The Cardiac Cycle Flashcards
What is cardiac systole?
Contraction of the heart
What is cardiac diastole?
Relaxation of the heart
How long does diastole last?
2/3rds of each beat
How long does systole last?
1/3 of each beat
How many stages is diastole split into?
4
How many stages is systole split into?
3
How many distinct stages of the cardiac cycle are there?
7
What are the names of the 7 distinct stages of the cardiac cycle?
Atrial Systole
Isovolumetric contraction
Rapid ejection
Reduced ejection
Isovolumetric relaxation
Rapid passive filling
Reduced passive filling
What happens during ventricular relaxation?
The ventricles fill with blood
What happens during ventricular contraction?
The ventricles generate pressure and then eject the blood into the arteries
What is the end diastolic volume?
The volume of blood in the ventricles just before systole
What is the end systolic volume?
The volume of blood that remains in the ventricles after systole has occurred
What is the stroke volume in relation to EDV and ESV?
The stroke volume is the EDV - ESV
This is because the stroke volume is the amount of blood which is ejected from the ventricles with each contraction of the heart
What are the common figures for EDV, ESV and SV?
EDV = 120 ml
ESV = 50 ml
Therefore stroke volume = 70ml
What is the ejection fraction?
The (SV / EDV ) x 100
What is the normal range for the ejection fraction?
50-70%
What happens to the ejection fraction during heart failure?
The ejection fraction decreases to about 30%
How is the ejection fraction used clinically?
It is used to assess the degree of heart failure a patient may have
Where is the tricuspid valve located?
Between the right atrium and right ventricle
Where is the bicuspid or mitral valve located?
Between the left atrium and the left ventricle
Where is the pulmonary valve located?
Between the right ventricle and the pulmonary artery
Where is the aortic valve located?
Between the left ventricle and the aorta
What is atrial systole?
Contraction of the atria to top up the volume of blood in the ventricle
What wave on the ECG correlates with atrial systole?
P wave
What might be heard during atrial systole?
An abnormal heart sound due to valve incompetence of the atrioventricular valves (tricuspid)
In what conditions might a sound be heard during atrial systole?
Congestive heart failure, pulmonary embolism or tricuspid incompetence
What does the QRS complex symbolize?
Depolarization of the ventricular muscle
What is isovolumetric contraction?
When there is contraction of the ventricles to build pressure (isometric contraction), but no change in the volume of blood in the ventricles
What heart sound is heard during isovolumetric contraction?
Lub
What is the status of the AV and SL valves during isovolumetric contraction?
They are all closed
What causes the first heart sound, “lub”?
The closure of the AV valves
What marks the start of the rapid ejection phase?
The opening of the SL valves
What happens during the rapid ejection phase?
The ventricular pressure is larger than the aortic pressure, (overcomes the afterload) meaning the blood pushes against the aortic valve and pushes out the ventricle
What type of muscle contraction occurs during rapid ejection stage of cardiac cycle?
Isotonic contraction
What happens to the pressure in the ventricles during reduced ejection stage?
The ventricular pressure starts to fall
What phase marks the end of systole?
Reduced ejection
What causes the SL valves to start to close in the reduced ejection phase?
The reduced pressure gradient
What happens to the calcium during the reduced ejection phase?
The calcium is being pumped back into the extracellular space, out the cell, causing the calcium levels to fall back to diastolic calcium levels
What part of the ECG represents reduced ejection?
T wave
What happens when the ventricular pressure is less than aortic pressure?
The semilunar valves close to prevent the back flow of blood
What happens to the ventricular pressure during isovolumetric relaxation?
Large decrease
What happens to atrial pressure during isovolumetric relaxation?
It continues to rise
What causes the dichrotic notch seen on the ECG?
Rebound pressure against the aortic valve as distended aortic wall relaxes
What causes the second heart sound “dub”?
The complete closure of the SL valves
What happens during the rapid passive filling phase?
The AV valves open and so blood from the atria flows into the ventricles, resulting in a large increase in ventricular volume
What might a sound heard during rapid passive filling signify?
Turbulent ventricular filling, hypertension or mitral incompetance
What is the abnormal S3 sound called?
Ventricular gallop
What is diastasis?
Reduced passive filling phase
What happens to ventricular volume during reduced passive filling?
The ventricles fill slowly with blood, without the contraction of the atria
What is the relationship between the pressure change patterns in the right and the left of the heart?
They are identical
Which side of the heart has quantitively a higher pressure?
The left side has a higher pressure
Which side of the heart pumps more blood?
They pump the same amount
What is the average blood pressure in the systemic circuit?
Let side of the heart pumps blood to body - 120/80
What is the average blood pressure in the pulmonary circuit?
Right side of the body pumps deoxygenated blood to the lungs - 25/5 mmHg
What is the pressure of the atria relative to the ventricle?
The pressure in the right atrium is significantly lower than the right ventricle
How are pressure volume loops used clinically?
They are used to assess contractility
What do the A,B,C AND D points on a pressure volume loop relate to?
A = End Diastolic volume, preload
B = when the ventricle encounters the Afterload
C = End systolic volume
D = ventricular pressure has dropped as blood is pumped out the heart
What happens to the stroke volume if you increase the preload?
Increasing the stretch, means that the length of the muscle fibers increase, which increases the force (due to more Ca2+ sensitivity), so more blood can be expelled with each beat of the heart
What happens to stroke volume when you increase the afterload?
If you increase the pressure which the ventricles face, the fibers cannot shorten as much as there is a heavy weight acting against them, so the stroke volume decreases
If you increase the afterload, what happens to the amount of shortening the muscle fibres undergo?
They shorten less
What does the End Systolic PV line show?
The maximal pressure that can be developed by the ventricle at any given volume
What happens to the pressure volume loop when you increase preload?
Points A and B shift to the right, which increases the stroke volume due to an increase in venous return
Why does an increase in preload also increase the SV?
More stretch on the muscle due to more venous return changes their sensitivity to Ca2+ so more cross bridges can form which increases the force of contraction, hence SV increases as more blood can then be expelled per beat
Describe what happens to the pressure volume loop when there is an increase in afterload?
Points C and D shift to the right
Point C also rises
How do you calculate cardiac output?
Cardiac output = stroke volume x heart rate
What three factors does stroke volume depend on?
Preload, afterload and contractility
What is contractility?
The contractile capability of the heart
What happens to the ESPVR line when contractility is increased?
It gets steeper = more Ca2+ is delivered to the myofilaments so for a smaller stretch there is more force produced
What happens to the ESPVR line when there is a decrease in contractility?
Less Ca2+ to myofilaments, therefore less force is produced as fewer cross bridges are formed
What increases the contractility?
Sympathetic stimulation
What factors increase venous return?
Muscle and Respiratory pump
What happens when the myocytes are sympathetically activated?
The ventricular contractility increases which decreases the end systolic volume so stroke volume increases
What happens to atrial pressure during exercise? And what affect does this have on the afterload?
It increases, and increases afterload as well
What happens if the HR increases to very high rates?
The diastolic filling time can be reduced, which increases EDV
What is the end systolic volume?
The volume of blood that remains in the heart even after the ventricle has contracted fully
What are the two mechanisms by which the SA node rate is increased sympathetically?
- Hormonal - adrenaline
- Neural - noradrenaline from nerves
What affect does hardening of the aortic valve have on the afterload?
Increases the afterload
