the EDV
The more the heart is stretched
The longer the cardiac fibres before contraction
Increased length > greater force in cardiac contraction > greater stroke volume
The heart normally pumps out during systole, the volume of blood returned during diastole
Increased venous return = increased SV
Preload = the extent of filling

Question 18

What is inotropy?

Answer 18

The force of muscle contraction
Increase inotropy, increase velocity of the muscle fibres shortening preload/afterload
When a muscle fibre contracts, it shortens

Question 19

What happens if inotropy is increased?

Answer 19

There will be little volume left in the vent files and the ESV will shift to the left

Question 20

What happens when inotropy is decreased?

Answer 20

There will be more volumes in the left ventricles

ESV shift to right

Question 21

Inotropy: what happens when the heart has increased contractility ?

Answer 21

The end systolic volume is lower because heart squeezes faster, there is almost no blood left in the ventricle

Question 22

What does afterload do?

Answer 22

Increase arterial (aortic) pressure