Control of Cardiac Output Flashcards
Define Afterload
The load the heart must eject blood against (the aortic pressure)
Define Preload
Amount the ventricles are stretched in diastole- related to the EDV or CVP
Define Total Peripheral Resistance
Resistance to blood flow offered by all the systemic vasculature (systemic vascular resistance)
What is the effect of constriction of arterioles
This will increase the resistance of the arterioles
This causes a pressure drop distally/venous side
Causes an increase in the pressure proximally/arterial side
What happens when TPR is decreased but CO remains unchanged
Fall in the arterial pressure
Increase in venous pressure
There is dilation of the vessels which causes the TPR to decrease
What happens when TPR is increased but CO remains unchanged
Increased arterial pressure
Decreased venous pressure
Due to the constriction of the vessels causing the TPR to increase
What happens when CO is increased but TPR remains unchanged
Increased arterial pressure
Decreased venous pressure
Increased CO results in a faster drainage of the venous system decreasing venous pressure but also causes there to be a greater volume of blood in the arteries due to the faster pumping
What happens when CO is decreased but TPR remains unchanged
Increased venous pressure
Decreased arterial pressure
Blood is being pumped out of the heart at a slower rate so the drainage of the venous system is slow so its pressure increases.
Often results in heart failure due to output not being enough to meet demands of tissues
Describe Ventricular Filling and draw the ventricular compliance curve
Ventricle fills until the walls stretch enough so that the intraventricular pressure equals venous pressure
Therefore the higher the venous pressure, the more the heart fills
Compliance can increase or decrease in diseased states:
Decreased compliance- hypertrophy of ventricle wall
Increased compliance- dilation of ventricles and walls becoming thin
What is the Frank-Starling Law
If you strech the fibres of the heart before contracting, it will contract harder
The more the heart fills, the harder it contracts and the bigger the stroke volume
What factors determine cardiac output
How much the ventricle empties which depends on:
- Force of contraction- determined by EDV and contractility
- How hard it is to eject blood- determined by aortic impedance
Contractility and heart rate- both controlled by ANS
How does the body respond to an increase in metabolism
- TPR decreases to supply more blood
- Results in arterial pressure decreasing and venous pressure increasing
- Heart responds to this by increasing cardiac output
- This is to increase the arterial pressure and decrease the venous pressure
Why do we measure jugular venous pressure and what causes it to increase
JVP is measured to determine the right atrial pressure
JVP can increase due to:
- Right side ot the heart not pumping properly
- Volume overload with IV infusion
- Something impairing the filling of the heart
