Lecture 11

Question 1

How are cardiac function (output) curves generated

What factors cause changes in contractility in the heart can alter the shape of cardiac function curves.

Answer 1

• Relationship between cardiac output and right atrial pressure (RAP) –> direct relationship
• Shows effects of increase EDV (aka RAP) on cardiac output

Factors that can alter the curve/contractility:

1) Ventricular compliance

2) Afterload (alters SV)
- Inverse relationship

3) Contractility
- Direct relationship

4) Preload (Alters SV)
- Direct relationship

5) Venous tone
6) HR (altered by ANS) and SV

Question 2

Understand the concept of “mean circulatory (filling) pressure,” its normal value, and how various factors can alter its value

Answer 2

Definition:
-avg pressure in circulatory system w/o blood flow

Normal Value:

Factors that affect it:

Question 3

Define venous return and factors that affect it

Answer 3

-Deoxygenated Blood that returns to the heart via the vena cavas –> right atrium
(Flow = change pressure/Resistance)

Factors that affect VR:
1) Mean systemic Filling Pressure

2) Blood volume
- Direct relationship

3) Right atrial pressure
- Inverse relationship

4) Arteriole Resistance/tone -TPR (Arteriolar vasoconstrict)
- Inverse relationship

5) Venomotor tone = venous compliance (venoconstricts)
- Direct relationship

Question 4

Construct a vascular function curve. Predict how changes in total peripheral resistance, blood volume, and venous compliance influence this curve

Answer 4

-Relationship between venous return (y-axis) and Right atrial pressure (x-axis)
(Inverse relationship)

Factors that affect curve:
1) Blood volume
-Direct relationship
(Shifts MSFP to right)

2) Venomotor tone
-Direct relationship
-Venoconstricts:
Shifts MSFP up and right- increased
-Venodilates:
Shifts MSFP down and left-decreased

3) Arteriolar resistance (TPR)
-Inverse relationship
(BUT No change in MSFP)

(Same factors that affect venous return)

Question 5

Describe Guyton’s Cross plot

• Axis
• Intersection

Answer 5

-x-axis = Right atrial pressure
y= Venous return/CO
Graph shows:
1) Vascular function curve
2) Cardiac function curve

-Steady state: Venous return = cardiac output at intersection

Factors that affect it:
1) TPR
-CPC –> Inverse
-

Question 6

How will the following affect Guytons Cross Plot?

1) hemorrhage
2) heart failure
3) autonomic stimulation
4) exercise

Predict how physiological compensatory changes would alter acute
changes

Answer 6

1) Hemorrhage
- Moves curve to the left
- Increases TPR
- Increases CO and contractility
- No change in CPC

2) Heart failure = decrease contractility
- Decrease cardiac output
- Compensated VFC (moves right)

3) Exercise
- Increases contractility and venoconstriction
- TPR no change
- Increase CO and VR

Question 7

What is central venous pressure

Answer 7

Factors that affect it:

1) Upright body posture
- Venous pooling/decreases venous return

2) Venomotor tone
- Direct relationship

Question 8

What is central blood volume and what affects it?

Answer 8

F

Question 9

Primary controller of Cardiac Output at rest and in stressful situations (Ex: Exercise)

Answer 9

At rest:

1) Central venous pressure
2) Venous return

Stressful condition:
1) The heart itself (So Co matches VR)