Central Venous Pressure - Nordgren

Question 1

What is the overall arrangement of the systemic venous circulation?

Answer 1

• Vasculature
  
  • Venous compartment further separated:
    
    • Peripheral
      
      • venuoles
      • veins
    • Central
      
      • great veins
      • right atrium

Question 2

What is mean circulatory filling pressure?

Answer 2

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Mean circulatory filling pressure is a theoretical measure of pressure (7mmHg) in the systemic circuit when flow is stopped and is influenced primarily by blood volume and peripheral venous tone.

Question 3

What are the primary factors that determine mean circulatory filling pressure?

Answer 3

1. Circulating blood volume
2. State of peripheral venous tone

(Arterioles don’t have much volume, Arteries & capillaries essentially do not actively change their volume)

Question 4

What is venous return? How it is distinguished from cardiac output?

Answer 4

• Venous Return:
  
  • rate at which blood is COMING BACK to the central venous compartment
  • the rate at which blood returns to the thorax from the peripheral vascular beds and is thus the rate at which blood enters the central venous compartment.
• Cardiac Output:
  
  • rate at which blood is LEAVING central venous compartment

Question 5

Why must cardiac output and venous return be equal in the steady state?

Answer 5

• If unequal = produce change in central venous pressure
  
  • In any stable situation, venous return must equal cardiac output or blood would gradually accumulate in either the central venous compartment or the peripheral vasculature

Question 6

What effect does a change in Central Venous Pressure have on Stroke Volume? Venous Return?

Answer 6

• Positive influence on Stroke Volume (CO)
• Negative influence on Venous Return

Because of its opposing influences on cardiac output and venous return, central venous pressure automatically assumes a value that makes cardiac output and venous return equal.

Question 7

What factors control venous return?

Answer 7

• the pressure difference between the peripheral and central venous compartments
  
  • changes in blood Volume
  • changes in venous Tone
    
    • sympathetic vasoconstrictor nerves
    • external compression

Question 8

What is the relationship between central venous pressure and venous return?

Answer 8

• Decreasing central venous pressure:
  
  • decrease venous resistance
  • increase venous return (more flow)
• Increasing central venous pressure:
  
  • increase venous resistance
  • decrease venous return (less flow)

Question 9

What is peripheral venous pressure?

Answer 9

essentially the same as mean circulatory filling pressure

(pressure in the peripheral circuit due to blood volume and peripheral venous tone)

Question 10

What are the factors that determine peripheral venous pressure?

Answer 10

• Changes in blood VOLUME
  
  • veins are elastic
  • increase volume → increase pressure
• Changes in venous TONE
  
  • increase sympathetic activity → increase vasoconstriction → increase pressure
  • External compression → increase pressure

Question 11

How is the output of the left heart pump matched to that of the right heart pump?

Answer 11

Starling’s Law: cardiac filling pressure influences the cardiac output.

The heart pumps what it receives!

Question 12

What are possible conditions that result in abnormally high or low central venous pressure?

Answer 12

• Causes of high central venous pressure:
  
  • CHF
• Causes of low central venous pressure:
  
  • Significant blood loss (hemorrhage)