Cardiac Cycle PDF

THE CARDIAC CYCLE 2 Prof. Tarig Hakim Merghani RAKCOMS- RAKMHSU  OBJECTIVES Distinguish the mechanical and electrical events in the cardiac cycle II- VENTRICULAR DIASTOLE - Ventricular relaxation= Reduction in ventricular pressure= closure of semilunar valves= the second heart...

THE CARDIAC CYCLE 2 Prof. Tarig Hakim Merghani RAKCOMS- RAKMHSU  OBJECTIVES Distinguish the mechanical and electrical events in the cardiac cycle II- VENTRICULAR DIASTOLE - Ventricular relaxation= Reduction in ventricular pressure= closure of semilunar valves= the second heart sound (S2). II- VENTRICULAR DIASTOLE a -Isometric relaxation phase. -Ventrilcles relax while all valves are closed= Isovolumetric relaxation -Volume of blood in ventricles= End systolic volume “ESV”= 50 ml II- VENTRICULAR DIASTOLE The aortic dicrotic notch. coincides with closure of the aortic valve II- VENTRICULAR DIASTOLE - Further ventricular relaxation = Further reduction in pressures = Opening of the A-V valves = Filling of the ventricles (= Passive filling, = 70% of End diastolic volume “EDV”) II- VENTRICULAR DIASTOLE - The passive ventricular filling causes the third heart sound (S3) II- VENTRICULAR DIASTOLE - Atrial pressure decreases due to flow of blood into the ventricles. II- VENTRICULAR DIASTOLE  III- ATRIAL SYSTOLE & DIASTOLE -Atrial diastole continues throughout most of the cycle -Allows venous return  III- ATRIAL SYSTOLE - The atria contract to complete ventricular filling (provide 25-30% of the end diastolic volume). - EDV= 120 ml  III- ATRIAL SYSTOLE - Atrial pressure increases due to atrial systole (a wave)  III- ATRIAL SYSTOLE - May cause the4th heart sound (S4) in hypertensive patients (Normally No sound is heard)  A NEW CYCLE -A new ventricular systole raises the ventricular pressure higher than the atrial pressure= -Closure of AV valves -The cycle is repeated PRESSURE VOLUME CURVE