CVS Revision part -3 Cardiac cycle

                     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