Regulation of Cardiac Function 1

Question 1

What are the steps of the cardiac cycle?

Answer 1

1. Diastole (passive filling)
2. Atrial systole
3. Ventricular systole (isovolumetric contraction)
4. Systole (ejection)
5. Diastole (isovolumetric relaxation)

Question 2

What occurs during diastole (passive filling)?

Answer 2

Blood flows into heart from vena cava and pulmonary veins

AV valves open; semilunar valves closed

Consistent pressure increase in atria and ventricles

Question 3

What occurs during atrial systole?

Answer 3

Last of blood ejected from atria into ventricles

Small increase in pressure in both atria and ventricles

Question 4

What occurs during ventricular systole (isovolumetric contraction)?

Answer 4

No flow as all valves closed

Pressure increases sharply in ventricles with no change in volume

Question 5

What occurs during systole?

Answer 5

Ejection of blood

Ventricular pressure > outflow vessel pressure so semilunar valves open

Question 6

What occurs just before and during diastole (isovolumetric relaxation)?

Answer 6

Ejection slows as ventricular contraction loses force

When ventricular pressure falls below pressure of outflow vessels, semilunar valves close

Rapid decrease in ventricular pressure without changing volume

Question 7

What aids ventricular filling?

Answer 7

Elastic recoil of ventricle walls

Question 8

What is the dicrotic notch?

Answer 8

Aortic pressure trace dips when aortic valve closes due to brief backflow of blood against valve

Question 9

What percentage of ventricular filling is accounted for by atrial systole?

Answer 9

<20%

Question 10

Why does the atrial pressure increase slightly during systole?

Answer 10

Ventricular contraction causes flexible AV valve to bulge into atrium

Question 11

What does an electrocardiogram do?

Answer 11

Measures electrical activity of heart

Question 12

What are the waves shown on a typical electrocardiogram caused by?

Answer 12

P - atrial depolarisation

QRS complex - ventricular depolarisation

T - ventricular repolarisation

Question 13

Approximately how much time passes between P and R on an ECG?

Answer 13

120ms

Question 14

Approximately how much time passes during the QRS complex on an ECG?

Answer 14

80ms

Question 15

Approximately how much time passes between Q and T on an ECG?

Answer 15

300ms

Question 16

What does a phonocardiogram do?

Answer 16

Measures heart sounds

Question 17

What causes the S1 on a phonocardiogram?

Answer 17

AV valves closing (initiation of ventricular systole)

Question 18

What kind of sound does the closing of the AV valves create?

Answer 18

Low frequency ‘lub’

Question 19

What causes the S2 on a phonocardiogram?

Answer 19

Semilunar valves closing

Question 20

What kind of sound does the closing of the semilunar valves create?

Answer 20

High frequency, short ‘dup’

Question 21

What causes the S3 on a phonocardiogram?

Answer 21

Opening of AV valves and rapid refilling

Question 22

What causes the S4 on a phonocardiogram?

Answer 22

Atrial systole (due to blood flow in) when end diastolic pressure is raised

Question 23

What happens to the heart sounds when end diastolic pressure is raised?

Answer 23

S4 is heard

S3 and S4 give rise to a galloping rhythm

Question 24

What causes heart murmurs?

Answer 24

Turbulent blood flow

Question 25

What causes turbulent flow in the heart?

Answer 25

Increased blood velocity Exercise

Question 26

What can increase blood velocity in the heart?

Answer 26

Stenosis

Question 27

What kind of murmur does mitral stenosis cause?

Answer 27

Diastolic murmur as ventricle fills

Question 28

What kind of murmur does aortic stenosis cause?

Answer 28

Systolic murmur

Question 29

What murmur does mitral valve incompetence cause?

Answer 29

Systolic murmur ("lush" from blood flowing into left atrium during contraction)

Question 30

What murmur does aortic valve incompetence cause?

Answer 30

Early diastolic murmur with softening and prolongation of S2 (blood flows into heart from aorta)

Question 31

How can pulsing veins in the neck show valve incompetence?

Answer 31

Reclining patient sat upright - if pulsing stops then pulse was in jugular vein Incompetence of tricuspid valve

Question 32

What can cause valve incompetence?

Answer 32

Endocarditis

Question 33

What is endocarditis?

Answer 33

Rare life-threatening inflammation of lining of heart muscles/valves

Question 34

What can cause endocarditis?

Answer 34

Bacterial infection during dental procedures Severe gum disease

Question 35

What influences stroke volume?

Answer 35

Energy of ventricular contraction Resistance to outflow from left ventricle/TPR

Question 36

What affects the energy of ventricular contraction?

Answer 36

Preload/filling pressure of right heart which in turn influences diastolic stretch Sympathetic innervation

Question 37

What was the Otto Frank experiment?

Answer 37

Frog hearts connected to a fluid reservoir at varying heights to see effect of filling pressure on contractile force

Question 38

How does filling pressure affect contractile force (relationship)?

Answer 38

Increased filling pressure increases contractile force (and ventricular pressure)

Question 39

What is the Frank-Starling law?

Answer 39

Energy of heart contraction increases as a function of diastolic distention/stretching

Question 40

Why does increased filling pressure increase contractile force?

Answer 40

Increased stretch/distention Increased initial muscle fibre length Increased cross-bridging Increased tension

Question 41

What is the optimal length of a sarcomere to maximise contractile force?

Answer 41

1.75-2.25um

Question 42

Why would overstretching a sarcomere result in no/less tension formed?

Answer 42

Little/no overlap of actin and myosin So little/no cross-bridging

Question 43

Why does heart failure decrease contractile force?

Answer 43

Enlargement of cardiac myocytes and ventricles Inappropriate alignment of actin and myosin

Question 44

How does sympathetic stimulation affect the EDP/stroke volume graph and why?

Answer 44

Upward shift Stimulation affects contractility not EDP/volume entering

Question 45

How will increasing the stroke volume of the left heart affect the stroke volume of the right heart?

Answer 45

Increase as it's a closed/loop system