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.
What effect does increasing sympathetic activity have on the vascular function curve?
the lesser the unstressed volume (vasoconstriction) and compliance (stiffer) → counterclockwise turn (increased fill pressure)
What effect does decreasing sympathetic activity have on the vascular function curve?
the greater the unstressed volume (vasodilation) and compliance. → clockwise turn (decrease fill pressure)
The filling pressure can ONLY be measured under what condition?
at zero cardiac output (inject w/ potassium chloride)
How do you increase the filling pressure?
Increase blood volume or increase in sympathetic activity
How do you decrease the filling pressure?
Decrease blood volume or decrease in sympathetic activity
What is the equation for venous return?
Venous Return= ΔP/TPR.
What happens to the venous return if you double the filling pressure (ΔP) with a constant TPR?
double the venous return
What happens to the venous return if you double the TPR with a constant filling pressure?
half the venous return
What happens to the vascular function curve if you increase the TPR (resistance to venous return)?
the curve shifts counterclockwise
What happens to the vascular function curve if you decrease the TPR (resistance to venous return)?
the curve shifts clockwise
What is the relationship between ventricular output and venous return in an intact system?
ventricular output occurring in the intact system (heart and blood vessels operating together)—this, by definition, equals venous return
How do you determine venous output and atrial pressure with a steady state curve?
Venous output and atrial pressure (EDV) are determined by the point of intersection of the cardiac function curve and the vascular function curve.
What happens if you decrease atrial pressure from a steady state system?
At any lower atrial pressure, the venous return would be higher than the ventricular function, and the (returning volume greater than the leaving volume), so the atrial pressure would increase due to the excess blood.
What happens if you have increased sympathetic activity TO THE HEART ONLY in a steady state?
We can shift up the ventricular function curve. This would lead to a higher cardiac output but a lower atrial pressure (which reflects the venous pressure!).
What happens if you increase volume in the veins in a steady state?
Shift the vascular function curve to the right (without changing the slope), we see that this causes a higher cardiac output and a higher atrial pressure (preload).
What happens to the ventricular curve in exercise?
shifts up (sympathetic activity and negative intrathoracic pressure due to deep breathing)
What happens to the vascular curve in exercise?
1) filling pressure increases (due to sympathetic activity and mechanical pressure, veins get smaller and less compliant)
2) Curve is moved clockwise (decreased TPR due to active hyperemia)
What is the effect of exercise on steady state cardiac function?
a large increase of cardiac output with little or no increase in atrial pressure (aka end diastolic pressure or preload—good so you don’t get edema). Also, no real change in arterial pressure!
Atrial pressure ends up being what value?
EDP
What initially happens to the vascular curve when you hemorrhage? What happens to the cardiac output and atrial pressure?
drop in filling pressure due to drop in blood volume- move to left. Cardiac output decreases and atrial pressure decreases.
What happens to the vascular curve as the body compensates to hemorrhage?
Drop in arterial pressure causes increase in sympathetic activity so:
- Increased peripheral resistance (counterclockwise shift)
- Increased filling pressure (move to right)
What is the effect of vascular compensation for hemorrhage?
brings the cardiac output back up to around normal
What is the overall effect on the vascular curve as the body compensates?
Water retention in the kidneys increases blood volume and the filling pressure eventually returns to normal.
What is the effect of hemorrhage on the Ventricular Function Curve?
Curve shifted up due to increased sympathetic activity
What does a heart attack (hypoeffectiveness) do to the ventricular function curve?
curve is shifted down, because heart is malfunctioning
What is the compensatory reaction when the ventricular function curve is shifted down during MI?
This rapid decline in CO will decrease atrial pressure, inactivate baroreceptors, and trigger an increase in sympathetic activity (which will shift the curve up a little).
What effect does an MI have on the vascular function curve? On arterial pressure?
Filling pressure is increased initially due to the increase in sympathetic activity (from compensatory ventricular action) AND you will get a counterclockwise rotation due to increased vascular pressure (this will increase arterial pressure)
What is the compensatory reaction when the vascular function curve is shifted right during an MI?
Several days later, filling pressure will increase even higher (due to increased fluid retention in the kidneys) which will increase CO to a range that is around normal
