Cardiac cycle
Coordinated sequence of events which culminates in ejection of blood from ventricles
Each cycle - periods of chamber contraction, blood expelled - systole, periods of myocardial relaxation, chamber refills - diastole
Phases of cardiac cycle:
Phase of the Cardiac Cycle | Mitral and Tricuspid Valve Position | Aortic and Pulmonary Valve Position | Cardiac Chamber Physiology |
|---|---|---|---|
Atrial systole | Open | Closed | Atria contract, blood is pumped into the ventricles |
Isovolumetric ventricular contraction | Closed | Closed | Ventricular volumes unchanged, but ventricles begin to contract, resulting in rapid rise in ventricular pressures |
Ventricular systole (ejection) | Closed | Open | Ventricles contract fully and eject blood into the aorta and pulmonary artery |
Isovolumetric ventricular relaxation | Closed | Closed | Ventricular volumes unchanged, ventricles relax. Rapid decrease in ventricular pressures. The atria are filling (atrial diastole) |
Ventricular diastole (ventricular filling) | Open | Closed | Ventricles relaxed and passively fill with blood from the atria. Atrial contraction signals return to phase 1 of the cycle |
Pressure-volume loop:
LV diastole - ventricle fills passively when mitral valve opens, ventricle relaxes and distends so volume increases but pressure falls, small rise in p and v occurs at end of diastole when atrium contracts
LV systole - pressure due to Isovolumetric contraction when aortic valve still closed
Opening of aortic valve and ventricular ejection leads to decrease in volume, pressure falls abruptly when aortic valve closes to do Isovolumetric relaxation, loop returns to original position