3: The cardiac cycle Flashcards
When do cardiac valves produce a sound?
When they shut (not when they open!)
Give a simple definition of the cardiac cycle.
All the events occuring from the beginning of one heart beat to the beginning of the next
Give a technical definition of the cardiac cycle.
The orderly depolarisations / repolarisations causing atrial / ventricular contractions and relaxations.
Put simply, what happens during diastole?
The heart chambers relax and are filled with blood
Put simply, what happens during systole?
The heart ventricles contact and pump blood into:
a) the aorta
b) the pulmonary artery
How long is diastole compared to systole?
Diastole is about twice as long as systole
Name the five events which take place during the cardiac cycle.
- Passive Filling
- Atrial Contraction
- Isovolumetric Ventricular Contraction
- Ventricular Ejection
- Isovolumetric Ventricular Relaxation
During the passive filling phase, what is the pressure in the atria and ventricles?
Nearly zero
During passive filling, which valves open and what flows into the ventricles?
1) The AV valves (RA tricuspid valve, LA mitral valve)
2) Venous return from the systemic and pulmonary circulations flows into the ventricles
During passive filling, the aortic and pulmonary valves are…
closed.
How full do the ventricles become simply through passive filling?
Around 80% full
Which wave on an ECG signals atrial depolarisation?
P wave
Which interval on an ECG represents the whole of atrial contraction?
PR interval
Which wave(s) on an ECG signal ventricular depolarisation?
QRS complex
When does ventricular contraction start on an ECG?
After the QRS complex
During isovolumetric ventricular contraction, what pressure change occurs in the ventricles?
Ventricular pressure rises
When do the AV valves shut?
When ventricular pressure EXCEEDS atrial pressure
In which phase of the cardiac cycle do the AV valves first shut - why?
Isovolumetric ventricular contraction
Ventricular pressure exceeds atrial pressure - valves shut to prevent backflow of blood into the atria
When is the first heart sound heard in the cardiac cycle - why?
Isovolumetric ventricular contraction - because the AV valves shut
In the isovolumetric ventricular contraction phase, the AV valves shut - what sound does this produce?
First heart sound - LUB
During the isovolumetric ventricular contraction phase, the aortic valve is…
shut.
Why is the ventricular contraction phase “isovolumetric”?
Tension (pressure) increases in a closed volume (the ventricle itself)
In which phase of the cardiac cycle do the aortic / pulmonary valves open?
Ventricular ejection
Is a sound produced when the aortic and pulmonary valves open?
No - silent event
Which volume is ejected by the ventricles during the 4th phase of the cardiac cycle?
Stroke volume
Which volume remains after the stroke volume has been ejected in the 4th phase of the cardiac cycle?
End systolic volume (ESV)
Write an equation for stroke volume.
Stroke volume = end diastolic volume - end systolic volume
What occurs after the ejection of the stroke volume?
Aortic pressure rises
Which wave on an ECG signals ventricular repolarisation?
T wave
After the ejection of blood from the ventricles, when ventricular pressure falls, what happens?
The aortic and pulmonary valves SHUT
Why is the second heart sound produced?
Ventricular pressure falls below aortic pressure and the valves shut
What is the second heart sound and when does it occur?
DUB - at the end of ventricular ejection
When does isovolumetric ventricular relaxation start?
When the aortic/pulmonary valves close
Why is ventricular relaxation “isovolumetric”?
Tension (pressure) falls in a closed volume (the ventricle)
What happens when ventricular pressure falls below atrial pressure during the 5th phase of the cardiac cycle?
AV valves open
When the AV valves open in the 5th phase of the cardiac cycle, is any sound produced?
No - opening of valves is silent
The first heart sound occurs when the AV valves ___ and signals the beginning of ___.
shut , systole
The second heart sound occurs when the aortic / pulmonary valves ___ and signals the beginning of ___.
close , diastole
Where would you place your stethoscope to auscultate the aortic valve?
Right sternal edge, 2nd intercostal space
Where would you place your stethoscope to auscultate the pulmonary valve?
Left sternal edge, 2nd intercostal space
Where would you place your stethoscope to auscultate the mitral valve?
Mid-clavicular line, 5th intercostal space
or wherever the apex beat is in reality
What happens after isovolumetric ventricular contraction?
Passive filling (the heart begins a new cardiac cycle)
What prevents arterial pressure from falling to zero during diastole?
Elastic recoil
