Phys Lecture 3 and 4: Regulation of CO

Question 1

What mainly determines arterial resistance?

Answer 1

radius of vessel

Question 2

T or F: Ventricular output influences venous return and venous return influences ventricular output

Answer 2

T

Question 3

What defines ventricular output as a function of atrial pressure?

Answer 3

cardiac function curve

Question 4

What defines venous return as a function of atrial pressure?

Answer 4

vascular function curve

Question 5

In an intact system, cardiac output is (higher, lower, or equal to) venous return

Answer 5

=

*closed loop system!

Question 6

in the cardiac function curve, what determines ventricular output?
How is this different than in an intact system?

Answer 6

atrial pressure (or preload)

in an intact sys, ventricular output is determined by simultaneous function of ventricles and blood vessels

Question 7

What determines atrial pressure?

Answer 7

volume of fluid in atria

-which is determined by vascular function/venous return and ventricular function

Question 8

As you increase atrial pressure (preload), ventricular output (inc, dec, stays the same)

Answer 8

increases (to a point)

Question 9

Why is increased atrial pressure assc with inc ventricular output?

Answer 9

1. causes inc HR via stretch receptor activation = sympathetic activation if SA node –> inc CO
2. inc fluid delivery from atrial to ventricle (EDV) –> inc stroke volume –> inc CO

Question 10

How does an increase in afterload affect ventricular output? Why?

Answer 10

decreases it

bc SV is decreased (think pressure-volume loop curves)

Question 11

How does a more negative intrapleural pressure effect the cardiac function curve? Why?

Answer 11

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

Question 12

An increase in atrial pressure causes an (inc, dec, no change) in venous return. Why?

Answer 12

decrease (bc the pressure gradient/differential is decreased btwn atria and vessels)

Question 13

What is the mean systemic filling pressure?

Answer 13

7 mmHg

or the atrial pressure when there is no blood flow/stop the heart (aka VR = 0) / no pressure gradient

Question 14

What sets the x-axis intercept for the vascular function curve?

Answer 14

mean systemic filling pressure (aka atrial pressure when VR = 0)
**depends on blood volume and size of veins

Question 15

What sets the slope of the vascular function curve?

Answer 15

resistance to venous return (~TPR)

inc resistance and dec VR/slope

Question 16

Decreasing change in P will (inc, dec, keep the vascular return the same)

Answer 16

decrease

Question 17

Why is there a plateau at the end of the vascular function curve?

Answer 17

at very low (-4 mmHg)) the veins collapse and flow stops

Question 18

What is filling pressure?

Answer 18

the pressure that is required to fill blood vessels beyond their intrinsic/unstressed volume

AKA the volume needed to stretch the vessels (veins)

Question 19

another term for unstressed volume

Answer 19

intrinsic volume

Question 20

T or F: In order to measure the filling pressure, the heart must be stopped

Answer 20

T

Question 21

With inc sympathetic stimulation, will filling pressure increase, decrease or stay the same? (keeping blood volume constant)

Answer 21

increase

bc radius decreases

Question 22

If the slope does not change on the vascular function curve, what has been held constant?

Answer 22

TPR

Question 23

If the x intercept on the vascular function curve increased, what has changed? (give situations in which this would occur)

Answer 23

there has been an increase in filling pressure (i.e. increase in blood volume (hypervolemia) or decrease in vessel size)

Question 24

How does the vascular function curve change when TPR increases?

Answer 24

CCW rotation (decrease in VR)

Question 25

T or F: changes in TPR play a greater role than changes in systemic filling pressure in determining a new vascular function curve.

Answer 25

F: changes in sfp play a greater role than changes in TPR

**except in exercise

Question 26

What is the point of intersection between vascular function and cardiac function curves?

Answer 26

CO and atrial pressure at steady state

Question 27

How is preload and afterload determined on the cardiac-vasculr function curve?

Answer 27

At point of intersection,
preload = atrial pressre
afterload = CO