Cardiac cycle physiology_4_dpt

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Cardiac cycle

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  • 2. Need functional syncitium so all contracting at same time
  • Cardiac cycle physiology_4_dpt

    1. 1. Cardiac Cycle By Mubin Mustafa Kiyani
    2. 2. Cardiac cycle
    3. 3. The Conducting System • Heartbeat – A single contraction of the heart – The entire heart contracts in series • First the atria • Then the ventricles
    4. 4. The Conducting System • Structures of the Conducting System – Sinoatrial (SA) node - wall of right atrium – Atrioventricular (AV) node - junction between atria and ventricles – Conducting cells - throughout myocardium
    5. 5. The Conducting System • Conducting Cells – Interconnect SA and AV nodes – Distribute stimulus through myocardium – In the atrium • Internodal pathways – In the ventricles • AV bundle and the bundle branches
    6. 6. The Conducting System Figure : The Conducting System of the Heart
    7. 7. The Conducting System • Heart Rate – SA node generates 80–100 action potentials per minute – AV node generates 40–60 action potentials per minute
    8. 8. The Conducting System • The Sinoatrial (SA) Node – In posterior wall of right atrium – Contains pacemaker cells – Connected to AV node by internodal pathways – Begins atrial activation (Step 1)
    9. 9. The Conducting System Figure : Impulse Conduction through the Heart
    10. 10. The Conducting System • The Atrioventricular (AV) Node – In floor of right atrium – Receives impulse from SA node (Step 2) – Delays impulse (Step 3) – Atrial contraction begins
    11. 11. The Conducting System Figure: Impulse Conduction through the Heart
    12. 12. The Conducting System Figure: Impulse Conduction through the Heart
    13. 13. The Conducting System • The AV Bundle – In the septum – Carries impulse to left and right bundle branches • Which conduct to Purkinje fibers (Step 4) – And to the moderator band • Which conducts to papillary muscles
    14. 14. The Conducting System Figure: Impulse Conduction through the Heart
    15. 15. The Conducting System • Purkinje Fibers – Distribute impulse through ventricles (Step 5) – Atrial contraction is completed – Ventricular contraction begins
    16. 16. The Conducting System Figure: Impulse Conduction through the Heart
    17. 17. An Overview of Cardiac Physiology
    18. 18. Cardiac Cycle The cardiac events that occur from the beginning of one heartbeat to the beginning of the next are called the cardiac cycle.
    19. 19. • The cardiac cycle consists: – Period of relaxation - diastole, • during which the heart fills with blood, – Followed by a period of contraction called systole. • during which heart ejects blood
    20. 20. Cardiac Cycle • During systole there is contraction of the cardiac muscle and pumping of blood from the heart through arteries. • During diastole, there is relaxation of cardiac muscle and filling of blood. • Various changes occur in different chambers of heart during each heartbeat. These changes are repeated during every heartbeat in a cyclic manner. • Each cycle is initiated by spontaneous generation of action potential in the S.A node.
    21. 21. Divisions of cardiac cycle • 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. • The contraction and relaxation of atria are called atrial systole and atrial diastole respectively. • The contraction and relaxation of ventricles are called ventricular systole and ventricular diastole respectively.
    22. 22. Requirements for Efficient Cardiac Contraction 1. Atrial excitation and contraction need to be complete before ventricular contraction occurs. 2. Excitation of cardiac muscle fibers should be coordinated so that each chamber contracts as a unit. 3. Pair of atria and pair of ventricles should be coordinated so that both members of the pair contract simultaneously.
    23. 23. Cardiac cycle • First assembled by Lewis in 1920 but first conceived by Wiggers in 1915 • It is named after Dr. Carl J. Wiggers, M.D. • A Wiggers diagram is a standard diagram used in cardiac physiology • The X axis is used to plot time, while the Y axis contains all of the following on a single grid: • Blood pressure Aortic pressure Ventricular pressure Atrial pressure • Ventricular volume • Electrocardiogram • Arterial flow (optional) • Heart sounds (optional)
    24. 24. Wiggers diagram
    25. 25. Phases of Cardiac cycle 1. Atrial systole 2. Isovolumic contraction 3. Ejection 4. Isovolumic relaxation 5. Rapid inflow 6. Diastasis
    26. 26. Phases of the Cardiac Cycle Figure 20.16
    27. 27. The Cardiac Cycle • Cardiac Cycle and Heart Rate – At 75 beats per minute • Cardiac cycle lasts about 800 msecs – When heart rate increases • All phases of cardiac cycle shorten, particularly diastole
    28. 28. The Cardiac Cycle Figure 20–17 Pressure and Volume Relationships in the Cardiac Cycle Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
    29. 29. The Cardiac Cycle Eight Steps in the Cardiac Cycle 1. Atrial systole • Atrial contraction begins • Right and left AV valves are open 1. Atria eject blood into ventricles • Filling ventricles 3. Atrial systole ends • AV valves close • Ventricles contain maximum blood volume • Known as end-diastolic volume (EDV)
    30. 30. The Cardiac Cycle Eight Steps in the Cardiac Cycle 4. Ventricular systole • Isovolumetric ventricular contraction • Pressure in ventricles rises • AV valves shut 5. Ventricular ejection • Semilunar valves open • Blood flows into pulmonary and aortic trunks • Stroke volume (SV) = 60% of end-diastolic volume
    31. 31. The Cardiac Cycle Eight Steps in the Cardiac Cycle 6. Ventricular pressure falls • Semilunar valves close • Ventricles contain end-systolic volume (ESV), about 40% of enddiastolic volume 7. Ventricular diastole • Ventricular pressure is higher than atrial pressure • All heart valves are closed • Ventricles relax (isovolumetric relaxation)
    32. 32. The Cardiac Cycle Eight Steps in the Cardiac Cycle 8. Atrial pressure is higher than ventricular pressure • AV valves open • Passive atrial filling • Passive ventricular filling • Cardiac cycle ends
    33. 33. Pressure changes in the atria • a, c and v atrial pressure waves are noted in atria • The ‘a’ wave is caused by the atrial contraction, during right atrial contraction pressure increases 4-6 mm of Hg, while in left atrium it is 7-8 mm of Hg. • The ‘c’ wave occur when the ventricles begin to contract, it is caused partially by slight back flow of blood when there is ventricular contraction, but mainly by bulging the A-V valves backward toward the atria because of increasing pressure in ventricles • The ‘v’ wave occur toward the end of ventricular contraction, this is caused by the slow flow of blood from great veins while the A-V valves are closed, when A-V valves opens allowing the store blood into ventricle this ‘v’ wave disappear.
    34. 34. Wiggers diagram
    35. 35. Summary: Pathway of Heartbeat • Begins in the sinoatrial (S-A) node • Internodal pathway to atrioventricular (A-V) node • Impulse delayed in A-V node (allows atria to contract before ventricles) • A-V bundle takes impulse into ventricles • Left and right bundles of Purkinje fibers take impulses to all parts of ventricles KEY Red = specialized cells; all else = contractile cells
    36. 36. Impulse Conduction through the Heart
    37. 37. Time Intervals Total ventricular systole 0.3 sec • Isovolumic contraction (b) 0.05 sec (0.015sec for RV) • Maximal ejection (c) 0.1 sec • Reduced ejection (d) 0.15 sec Total ventricular diastole 0.5 sec • Isovolumic relaxation (e) 0.1 sec • Rapid filling phase (f) 0.1 sec • Slow filling (diastasis) (g) 0.2 sec • Atrial systole or booster (a) 0.1 sec GRAND TOTAL (Syst+Diast) = 0.8 sec
    38. 38. Cardiac cycle

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