Vascular Control I and II

Question 1

CO and control

Answer 1

• closed system- CO= venous return
• heart can be considered a dynamic system that acts upon an input in order to produce an output
• input is venous return
• output is CO

Question 2

changes in input

Answer 2

• require changes in output

- dynamic system

Question 3

preload

Answer 3

• fuel gauge
• determined by the amount of blood in the ventricle at the EDV
• technically the pressure associated with myocyte stretch at this point

Question 4

afterload

Answer 4

-pressure needed to be generated by the ventricle to begin the ejection phase

Question 5

functionally distinct compartment of cardiovascular system

Answer 5

• arteriole- TPR
• capillaries-diffusion
• peripheral venous compartment- reserves, compliant
• central venous compartment

Question 6

overview of the operation of the vascular system

Answer 6

• closed hydraulic circuit that includes the heart, arteries,, arterioles and veins
• pulm not huge influence on Starling’s Law
• each segment has a distinct role to play in the overall operation because of inherent differences in anatomical volume, resistance to flow, and compliance
• two conceptually different compartments:large/diverse peripheral section and a smaller intrathoracic section includes the vena cava and right ventricle

Question 7

peripheral venous compartment

Answer 7

• holds most volume and highest compliance

- blood will pool there

Question 8

arterioles

Answer 8

• highest resistance, only 100 ml vol

- determines afterload

Question 9

central venous compartment

Answer 9

• only 80 ml

- responsible for preload

Question 10

cardiac output and venous return

Answer 10

• must be equal
• central venous compartment is volume in right atrium and great veins in thorax
• blood leaves central venous compartment by entering the right ventricle at a rate that is equal to the CO
• venous return is the rate at which blood returns to the thorax from peripheral beds and thus the rate at which blood enters the central venous compartment
• often temporary differences between CO and venous return
• change in central venous volume changes central venous pressure

Question 11

venous function curve

Answer 11

• venous return vs central venous pressure
• DF from Ppv if it’s greater than Pcv
• point where curve touches central venous pressure is mean systemic filling pressure
• when you increase blood volume or ton the curve shifts to the right, decrease shifts to the left
• less return, less central pressure
• at 0 flow the two systems have equal pressure

Question 12

interaction of cardiac function curve and venous function

Answer 12

• intersect to there is 5 L/min CO. if you move up cardiac function, you will go down venous function and equilibrate again
• need to shift in a person with CHF because they have decreased CO, need to increase fluid to shift curve
• if hemorrhage, venous constriction gets back closer to normal and SNS moves heart curve to normalize CO
• can decrease venous return but body then increases venous tone

Question 13

vascular function curve

Answer 13

• in steady state, CO=VR
• increased flow shifts blood from veins to arteries, increasing venous pressure and central venous pressure
• partial venous collapse at negative central venous pressure produces plateau in vascular function curve
• MSFP occurs at zero flow and reflects blood volume
• CVP declines at any constant venous return with an increase in pump flow (CO or venous return)

Question 14

increasing blood volume

Answer 14

• increases MSFP and shifts vascular curve up
• MSFP is pressure after cardiac death
• VR increases with increased CVP and decreased venous resistance

Question 15

arteriolar tone

Answer 15

• affects venous return but not MSFP because they only have 100 ml blood compared to veins total blood
• but vasoconstriction does decrease CVP and therefore VR