L13 Heart- Heart and Peripheral Vasculature

Question 1

Define venous return.

Answer 1

Rate at which blood returns to the thorax from the peripheral vascular beds (blood entering central venous pool)

Question 2

Define central venous pool.

Answer 2

Volume enclosed by the right atrium and great veins of the thorax

Question 3

Define cardiac output.

Answer 3

Rate at which blood leaves central venous pool and pumped out of the heart

Question 4

Explain vascular function curve.

Answer 4

Increase in cardiac output= decrease in central venous pressure= increase in venous return

• When CVP=Pmc, blood flow ceases (no pressure gradient for venous return)
• At negative CVP, veins collapses= 0 venous return

Question 5

Define mean circulatory pressure.

Answer 5

Mean pressure that exists in the circulatory system when CO= 0 and pressures in venous system redistribute
-Relationship between blood V in circulation vs. fxnal capacity of system

Question 6

What factors influence venous return?

Answer 6

• Increase peripheral venous pressure (increase symp. venoconstriction, increase blood V, increased leg muscle activity)
• Decrease central venous pressure/R atrial (respiratory pump activity, cardiac suction)
• Venous valves (maintain pressure gradient btw. peripheral and central venous pools against gravity)
• Cardiac contraction (generates peripheral venous P)

Question 7

How does venoconstriction determine venous return?

Answer 7

Increased venoconstriction= increased venous return

Question 8

How does venodilation determine venous return?

Answer 8

Increased venodilation= decreased venous return

Question 9

How does venous capacitance determine venous return?

Answer 9

1

Question 10

How is venous return determined by respiration?

Answer 10

Increased respiration= decreased intrathoracic pressure= increased venous return

Question 11

How is venous return determined by venous valves?

Answer 11

Venous valves create unidirectional blood flow= increased venous return

Question 12

How is venous return determined by cardiac relaxation?

Answer 12

Increased cardiac relaxation= decreased venous return

Question 13

How is venous return determined by cardiac contraction?

Answer 13

Increased cardiac contraction= increased venous return

Question 14

How is venous return determined by contraction of leg muscles?

Answer 14

Increased skeletal leg muscle pump= increased venous return

Question 15

How is venous return determined by blood volume?

Answer 15

Increase in blood V= increased venous return

Question 16

How does sympathetic nerve activity influence cardiac fxn curve?

Answer 16

Increase in sympathetic nerve activity= increase in venous tone/venoconstriction= increased venous return/CO and decreased CVP

Question 17

How do inotropic drugs influence cardiac fxn curve?

Answer 17

Positive inotropic drugs= increase venoconstriction= increased venous return/CO, decreased CVP

Question 18

How does heart failure influence cardiac fxn curve?

Answer 18

Heart failure decreases CO and increases CVP

Question 19

Describe the circulatory and cardiac adjustments to heart failure.

Answer 19

CO decreases, CVP increases

• Kidneys increase blood V
• Fluid retention= increased CVP
• Elevated CVP= improved preload= good CO in mod. heart failure
• Severe heart failure- contractility so bad that CO not improved by elevated CVP
• Increased CVP= pulmonary congestion and pitting edema

Question 20

Describe the circulatory and cardiac adjustments to hemorrhage.

Answer 20

• Venoconstriction= increased venous return
• Arterial vasoconstriction= increased BP, organs damaged by ischemia b/c of shunting
• Increase in symp. activity and catecholamines= increased contractility
• Dialysis of fluid from tissues to restore blood V= low BP