CVS - cardiac cycle Flashcards
What is the role of capacitance vessels?
Enable system to vary amount of blood pumped around the body.
What is the role of resistance vessels?
Restrict blood flow to drive supply to hard to perfuse areas of the body.
Define systole
Contraction and ejection of blood from ventricles
Define diastole
Relaxation and filling of ventricles
Heart muscle is made from discrete cells. How are they electrically interconnected?
Gap junctions (part of intercalated discs along with adherens-type junctions for anchorage of cells and actin filaments).
Cardiac myocyte action potential lasts a relatively long time, so it lasts for the duration of a single heart beat. Approximately how long does it last?
280ms
Which valves are attached to papillary muscles via chordae tendinae? What is the purpose of these structures?
Tricuspid and mitral valves. Prevents inversion of valves on systole.
How long does the AV node delay excitation for?
~120ms
Which direction does ventricular myocardium contract during systole?
- Endocardial to epicaridal
2. Apex to base
What are the 7 stages of the cardiac cycle?
- Atrial contraction
- Isovolumetric contraction
- Rapid ejection
- Reduced ejection
- Isovolumentric relaxation
- Rapid filling
- Reduced filling
Approximately how long is systole?
~0.35s
A Wiggers diagram typically plots which side of the heart?
Left side of the heart
What is meant by end diastolic volume?
It is at the end of atrial contraction when the ventricles containe their maximum volume of blood.
What happens during phase 1 (atrial contraction)?
- Atrial pressure rises due to atrial systole. This is called the “A wave”
- Atrial contraction accounts for final ~10% of ventricular filling (varies with age and exercise)
- P wave in ECG signifies onset of atrial depolarisation
What is a typical end-diastolic volume?
~120ml
What happens during phase 2 (isovolumetric contraction)?
- Mitral valve closes - as ventricular pressure exceeds atrial pressure
- Rapid rise in ventricular pressure as ventricle contracts
- Closing of mitral valve creates the “C wave” in the atrial pressure curve.
Describe the state of the valves in the isovolumetric contraction/relaxation phases
All valves are closed.
What causes S1 - the first heart sound?
Closing of the mitral and tricuspid valves
When does the rapid ejection phase start?
When intraventricular pressure exceeds aortic pressure, causing the aortic valve to open.
What causes the X descent in atrial pressure?
Pulling of the atrial base downwards that occurs as the ventricle contracts.
Whilst rapid ejection is occurring, what else is simultaneously occurring in the atria?
Blood is continuing to flow into the atria from their respective venous inputs.
What causes the rate of ejection to begin to fall and therefore causes phase 4 (reduced ejection)?
Repolarisation of the ventricle which leads to a decline in tension.
What causes the “V wave” of atrial pressure?
Atrial pressure gradually rises due to the continued venous return from the lungs.
What causes the aortic valve to close?
The brief backflow of blood that occurs when intraventricular pressure falls below aortic pressure.
What causes the “dicrotic notch” in aortic pressure?
Closure of the aortic valve
What is end systolic volume (ESV)?
The volume of blood in the ventricles at the end of systole
How do you calculate the stroke volume?
EDV-ESV
What is a typical stroke volume?
~80ml
What is the cause of S2 (the second heart sound)?
Closure of the aortic and pulmonary valves.
What causes the “Y descent” in atrial pressure?
Fall in atrial pressure due to the opening of the mitral valve.
What causes the mitral valve to open and the rapid filling phase to begin?
Fall of intraventricular pressure below that of atrial pressure. This is PASSIVE FILLING of the ventricle, the atria are not contracting.
S3 (third heart sound) is sometimes present. What causes it? When can it be heard?
It’s caused by ventricular filling (though this is normally silent). The S3 sound is normal in children but can be sign of pathology in adults.
What causes ventricular filling to slow down?
Diastasis (slowing down of rate of filling) occurs as the ventricle reaches its inherent relaxed volume. Further filling is driven by venous pressure.
How full are the ventricles (at rest) at the end of phase 7 (the reduced filling phase)?
~90%
