Cardiac cycle

Cardiac cycle

1. Systole

   • Time period is 0.3 secs 
   • Atrium
     • s4 can be heard due to inrush of blood into the ventricles (pathological )
     • Atrial depolarization Blood flows from atrium to ventricles( Contribute to the 20% of active ventricle filling) , AV valves are open but the semilunar valves are closed ,Pressure increases increases in the atrium , volume increases in the ventricles, Aortic pressure remains constant
       • Time period is 0.1 sec input : right - SVC, IVC, Coronary            left - pulmonary vessels  pumping : Atrium  Output : ventricles R ( DO2)                ventricles L ( O2)
   • ventricles
     • Isovolumetric contraction
       • Rapid ejection
         • Reduced ejection
           • 30% blood empty in this phase . End systolic volume is left . ventricular and aortic pressure decreases
             • Dicrotic notch is shown in the aortic pressure curve  V pressure wave in atrial pressure curve due to slow filling of blood in atrium T wave start from this phase 
         • The pressure increase pushes the semilunar valve open and blood begins to pour out into aorta and pulmonary trunk . 70% flows during this phase
           • Atrial pressure gives C pressure wave due to bulging of Av valves in the atrium .  The ventricular & Aortic pressure increases and the decrease 
       • Ventricle depolarization ,Atrial repolarization, AV valves close due to increase in ventricular pressure and semilunar valves remain close so there is no entry or exit of blood. This led to rapid increase of ventricular pressure . This end with opening of semilunar valves
         • AV closure creates S1 sound  Input : Atrium this repolarize and works as a tank  pumping : ventricles  pressure increase with first led to closure of AV valves and then opening of semilunar valves  output : Aorta & Pulmonary trunk  elastic property of vessel pushes the blood to the peripheral vessel trunk 

2. diastole

   • Atrium
     • This is the longest phase of 0.7 secs . It overlap with ventricular systole and diastole . there is filling of blood from SVC,IVC in right atrium(DO2) and pulmonary veins in left atrium(O2). the atrium act as a tank. the AV valves are closed . volume increases atrium
   • Ventricles
     • isovolumetric relaxation
       • Closure of the Semilunar valves produce S2. aortic pressure decreases due to runoff blood from aorta to peripheral arterial tree  ventricular pressure decreases expansion .  the atrial pressure shows a v wave due to slow filling of atrium 
       • Rapid filling (passive)
         • s3 due to rapid rush of blood into the ventricles 
         • Diastasis
           • reduced active filling
             • Atrial repolarization starts . this is due to atrial contraction. the end diastolic volume act as preload in ventricular . EDV right = left
           • the atrium no longer act as a tank . there is no change in the ventricle and atrial pressure . slow increase in the ventricular volume
         • Ventricles expand and ventricle and atrial pressure drops. blood quickly enters
       • Elastic recoil and expansion cause the pressure in ventricles to decreases rapidly and sucking the blood . this led to closure of the semilunar valves . this ends with the opening of AV valves
         • protodiastole : brief period during which there is a brief backflow of blood associated with the semilunar valve closure

3. Blood flows from high pressure to low pressure

4. Pressure is inversely proportional to volume

5. Both the phases happens together in the right and left side

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