Contractility & Cardiac Output

Question 1

What is preload?

Answer 1

aka left ventricular end diastolic volume

-amount of blood ready to be pumped

Question 2

What is preload directly related to?

Answer 2

-fiber length @ end of diastole

–> as ventricle fills with more blood, fibers get longer

Question 3

How does venous return affect preload?

Answer 3

> venous return -> > preload

Question 4

What is the tension relationship & preload?

Answer 4

cardiac output = venous return at a steady state

Question 5

What is frank starling relat?

Answer 5

-volume of blood ejected by ventricle depends od the volume present in the ventricle at end of diastole

Question 6

What is after load?

Answer 6

(for LV) the aortic pressure aka the force opposing contraction

–> pressure required to eject blood by opening the aortic valve

Question 7

What is the relationship b/w velocity of shorting and after load?

Answer 7

-velocity of shortening DECREASES as after load INCREASES

greatest if after load = 0

Question 8

What is stroke volume and how do you calculate for it?

Answer 8

volume of blood ejected by ventricle with each beat

SV = EDV - ESV (~70mL)

Question 9

What is ejection fraction and how do you calculate it?

What does it measure?

Answer 9

• fraction of EDV ejected in each stroke volume
• measures efficiency and contractility
• EF% = SV / EDV (~55%)

Question 10

What physiological state would cause the ejection fraction to decrease?

Answer 10

heart failure

Question 11

What is cardiac output and how to you calculate it?

Answer 11

-total volume of blood ejected by ventricle per minute

Question 12

What are the two coupling factors that contribute to cardiac output?

Answer 12

• preload
• afterload

both relate to contractility

Question 13

What happens to contractility as you increase preload?

Answer 13

-increase contractility and increase CO

Question 14

What happens to CO as you increase after load?

Answer 14

decrease in CO

heart must overcome by increasing contractility or HR

Question 15

What is the positive staircase effect?

Answer 15

an auto regulation method by which increased HR increases contractility (via more Ca2+ in cell and into SR)

aka positive chronotropic effect creates a positive inotropic effect

Question 16

How does sympathetic input affect cardiac output?

activation of what which does what?

Answer 16

• • iontropic effect via B-AR activation

- phosphorylation of sarcolemma Ca2+ channels, phospholamban (stimulatory), and troponin 1 (inhibititory)

Question 17

How does parasympathetic input affect cardiac output?

Answer 17

• (-) iontropic effect via muscarinic receptor activation
• decrease inward Ca2+ current during plateau
• ACh increased outward flow of K+ current via K+-(-)ACh channels

Question 18

What does administering isoproterenol (B-AR agonist ) do ?

Answer 18

increases HR and contractility

treats bradycardia

Question 19

What factors can increase preload?

Answer 19

• increased venous return

- high blood volume

Question 20

What factors can increase after load?

Answer 20

• aortic stenosis

- hypertension

Question 21

What factor can increase contractility directly?

Answer 21

adrenergic stimulation

Question 22

What is volume work and how do you calculate it?

Answer 22

-cardiac output (SV x HR)

Question 23

What is pressure work?

Answer 23

aortic pressure

Question 24

How do you calculate minute work?

Answer 24

CO x aortic pressure (SV x HR x aortic pressure)

Question 25

How do you calculate stroke work?

Answer 25

SV x aortic pressure (LV)

-the area within the volume pressure loop?

Question 26

What is the difference b/w volume work (cardiac output) and stroke work?

Answer 26

Stroke work takes into account the pressure in the aorta; volume work factors in HR

Question 27

What is the Fick Principle? (myocardial O2 consumption)

Answer 27

States that he largest % of O2 consumption is pressure work rather than CO (SV x HR)

-LV must work proportionally harder than RV due to systemic pressure > aortic pressure

Question 28

What further accents increase LV pressure work ?

Answer 28

• aortic stenosis
• systemic hypertension

aka the LV myocytes are using more oxygen to accomplish their tasks to overcome a higher after load pressure and thus more “work”

Question 29

How do you calculate Os consumption ?

Answer 29

O2 consumption = CO x ( [O2]pulm v. - (CO x [O2]pulm a.) )

CO = O2 consumption / ( [O2]pulm v. -[O2]pulm a. )

Question 30

What 3 factors play major roles on the cardiac function curve?

Answer 30

• venous return
• RA pressure
• EDV and end diastolic fiber length

Question 31

What is the relationship of venous return and CO at equilibrium?

Answer 31

• venous return = CO

- aka volume of blood as cardiac output ejected by ventricle matches the volume it reaches in venous return

Question 32

What happens to the RA pressure and venous return when you increase iontropy vs decrease?

Answer 32

increase = RA pressure decreases ; CO/venous return increases

Decreases = RA pressure increases ; Venous return decreases

Question 33

What occurs to RA pressure and venous return when you increase TPR vs decrease TPR?

Answer 33

increase : RA pressure remains constant ; venous return decreases

decrease : RA pressure remain constant ; Venous return increases

Question 34

What occurs to RA pressure and venous return when you increase blood volume vs decrease blood volume?

Answer 34

increase : RA pressure increases ; venous return increases

Decrease : RA pressure decreases; venous return decreases

Question 35

What happens during cardiac failure?

Answer 35

• decrease iontropy (contractility)
• decrease vascular compliance
• increase BP
• increase SVR/TPR

Question 36

What happens to the pressure in the RA and venous return in cardiac failure?

Answer 36

• RA pressure increases
• cardiac output decreases

-increase in volume, decrease contractility of ventricle , and increase TPR