16. Contractility and Cardiac Output

Question 1

What is the difference between positive and negative inotropy?

Answer 1

Positive increases the force of contraction
Negative inotropy decreases the force of contraction of the heart
(proportional to the amount of Calcium)

Question 2

The cardiac muscle in the heart follows the same length-tension curve as skeletal muscle (smooth muscle does not!), what happens when pressure or volume in the LV increases?

Answer 2

Greater tension is generated

Question 3

Afterload is the pressure required to cause ejection of blood. What is true regarding velocity of contraction and afterload?

Answer 3

As afterload increases, the velocity of contraction decreases

Question 4

How do you calculate stroke volume?

Answer 4

SV= End diastolic volume (EDV)- end systolic volume (ESV)

Question 5

How do you calculate cardiac output? (2 wAYS)

Answer 5

1. CO = SV x HR

2. CO= [O2 consumed] / [O2artery]-[O2veins]

Question 6

How do you calculate ejection fraction? (usually 55%)

Answer 6

EF= SV (EDV-ESV) / EDV

Question 7

‘Volume of blood ejected by the ventricles depends on the volume present in the ventricles at the end of diastole’ is what relationship?

Answer 7

Frank-Starling relationship

Question 8

How would a positive or negative inotropic effect change Cardiac output?

Answer 8

Postitive would increase cardiac output

Negative would decrease cardiac output

Question 9

If you have increased preload (increased venous return, increased volume), what will occur to the pressure volume loop and CO?

Answer 9

Pressure volume loop will increase in width to accomadate high volume, cardiac output will increase since there is more stroke volume

Question 10

If you have increased afterload (aortic pressure high), how does this change the pressure volume loop and cardiac output?

Answer 10

the loop will have an increased height due to increased pressure needed to eject and a lesser cardiac output (because decreased stroke volume)

Question 11

Increased contractility via adrenergic stimulation would do what to CO and volume loop?

Answer 11

Would increase SV and CO, causing more blood to be ejected at a higher pressure

Question 12

How does the sympathetic NS cause positive intropy effect to increase strength of muscle contraction?

Answer 12

Via B1 receptors, activate adenylyl cyclase, which phosphorylates sarcolemmal Ca+ channels and SR, releasing MORE Ca = higher muscle contraction = increased CO

Question 13

How does the parasympathetic NS cause negative intropy (dec. contractility) in the atria only?

Answer 13

Via muscarinic receptor activation, which decreases inward Ca2+ and increases outward K+

Question 14

An increase in heart rate can also increase contractility. What is the positive staircase effect/bowditch staircase?

Answer 14

Increased HR increases force of contraction in stepwise fashion as the intracellular Ca2+ increases (inc Ca2+ = increase in contractility strength)

Question 15

an increase in heart rate can also increase contractility. What is postextrasystolic potentiation?

Answer 15

The beat that occurs after an extrasystolic beat has increased force of contraction because extra Ca2+ enter the cells during extrasystole

Question 16

How do cardiac glycosides allow a positive inotropic effect, resulting in increased contractility?

Answer 16

They inhibit NaKATPase, so [Na] intracellular increases, leading to a decrease in Ca out/Na in exchanger, so [Ca] intracellularly increases

Question 17

Cardiac work is comprised of volume work (cardiac output) and pressure work (aortic pressure) how is it calculated?

Answer 17

CO x aortic pressure

Pressure work is costlier than volume work. if pt has failing heart d/t aortic stenosisi or HTN –> REDUCE AFTERLOAD

Question 18

The volume of blood ejected by cardiac output is equal to the volume it receives from?

Answer 18

venous return = CO @ equilibrium

as venous return increases, atrial pressure increases

Question 19

As you decrease mean systemic pressure (MSP), the SV will be become?

Answer 19

Less

Question 20

Enhanced cardiac function curve: inc. inotropy, inc. HR, ___ afterload
Depressed cardiac function curve: dec. inotropy, dec. HR, ____ afterload?

Answer 20

Enhanced: decreased afterload
Depressed: increased afterload

Question 21

If you decrease volume, systemic pressure will decrease. As you increase vascular volume, systemic pressure will?

Answer 21

increase

Question 22

If systemic vascular resistance decreases, your cardiac output increases and mean pressure will stay they same. If systemic vascular resisitance increases, your cardiac output decreases, and mean systemic pressure will?

Answer 22

stay the same

Question 23

With a positive inotropic effect, what will occur to preload and CO?

Answer 23

CO will increse, preload will decrease

Question 24

What will happen if blood volume is increased?

Answer 24

increased preload, increased CO and BP

Question 25

What will happen if blood volume is decreased?

Answer 25

decreased preload, CO and BP

Question 26

If TPR or SVR is increased, the cardiac output will decrease. What will happen if TPR or SVR decrease?

Answer 26

Cardiac output will increase

Question 27

In cardiac failure/heart attack, there will be a decrease in inotropy, decrease in vascular compliance, increase in blood bolume and an?

Answer 27

increase in SVR