2. The cardiac cycle Flashcards
What are the 7 phases of the cardiac cycle? Which phases constitute systole and diastole?
- atrial contraction
Systole:
- isovolumetric contraction
- rapid ejection
- reduced ejection
Diastole:
- isovolumetric relaxation
- rapid filling
- reduced filling
How long do the cardiac cycle, systole and diastole last?
- Cardiac cycle = 0.9 secs (at 67 beats/min)
- Systole = 0.35 secs
- Diastole = 0.55 secs
How will the length of systole and diastole change when heart rate increases?
Systole will always stay the same, diastole shortens.
What is a Wiggers diagram?
Measures changes in volume and pressure in the left side of the heart over time.
Describe the atrial pressure, ventricular pressure and ventricular volume during phase 1 (atrial contraction).
Which valves are open/closed?
- Mitral/tricuspid valves are open, aortic/pulmonary valves are closed.
- Increased atrial pressure (due to atrial systole) = A wave.
- Low ventricular pressure.
- Maximal ventricular volume (120 ml) = End-Diastolic Volume (EDV) as atrial contraction accounts for final 10% of ventricular filling.
Describe the atrial pressure, ventricular pressure and ventricular volume during phase 2 (isovolumetric contraction).
Which valves are open/closed?
- All valves are closed.
- Slight increase in atrial pressure = C wave (due to closing of mitral valve).
- Rapid increase in ventricular pressure (ventricular systole).
- No change in ventricular volume (120 ml) as all valves closed = isovolumetric.
Describe the atrial pressure, ventricular pressure and ventricular volume during phase 3 (rapid ejection).
Which valves are open/closed?
- Mitral/tricuspid valves closed, aortic/pulmonary valves open.
- Atrial pressure initially decreases (as atrial base is pulled downwards as ventricle contracts) = X descent.
- Increasing, high ventricular pressure (systole).
- Rapid decrease in ventricular volume (as blood is ejected into aorta).
Describe the atrial pressure, ventricular pressure and ventricular volume during phase 4 (reduced ejection).
Which valves are open/closed?
- Mitral/tricuspid valves closed, aortic/pulmonary valves open.
- Atrial pressure gradually rises (due to continued venous return from the lungs) = V wave.
- Decreasing (but still high) ventricular pressure.
- Continued decrease in ventricular volume.
Describe the atrial pressure, ventricular pressure and ventricular volume during phase 5 (isovolumetric relaxation).
Which valves are open/closed?
- All valves are closed.
- “Dicrotic notch” in aortic pressure curve (due to valve closure).
- Rapid decline in ventricular pressure.
- Ventricular volume remains constant = End Systolic Volume.
Describe the atrial pressure, ventricular pressure and ventricular volume during phase 6 (rapid filling).
Which valves are open/closed?
- Mitral/tricuspid valves open, aoritic/pulmonary valves closed.
- Fall in atrial pressure (after opening of mitral valve) = Y-descent.
- Continued decline in ventricular pressure.
- Increase in ventricular volume (as ventricular pressure falls bellow atrial pressure).
Describe the atrial pressure, ventricular pressure and ventricular volume during phase 7 (reduced filling).
Which valves are open/closed?
- Mitral/tricuspid valves open, aoritic/pulmonary valves closed.
- No change in atrial pressure.
- No change in ventricular pressure.
- Small increase in ventricular volume (but rate of filling decreases as ventricle reaches inherent relaxed volume).
When do S1 and S2 occur, and what causes these sounds?
S1 (start of systole) = closure of mitral and tricuspid valves.
S2 (start of diastole) = closure of aortic and pulmonary valves.
What is S3?
Sound associated with ventricular filling.
S3 is normal in children but can be sign of pathology in adults.
What is diastasis?
The slowing of ventricular filling in phase 7 as ventricles reaches its inherent relaxed volume.
How full do ventricles get by the end of phase 7 (reduced filling)? what causes ventricular filling?
- 90% full by end of phase 7 at rest.
- Filling caused first by intraventricular pressure falling below atrial pressure in phase 6 (rapid filling).
- Further filling driven by venous pressure in phase 7.
