cardiac cycle

Question 1

how many phases is each heart beat split into

Answer 1

2

Question 2

what is diastole and how long does it last

Answer 2

ventricular relaxation
lasts 2/3 of each heart beat
and is split into 4 distinct phases

Question 3

what is systole and how long does it last

Answer 3

ventricular contraction
lasts approx 1/3 of each heart beat
split into 3 distinct phases

Question 4

what is isovolumetric contraction

Answer 4

heart is exerting pressure on the end diastolic volume

Question 5

what is end diastolic volume

Answer 5

volume present at maximum filling of the heart

Question 6

what is end systolic volume

Answer 6

not all blood is ejected from the heart - some blood remains at the end of systole

Question 7

what is stroke volume

Answer 7

the difference between end diastolic and end systolic

Question 8

equation for stroke volume

Answer 8

end diastolic - end systolic

Question 9

how do you calculate ejection fraction

Answer 9

stroke volume / end diastolic x 100

Question 10

what is the normal range for ejection fraction

Answer 10

52-72%

Question 11

what happens in bad heart failure

Answer 11

low ejection fraction > contractility of the ventricle is decreased
heart cannot sustain enough cardiac output for the needs of the body
used clinically to address degrees of failure of the heart

Question 12

STEPS for what happens in atrial systole

Answer 12

contraction of the atria (already blood in the ventricles)
1) the P wave starts the process off
2) atria is stimulated by the pacemaker potential fired off by the SAN (excites atrial muscle cells and depolarisation excites atrial cells)
(P wave on ECG signifies start of atrial systole)
3) atria are already almost full from passive filling driven by pressure gradient
4) atria contract to “top up” volume of blood in ventricle

Question 13

what is the 4th heart sound

Answer 13

abnormal, valve incompetence (leaky blood) - occurs with congestive heart failure, pulmonary embolism or tricuspid incompetence

Question 14

STEPS for isovolumetric contraction

Answer 14

QRS complex - signifies depolarisation of ventricular muscle > activates the muscles (allows Ca influx into cells > calcium release from SR > Ca dumped into cytosol and activates myofilaments and produce contraction)
2) ventricles start to contract against closed valves (2 semi lunar and pulmonary and aortic valves are closed)
3) QRS complex marks the start of ventricular depolarisation (this is the interval between AV valves - tricuspid and bicuspid/mitral - closing and semilunar valves - pulmonary and aortic - opening)
4) ventricular volume doesn’t change - but build up in ventricular pressure
5) contraction of ventricles with no change in volume = isometric
1st heart sound (lub) due to closure of AV valves and associated vibrations

Question 15

STEPS for rapid ejection

Answer 15

signifies ventricular pressure overcomes back pressure/diastolic blood pressure in the aorta and the blood pushes against aortic valve which opens and flows out of the ventricle > decreases volume
2) contraction has moved from isometric to isotonic (shortening of muscle fibres > efflux of blood from both ventricles)
3) opening of the aortic and pulmonary valves marks the start of this phase
4) as ventricles contract, pressure within them exceeds pressure in aorta and pulmonary arteries
5) semi lunar valves open, blood pumped out and the volumes of ventricles decrease (isotonic contraction)
no heart sounds

Question 16

what are heart sounds associated with

Answer 16

closing of a valve

Question 17

STEPS for reduced ejection

Answer 17

pressure and volume fall
2) ventricular pressure falls and aortic pressure falls too
3) contraction is subsiding and calcium is being pumped into SR into stores and effluxed outside of cells
4) cells start to relax > repolarisation of the cell
T wave on ECG
5) ventricular repolarisation - marking the end of systole
6) reduced pressure gradient means aortic and pulmonary valves begin to close
7) blood flow from ventricles and ventricular volume decreases more slowly
8) as pressure in ventricles fall below than in arteries, blood begins to flow back causing semi lunar valves to close
9) ventricular muscle cells repolarise producing T wave

Question 18

STEPS for isovolumetric relaxation

Answer 18

pressure in ventricle decreases but volume remains unchanged
2) closure of aortic and pulmonary valves give rise to heart sound s2
3) aortic and pulmonary valves shut but the AV valves remain closed until ventricular pressure drops below atrial pressure
4) atrial pressure continues to rise, dichrotic notch (green line) caused by rebound pressure as distended aortic wall relaxes
2nd heart sound “dub” due to closure of semi lunar valves and associated vibrations

Question 19

STEPS for rapid passive filling and _ heart sound?

Answer 19

valves from atria to ventricle open
2) blood moves passively from the left and right atria into the ventricles
3) increases ventricular volume
4) no excitation
5) ventricles are repolarised
6) passive filling
7) occurs during isoelectric (flat) ECG between cardiac cycles
8) once AV valves open, blood in atria flows rapidly into the ventricles
3rd heart sound - usually abnormal and may signify turbulent ventricular filling
can be due to severe hypertension or mitral incompetence

Question 20

STEPS for reduced passive filling

Answer 20

phase can also be called diastasis

2) ventricular volume fills more slowly
3) the ventricles are able to fill considerably without the contraction of the atria

Question 21

describe pulmonary circuit pressures

Answer 21

• the pattern of pressure changes in the right heart are essentially identical to those of the left heart
  quantitatively - pressure in right heart and pulmonary circulation = much lower but even despite this - ejects same volume as the left heart
  IT IS SIMPLY PUMPING THE SAME QUANTITY OF BLOOD INTO A LOWER PRESSURE CIRCUIT

Question 22

describe pressure volume loops

Answer 22

a) ventricles are completely full of blood - topped up by atrial contraction - volume is high and pressure is low
b) ventricles contract - generates pressure but no change in volume (ventricular pressure overcomes that back pressure/afterload in the aorta) - aortic valve opens and volume decreases
c) end systolic volume - volume is decreased but high pressure until aortic valve closes again
d) drop in pressure

Question 23

what determines the preload that stretches the resting ventricular muscle

Answer 23

blood filling the ventricles during diastole

Question 24

what represents the afterload

Answer 24

the blood pressure in great vessels (aorta and pulmonary artery)

Question 25

describe the F-S relationship

Answer 25

stretch muscle fibres > change sensitivity to calcium > change crossbridge amount they can form > increases force of contraction

Question 26

what does increasing afterload do to muscle fibres

Answer 26

they don’t shorten as much > greater aortic pressure > decreased stroke volume

Question 27

what is end systolic pressure volume relationship

Answer 27

the maximal pressure that can be developed by the ventricle at any given volume

Question 28

what is the Frank Starling relationship

Answer 28

increases in preload results in increased stroke volume

Question 29

what does increasing afterload do to stroke volume

Answer 29

increases in afterload results in decreased stroke volume

amount of shortening decreases as working against increased afterload - greater pressure requires to open aortic valve

Question 30

what is the equation for cardiac output

Answer 30

cardiac output = heart rate x stroke volume

Question 31

what is stroke volume affected by

Answer 31

preload
afterload
contractility (contractile capability of the heart) increased by sympathetic stimulation of the heart

Question 32

what happens as contractility changes in terms of F-S relationship

Answer 32

increase contractility > more Ca delivered to myofilaments = more force produces
decrease contractility > less calcium > more stretch needed to produce the same force

Question 33

what happens to PV loops during exercise

Answer 33

1) increased venous return aided by muscle and respiratory pump increases EDV (end diastolic volume)
2) main factor - sympathetic activation of the myocytes increases ventricular contractility - decreases end systolic volume
3) the increase in arterial pressure that occurs during exercise increases afterload (and can lessen the reduction in end systolic volume but offset by large increase in conractility)
4) combination of increased cardiac contractility and increased venous return generates increased stroke volume and (ejection fraction)

Question 34

what can happen if HR increases to a high rate

Answer 34

diastolic filling time can be reduced and this decreases EDV

Question 35

what does hardening of the aortic valve do

Answer 35

reduces flow and increases afterload

Question 36

what does acute blood loss do

Answer 36

loss of blood reduces venous return which decreases preload

Question 37

summary of what exercise does (PV loop)

Answer 37

venous return increases due to venoconstriction and skeletal muscle pump, and contractility is increased via sympathetic nervous system

Question 38

does hardening/stenosis of the pulmonary valve change afterload

Answer 38

yes but it does not affect preload

Question 39

what is the longest phase of the cardiac cycle

Answer 39

reduced passive filling