Lecture 6

Question 1

What happens to blood in the heart during systole and diastole?

Answer 1

Systole: Ejects blood

Diastole: Fills w blood

Question 2

What is preload

Answer 2

Tension or load on the ventricular muscles when it begins to contract/at the end of diastole

(Changes in myocardial muscle fibre length)

Question 3

What is afterload

Answer 3

The force the muscle must overcome to open the valves and to eject a given volume of blood)

-Systemic vascular resistance/peripheral resistance = best marker for afterload

Question 4

What is contractibility

Answer 4

Change in performance at a given preload or afterload

Question 5

Isometric contractions

How does stretching a cardiac muscle affect the
tension (force) it can develop?

Answer 5

• Will increase passive tension

- Will increase the active tension up to a certain point

Question 6

What is Lmax?

Answer 6

the optimum muscle length at which max tension can occur

Cardiac muscle usually around 85% Lmax

Question 7

What does increasing preload do?

Answer 7

Increases force of contraction

Question 8

What does increasing resting muscle fibre length do

Answer 8

Increases force of contraction

Question 9

Isometric tension:

What can increase Tension-Length Profile upward?

Answer 9

Sympathetic stimulation

Ex: Norepinephrine, B1 activation

Question 10

Define Inotropism

Answer 10

A change in active force

development in the absence of a change in preload

Question 11

Explain the length-tension relationship

Answer 11

Increasing the resting length of a myocardial fibre will
increase the tension developed when the fibre
contracts

Question 12

What effect does sympathetic simulation have?

Answer 12

• It increases force/tension at a particular length
• increases force of contraction
• Shifts isometric peak up and to the left

(Increases extent of shortening on a muscle)

Question 13

What effect does afterload and preload have on shortening velocity?

Force-Velocity relationship

Answer 13

Increasing afterload:
-Smaller the shortening velocity (Ability for muscle to shorten is less)

Increasing preload:
-Greater the shortening velocity (Ability for muscle to shorten is more)

Question 14

What effects do positive inotropes have

Answer 14

• Increase contractility = increase Vmax = improve rate of crossbridge cycling
• Increase the amount of shortening possible

Question 15

Define inotropic state

Answer 15

Contractile ability of the heart

Question 16

What are the major influential factors affecting stroke volume?

Answer 16

1) Preload
2) Afterlaod
3) Intropic state

Question 17

As End diastolic volume increases stroke volume _____?

Answer 17

Increases

Question 18

What’s Staring’s law of the heart?

Answer 18

Increasing preload = Increase stroke volume by increasing end diastolic volume

Question 19

Cardiac performance curve

Answer 19

-A ventricular curve w/

Y-axis: Stroke volume

X-axis: Right atrial pressure

Question 20

Functions of myocardial muscle fibre length

Answer 20

1) Central venous pressure
2) End diastolic volume
3) End diastolic pressure
4) Right atrial pressure

Question 21

Functions of force of contraction

Answer 21

1) ventricular pressure
2) cardiac output
3) stroke work
4) cardiac output

Question 22

Ventricular function curve

Answer 22

-Any graph whose x-axis is a function of myocardial muscle fibre length and whose y-axis is a reflection of contractile energy

Question 23

What situations increase afterload?

Answer 23

1) Increasing aortic pressure
2) Increasing systemic vascular/total peripheral resistance
3) Aortic stenosis (Pressure overload on the left ventricle)

Question 24

Explain Laplace’s Law of the dilated heart

Answer 24

Tension (Stress)= Pressure x radius/2xh (wall thickness)

-Dilated hearts need greater tension to generate same pressure = working harder = increased afterload

Question 25

Explain laplace’s law and hypertrophy

Answer 25

Thickening of the walls of the ventricles through hypertrophy to combat to increase tension making ejection of blood easier

(Common in athletes)

Question 26

What are some positive inotropes?

Answer 26

1) B receptor agonists
- Isoprenaline
- Dobutamine

2) Cardiac Glycosides
- Digoxin (Increases cytoscolic ca+ = increase contractibility)