cardiac cycle.ppt and events occurring during cardiac cyclex
- 2. FUCTIONAL ANATOMY OF CARDIAC MUSCLE Cardiac muscle is excitable Cardiac muscle requires calcium in extra cellular fluid to contract Cardiac muscle is contractile Cardiac impulses conducts electrical impulses,(have intercalated discs to allow better conduction) Cardiac muscle is a syncytium .
- 3. The all and none law applies to entire syncytium .(A stimulus greater or equal to threshold stimulus when applied results in contraction of entire syncytium. The action potential in cardiac muscle is prolonged and has a long refractory period. Cardiac muscle have autorhythmicity (self - excitatory )
- 4. Cardiac muscle contraction is dependent on the initial length of fiber. (Frank – starling’s law of the heart and concepts of preload and after load .) Cardiac muscle does not fatigue.
- 6. Conducting system of heart Consists of Sinoatrial node (SAN Pacemaker of the heart ) Internodal pathways( tract of thorel, wenckeback and tract of Bachman) Atrioventricular node(AVN) Right and left bundle branches Purkinje fibers.
- 8. CARDIAC CYCLE DEFINITION: The electrical and mechanical cardiac events that occur from the beginning of one heartbeat to next are called the cardiac cycle. Cardiac cycle consists of 1 systole and 1 diastole. Cardiac cycle duration is reciprocal of heartbeat ie,1/72=0.013 min or 0.8 sec.
- 9. Events occurring in each cardiac cycle Atrial systole Atrial diastole Ventricular systole Ventricular diastole Ventricular systole is merged with atrial diastole. ventricular diastole is merged with atrial systole. Hence, each cardiac cycle has 1 systole and 1 diastole.
- 10. Events occurring during ventricular systole and ventricular diastole Ventricular diastole 1. Isovolumetric relaxation 2. Rapid passive ventricular filling phase 3. Slow passive ventricular filling phase 4. Atrial contraction
- 11. Atrial systole This event starts at the end period of ventricular diastole. When ventricular pressure falls lower to atrial pressure Opening of atrio –ventricular valves Period Of Rapid Filling Period Of Rapid Filling Lasts For First Third Of Ventricular Diastole ( 80 % Of Filling) During Middle Third Only A Small Amount Of Blood Flows Into Ventricles Slow Filling Of Ventricles During Last Third Of Ventricular Diastole Atria Contracts causing 20% Of Ventricular Filling
- 12. Events occurring during atrial contraction Its corresponds to the last part of ventricular relaxation. Pressure changes- Atria –a wave produced due to an increase in atrial pressure Ventricles –pressure increases Volume changes: In ventricles increases. ECG changes: contraction is preceded by p wave Heart sound- beginning of atrial contraction –gush of blood into ventricles causes S4
- 13. VENTRICULAR SYSTOLE:- 1. Period of isovolumetric contraction Electrical impulse reaches ventricles through AVN. Ventricular contraction Ventricular pressure increases Atrio ventricular valve closes Production of first heart sounds S1 The atrioventricular valve bulges into atria .(formation of pressure wave “c” in atria )
- 14. More contraction of ventricles leads to increases in pressure. (from 5-80 mmhg in left ventricles & from 2-8 mmhg in right ventricles ) During this phase contraction occurs but there is no emptying Hence known as isovolumetric contraction As soon as the pressure increases more than 80mmhg in left ventricle and 8mmhg in right ventricle. Opening of semilunar valves (aortic and pulmonary valve)
- 15. Major events Pressure changes : ventricle - 0-80 mmhg in left ventricle 0-8 mmhg in right ventricle Atria - C wave produced in atrium due to bulging of AV valves Volume change-remains same Heart sounds –S1 ECG changes –peak of QRS starting of isovolumetric contraction.
- 16. 2. Period of ejection rapid and passive ejection: When left ventricular pressure increases >80 mmhg and > 8 mmhg in right ventricle Semi lunar valves open Rapid blood flow into aorta and pulmonary trunk (70% of ejection occurs in this phase) Pressures from ventricles transferred to aorta and pulmonary arteries. Pressure decreases after reaching its max (120mmhg – aorta,25mmhg –pulmonary arteries) Period of passive ejection (30%of blood ejection occurs in this phase )
- 17. Events occurring in Periods of rapid and passive ejection: Pressure changes: In ventricles - from 80-120 mmhg in left ventricle,8- 25mmhg in right ventricles, and same pressures transferred to aorta and pulmonary veins ) In atria’s v wave is produced. Volume changes: Blood volume in ventricles decreases. ECG: Rapid ejection –ST Segment. passive ejection – t wave beginning.
- 18. VENTRICULAR DIASTOLE 1.ISOVOLUMETRIC RELAXATION Starting of repolarisation and End of systole Ventricles begin to relax Intraventricular pressure decreases Elevated pressure in great arteries that have just been filled with blood, pushes blood back towards the ventricles Snaps the aortic and pulmonary valves close & S2 heart sound produced
- 19. For another 0.03 -0.06 sec ventricles continue to relax Volume does not change hence known as isovolumetric relaxation
- 20. Isovolumetric relaxation events Pressure: ventricles- decreases. Atria- remain increases (v wave produced) Volume: remains same, end-systolic volume -50 ml in left ventricle. ECG: T wave continuation. Heart sounds - S2 heart sounds produced at the beginning of ventricular diastole
- 21. protodiastole This brief period during which backflow of blood is associated with closure of aorta and pulmonary valves is called proto- diastole.
- 22. Rapid passive ventricular filling As soon as left ventricular pressure falls below left atrial pressure, mitral valve opens The blood that accumulated in atria during ventricular systole Rapidly enters into the ventricles as soon as AV valve opens Rapid ventricular filling occurs 3rd heart sound produced
- 23. Slow passive ventricular filling Filling of ventricles occurs slowly Pressure: Atria –decreases. Ventricles –decreases Volume: Atria –decreases. Ventricles- increases. Heart sound produced- S4, at the end of this phase due to atrial contraction and force blood into ventricles.
- 24. Pressure –volume loop Introduced by SIR JAMES MACKENZIE Divided into 4 phases 1. PERIOD OF FILLING 2. ISOVOLUMETRIC CONTRACTION 3. PERIOD OF EJECTION 4. ISOVOLUMETRIC RELAXATION .
- 25. Image Reference: Guyton & Hall Textbook of Physiology
- 26. WIGGERS DIAGRAM
- 27. THANK YOU !