Lecture 6 Flashcards

1
Q

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

A

Systole: Ejects blood

Diastole: Fills w blood

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2
Q

What is preload

A

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

(Changes in myocardial muscle fibre length)

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3
Q

What is afterload

A

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

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4
Q

What is contractibility

A

Change in performance at a given preload or afterload

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5
Q

Isometric contractions

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

A
  • Will increase passive tension

- Will increase the active tension up to a certain point

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6
Q

What is Lmax?

A

the optimum muscle length at which max tension can occur

Cardiac muscle usually around 85% Lmax

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7
Q

What does increasing preload do?

A

Increases force of contraction

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8
Q

What does increasing resting muscle fibre length do

A

Increases force of contraction

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9
Q

Isometric tension:

What can increase Tension-Length Profile upward?

A

Sympathetic stimulation

Ex: Norepinephrine, B1 activation

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10
Q

Define Inotropism

A

A change in active force

development in the absence of a change in preload

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11
Q

Explain the length-tension relationship

A

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

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12
Q

What effect does sympathetic simulation have?

A
  • 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)

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13
Q

What effect does afterload and preload have on shortening velocity?

Force-Velocity relationship

A

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)

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14
Q

What effects do positive inotropes have

A
  • Increase contractility = increase Vmax = improve rate of crossbridge cycling
  • Increase the amount of shortening possible
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15
Q

Define inotropic state

A

Contractile ability of the heart

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16
Q

What are the major influential factors affecting stroke volume?

A

1) Preload
2) Afterlaod
3) Intropic state

17
Q

As End diastolic volume increases stroke volume _____?

18
Q

What’s Staring’s law of the heart?

A

Increasing preload = Increase stroke volume by increasing end diastolic volume

19
Q

Cardiac performance curve

A

-A ventricular curve w/

Y-axis: Stroke volume

X-axis: Right atrial pressure

20
Q

Functions of myocardial muscle fibre length

A

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

21
Q

Functions of force of contraction

A

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

22
Q

Ventricular function curve

A

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

23
Q

What situations increase afterload?

A

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

24
Q

Explain Laplace’s Law of the dilated heart

A

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

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

25
Explain laplace's law and hypertrophy
Thickening of the walls of the ventricles through hypertrophy to combat to increase tension making ejection of blood easier (Common in athletes)
26
What are some positive inotropes?
1) B receptor agonists - Isoprenaline - Dobutamine 2) Cardiac Glycosides - Digoxin (Increases cytoscolic ca+ = increase contractibility)