Cardiac Cycle PDF

physiology department ‫جامعــة البيضـــــاء‬ D. hamidaddin Mohamed ‫كلية الطب والعلوم الصحية رداع‬ ‫ح‬ „ CARDIOVASCULAR SYSTEM  cardiac cycle  Cardiac cycle is defined as th...

physiology department ‫جامعــة البيضـــــاء‬ D. hamidaddin Mohamed ‫كلية الطب والعلوم الصحية رداع‬ ‫ح‬ „ CARDIOVASCULAR SYSTEM  cardiac cycle  Cardiac cycle is defined as the succession of (sequence of) coordinated events taking place in the heart during each beat  Each heartbeat consists of two major periods called systole and diastole EVENTS OF CARDIAC CYCLE  Events of cardiac cycle are classified into two:  1. Atrial events 2.Ventricular events 1. „ ATRIAL EVENTS 1. Atrial systole = 0.11 (0.1) sec 2. Atrial diastole = 0.69 (0.7) sec 2. VENTRICULAR EVENTS 1. Ventricular systole = 0.27 (0.3) sec 2. Ventricular diastole = 0.53 (0.5) sec.  Ventricular systole is divided into two subdivisions and ventricular diastole is divided into five subdivisions. 1   Ventricular Systole Time (second) 1. Isometric contraction = 0.05 2. Ejection period = 0.22 total time =0.27  Ventricular Diastole 1. Protodiastole = 0.04 2. Isometric relaxation = 0.08 3. Rapid filling = 0.11 4. Slow filling = 0.19 5. Last rapid filling = 0.11 total time 0.53  atrial systole occurs during the last phase of ventricular diastole  Atrial diastole is not considered as a separate phase, since it coincides with the whole of ventricular systole and earlier part of ventricular diastole. ATRIAL EVENTES 1. ATREIAL SYSTOLE  known as last rapid filling phase or presystole. It is usually considered as the last phase of ventricular diastole. Its duration is 0.11 second.  During this period only a small amount, i.e. 10% of blood is forced from atria into ventricles 2   During atrial systole, the intra-atrial pressure increases. Intraventricular pressure and ventricular volume also increase but slightly 2. ATRIAL DIASTOLE  Simultaneously, ventricular systole also start lasts for about 0.7 sec  This long atrial diastole is necessary because, this is the period during which atrial filling takes place Atrial Events Vs Ventricular Events  Out of 0.7 sec of atrial diastole, first 0.3 sec coincides with ventricular systole  Then, ventricular diastole starts and it lasts for about 0.5 sec  Later part of atrial diastole coincides with ventricular diastole for about 0.4 sec.  So, the heart relaxes as a whole for 0.4 sec „ DESCRIPTION OF VENTRICULAR EVENTS  „ ISOMETRIC CONTRACTION PERIOD OR called (also called isovolumetric contraction.)  is the first phase of ventricular systole. It lasts for 0.05 second  characterized by increase in tension, without any change in the length of muscle fibers 3   Immediately after atrial systole, the atrioventricular valves are closed due to increase in ventricular pressure.  Semilunar valves are already closed. Now, ventricles contract as closed cavities, in such a way that there is no change in the volume of ventricular chambers or in the length of muscle fibers  Only the tension increases in ventricular musculature.  Because of increased tension in ventricular musculature during isometric contraction, the pressure increases sharply inside the ventricles.  Closure of atrioventricular valves at the beginning of this phase produces first heart sound. „ EJECTION PERIOD is 0.22 second  Due to the opening of semilunar valves and isotonic contraction of ventricles, blood is ejected out of both the ventricles  Ejection period is of two stages: a) First Stage or Rapid Ejection Period large amount of blood is rapidly ejected from both the ventricles. It lasts for 0.13 second. b) the blood is ejected slowly with much less force. Duration of this period is 0.09 second  End-systolic Volume Amount of blood remaining in ventricles at the end of ejection period (i.e. at the end of systole) is called endsystolic volume. It is 60 to 80 mL per ventricle 4  Ejection fraction  refers to the blood fraction (or portion) of end diastolic volume that is ejected out by each ventricle per beat.  From 130 to 150 mL of end-diastolic volume, 70 mL is ejected out by each ventricle (stroke volume).  Normal ejection fraction is 60% to 65%.  Ejection fraction is the measure of left ventricular function.  Clinically, it is considered as an important index for assessing the ventricular contractility.  Ejection fraction decreases in myocardial infarction and cardiomyopathy.  5