Cardiac cycle Flashcards
What is dystole?
Lasts approximately 2/3 of each beat
Ventricular relaxation
The ventricles fill with blood ( from atriums into ventricles on both right and left )
What is systole?
Lasts approximately 1/3 of each beat
Ventricular contraction
Ventricles generate pressure then eject blood into the arteries ( aorta and pulmonary )
How many phases is diastole split into?
4
How many phases is systole split into?
3
How to calculate stroke volume?
end diastolic Volume - End systolic volume
What are the phases on Diastole?
Isovolumetric relaxation –> rapid passive filling –> slow passive filling –> atrial systole
What is the end systolic volume?
Amount of blood in heart after contraction is completed - residual volume
What is end diastolic volume?
The maximum volume of blood in the heart just before the ventricles start to contract. So at maximum relaxation
What are the phases of systole?
Isovolumetric contraction –> rapid ejection –> slow ejection
How to calculate Ejection fraction?
( Stroke volume / End-diastolic volume ) x 100
Normal range of Ejection fraction?
52-72 %
- clinical indicator of heart function
What is the Mitral valve?
Bicuspid valve - left side of heart between atrium and ventricle
What on the ECG signifies the start of atrial systole?
P-wave
Why do the atria contract?
To ‘top up’ the volume of blood in the ventricle so there is more than what is passively filled.
- Atrial contribution to ventricular filling varies inversely with the duration of diastolic period. e.g. when diastolic interval is small the ventricular filling is aided by atrial contraction
What may a 4th heart sound be?
abnormal = congestive heart failure, pulmonary embolism, valve incompetence. ( heard during atrial systole )
What on the ECG signifies the start of ventricular depolarisation?
QRS complex
What is the isovolumetric contraction interval?
Interval between AV valves closing and semi-lunar opening
What is the contraction of ventricles with no change of volume?
Isovolumetric contraction
Because both valves have closed
But pressure of ventricles increase to the extent of aortic pressure
What is the 1st heart sound attributed to?
‘lub’
closure of AV valves and their vibrations
What marks the start of rapid ejection?
Opening of aortic and pulmonary valves.
= ejection begins when intraventricular pressure exceed aorta and pulmonary arteries. Causing valves to open
- as blood is pumped out ventricular volume falls
Is there a heart sound for rapid ejection?
No - valves opening doesn’t cause sound
When is maximum blood velocity reached in the ejection phase
Very early on
What does reduced ejection represent?
The end of the systole, T wave on the ECG = ventricular repolarisation occuring
What does the ventricular repolarisation do?
Decline in ventricular active tension and pressure. So rate of ejection and ventricular emptying falls.
As this falls aortic and pulmonary valves close. and blood flow slows.
What causes the semi-lunar valves to close
As pressure in ventricles falls below arterial pressure, blood begins t flow back closing the valves.
What causes the second heart sound?
‘dub’
closure of semilunar valves
What happens to the AV valves when the aortic and pulmonary valves shut?
( isovolumetric relaxation )
Remain closed until ventricular pressure drops below atrial pressure * volume does not change
What is the dichrotic notch?
Caused by rebound pressure against aortic valve as distended aortal wall relaxes, increasing aortic pressure for a few msecs before lowering.
- notice on graph
What on the ECG signifies the rapid passive filling?
No electrical activity : flat area after T wave
What occurs during rapid passive filling?
AV valves open and blood flows from atrium to ventricles
What may a 3rd heart sound be?
usually abnormal and may signify turbulent ventricular filling
Can be due to severe hypertension or mitral incompetence
What is Reduced passive filling?
Also known as diastasis
Ventricular volume fills more slowly. To a considerable amount before atrial contraction.
- End of diastole
The patterns of pressure changes in the right heart are ( x ) to those of the left
Identical
The pressure in the right heart and pulmonary circulation are ( x ) than left
Much lower
- despite lower pressure right ventricles ejects same volume of blood as left
What does measuring pulmonary capillary wedge pressure give a clinical measurement of?
Left atrial pressure
- Gives an idea of left ventrical failure and mitral valve stenosis. These are due to increase in left atrial pressure. This tends to lead to increased pulmonary oedema
Why cannot we put a catheter in the left atrium to measure its pressure?
Although left ventricular pressure can be directly measured by placing a catheter within the left ventricle, it is not feasible to advance this catheter back into the left atrium.
Referring to pressure volume loops; what happens when aortic pressure is encountered?
Left ventricular volume decreases and this is represented by the top curve towards end-systolic volume
Referring to pressure loops, what does a larger preload do?
More blood moved into the L ventricle so more stretch occurs. And pressure increases ( larger Y axis value ) towards afterload.
The blood pressure in the aorta represent the preload or afterload?
Afterload
Affects of increased afterload?
less shortening of muscle fibres and so less able to expel blood from ventricles.
When afterload increases, there is an increase in end-systolic volume and a decrease in stroke volume.
Because a greater pressure is required to open the aortic valve.
- slide 21
What is the ESPVR?
End systolic PV line.
maximal pressure that can be developed by the ventricle at any given volume
Increases in preload result in what change in stroke volume?
Increases ( Frank-starling relationship )
Venous return increase = left ventricular volume increase
How to calculate cardiac output?
Heart rate x Stroke volume
Stroke volume affected by preload, afterload and contractility.
What is Contractility?
strength of contraction of the heart
Increased by: Sympathetic stimulation
Extrinsic mechanism: Changes Ca2+ delivery to myofilaments
Cardiac contractility affects ( x ) of the Frank starling relationship?
Steepness
Can produce a ‘family’ of ESPVR lines
As contractility increases, ESPVR lines?
Increase steepness
Generates more force due to more calcium to myofilaments and vice versa
During exercise, an (a) in end systolic volume and (b) in end diastolic volume leads to a (c) stroke volume
a - decrease
b - increase
c - greater
What can happen to the end diastolic volume is heart rate is increased a lot?
Can lower it because less time is spent filling during diastole
