Physiology Lecture 2 -- Cardiac Output and Venous Return Flashcards Preview

Block C - Circulation > Physiology Lecture 2 -- Cardiac Output and Venous Return > Flashcards

Flashcards in Physiology Lecture 2 -- Cardiac Output and Venous Return Deck (39):
1

Average cardiac output

5 L/min

2

Average pumping capacity

10 - 13 L/min

3

Effect of athleticism on cardiac output and pumping capacity

Multiply by 2

4

How does periphery impact CO

Dilation causes increased bloodflow = higher CO

5

Effect of AV fistula on cardiac output and why

Causes compensatory response in peripheral veins to decrease resistance to venous return, causing increase in CO

6

Cardiac output equation

CO = HR x SV

7

Cardiac output curve

RAP vs. CO

8

Normal intrapleural pressure

-4 mm Hg

9

Effect of intraplerual pressure on cardiac output

Increase = shift curve to right

Decrease = shift curve to left

10

Where does the venous return curve plateau

Great veins (SVC, IVC)

11

Why does the venous return curve plateau?

Pressure in great veins becomes subatmospheric = collapse so that venous return cannot increase any further

12

Venous return equation

Pv = venous pressure = mean systemic pressure

PRA = right atrial pressure

Rv = venous resistance

13

What variable is most significant in determining venous return? Explain why

In steady state, PRA is usually 0

Mean systemic pressure is usually kept constant

Therefore resistance is the biggest factor

14

Effect of right atrial pressure on venous return

Increased right atrial pressure = decreased venous return

15

Define right atrial pressure

Pressure that the periphery must overcome to bring blood back to the heart (must have P gradient)

16

Define mean systemic filling pressure

If heart is in cardiac arrest (i.e. no pumping = venous return is 0), P would be equal in ANY vessel

17

Normal mean systemic filling pressure

7 mm Hg

18

What influences mean systemic filling pressure?

Blood volume in heart and veins

19

Venous return curve 

20

Equation for PMS

mean systemic filling pressure = central volume / peripheral compliance

21

How can one induce an increase in PMS

Give physiological saline to increase volume

Activate sympathetic nervous system

22

Effect of sympathetic nervous system on PMS

Sympathetic nervous system decreases venous compliance to move blood from veins to the heart = increase PMS

23

Normal percentage of blood in veins

80%

24

Effect of PMS on VR

Increase PMS = shift VR curve to the right

Decrease = shift to left

25

General roles of arteries and veins in terms of physical characteristics

Arteries = resistance (high resistance)

Veins = storage (high compliance)

26

When talking about resistance and VR, what kind of resistance is it?

Resistance to venous return = TPR (total peripheral resistance)

27

Effect of TPR on VR

Change slope of VR curve

Decrease R (i.e. by dilation) = shift curve right and up

Increase R (i.e. by constriction) = shift curve left and down

28

When can veins have a significant role in TPR?

Normally they don't

Increased resistance in veins can occur if a great mass compresses a great vein (i.e. large tumor or a really large multi-child pregnancy)

29

How can one determine cardiac output at a given point using CO and VR curves?

Intersect

30

Effect of transfusion on CO VR curves

Increase volume = increase PMS = increase CO

 

31

Why does the slope of the VR curve change in the event of a transfusion?

Fluid given is saline, so blood becomes dilated, thus decreasing resistance

If given blood, R would not change, so no slop change

32

Effect of exercise on CO VR curve

Sympathetic NS activates so PMS increases

Muscles pump veins = blood pushed to heart = increase central V = increase PMS

Arterioles vasodilate = decrease resistance to venous return (net effect despite sympathetic activation)

33

Explain the sequence of events A to B in this diagram involving heart failure

A --> B = Super hypoeffective pump decreases CO due to myocardial infarct

34

Explain the events B --> C in this diagram involving heart failure

B --> C = ANS activates to attempt restoration of BP so shift curve to the right (decreased peripheral C)

35

Explain events C --> D in this diagram involving heart failure

Kidneys retain fluid, so VR shift due to increased V

36

Explain the net effect of events A --> D in this diagram involving heart failure

D reaches the same CO as A, however PRA is increased, so more susceptible to pulmonary congestion since fillling pressure in increased

37

Define decompensated heart failure

Non-viable heart (i.e. EF of 5 - 10%) that cannot surpass the critical point, so essentially drowning due to too much fluid retention

38

NYHA clasification for decompensated heart failure

NYHA class 4

39

Critical CO for normal fluid balance

5 L/min