Cardiac Cycle PDF

THE CARDIAC CYCLE 1 Prof. Tarig Hakim Merghani RAKCOMS- RAKMHSU  OBJECTIVES Distinguish the mechanical and electrical events in the cardiac cycle  THE CARDIAC CYCLE = The events that occur during one cardiac beat (systole & diastole) THE CARDIAC CYCLE Takes about 0.8 s (60/75...

THE CARDIAC CYCLE 1 Prof. Tarig Hakim Merghani RAKCOMS- RAKMHSU  OBJECTIVES Distinguish the mechanical and electrical events in the cardiac cycle  THE CARDIAC CYCLE = The events that occur during one cardiac beat (systole & diastole) THE CARDIAC CYCLE Takes about 0.8 s (60/75)  THE CARDIAC CYCLE The cardiac cycle can be divided into: Ventricular systole (0.3 s) Ventricular diastole (0.5 s) Atrial systole (0.1s) & diastole (0.7s) (occurring during the same 0.8 sec) THE CARDIAC CYCLE  I- VENTRICULAR SYSTOLE - Ventricular contraction= Immediate closure of the AV valves - First heart sound (S1)  I- VENTRICULAR SYSTOLE Isometric contraction phase : - The ventricles continue to contract isometrically while the 4 valves are closed.  I- VENTRICULAR SYSTOLE - Atrial pressure is increased (c wave)  I- VENTRICULAR SYSTOLE - Sudden opening of the semilunar valves (at 80 or 10 mmHg) - Rapid ejection  I- VENTRICULAR SYSTOLE Pressures continue to rise (Reach a max 120 or 25 mmHg)  I- VENTRICULAR SYSTOLE The volume ejected from each ventricle = stroke volume =70 ml  I- VENTRICULAR SYSTOLE Atrial pressure decreases (when the ventricles shorten with contraction) then gradually increases (due to venous return)  I- VENTRICULAR SYSTOLE Aortic & pulmonary pressures increase (due to ejection of blood)  I- VENTRICULAR SYSTOLE -About 50 ml remain in each ventricle = End systolic volume “ESV”  I- VENTRICULAR SYSTOLE Atrial pressure is still increasing (v wave). II- VENTRICULAR DIASTOLE - Ventricular relaxation= Reduction in ventricular pressure= closure of semilunar valves= the second heart sound (S2).