Nordgren: Central Venous Pressure Flashcards
What components of the CVS system are crucial factors that determine how well the CV system will be operating?
- Ventricular EDV is VERY sensitive to small changes in filling pressure
- Cardiac filling pressure
How much volume does it take to fill the circulatory system if there is no pressure or stretching?
3.56 L
About 20 mmHg
What is our total systemic volume?
4.5 L
What does the extra volume in our system do?
The extra volume causes steretching and in turn pressure to build inside the system and …about 7 mmHG
What are the two major variables that affect mean circulator filling pressure?
- circulating blood volume
2. state of peripheral venous tone*
What does constriction of the venous vessels do?
Increase pressure throughout the system
What happens when there is increased tone in the other compartments?
- Arterioles don’t have much volume—very small effect
2. arteries and capillaries essentially do not change their volume (no effect)
How does cardiac pumping affect flow?
It shifts the location of some blood from venous to arterial.
What happens to veins and arteries when flow changes?
Veins- are VERY compliant, so pressure doesn’t change much in them when this happens
Arteries- NOT compliant (added blood causes pressure to rise above the mean circulatory pressure)
What is central venous pressure?
An indicator of circulatory status
How would you describe the CV system?
It’s a CLOSED hydraulic system. Changes in one area WILL cause changes in pressure, flow and volume throughout the circuit.
What is cardiac output?
The rate at which blood is LEAVING the central venous compartment (RA)
What is venous return?
The rate at which blood is COMING BACK to the central venous compartment (RA)
How are venous return and cardiac output related in a stable situation?
They’re equal!!
What happens when venous return and CO aren’t equal?
This produces a CHANGE in central venous pressure
What effects central venous pressure?
- Increased stroke volume
- decreased venous return
THEREFORE CVP is always driven to a value that makes CO = VR
What governs the flow between PV and CV compartments?
Q= change in pressure (drop between peripheral and central venous compartments) / resistance (small resistance associated with peripheral veins)
What does a crop in central venous pressure do?
It increases the pressure drop across the venous resistance and consequently causes an elevation in venous return
What does the venous function curve demonstrate?
As central venous pressure DECREASES, venous return INCREASES (to RA)
True or false…An increase in peripheral venous pressure can be just as effect at increasing venous return as a drop in central venous pressure.
True
What are two components that influence peripheral venous pressure?
- changes in blood VOLUME
2. changes in venous TONE
What does an increase in blood volume do to veins?
Increase in volume > increase in pressure (veins are elastic)
What does an increase in sympathetic activity do to venous tone?
Increase in sympathetic activity > increased vasoconstriction > increase pressure (external compression of veins does the same thing)
What happens to the CVS when there is significant blood loss?
- Increased sympathetic nerve activity (subnormal CO evokes compensatory mechanisms)
- Venous constriction after hemorrhage
