Phys Lecture 3 and 4: Regulation of CO Flashcards
What mainly determines arterial resistance?
radius of vessel
T or F: Ventricular output influences venous return and venous return influences ventricular output
T
What defines ventricular output as a function of atrial pressure?
cardiac function curve
What defines venous return as a function of atrial pressure?
vascular function curve
In an intact system, cardiac output is (higher, lower, or equal to) venous return
=
*closed loop system!
in the cardiac function curve, what determines ventricular output?
How is this different than in an intact system?
atrial pressure (or preload)
in an intact sys, ventricular output is determined by simultaneous function of ventricles and blood vessels
What determines atrial pressure?
volume of fluid in atria
-which is determined by vascular function/venous return and ventricular function
As you increase atrial pressure (preload), ventricular output (inc, dec, stays the same)
increases (to a point)
Why is increased atrial pressure assc with inc ventricular output?
- causes inc HR via stretch receptor activation = sympathetic activation if SA node –> inc CO
- inc fluid delivery from atrial to ventricle (EDV) –> inc stroke volume –> inc CO
How does an increase in afterload affect ventricular output? Why?
decreases it
bc SV is decreased (think pressure-volume loop curves)
How does a more negative intrapleural pressure effect the cardiac function curve? Why?
increase ventricular output
moves to the left!
When intra pleural pressure decreases, the ventricles stretch more (due to greater difference in pressures) –> inc in SV
An increase in atrial pressure causes an (inc, dec, no change) in venous return. Why?
decrease (bc the pressure gradient/differential is decreased btwn atria and vessels)
What is the mean systemic filling pressure?
7 mmHg
or the atrial pressure when there is no blood flow/stop the heart (aka VR = 0) / no pressure gradient
What sets the x-axis intercept for the vascular function curve?
mean systemic filling pressure (aka atrial pressure when VR = 0)
**depends on blood volume and size of veins
What sets the slope of the vascular function curve?
resistance to venous return (~TPR)
inc resistance and dec VR/slope
Decreasing change in P will (inc, dec, keep the vascular return the same)
decrease
Why is there a plateau at the end of the vascular function curve?
at very low (-4 mmHg)) the veins collapse and flow stops
What is filling pressure?
the pressure that is required to fill blood vessels beyond their intrinsic/unstressed volume
AKA the volume needed to stretch the vessels (veins)
another term for unstressed volume
intrinsic volume
T or F: In order to measure the filling pressure, the heart must be stopped
T
With inc sympathetic stimulation, will filling pressure increase, decrease or stay the same? (keeping blood volume constant)
increase
bc radius decreases
If the slope does not change on the vascular function curve, what has been held constant?
TPR
If the x intercept on the vascular function curve increased, what has changed? (give situations in which this would occur)
there has been an increase in filling pressure (i.e. increase in blood volume (hypervolemia) or decrease in vessel size)
How does the vascular function curve change when TPR increases?
CCW rotation (decrease in VR)
T or F: changes in TPR play a greater role than changes in systemic filling pressure in determining a new vascular function curve.
F: changes in sfp play a greater role than changes in TPR
**except in exercise
What is the point of intersection between vascular function and cardiac function curves?
CO and atrial pressure at steady state
How is preload and afterload determined on the cardiac-vasculr function curve?
At point of intersection,
preload = atrial pressre
afterload = CO
