Regulation of Cardiac Output Flashcards
Equation for arterial pressure.
Arterial pressure = CO X TPR
Cardiac Output is dependent on what 2 variables?
ventricular function (blood out) vascular function (blood in)
Definition of cardiac function curve
The cardiac function curve is formally independent of venous return. It defines ventricular output (dependent variable) as a function of ATRIAL pressure (independent variable).
How does atrial pressure affect CO?
The greater the atrial pressure (greater EDV, since atrial volume becomes ventricular volume once the volume has moved down from atria into ventricles), the greater is the ventricular output, up to a physiological limit represented by the flat part of the curve.
What is the Bainbridge reflex?
high venous pressure stimulates pacemaker to increase heart rate
How does EDV affect stretch?
increase EDV increases stretch
What effect does the Frank Starling Mechanism have on the heart?
increases SV at optimal stretch
What are the 4 factors that directly influence the cardiac function curve?
- Sympathetic and parasympathetic activity
- Intrinsic ventricular effectiveness
- Afterload (aortic pressure)
- Intrapleural (intrathoracic) pressure
What effect does sympathetic activity have on the cardiac funciton curve?
Sympathetic activity will shift the curve up to increase SV and HR
What effect does parasympathetic activity have on the cardiac funciton curve?
Parasympathetic activity can shift the curve down to decrease SV and HR
What effect does increased intrinsic ventricular effectiveness have on the cardiac function curve?
Hypereffectiveness can shift the curve up to increase SV and HR
What effect does decreased intrinsic ventricular effectiveness have on the cardiac function curve?
Hypoeffectiveness or heart failure can shift the curve down to decrease SV and HR
What effect does increased afterload have on the cardiac function curve?
Increased afterload shifts the cardiac function curve downward, via a reduction of stroke volume
What is the equation for net ventricle stretch?
Net Stretch on Ventricle= intraventricular pressure – extraventricular pressure
What is another name for extraventricular pressure? What is it?
intrapleural or intrathoracic pressure and is the pressure surrounding the ventricles
How do you decrease intrapleural pressure?
breathing (inhale)
What effect does decreased intrapleural pressure have on the cardiac function curve?
Net stretch increases for greater ventricular output!—shifts the curve to the left (flat part remains the same)
What is the definition of the vascular function curve?
The vascular function curve is formally independent of ventricular output. It defines venous return as a function of ATRIAL pressure.
What is the intercept of the vascular function curve?
systemic filling pressure
What is the slope of the vascular function curve?
resistance to venous return
What is the equation for change in pressure driving venous flow?
ΔP driving venous flow= systemic filling pressure – right atrial pressure
Why does the vascular function curve plateau?
Venous collapse, due to the fact that venous pressure becomes more negative than the ambient pressure.
What is the “filling pressure”?
- pressure required to fill the blood vessels beyond their intrinsic volume (think of this as the “over-filling pressure.”
What is intrinsic volume?
(unstressed volume) is the volume that just fills the blood vessels completely without stretching them. Filling pressure = 0.