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Understanding the Cardiac Cycle: General Principles and Phases

In this lecture, Prof. Sultan Ayoub Meo explains the general principles of the cardiac cycle and the various events that occur during it, including mechanical, electrical, volume and pressure changes, and heart sounds. By the end of the lecture, students will be able to understand the different phases of the cardiac cycle.

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Understanding the Cardiac Cycle: General Principles and Phases

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  1. CARDIC CYCLE Prof. Sultan Ayoub Meo MBBS, M.Phil, Ph.D (Pak), PG Dip Med Ed, M Med Ed (Scotland) FRCP (London), FRCP (Dublin), FRCP (Glasgow), FRCP (Edinburgh) Professor and Consultant, Department of Physiology, College of Medicine, King Saud University, Riyadh, Saudi Arabia

  2. LECTURE OUTLI NES / OBJECTIVES • General principle of the cardiac cycle • Identify events occurring during cardiac cycle: mechanical, electrical, volume & pressure changes, heart sounds. • Understand the various phases of the cardiac cycle STUDENTS ABLE TO UNDERSTAND:

  3. CARDIAC CYCLE The cardiac events that occur from the beginning of one heart beat to the beginning of the nextis called the cardiac cycle.Cardiac cycle is a complete beat of the heart. Each cycle is initiated by spontaneous generation of an action potential in the sinus node. The cardiac cycle consists of a period of relaxation called diastole during which the heart fills with blood. This period is followed by a period of contraction called systole.

  4. CARDIAC CYCLE: CARDIAC VALVES

  5. CARDIAC CYCLE: CARDIAC VALVES

  6. CARDIAC CYCLE: CARDIAC VALVES

  7. PRESSURES IN THE CARDIAC CHABERS Aortic pressure (left ventricular pressure) Maximum pressure (during systole): 120 mm Hg. Minimum pressure (during dystole): 80 mm Hg. Pulse pressure (difference between systolic and diastolic) : 120-80 = 40 mm Hg. Right ventricular pressure  Maximum pressure = 25mm Hg Minimum pressure = 0-2mm Hg Atrial pressure Maximum right atrial pressure 6-8 mm Hg Minimum right atrial pressure 0-2 mm Hg Maximum left atrial pressure 6-9 mm Hg Minimum left atrial pressure 0-2 mm Hg Pulmonary pressure (mm Hg) Systolic pulmonary arterial pressure: 25 Diastolic pulmonary arterial pressure : 8

  8. CARDIAC CYCLE I. VENTRICULAR SYSTOLE Iso-volumetric contraction of ventricles (0.05 sec ) Maximum ejection phase (0.112sec) Reduced ejection phase. (0.141 sec ) ------------- 0.303 Sec 2. VENTRICULAR DIASTOLE Protodiastole (0. 033 sec) Isovolumetric (isovolumic ) relaxation (0. 071 sec) Rapid inflow (0.110 sec) Reduced inflow (0.161 sec) Atrial systole (0.12 sec ) -------------- 0.495 sec. [0.8 Sec]

  9. CARDIAC CYCLE: DURATION OF SYSTOLE AND DIASTOLE

  10. CARDIAC CYCLE: VENTRICULAR SYSTOLE Isovolumetric contraction: The left ventricle begins to contract, at this stage the pressure in the ventricles is slightly above 0-2mm Hg. As the intra-ventricular pressure rises, it pushes the cusps of the A-V valve up and the A-V orifices are closed. The pressure in the ventricular cavities continues to rise but remains less than that in the large arteries. Thus, the semilunar valves (aortic and pulmonary) also remain closed and no blood enters or leaves the ventricles.

  11. CARDIAC CYCLE: VENTRICULAR SYSTOLE

  12. CARDIAC CYCLE: VENTRICULAR SYSTOLE • MAXIMUM EJECTION PHASE:The ventricles contract and increase the pressure more than in the large arteries. • The left ventricular pressure rises up to 120 mm Hg causes the opening of the aortic valves • Right ventiricular presssure rises more than 25 mm Hg and causes the opening of pulmonary valves so blood leaves the ventricles rapidly to the aorta and pulmonary artery • At the end of this stage, intraventricular pressure reaches its peak level.

  13. CARDIAC CYCLE: VENTRICULAR SYSTOLE • REDUCED EJECTION PHASE • In this phase of the cardiac cycle, the force of contraction of the ventricles becomes weaker than the force of contraction during the maximum ejection phase. Now the pressure within the ventricles also decreases, but is still higher than that of the aorta so ventricular emptying continues. • In this phase less volume of blood flows into the aorta and pulmonary artery due to weaker contraction of the ventricles.

  14. CARDIAC CYCLE: VENTRICULAR SYSTOLE

  15. CARDIAC CYCLE: VENTRICULAR SYSTOLE

  16. CARDIAC CYCLE: VENTRICULAR DIASTOLE • VENTRICULAR DIASTOLE [PROTO DIASTOLE] • In this stage, the ventricles relax and the intraventricular pressure decreases, becoming less than the aortic and pulmonary artery pressures. • Blood present in the aorta and pulmonary artery tends to move back into the ventricles. • At this stage the semilunar valves ( aortic and pulmonary ) are closed and do not allow entry of blood into the ventricles

  17. CARDIAC CYCLE: VENTRICULAR DIASTOLE • ISOVOLUMETRIC RELAXATION • In this stage the ventricles relax further and intraventricular pressure falls. • The semilunar valves remain closed due to higher pressure in the large arteries as compared to intraventricular pressure. • The pressure within the ventricles is still higher than the atria, so the A-V valves remain closed and no blood enters or leaves the ventricles.

  18. CARDIAC CYCLE: VENTRICULAR DIASTOLE

  19. CARDIAC CYCLE: VENTRICULAR DIASTOLE RAPID INFLOW The ventricular volume increases, the pressure within the ventricles is further decreased to lower than intra atrial pressure. The left ventricular pressure decreases up to 2-4 mm Hg. This pressure is less than the maximum left atrial pressure (6-9mm Hg). This change in pressure causes the opening of left AV (biscuspid / mitral) valve. So blood which was accumulate in the left atrium rush into the left ventricle.

  20. CARDIAC CYCLE: VENTRICULAR DIASTOLE RAPID INFLOW Right ventricular pressure decreased up to 0-2mm Hg. This pressure is less than the maximum right atrial pressure (6-8mm Hg). This change in pressure causes the opening of right AV (tricuspid) valve. So the blood which was accumulate in the right atrium rush into the right ventricle.

  21. CARDIAC CYCLE: VENTRICULAR DIASTOLE

  22. CARDIAC CYCLE

  23. CARDIAC CYCLE: VENTRICULAR DIASTOLE Reduced inflow At the beginning of this phase most of the blood has already entered the ventricles. Remaining blood in the atria also flows into the ventricles. Atrial systole Once again the atrial muscle fibers start to contract, indicating the beginning of a new cardiac cycle.

  24. SUMMARY CARDIAC CYCLE EVENTS: OPENING AND CLSOSING OF VAVLVES

  25. CARDIAC CYCLE: ASSOCIATION WITH HEART SOUNDS

  26. CARDIAC CYCLE: ASSOCIATION WITH HEART SOUNDS

  27. CARDIAC CYCLE: ASSOCIATION WITH HEART SOUNDS

  28. CARDIAC CYCLE: ASSOCIATION WITH HEART SOUNDS 1 st Heart Sound 2 nd Heart Sound 3 rd Heart Sound 4 th Heart Sound HEART SOUNDS

  29. CARDIAC CYCLE: ASSOCIATION WITH HEART SOUNDS 1 st Heart Sound 2 nd Heart Sound Maximum ejection period Reduced ejection period Isovolumetric contraction period Ventricular Systole

  30. CARDIAC CYCLE: ASSOCIATION WITH HEART SOUNDS 3 rd HS 2 nd HS 4 th HS Reduced Filling Phase Maximum Filling Phase Isovolumetric Relaxation Phase 1 st HS Ventricular Diastole

  31. TAKE HOME MESSAGE Beginning of one heart beat to the beginning of the next is called the cardiac cycle. consists of a period of relaxation called diastole followed by a period of contraction called systole. Cycle duration is 0.8 Sec [Systole 0.3 sec and Diastole 0.5 Sec]

  32. THANK YOU College of Medicine, King Khalid University Hospital, King Saud University, Riyadh, Saudi Arabia

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