Chapter 3: The Heart Pump

Question 1

What does proper filling of the ventricles depend on?

Answer 1

• adequate filling pressures of the heart (preload)
• ability of the ventricular myocytes to stretch (high compliance)
• opening of the AV valves

Question 2

How much does atrial contraction contribute to ventricular filling in health at rest?

Name and explain 2 situations where atrial contraction is important for adequate ventricular filling

Answer 2

• minimally - ventricles are almost at peak diastolic volume before atrial contraction
• becomes important when the HR is elevated –> not as much time for diastolic filling
• becomes important when ventricle is stiff and less compliant/doesn’t fill as easily (age or disease)

Question 3

Explain the dicrotic notch. What is a different name for the dicrotic notch?

Answer 3

incisura

when the pressure in the aorta exceeds the LV pressure, the aortic valve closes –> rebound effect because some blood has to flow “backwards” to fill the space behind the aortic valves as they close –> transient pressure drop

Question 4

What is the normal/healthy ejection fraction?

Answer 4

60%

Question 5

What are typical values for aortic and pulmonary arterial systolic and diastolic pressures?

Answer 5

Aorta: 120/80
PA: 24/8

Question 6

What proportion of a complete cardiac cycle does the heart spend in diastole versus systole?

Answer 6

diastole 2/3

Question 7

Why are the RV and PA pressures so much lower than the LV and Ao pressures?

Answer 7

because of the low pulmonary vascular resistance –> RV does not have to create as high of a pressure to open the PA valves and to push blood forward through the lungs

Question 8

Explain what happens during the a, c, and v waves of a right atrial pressure waveform

Answer 8

a wave - atrial contraction, happens right after P wave of ECG
c wave - ventricular contraction –> causes bulging of the AV valve up into the atria and increaes their pressure - right after QRS complex
v wave - atrial filling against a closed AV valve - right after T wave

Question 9

What phases of the cardiac cycle do the cardiac sounds S1, S2, S3, and S4 represent?

Answer 9

S1 - closing of the AV valves - heart sounds presents beginning of systole - immediately after QRS
S2 - closing of the Aortic and pulmonic valves, presents beginning of diastole - near the end of the T wave
S3 - ventricular filling
S4 - atrial contraction

Question 10

Explain the physiologic splitting of the second heart sound

Answer 10

usually pulmonic valve closure happens only very shortly after aortic valve closure –> not audible

reminder: pulmonic valve closes once RV is done ejecting

during inspiration difference more pronounced:
* negative intrathoracic pressure increases preload/filling pressures of the RV - volume will be ejected but takes longer to do so
* decreases pulmonary vascular resistance - PA pressure does not exceed RV pressure as fast, so more time for filling until PA valves close - i.e., reduced RV afterload

Question 11

Explain ventricular and atrial gallop rhythms

Answer 11

ventricular gallop S3 - ventricular filling - heard in patients with ventricular failure - shortly after S2

atrial gallop S4 - atrial contraction - pronounced when atrial contraction contributes to filling, e.g., stiff/noncompliant ventricle - heard shortly after S1

Question 12

Define ventricular preload

Answer 12

End-diastolic ventricular pressure

Question 13

State the Starling’s law

Answer 13

with other factors equal, stroke volume with increase as cardiac filling increases

Question 14

Describe the consequences of “diastolic failure” on a pressure/volume loop

Answer 14

diastolic failure = ventricles unable to stretch and adequately fill

end-diastolic volume will be smaller and hence the stroke volume will be smaller as well

Question 15

What determines the LV afterload?

Answer 15

MAP

Question 16

Describe the consequences of systolic cardiac failure on a pressure/volume loop

Answer 16

systolic failure = failure to contract

heart will reach same end-diastolic volume but end-systolic volume will be higher - less stroke volume

especially pronounced with situations of increased afterload, increasing work on the heart

Question 17

Describe the consequences of increased ventricular afterlaod on a pressure/volume loop

Answer 17

increased afterload (i.e., increased MAP) will require the heart to build up a stronger contraction to overcome this opposing pressure to create forward flow, i.e., pressure during systolic higher

also end-systolic volume will be higher, because aortic pressure will exceed LV sooner

Question 18

Describe the consequences of an increased preload on a pressure/volume loop

Answer 18

increased preload –> increased filling, according to starling’s law this will lead to an increased SV

Question 19

Name the equation for ejection fraction

Answer 19

EF = SV/EDV

or

EF = (EDV-ESV)/EDV

Question 20

Describe the effects of giving norepinephrine on a pressure/volume loop

Answer 20

increases contractility, will decreased end-systolic volume and therefore increased SV

Question 21

List the 5 cardiac effects of an increased sympathetic tone/norepinephrine

Answer 21

1) increased heartrate from effects on the SA node’ pacemaker current (makes HCN channels more permeable to Na and Ca)
2) increased contractility from increased cAMP –> phosphorylates Ca channel –> more permeable –> more IC Ca
3) increases conduction velocity through AV node, shorter PR interval
4) lusitropic effect (increased rate of relaxation) from SERCA upregulation
5) prolonged diastolic phase –> shorter AP, increased IC Ca cc increases K permeability - delayed rectifying K current faster –> plateau phase shorter

Question 22

List the substrates used by the heart for ATP production. Which one is used mostly in a healthy adult (and what percentage)?

Answer 22

glucose
lactate
pyruvate
fatty acids

fatty acids used for the most part in adults

Question 23

What subtrates does the fetal or newborn heart use mostly for cardiac ATP production

Answer 23

lactate and pyruvate

Question 24

what is the subtrate that enters the Krebs cycle in the mitochondria?

Answer 24

CoA

Question 25

Explain the role of myoglobin for maintaining energy levels

Answer 25

myoglobin stores O2 - can release this O2 if DO2 to muscle cells is decreased and preserve aerobic metabolism

Question 26

What percentage of the cardiac energy use is by muscle contraction?

Answer 26

75%

Question 27

What are the 3 main determinants of the cardiac energy consumption?

Answer 27

• HR
• contractility
• afterload

Question 28

Explain how afterload and preload affect the cardiac energy consumption

Answer 28

afterload - increased MAP, heart has to create a higher tension to create forward flow - more work load

preload - increases SV, more stretched myocytes will contract further down - more work load