Cardiac Output and Contractility

Question 1

• What is the effect of a positive inotropic agent?

Answer 1

Increase in contractility

• Increase in EDV
• Increase in CO
• Increase in SV

Question 2

• What is the effect of a positive chonotropic agent?

Answer 2

• Increase in HR

Question 3

• What is the effect of a negative inotropic agent?

Answer 3

• Decrease contractility

Question 4

• What is the effect of a negative chonotropic agent?

Answer 4

• Decrease HR

Question 5

• What is preload? (General sense)

Answer 5

• End Diastolic Volume

Question 6

• What is preload in a more detailed sense?

Answer 6

• Amount of wall tension in RV or LV just before contraction is initiated

Question 7

• What is afterload (in a general sense)?

Answer 7

• Aortic diastolic pressure

Question 8

• What is afterload in a more detailed sense?

Answer 8

• The amount of diastolic pressure in the aorta/pulmonary arteries that must be exceeded for semilunar valves to open

Question 9

• How are afterload and velocity related?

Answer 9

• They are inversely related
• Increase in afterload leads to a decrease in velocity of contraction/shortening of muscle fibers

Question 10

• How do you calculate stroke volume ?

Answer 10

• SV=EDV-ESV
• Note that in normal conditions, this is approx 70 mL
• Represents volume of blood ejected by ventricle with each beat

Question 11

• How do you calculate ejection fraction?

Answer 11

• EF%=SV/EDV
• Usually around 55%
• Represents the fraction of EDV that is ejected in each stroke volume

Question 12

• How do you calculate cardiac output?

Answer 12

• CO=HR x SV
• Volume of blood ejected by the ventricle per minute
• Normal=5 L/min

Question 13

• What does the Frank Starling relationship tell us?

Answer 13

• The volume of blood ejected by the ventricle depends on the volume present in the ventricle at the end of diastole (EDV)
• Note that EDV relates to venous return (more venous return, larger EDV)
• In a steady state CO=venous return

Question 14

• Will a chonotropic effect have an inotropic effect?

Answer 14

• Yes
• Positive chonotropic effect will have positive effect on inotropy and vice versa

Question 15

What is represented by points 1-2 in the following pressure volume curve?

Answer 15

• Isovolumetric contraction

Question 16

• What is represented by points 2-3 in the pressure volume loop?

Answer 16

• Ejection of blood

Question 17

• What is represented from points 3-4 in the pressure volume loop?

Answer 17

• Isometric relaxation

Question 18

• What is represented by points 4-1 in the pressure volume loop?

Answer 18

• Ventricular filling

Question 19

• Which point on the curve represents preload?

Answer 19

• 1
• Remember preload=EDV

Question 20

• Which point on the loop represents afterload?

Answer 20

• 2
• Remember that afterload is the aortic pressure that must be exceeded in order for the aortic valve to open and blood to be ejected from the ventricle

Question 21

• On which points of the loop are the AV valves opening and closing?
• On which points of the loop are the semilunar valves opening and closing?

Answer 21

• AV valves open during 4
• AV valves close during 1
• Semilunar valves open at 2
• Semilunar valves close during 3

Question 22

• What are the effects of increased pre-load on the pressure volume loop?

Answer 22

• Increase in EDV
• Afterload and contractility remain constant
• Increased stroke volume

Question 23

• What are the effects of increased afterload on the pressure volume loop?

Answer 23

• Greater pressure in aorta
• Reduced SV
• Reduced EF%

Question 24

• What are the effects of increased contractility on pressure volume loop?

Answer 24

• Increased SV
• Increased aortic pressure
• Decreased ESV

Question 25

• What type of effect does sympathetic stimulation have on CO?
• Via what receptors does this act?
• Via what NTX does this act?
• What are the biochemical effects that occur as a result of sympathetic stimulation?

Answer 25

• Positive inotropic effect
• Beta 1 adrenergic receptors
• NE
• Phosphorylation of sarcolemma Ca2+ channels (leads to increased intracellular Ca2+ concentrations)
• Phosphorylation of phospholamban (increased sequestering of Ca2+ in the SR; important for subsequent contractions)
• Phosphorylation of Troponin I (Inhibits troponin i so that troponin c can bind to Ca2+ and help enable cross bridge formation)

Question 26

• What type of effect does the parasympathetic nervous system have on cardiac output?
• Through which receptor does it work?
• What biochemical events occur as a result?

Answer 26

• Negative inotropic effect in ATRIA ONLY
• Muscarinic receptor activation
  
  • ​Decreases inward Ca2+ current during plateau
  • AcH increases outward K+ current via K+-ACh channel (hyperpolarizes membrane)

Question 27

• How does increasing HR affect contractility?

Answer 27

• Positive chonotropic effect increases HR and increased HR increases contractility (positive inotropic effect)
• Positive staircase effect (Bowditch staircase)
  
  • ​More Ca2+ enters into cell and taken up into SR
• Postextrasystolic potentiation (arrythmia, extra beat)

Question 28

• What is volume work equivalent to?
• What is pressure work equal to?
• Which is greater?

Answer 28

• Cardiac output
• Aortic pressure
• Pressure work

Question 29

• What is minute work?

Answer 29

Minute work=CO x aortic pressure (pressure work)

Question 30

• What is stroke work?

Answer 30

• Performed by the LV
• Stroke Work=SV X aortic pressure
• Represents the area within the pressure volume loop

Question 31

• What is the Fick principle?

Answer 31

• Cardiac output=O2 consumption/([O2]pulmonary vein-[O2]pulmonary artery)

Question 32

• What is the relationship between CO and venous return at a steady state?

Answer 32

• At a steady state, the volume of blood ejected by Lv (CO)=venous return

Question 33

• Changing what factor will shift which part of the cardiac curve ONLY?

Answer 33

Inotropy

Question 34

• Changes in what parameter will change the vascular function curve only?

Answer 34

• Changes in blood volume

Question 35

• What parameter affects both Cardiac and Vascular function curves?

Answer 35

TPR

Question 36

What is represented by the blue dot in the following figure?

Answer 36

Equilibrium-where CO=venous return

Question 37

What is represented by the arrows in the following diagram?

Answer 37

• 1st arrow=equilibrium where CO=venous return
• 2nd arrow=Mean systemic pressure; proportional to blood volume and preload**

Question 38

• What parameter is causing the changes in the cardiac function curve?

Answer 38

• Left represents a positive inotropic effect (increased inotropy, increased HR, increased afterload)
• Left represents a negative inotropic effect (decreased inotropy, decreaed heart rarte, increased afterload)

Question 39

• Changing what parameter has caused the shifts in the following figures?

Answer 39

• Right
  
  • Increasing blood volume
  • Decreasing systemic vascular resistance (SVR)
  • Decreasing mean circulatory filling pressure/mean systemic pressure
• Left
  
  • Decreasing blood volume
  • Increasing systemic vascular resistance
  • Increasing mean circulatory filling pressure/mean systemic pressure

Question 40

• What parameter has been changed to cause the shifts in the diagrams below?

Answer 40

• TPR
• Left diagram shows an increase in TPR which leads to a right shift of the cardiac function curve and a left shift of the vascular function curve
• Right diagram shows a decrease in TPR which leads to a left shift of the cardiac function curve and a right shift of the vascular function curve

Question 41

• What is the relationship between CO and venous return in an individual with heart failure?

Answer 41

• Decreased inotropy
• Decreased vascular complaince
• Increased blood volume
• Increased SVR