Contractility and Cardiac Output

Question 1

Positive vs. negative inotropy

What is it in proportion to?

Answer 1

Positive: increased force of contraction.
Negative: decreased force of contraction.
The amount of Ca that is available to troponin on actin.

Question 2

Length-tension relationship

Answer 2

Relates to the degree of myofilament overlap.

As pressure/volume increases, greater tension is generated.

Question 3

Preload

Answer 3

End diastolic volume that is the greatest the ventricle can stretch prior to contraction (at the end of diastolly).

Question 4

Afterload

Answer 4

Pressure required to eject blood (to open the aortic valve).
Should be nearly equal to the aortic/pulmonary pressure

Question 5

Afterload and velocity

Answer 5

Increased afterload causes a decrease in velocity shortening.

Question 6

Stroke volume

Answer 6

Volume of blood ejected by ventricle with each beat.

SV = EDV - ESV

Question 7

Ejection fraction

Answer 7

Fraction of EDV ejected in each stroke volume.
Measure of efficiency and ocntractility.
EF% = SV/EDV

Question 8

Cardiac output

Answer 8

Amount of blood ejected by ventricle each minute.

CO (Q) = SV x HR

Question 9

Frank Starling relationship

Answer 9

Volume of blood ejected by the ventricle depends on the volume present in the ventricle at the end of diastolly.

Question 10

CO must equal

Answer 10

Venous return

Question 11

Ventricular pressure-volume loop

Point 1 to 2

Answer 11

Isovolmetric contraction

Pt 1 is end of diastole.

Question 12

Ventricular pressure-volume loop

Point 2 to 3

Answer 12

Ventricular ejection

Pt 2 marks where ejection begins.

Question 13

Ventricular pressure-volume loop

Point 3 to 4

Answer 13

Isovolumetric relaxation
End of systole, ventricles relax.
Pressure falls but volume is constant.
Pressure must reach the level where the semilunar valves open.

Question 14

Ventricular pressure-volume loop

Point 4 to 1

Answer 14

Ventricula filling.

Question 15

Increased preload

Answer 15

Increased venous return (more blood vol.).
Greater EDV.
Afterload and contractility are same.
Increased stroke vol.

Question 16

Increased preload can cause

Answer 16

Aortic stenosis, HTN.
Greater pressure needed.
Reduced SV and EF%

Question 17

Increased contractility

Answer 17

Adrenergic stimulation
Increased SV and EF%
Less blood left in heart.

Question 18

Sympathetic effect on inotropy

Answer 18

Positive inotropic effect.

beta-AR activation

Question 19

Forms of sympathetic activation (3):

Answer 19

Phosphorylation of sarcolemmal Ca2+ channels.
Phosphorylation of phospholamban (stimulatory)
Phosphorylation of troponin I (inhibitory)

Question 20

Parasympathetic effect on inotropy

Answer 20

Negative inotropic effect in atria only.

Muscarinic receptor activation.

Question 21

Forms of parasympathetic activation (2):

Answer 21

Decrease inward Ca2+ current during plateau.

ACh increases outward K+ current via K+-ACh channel

Question 22

Positivie staircase effect

Answer 22

Myocardial tension increases with an increase in HR.

More Ca enters cells and is taken up into the SR.

Question 23

Cardiac glycosides (5)

Answer 23

Used to treat HF.
Inhibits Na/K ATPase
Increases Na conc.
Decreases cA EFFLUX
Increases IC Ca.
Positive inotropic effect.

Question 24

Volume work
Pressure work
Minute work
Stroke work

Answer 24

CO
Aortic pressure
CO x aortic pressure
SV x aortic pressure (area within pressure-vol loop).

Question 25

Cardiac function curve

Answer 25

Venous return increases
RA pressure increases
End diastolic vol and end diastolic fiber length increase (Frank-Starling).