Mechanical events of the cardiac cycle

Question 1

cardiac cycle

Answer 1

recurring atrial and ventricular contractions and relaxations

Question 2

systole

Answer 2

ventricular contraction and blood ejection

Question 3

diastole

Answer 3

alternating period of ventricular relaxation and blood filling

Question 4

how long does the cardiac cycle last?

Answer 4

for typical rate of 72 beats/min

0.8 sec - 0.3 in systole and 0.5 in diastole

Question 5

2 parts of systole

Answer 5

isovolumetric ventricular contraction

ventricular ejection

Question 6

isovolumetric ventricular contraction

Answer 6

ventricles are contracting but all valves in the heart are closed, so no blood is ejected. atria are relaxed

ventricular walls are developing tension and squeezing on blood, increasing ventricular blood pressure

ventricular muscle fibres can’t shorten because volume of blood is constant and blood is incompressible

Question 7

ventricular ejection

Answer 7

increasing pressure in the ventricles exceeds pressure in the aorta and pulmonary trunk - aortic and pulmonary valves open. blood is forced into the aorta and pulmonary trunk.
ventricular muscle fibres shorten
atria are relaxed and AV valves are closed

Question 8

what is the stroke volume?

Answer 8

volume of blood ejected from each ventricle during systole

Question 9

parts of diastole

Answer 9

isovolumetric ventricular relaxation

ventricular filling

Question 10

isovolumetric ventricular relaxation

Answer 10

ventricles begin to relax and aortic and pulmonary valves close
AV valves are closed, no blood is entering or leaving the ventricles
atria are relaxed

Question 11

ventricular filling

Answer 11

AV valves open, blood flows in from the atria
after most of ventricular filling, the atria contract
approx. 80% of ventricular filling occurs before atrial contraction

Question 12

mid-diastole to late diastole: 1

Answer 12

left atrium and ventricle are both relaxed

atrial pressure slightly higher than ventricular pressure because it’s filled with blood entering from the veins

Question 13

mid-diastole to late diastole: 2

Answer 13

AV valve held open by the pressure difference, and blood entering the atrium from the pulmonary veins continues into the ventricles

Question 14

mid-diastole to late diastole: 3

Answer 14

aortic valve is closed because aortic pressure is higher than the ventricular pressure

Question 15

mid-diastole to late diastole: 4

Answer 15

throughout diastole, pressure in the aorta is slowly decreasing because blood is moving out of the arteries and through the vascular system

Question 16

mid-diastole to late diastole: 5

Answer 16

ventricular pressure is increasing slightly due to blood entering relaxed ventricle from the atrium and expanding ventricular volume

Question 17

mid-diastole to late diastole: 6

Answer 17

near the end of diastole, the SA node discharges and the atria depolarise

Question 18

mid-diastole to late diastole: 7

Answer 18

contraction of the atrium increases atrial pressure

Question 19

mid-diastole to late diastole: 8

Answer 19

elevated atrial pressure forces a small additional volume of blood into the ventricle (atrial kick)

Question 20

mid-diastole to late diastole: 9

Answer 20

end of ventricular diastole

amount of blood in ventricle is the end-diastolic volume

Question 21

systole: 10

Answer 21

from the AV node, the wave of depolarisation passes into and throughout ventricular tissue, triggering contraction (QRS complex)

Question 22

systole: 11

Answer 22

as ventricle contracts, the ventricular pressure increases immediately, exceeding the atrial pressure

Question 23

systole: 12

Answer 23

change in pressure gradient forces AV valve to close, preventing blood from flowing back into the atria

Question 24

systole: 13

Answer 24

aortic pressure still exceeds ventricular pressure, so the aortic valve is closed.
isovolumetric ventricular contraction
backward bulging of the AV valves causes a small upward deflection in the atrial pressure wave

Question 25

systole: 14

Answer 25

rapidly increasing ventricular pressure exceeds aortic pressure

Question 26

systole: 15

Answer 26

pressure gradient forces aortic valve to open, and ventricular ejection begins

Question 27

systole: 16

Answer 27

ejection is rapid at first, then slows down

Question 28

systole: 17

Answer 28

amount of blood remaining in ventricle after ejection is the end systolic volume

Question 29

stroke volume and typical values

Answer 29

edv - esv sv = 70 mL edv = 135 mL esv = 65 mL

Question 30

systole: 18

Answer 30

aortic pressure increases with the ventricular pressure as blood flows into the aorta very small pressure changes exist between the ventricles and aorta due to the aortic valve having little resistance to flow

Question 31

systole: 19

Answer 31

peak ventricular and aortic pressures are reached before the end of ventricular ejection start to decrease in last part despite continued contraction

Question 32

systole: 20

Answer 32

force reduction evidenced by reduced rate of blood ejection in last part of systole

Question 33

systole: 21

Answer 33

volume and pressure in the aorta decreases as the rate of blood ejection from the ventricles becomes slower than the rate at which blood drains from arteries into tissues

Question 34

early diastole: 23

Answer 34

ventricles relax. ventricular pressure decreases below aortic pressure (elevated due to blood having entered). change in pressure gradient forces aortic valve to close. AV valves also closed due to ventricles having higher pressure than atria

Question 35

what is the dichrotic notch

Answer 35

combination of elastic recoil of the aorta and blood rebounding against the valve causes a rebound of aortic pressure

Question 36

early diastole: 24

Answer 36

isovolumetric ventricular relaxation. ends when rapidly decreasing ventricular pressure decreases below atrial pressure

Question 37

early diastole: 25

Answer 37

change in pressure gradient causes AV valve to open

Question 38

early diastole: 26

Answer 38

venous blood that accumulated in the atria since the AV valve closed flows into the ventricles

Question 39

how is the rate of blood flow enhanced in early filling?

Answer 39

rapid decrease in ventricular pressure

Question 40

what is the rapid decrease in ventricular pressure caused by?

Answer 40

previous contraction compressed elastic elements of the chamber so ventricle tends to recoil outward after systole may create subatmospheric pressure some energy is stored within the myocardium during contraction, and its release in relaxation aids filling

Question 41

importance of filling occurring in early diastole

Answer 41

ensures filling is not impaired when heart beats very rapidly - total filling time reduced

Question 42

early filling and conduction defects

Answer 42

conduction defects eliminating atria as effective pumps don't seriously impair ventricular filling

Question 43

atrial fibrillation

Answer 43

cells of atria contract in uncoordinated manner, so atria don't work as effective pumps

Question 44

pressure changes in pulmonary circulation

Answer 44

qualitatively similar | quantitative differences

Question 45

systemic arterial pressures vs pulmonary arterial pressures

Answer 45

systemic arterial systolic (120mmHg) and diastolic (80mmHg) | pulmonary arterial systolic (25mmHg) and diastolic (10mmHg)

Question 46

how are heart sounds heard?

Answer 46

stethoscope placed on chest wall

Question 47

first and second sounds and their associations

Answer 47

1st: soft, low-pitched lub - closure of AV valves 2nd: louder dup - closure of pulmonary and aortic valves lub is onset of systole dup is onset of diastole

Question 48

what do heart sounds result from?

Answer 48

vibrations caused by the closing valves

Question 49

heart murmurs

Answer 49

sounds other than 2 normal heart sounds

Question 50

what can heart murmurs be caused by?

Answer 50

heart defects causing blood flow to be turbulent

Question 51

laminar flow

Answer 51

blood flows in smooth concentric layers

Question 52

turbulent flow causes

Answer 52

stenosis insufficiency septal defect

Question 53

what is stenosis?

Answer 53

blood flowing in usual direction through an abnormally narrowed valve

Question 54

what is insufficiency?

Answer 54

blood flowing backwards through a damaged, leaky valve

Question 55

what is a septal defect?

Answer 55

blood flowing between 2 atria or 2 ventricles through a small hole in the wall separating them

Question 56

murmur heard throughout systole

Answer 56

suggests stenotic pulmonary or aortic valve, insufficient AV valve or hole in interventricular septum

Question 57

murmur heard throughout diastole

Answer 57

stenotic AV valve or insufficient pulmonary or aortic valve