Control of Cardiac Output Flashcards
How would the venous return / CO graphs change if volume were added or taken away?
What 2 things is venous return equal to?
The venous system is a […] capacitance system under […] control
High (means they’re very distensible)
Sympathetic
Below is a graph of the venous return curve. Explain what is seen in this image.
The pressure on the x axis is right atrial pressure and the “pressure” in question is due to blood in the right atrium. Thus, decreasing right atrial pressure reflects a decrease in the amount of blood in the right atrium and thus an increase in the amount of blood that is entering systemic circulation. Since the CV system is a closed system, increasing the amount of blood in systemic circulation also means increasing venous return, hence why low right atrial pressure reflects a high venous return.
Increasing right atrial pressure on the graph means that more blood is remaining in the atrium to exert a pressure. This means less blood is entering systemic circulation and less is thus coming back to the heart so with increasing right atrial pressure we see a decreasing venous return.
The point where the venous return is 0 reflects the mean systemic pressure. This means that this is the pressure in the atrium when the pressures across the entire cardiovascular system are equalized and there is no net blood flow.
- Hemorrhage
- Transfusion
- (+) ionotrope
- (-) ionotrope
- Decreased TPR
- Increased TPR
- Increased sympathetic tone
- Decreased TPR caused by decreased sympathetic tone
- Increased TPR caused by increased sympathetic tone
What effect do the following activities have on cardiac output:
- Changing from standing to lying down
- Sleeping
- Eating a meal
- Pregnancy
How would the venous return / CO graphs change if total peripheral resistance increased or decreased?
What type of system is the CV system?
Closed
What 2 things is cardiac output equal to?
SV x HR
Venous Return
- What is meant by stressed and unstressed volumes in the diagram below?
- What would cause a shift from unstressed to stressed? Or vice versa?
Below is the cardiac output curve. Explain what is seen in this image.
From the venous return graph, decreasing pressure in RA relatiave to veins means that more blood will be driven into RA, so increasing venous return. In the cardiac output graph, this is visualized as increasing pressure in the right atrium due to increasing blood volume in the right atrium due to increasing venous return. Increasing venous return increases the amount of blood that is pumped to the left side of the heart and thus increases cardiac output.
**I realize that this doesn’t quite make sense but this is how Dr. K explained it so just try to make sense of it, sorry!**
A normal adult range for cardiac output is […] to […] L/min.
4 to 7
What would cause blood to shift from unstressed to stressed? Or vice versa?
How would the venous return / CO graphs change in the presence of a positive ionotrope or a negative ionotrope?
What does the intersection of the venous return graph and cardiac output graph represent?
Steady state - when the volume of blood in the left ventricle ejects as cardiac output matches the volume of blood it receives as venous return
