Vascular Control

Question 1

what kind of system is the heart? what is its input and output?

Answer 1

a dynamic and closed system

• input = venous return
• output = cardiac output

Question 2

how can the heart change dynamically?

Answer 2

1. changes in input (venous return, such as eating more)

2. changes in its output (cardiac output, such as exercising more)

Question 3

what are the 2 venous compartments and what do they determine?

Answer 3

1. central venous compartment (volume enclosed by right atrium and great veins in the thorax)
2. peripheral venous compartment (allows holding all the blood; 2500 mL)

Question 4

what aspect of the systemic cardiovascular circuit determines afterload?

Answer 4

resistance of arterioles (13 mmHg/L/min)

Question 5

what aspect of the systemic cardiovascular circuit determines preload?

Answer 5

volume of the central venous compartment (80 mL)

Question 6

what is the connection between right atrial pressure and central venous pressure

Answer 6

they are the same thing (RAP = CVP = great veins in thorax + right atrium)

Question 7

what happens when venous return doesn’t equal cardiac output?

Answer 7

there is a change in the volume of the central venous compartment, thus the CVP changes too

Question 8

what is the purpose of measuring jugular venous pressure

Answer 8

external jugular serves as a barometer for CVP

Question 9

what is the purpose of a central venous catheter?

Answer 9

infect needle in internal jugular to cavoatrial junction and perfuse fluids to see CVP

Question 10

how does peripheral venous pressure compare to central venous (intrathoracic) pressure? what does this mean for venous return?

Answer 10

PVP is usually 7 mmHg, and CVP is usually 0 mmHg, so blood flows from PVC to CVC
-venous return usually 7L/min

Question 11

what is MSFP?

Answer 11

mean systemic filling pressure; pressure exerted by total blood volume (usually 7 mmHg, like central venous pressure) when there is zero flow

Question 12

what happens to the venous return and central venous pressure with increased blood volume or venous tone?

Answer 12

the curve shifts up/right, such that the VR is greater, and CVP is greater

• the slope is the same
• this happen if blood is introduced into the system

Question 13

what happens to the venous return and central venous pressure with decreased blood volume or venous tone?

Answer 13

the curve shifts down/left, such that the VR is smaller, and the CVP is smaller

• the slope is the same
• this happens if blood is taken away from the system

Question 14

what does the intersection between the cardiac function curve and the venous function curve mean?

Answer 14

it is the venous return at the given central venous pressure in a resting individual
-normally, VR (AKA CO) is 5 L/minute, and CVP is 2 mmHg

Question 15

what are the changes to the cardiac function curve and venous function curves during hemorrhage?

Answer 15

1. venous function curve shifts down/left due to decrease in blood (CO or VR decrease, CVP decreases)
2. cardiac function curve shifts up due to increased cardiac sympathetic nerve activity (CO increases, but CVP decreases)
3. venous function curve shifts up/right due to venous constriction (CO goes up to normal 5 L/min, but CVP is still < 2

Question 16

what are the changes to the cardiac function curve and venous function curves during CHF?

Answer 16

1. cardiac function curve shifts down, even though MFSP is the same, because heart cannot pump enough CO
2. venous function curve shifts up/right by retaining fluid to increase CO at a nigher CVP

Question 17

what does the partial venous collapse produce?

Answer 17

happens at negative RAP (CVP) that produces the plateau in the vascular function curve (steady flow at negative pressures)

Question 18

what happens to the venous function curve during vasodilation? why does this happen? what happens to the end systolic volume and peripheral venous pressure?

Answer 18

the slope is steeper, b/c MSFP doesn’t change (same amount of blood) while CO increases (SV increases b/c decreased resistance)

• ESV decreases
• PVP increases

Question 19

what happens to the venous function curve during vasoconstriction? why does this happen? what happens to the end systolic volume and peripheral venous pressure?

Answer 19

the slope is flatter, b/c MSFP doesn’t change (same amount of blood) while CO decreases (CV decreases b/c increased resistance)

• ESV increases
• PVP decreases

Question 20

when does CO equal VR?

Answer 20

at steady state

-with RAP, the three are interdependent (mismatches are quickly resolved)

Question 21

what are the effects of cardiac glycosides (like digitalis?)

Answer 21

increase contractility and elevate cardiac function curve and CO
-same effect as if increased HR or SV

Question 22

what is the effect of sympathetic activation on vascular and cardiac function curves?

Answer 22

heart becomes stronger pump, so MSFP increases due to venous contraction causing larger volume in smaller system
-VR and CO increase to higher match point, w/o much change in RAP

Question 23

how does constriction of veins compare to arterioles in terms of MSFP?

Answer 23

since there’s more blood in veins, venoconstriction increases MSFP while arterolar constriction only has a negligible or no effect

Question 24

how does anesthesia affect vascular and cardiac function curves?

Answer 24

inhibits sympathetic drive, causing venodilation, lower CVP, lower VR, and lower CO