CVS Revision part -3 Cardiac cycle
Mechanical events in the cardiac cycle
1.Late diastole
2.Atrial systole
3.Ventricular systole
a.Isometric ventricular contraction
b.Ventricular Ejection
4. Early diastole
a.protodiastole
b.Isovolumetric ventricular relaxation
Late diastole
- Atrioventricular valves opened, aortic and pulmonary are closed
- Blood flow into heart fills both atria and ventricles
- Rate of filling declines as ventricles distend
- The cusps of the AV valves drift towards closure
- Pressure remains low
- 70 % of filling occur
Atrial systole
- Atrial musculature contracts and propels additional blood to ventricles
- Opening of SVC, IVC and pulmonary veins narrows , but some regurgitation occurs
Ventricular systole
a.
Isovolumetric ventricular contraction (0.05 S)
- AV values closed
- Ventricular musculature shortens relatively little
- Pressure rises sharply until it exceeds the pressure in the aorta and pulmonary trunk
- AV value bulges towards atria, increasing atrial pressure
b.
Ventricular ejection
- Ventricular pressure has now exceeded aortic and pulmonary arterial pressure
- So, semilunar valves open and ejection begins
- Rapid at first. Slow down late
- AV valves are pulled down by the contraction of ventricular muscle and atrial pressure drops
- Inter- ventricular pressure rises to its maximum and decline somewhat until it reaches the end of ventricular systole
- Amount of blood ejected approximately 70 ml
4. Early diastole
a.Protodiastole ( 0.04 S )
- Ventricular muscle is fully contracted
- Already falling ventricular pressure drops more rapidly
- In ends when the momentum of ejected blood is overcome
- Semilunar valves close marking the end of ventricular systole
b.Isovolumetric ventricular relaxation
- Both AV and semilunar valves are closed
- Pressure in ventricles continues to drop rapidly
- Atria in diastole are filling and atrial pressure increases
- Ends when ventricular pressure falls below atrial pressure and AV valves open, permitting ventricles to fill
Rapid ventricular filling
- Once AV node valves open, blood accumulated in atria rapidly into the ventricles.
- Rate decrease as ventricles fills
Timing of events in cardiac cycles
- Similar on both sides, but take place at different times
- Right atrium starts to contract before the left
- Right ventricular starts to contract after the left
- However the pulmonary arterial pressure is lower than aortic pressure, So
- Right ventricular ejection begins before left ventricular ejection
- Resistance of the pulmonary vascular tree becomes lower in inspiration, so
- Pulmonary and aortic valves close almost at the same time during expiration
- But, aortic valve close before pulmonary valve at inspiration
- When measured over a period of time, the outputs of two ventricles are equal
Labels: CVS, CVS Revision, Revision