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Cardiovascular and Respiratory Medicine > Cardiovascular Mechanics > Flashcards

Cardiovascular Mechanics Flashcards

1
Q

What happens during contraction in a single ventricular cell

A

Electrical event, ca influx and ca release, contractile event

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2
Q

What is the structure of a single ventricular cell structure

A

T tubule openings up to 200nm in diameter

T tubule lies alongside each Z line

Carries surface depolarisation deep into cell

Ventricular cells 100micrometers long and 15 micrometres wide

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3
Q

What happens during the excitation-contraction coupling in the heart

A
  1. Myocyte depolarises
  2. Action potential travels down t-tubles
  3. Activates L-type Ca channels to open
  4. Calcium flows in and binds to SR Ca release channels (ryanodine receptor)
  5. Ca enters cytoplasm from sarcoplasmic reticulum
  6. Ca binds to troponin C
  7. Myosin head binds to actin
  8. Muscle fibres shorten
  9. Na/Ca exchanger removes Ca by usign the energy of the gradient of L type Ca channel
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4
Q

How to add calcium to SR

A

Sympathetic stimulations

Increase phosphorylation of protein which increases Ca influx

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5
Q

What type of relationship is cyotplasmic Ca contration and force

A

Sigmoidal

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6
Q

What is the passive force in cardiac muscle

A

Liek elastic band recoiling

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7
Q

What is active force in cardiac muscle

A

Caused by crossbridge formation from the calcium release from SR

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8
Q

How does cardiac muscle differ from skeletal muscle

A

Cardiac muscle is more resistant and less compliant

Due to properties of the extracellular matrix and cytoskeleton

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9
Q

Is the total force regardless of muscle length improatn

A

Only ascending limb of the relation is important

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10
Q

Why does skeletal muscle produce less passive force

A

It is strechier

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11
Q

What is isometric cardiac contraction

A

Muscle fibres do not change length but pressure inceases in both ventricles

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12
Q

What is isotonic cardiac contraction

A

Shorterning of fibres and blood is ejected from ventricles

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13
Q
A
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14
Q

What is preload

A

Weight that stretches muscle before it is stimulated to contract

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15
Q

What is afterload

A

Weight not apparent to muscle in resting state; only encountered when muscle has started to contract

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16
Q

Diagram of preload and afterload

A
17
Q

What is an example fo afterload

A

Backload of the aorta

18
Q

What is an example of preload

A

Ventricular filling

19
Q

What are measures of preload

A

End-diastolic volume

End diastolic pressure

Right atrial pressure

20
Q

What happens during invivo preload of the heart

A

Stretches the resting ventricular walls

Filling determines the preload

Preload is dependent on venous return

21
Q

What happens during invov cardiac afterload

A

Load against which the left ventricle ejects blood after opening of the aortic valve

22
Q

What is a measure of afterload

A

Diastolic blood pressure

23
Q

What is the Frank starling relationship

A

Increased diastolic fibre length increases ventricular contraction

Cardiac output exactly balances the augmented venous return

As the filling of the heart increases, the force of contraction also increases

24
Q

Why does the frank starling relationship happen

A

There are changes in the number of myofilament cross bridges that interact: more myofilament interact as stretching, more indigitation of thick and thin filaments and increase chance of crossbirdge formation

Change in Ca sensitivty: At longer sarcomere lengths, the affinity of TnC for Ca is increased due to conformational change in protein. Furthermore, with decreasing myofilament lattice spacing, probability of forming strong binding cross bridges increases

25
Q

What is stroke work

A

Work done by heart to eject blood under pressure into aorta and pulmonary artery

26
Q

What is the formula for stroke work

A

Stroke work = volume of blood ejected multiplied by the pressure as which the blood is ejected

27
Q

What is the Law of LaPlace

A

When the pressure within a cylinder is held constant, the tension on its walls increases with increasing radius

T=P X R

T= (PXR)/h

28
Q

Why is the radius of LV less than RV

A

LV generates higher pressures

29
Q

Picture of failing heart

A

Cardiovascular and Respiratory Medicine (11 decks)

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