Heart

Question 1

what structural detail is unique to the heart as a muscle? How does this effect its contractile motion?

Answer 1

origin and insertion is on the same CT, wringing contraction

Question 2

What is the all or none law of the heart?

Answer 2

cannot recruit additional muscle fibers in order to increase developed tension

Question 3

why is the length of the refractory periods of the heart so important functionally?

Answer 3

cannot get tetany of the heart

Question 4

What is the SNP?

Answer 4

supranormal period, increased susceptibility to AP with stimulus

Question 5

What determines cardiac output?

Answer 5

preload (Frank starling law of Heart/ VR), Contractility (positive inotropic agents, heart rate, state of heart- failure, hypoxia, ischemia), afterload (aortic diastolic pressure plus impedence), HR

Question 6

How does an increase in developed tension in working heart muscle change velocity of shortening?

Answer 6

as tension increase time for contraction remains relatively the same therefore velocity increases

Question 7

How does norepinephrine effect the Frank Starling curve?

Answer 7

upward shift along developed tension without changing the length, this meansthere is an increase in tension and work without changing length, this means it changes contractility

Question 8

If we are following the all or none law how does norepinephrine increase contractility?

Answer 8

more calcium available quicker so there is an increase in available actin myosin binding sites this increases the velocity of shortening and tension/work

Question 9

what is capillary wedge pressure? How is measurement achieved?

Answer 9

catheter feed venous system through to lungs just before LA, balloon is inflated to measure pressure on proximal venous side

Question 10

What causes a change in Vmax in cardiac tissue?

Answer 10

only norepinephrine due to increase in binding sites,

Question 11

what type of contraction does cardiac muscle use and why?

Answer 11

isometric due to the resistance from pressure

Question 12

what is stroke work?

Answer 12

SV*MAP (or area within PV loop)

Question 13

What is Cardiac work?

Answer 13

HR*SW

Question 14

which type of work done by the heart is harder? What is the other kind of work?

Answer 14

pressure work, volume work

Question 15

What effect does valve stenosis have on pressures?

Answer 15

decreased pressure after valve and increased pressure before valve

Question 16

What effect does mitral regurgitation have on pressures?

Answer 16

increase in pressure after valve closure

Question 17

What effect does aortic regurgitation have on pressures?

Answer 17

decrease in pressure after valve closure, no dicrotic notch observed

Question 18

If preload and afterload are fixed how does stroke volume change with changing contractility?

Answer 18

in PV loop upper sloped line changes its slope and starting height as a function of contractility, increased contractility increases stroke volume, decreased contractility decreases stroke volume

Question 19

what changes in a PV loop with a systolic dysfunction?

Answer 19

decreased contractility-> decreased SV; downward shift of upper sloped line

Question 20

what changes in a PV loop with a diastolic dysfunction?

Answer 20

compliance of ventricle decreased, therefore there is less filling and thus stroke volume is decreased; upward shift in bottom sloped line

Question 21

What causes the splitting of S2 with inspiration?

Answer 21

inspiration: decrease in intraplural pressure pulls blood into lungs and the right heart. More blood in right heart requires more time for ejection thus increased period for systole and a delayed S2. at the same time decreased intraplural pressure causes decreased venous return to the left side and decreased volume for ejection so less time needed to a shorter systole and an earlier S2

Question 22

How do the S2 sounds move back together on expiration?

Answer 22

expiration increases intraplural pressure which forces blood out of lung into left side of heart, increasing volume thus systole and delaying S2, increased plural pressure also impedes venous return on right side thus decreasing volume and systole causing a sooner S2

Question 23

How is cardiac output measured?

Answer 23

via O2 consumption, 200-150, consumption of 50 mL/L difference between before lungs and after, 250 mL O2/min; 250/50= 5mL/min CO

Question 24

What is cardiac output?

Answer 24

HR*SV (mL/min)

Question 25

What is venous return?

Answer 25

volume of blood returning to right atrium/min, determine preload

Question 26

What is inotropic?

Answer 26

change in contractility

Question 27

what does chronotropic mean?

Answer 27

change in rate

Question 28

What is another way to measure cardiac output other than oxygen consumption?

Answer 28

dye or thermal dilution, 1g of dye to a barrel, stir then measure concentration, inject into blood then measure dye concentration downstream

Question 29

What is the frank starling law of the heart?

Answer 29

heart pumps all that comes to it; preload determined by VR, CO=VR

Question 30

What all affects preload?

Answer 30

VR, TPR (Q=deltaP/R) and Tissue control cardiac output (CO=sum of flow through all systemic vascular beds, flow through vascular bed is determined by the needs of that vascular bed, each vascular bed with few notable exceptions determines amount of blood that it receives- autoregulation of blood flow); cardiac output is determined by the needs of the peripheral tissues

Question 31

How is venous return and its interrelationship with cardiac performance?

Answer 31

CV system is a closed system with variable capacitance; capacitance is about 20x greater in venous system than the arterial system. Cap=dV/dP; increasing heart rate decreases venous pressure

Question 32

On a graph with CO vs. venous pressure the point where line crosses venous is what? The slope is what?

Answer 32

MSFP or mean systemic filling pressure- avg pressure when no flow, changing resistance does not change MSFP; slope is based on resistance- dilation increases slope and constriction decreases slope

Question 33

How does volume changes effect the graph of CO vs venous pressure?

Answer 33

slope remains the same but entire line shifts left for hemorrhage and right for a transfusion; changes MSFP but not resistance