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Heart as a pump

Heart as a pump. Cardiac cycle . Phase1. Atrial systole: AV valves open; aortic and pulmonic valves closed. Heart as a pump. Cardiac cycle . Phase2. Isvolumetric contraction: all valves closed. Heart as a pump. Cardiac cycle . Phase3. Rapid ejection: Pulmonic valves open

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Heart as a pump

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  1. Heart as a pump Cardiac cycle Phase1. Atrial systole: AV valves open; aortic and pulmonic valves closed

  2. Heart as a pump Cardiac cycle Phase2. Isvolumetric contraction: all valves closed

  3. Heart as a pump Cardiac cycle Phase3. Rapid ejection: Pulmonic valves open AV valves closed

  4. Heart as a pump Cardiac cycle Phase4. Reduced ejection: Pulmonic valves open AV valves closed

  5. Heart as a pump Cardiac cycle Phase5. Isvolumetric relaxation All valves closed

  6. Heart as a pump Cardiac cycle Phase 6: Rapid filling: AV valves open Semilunar valves closed

  7. Heart as a pump Cardiac cycle Phase7. Reduced filling: AV valves open; aortic And pulmonic valves closed

  8. Heart as a pump

  9. Heart as a pump Summary of intracardiac pressures

  10. Heart as a pump At heart rates up to about 180, filling is adequate as long as there is ample venous return

  11. Heart as a pump Preload • Preload is the initial stretching of the cardiac myocytes prior to contraction.

  12. Heart as a pump Factors Determining Ventricular Preload • Pulmonic valve stenosis • Pulmonary Hypertension Tricuspid valve stenosis

  13. Heart as a pump Plays an important role in balancing the output of the two ventricles. Frank-Starling Mechanism ventricular function curve

  14. Heart as a pump Frank-Starling Mechanism

  15. Heart as a pump What mechanisms are responsible for the increase in force generation with increased preload in the heart? • length-dependent activation. • The intact heart under physiologic conditions operates at sarcomere lengths in the range of 1.8–2.2 • Experimental evidence supports three possible explanations: • Increased sensitization of troponin C to calcium • Change in calcium homeostasis within the cell • Closer of myosin molecules to each other

  16. Heart as a pump • Afterload

  17. Heart as a pump • Inotropy

  18. Heart as a pump • Inotropy

  19. Factors Increasing Myocardial Oxygen Consumption • ↑ Heart Rate • ↑ Inotropy • ↑ Afterload • ↑ Preload* Changes in preload affect oxygen consumption much less than do changes in the other factors Increasing the end-diastolic volume by 50% (by a factor of 1.5) represents only a 14% (cube root of 1.5) increase in wall stress at a given ventricular pressure, whereas a 50% increase in pressure increases wall stress by 50%.

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