Heart Pump

Question 1

What is the equation for Cardiac Output?

Answer 1

CO = SV x HR

Question 2

Proper filling of ventricles depends on three things:

Answer 2

1. Filling pressure of blood returning to heart and atria
2. Ability of AV valves to open fully (not stenotic)
3. Ability of ventricular wall to expand passively with little resistance (high compliance) - healthy heart is very compliant - filling occurs with only small increases in ventricular pressure

Question 3

What is diastolic pressure?

Answer 3

• The lowest pressure seen in the aorta

- Happens at the end of diastole (after filling)

Question 4

Hematocrit

Answer 4

Fraction of blood volume occupied by cells

Question 5

What is the initial stage of ventricular contraction called where the volume of the ventricle does not change?

Answer 5

Isovolumetric contractile phase of systole (both valves are closed)

Question 6

Why does increasing circulating catecholamines cause an increase in stroke volume?

Answer 6

It increases contractility via SNS

Question 7

Why does a decrease in arterial pressure cause an increase in stroke volume?

Answer 7

It decreases afterload

Question 8

Why does an increase in filling pressure increase SV?

Answer 8

It increases preload

Question 9

Isovolumetric Contraction

Answer 9

All valves are closed, no change in volume but heart is contracting

Question 10

Isovolumetric Relaxation

Answer 10

All valves are closed but heart is relaxing

Question 11

Arterial Pulse Pressure =

Answer 11

PP = Systolic - Diastolic

Question 12

What is different between the right and left heart during the cardiac cycle?

Answer 12

Magnitude of peak systolic pressure is lower in RIGHT because less resistance to flow from lungs vs. systemic organs
Ps = 24 mmHg
Pd = 8 mmHg

Question 13

What causes the Jugular Venous pulse?

Answer 13

• Pressure pulsations occurring in the right atrium
• Transmitted to large veins near the heart
• a wave: atrial contraction
• c wave: bulging of tricuspid valve into right atrium due to ventricular contraction
• v wave: RA and central veins re-filling behind closed tricuspid valve (blood returning from peripheral organs)

Question 14

What is S1?

Answer 14

Closure of the AV valves

Question 15

What is S2?

Answer 15

Closure of aortic and pulmonic valves

Question 16

What happens during the physiological splitting of S2?

Answer 16

Pulmonic valve closes slightly after aortic valve

• Inspiration causes increase in this gap to 30-60 ms
• Inspriation-induced changes in intrathoracic pressure and pulmonary vascular resistance lead to prolonged right ventricular ejection

Question 17

What is S3?

Answer 17

Not normally heard. Presence may indicate left ventricular failure (but can also sometimes be detected in normal children!)

Question 18

What is S4?

Answer 18

Presence may indicate ventricular diastolic stiffness

Question 19

Ejection Fraction (EF) =

Answer 19

SV/EDV
or
SV/Peak Volume

Question 20

Preload:

Answer 20

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

• -The passive/resting tension placed on cardiac muscle cells before contraction
• -EDV or arterial pressure are used as surrogates

Question 21

What is Starling’s Law of the Heart?

Answer 21

Stroke Volume increases as cardiac filling increases

Question 22

What will an increased preload do?

Answer 22

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

Question 23

What is afterload?

Answer 23

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

• The active tension placed on cardiac muscle cells during contraction (A fan of R the left ventricle must overcome to circulate blood)
• As afterload increases, CO decreases

Question 24

What is used as a surrogate for mean ventricular after load?

Answer 24

Mean Arterial Pressure

MAP = DP + 1/3 PP

Question 25

What does increased after load do?

Answer 25

Decreases SV | Ex: hypertension, aortic valve obstruction

Question 26

Increased contractility will ___ ESV.

Answer 26

Decrease, Thus it increases SV.

Question 27

What is Ejection fraction used for?

Answer 27

Clinically useful variable to assess cardiac muscle contractility (EF = SV/EDV)

Question 28

What 5 effects are initiated by NE interacting with Beta-1 Adrenergic receptors (sympathetic nervous system)?

Answer 28

1. Inc. HR 2. Inc. rate of AP conduction 3. Inc. in cardiac contractility 4. Inc. in rate of cardiac relaxation. 5. Dec. in cardiac action potential duration.

Question 29

What is the positive chronotropic effect?

Answer 29

Inc. in HR caused by NE. | Activates funny-current in SA node

Question 30

What is the positive dromotropic effect?

Answer 30

Inc. in rate of AP conduction | -Alters conductivity of gap junctions

Question 31

What is the positive iontropic effect?

Answer 31

Increases in cardiac contractility - Inc. contractile ability of cardiac muscle at any given preload - Activates the Ca2+ current and increases Ca2+ release from SR

Question 32

What is the lusitropic effect?

Answer 32

Inc. in rate of cardiac relaxation. - This minimizes the detrimental effects of high heart rates on diastolic filling time - Inc. Ca2+ uptake by SR

Question 33

What contributes to the lusitropic effect?

Answer 33

Dec. in cardiac AP duration, which promotes early relaxation and contributes to the positive lusitropic effect -Early activation of delayed K+ current

Question 34

What is the primary source of energy for the heart?

Answer 34

60-90% of fuel is ATP from oxidative phosphorylation

Question 35

What is the primary source of cardiac energy for adults? Fetal and newborn? Severe heart failure?

Answer 35

Adult --> Fatty acids Fetal & Newborn --> Glucose and Lactate Severe heart failure --> Observable shift back to glucose metabolism

Question 36

What does the heart have a lot of?

Answer 36

- Mitochondria | - Oxygen-binding protein myoglobin

Question 37

What does the heart rely on for ATP?

Answer 37

Aerobic pathways

Question 38

What percentage of myocardial O2 consumption/energy use is devoted to what things?

Answer 38

25% - basal metabolism 75% - muscle contraction --Isovolumetric - 50% --Isotonic contraction - 25%

Question 39

How to reduce O2 consumption?

Answer 39

``` Reduce cardiac preload -T = P x r (laplace) At larger radius, more tension needed, thus more work and energy Reduce cardiac afterload Reduce cardiac contractility Reduce heart rate ```

Question 40

What is the most important determinant of oxygen consumption?

Answer 40

Heart Rate - More O2 needed to contract fast - More efficient to achieve CO with low HR and high SV than vice versa