8/3- Cardiac Fct: Heart as a Pump Flashcards Preview

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Flashcards in 8/3- Cardiac Fct: Heart as a Pump Deck (49):
1

T/F: Preload is the ventricular volume before systole

True

Preload is the ventricular volume before systole

2

T/F: Afterload is measured after contraction starts

True

Afterload is measured after contraction starts

3

T/F: Wall stress is closely related to blood pressure

True

Wall stress is closely related to blood pressure

4

T/F: Starling's law states that an increase in preload improves cardiac performance

True

Starling's law states that an increase in preload improves cardiac performance

5

T/F: Decrease in afterload improves cardiac performance?

True

Decrease in afterload improves cardiac performance

6

T/F: The 3 key determinants of fiber shortening are preload, afterload, and contractility?

True

The 3 key determinants of fiber shortening are preload, afterload, and contractility

7

T/F: After a premature heart beat, the next beat is a stronger beat due to both better filling and better contractility?

True

 After a premature heart beat, the next beat is a stronger beat due to both better filling and better contractility

8

T/F: During diastole, IVR occurs first and atrial kick last?

True

During diastole, IVR occurs first and atrial kick last

9

What side/chamber of the heart is this? Labels/Characteristics? 

Q image thumb

Right ventricle

- Thin outer wall and septum

- Concave outer RV wall moves towards septum in bellows-like action allowing thin-walled RV to eject large volume against low outflow P

A image thumb
10

What is the resultant circulatory change for the right ventricle? (pressure)

PA (pulmonary artery) pressure of 15-35 mmHg

11

Left ventricle characterized by ___ axis

Left ventricle characterized by long axis

12

Characteristics of LV contraction?

- Decrease in chamber size and shortening of the long axis

- Apex moves towards MV and closer to chest wall (causing PMI)

13

What is the resultant circulatory change for the left ventricle (pressure)?

Generate 100-120 mmHg AoP (aortic pressure) with each LV ejection

14

Where is the PMI?

Left MCL (mid-clavicular line) between 5th and 6th ribs

15

What are the determinants of cardiac function (5)?

- Preload

- Afterload

- Wall stress

- Contractility

- Diastolic Function

16

What is preload? (def)

Blood volume in the ventricle at end-diastole

- Preload is a key determinant of cardiac performance (CO and SV)

17

What is Frank Starling/Starling's Law? Graph?

- Peak tension developed by muscle increases as preload increases... within physiologic limits 

A image thumb
18

What are the determinants of preload (4)?

- Intravascular volume*

- Venous return*

- Atrial contraction

- Pericardial function

(*most important)

19

What conditions involve increased intravascular volume (hypervolemia)?

- Congestive heart failure

- Renal failure

- Overhydration

20

What conditions involve decreased intravascular volume (hypovolemia)?

- Excessive Diuretics

- Blood Loss

21

What are the 3 main determinants of myocardial fiber shortening?

- Preload

- Afterload

- Contractility

22

Why is fiber shortening important for cardiac function?

Fiber shortening and ventricular size are key determinants of stroke volume (blood ejected with every heartbeat)

23

What is afterload? (def)

Tension or force acting on ventricular fibers after onset of contraction or fiber shortening

24

How do changes in afterload affect cardiac function?

- BP elevation increases afterload and worsens fiber shortening and cardiac performance (SV and CO)

- BP reduction decreases afterload and improves cardiac performance

25

What is the effect of mitral regurgitation and perceived afterload of left ventricle? Ejection fraction?

- Lower afterload

(- Greater ejection fraction too, based on change in volume)

26

Increase/decrease in preload improves cardiac function?

Increase in preload improves cardiac function?

27

Increase/decrease in contractility improves cardiac function?

Increase in contractility improves cardiac function

28

Increase/decrease in afterload improves cardiac function?

Decrease in afterload improves cardiac function?

29

In what clinical conditions is afterload important?

- Increased afterload

- Decreased afterload

- Heart failure

30

Examples of increased afterload?

- Hypertension

- Aortic stenosis

We call these conditions pressure overload conditions

31

Examples of decreased afterload?

Effect on cardiac function?

- Mitral regurgitation ("leaky" valve)

- LV contracts against a lower afterload (LA) thus cardiac performance (EF) is improved!!!

32

What happens to cardiac function after repair of MR?

Afterload is now higher(!) as the LV has to pump blood against the aorta ONLY rather than against lower pressure LA...

- Thus EF and CO worsen after MR repair

33

Which pt has higher cardiac performance?

A. Normal mitral valve

B. Mitral regurgitation

Which pt has higher cardiac performance?

A. Normal mitral valve

B. Mitral regurgitation

34

In heart failure, CO and EF are high/low?

What happens when we reduce afterload with vasodilators?

In heart failure, CO and EF are low

When we reduce afterload with vasodilators (ACEI), CO and EF improve

- Vasodilators are a key part of treatment of CHF

35

Why is wall stress important?

- Wall stress affects cardiac performance (adversely, just like afterload)

- Wall stress affects MVO2

36

What are the 3 main determinants of wall stress?

- P (intracavitary pressure)

- R (radius)

- h (wall thickness)

37

What equation is used to determine wall stress?

LaPlace Law

wall stress (WS) = PxR/2h

38

What condition is shown here? 

Q image thumb

Eccentric hypertrophy 

A image thumb
39

What condition is shown here? 

Q image thumb

Concentric hypertrophy

A image thumb
40

Which has increased wall stress? Why?

 Which has decreased walls tress? Why? 

Q image thumb

Increased wall stress: left, due to marked increase in ventricle size

Decreased walls stress; right, due to marked increase in wall thickness

(recall LaPlace's Law)

A image thumb
41

Eccentric hypertrophy is a pathophysiologic result of what?

Volume overload

- Mitral insufficiency

- Atrial septal defect

42

Concentric hypertrophy is a pathophysiologic result of what?

- Hypertension

- Aortic stenosis

43

What is contractility?

Contractility and inotropic state refer to the INHERENT ability of muscle to contract INDEPENDENTLY of loading conditions

44

Contractility vs. cardiac performance?

Contractility is load-dependent, unlike cardiac performance

45

What is positive inotropic effect?

Positive inotropic effect- improvement in cardiac performance due to greater contractility in the absence of change in preload or afterload

46

What is post-extrasystolic potentiation?

Contraction after a pause that follows a premature beat is more forceful than normal

- Greater contractility and greater preload mediates stronger beat

47

What are the 4 phases of diastole? graph

- IVR

- Rapid filling

- Slow filling (diastasis)

- Atrial kick

A image thumb
48

What is compliance? graph

Increase in volume with little increase in pressure (shallower slope of pressure/volume curve)

A image thumb
49

Cardiac Function: Key Points

- Contrast preload & afterload

- Frank-Starling: higher preload improves performance

- Three key determinants of myocardial fiber shortening: preload, afterload & contractility; how do they do it?

- Lower afterload in MR increases EF not contractility

- LaPlace law: What are 3 determinants of wall stress?

- Contrast contractility vs. cardiac performance

- Define and explain post-extrasystolic potentiation

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