Heart Pump

Question 1

Isovolumetric Contraction –

Answer 1

all valves are close, no change in volume but heart is contracting

Question 2

Isovolumetric Relaxation –

Answer 2

all valves are close but heart is relaxing

Question 3

Cardiac Cycle – Right Heart is different than left heart: pressure difference

Answer 3

Magnitude of the peak systolic pressure is lower in RIGHT because less resistance to flow from lungs vs. systemic organs
Systolic Pressure: 24 mm Hg
Diastolic Pressure: 8 mm Hg

Question 4

S3: presence may indicate

Answer 4

left ventricular failure (but can also sometimes be detected in normal children!)

Question 5

S4: presence may indicate

Answer 5

ventricular diastolic stiffness

Question 6

Preload: is

Answer 6

end-diastolic pressure/vol. that stretches the ventricle to its greatest dimensions under physiologic demand

The passive/resting tension placed on cardiac muscle cells before contraction. (A function of the volume and pressure at the end of diastole)

EDV or atrial pressure are used as surrogates

Question 7

Starling’s Law of the Heart:

Answer 7

stroke volume increases as cardiac filling increases

Question 8

Increased preload will:

Answer 8

Increase initial muscle fiber length, thus increase the extent of shortening during contraction
Increase end-diastolic volume and stroke volume

Question 9

Afterload: is the

Answer 9

tension or stress that develops in the cardiomyocytes of the left ventricle during ejection/contraction

The active tension placed on cardiac muscle cells during contraction. (A function of the resistance the left ventricle must overcome to circulate blood)

Abnormal: increased afterload will decrease SV –ex. hypertension, aortic valve obstruction

Question 10

As afterload increases, cardiac output

Answer 10

decreases.

Question 11

5 effects That are initiated by norepi interaction with BETA-1 ADRENERGIC RECEPTORS:

Answer 11

An increase in heart rate (positive chronotropic effect)-Activates funny–current in SA node

An increase in rate of action potential conduction, particularly evident in the AV node (positive dromotropic effect)–Alters conductivity of gap junctions

An increase in cardiac contractility (positive inotropic effect), which increases the contractile ability of cardiac muscle at any given preload–Activates the Ca2+ current and increases Ca2+ release from SR

An increase in the rate of cardiac relaxation (positive lusitropic effect) which minimizes the detrimental effects of high heart rates on diastolic filling time–Increase Ca2+ uptake by SR

A decrease in cardiac action potential duration, which promotes early relaxation and contributes to the positive lusitropic effect–Early activation of delayed K+ current

Question 12

chronotropic effect

Answer 12

changes the SA node rate

Question 13

dromotropic effect

Answer 13

changes the AV node rate

Question 14

lusitropic effect

Answer 14

changes the relaxation of the cardiac muscle cells

Question 15

main source of cardiac muscle energy

Answer 15

60 – 90% of fuel is ATP from oxidative phosphorylation
fatty acids in adults
Fetal and newborn is glucose and lactate
Severe heart failure there is an observable shift back to glucose metabolism

Question 16

Strategies to Reduce O2 Consumption

Answer 16

decrease heart rate-More efficient to achieve CO with low HR and high SV than vice versa.
Reduce cardiac preload (end-diastolic volume)
Reduce cardiac afterload (systemic arterial pressure)
Reduce cardiac contractility (sympathetic drive)