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Cardiac Output

Cardiac Output

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Cardiac Output

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  1. Cardiac Output

  2. Which Hearts Are Healthy?

  3. End-diastolic volume Stroke volume Left Ventricle Volume (ml) End-systolic volume Stroke Volume?

  4. A B C D E Heart Rate (beats/min) 88 159 81 70 75 Stroke Volume (ml) 92 100 67 79 70 Cardiac Output (L/min) 8.1 15.9 5.4 5.5 5.3 Cardiac Output? HR X SV

  5. What determines the stroke volume? • Preload: how stretched the muscle is when it starts to contract. • Afterload: the active stress the muscle has to generate in order to shorten • Contractility: something else, but what?

  6. fulcrum Preload

  7. The effect of changing preload highest preload lowest preload

  8. Afterload

  9. The effect of changing afterload

  10. Positive inotropism = contractility Normal Negative inotropism = contractility Contractility

  11. Cellular Mechanism of Preload Effect on Strength of Contraction Length sensitivity of cardiac and skeletal muscle result from different mechanisms.

  12. Myosin Heads ThinFilament 1.0 µm Length sensitivity of skeletal muscle Thick Filament 1.6 µm 0.2 µm Optimum Overlap

  13. Length sensitivity of cardiac muscle Skeletal Cardiac

  14. Stretch Muscle How does preload affect force of cardiac muscle contraction? Muscle Length Force of Contraction Cytoplasmic [Ca++] Force of Contraction

  15. Length Sensitivity of Cardiac Muscle • Increased Ca++ entry through Ca++L channels Ca++ • Increased sensitivity of troponin C to Ca++ Troponin Complex Myosin Head Myosin Binding Site

  16. Preload Afterload& Contractilityin the Working Heart

  17. mmHg kPa 16 120 12 80 End-diastolic LV pressure Pressure 8 40 4 0 0 Left Ventricle Volume (ml) 150 100 50 End-diastolic LV volume 0 Preload depends on end-diastolic LV pressure and volume

  18. Preload depends on end-diastolic LV pressure and volume

  19. Right atrial pressure as a measure of preload PRA Systole Diastole

  20. Starling’s Law of the Heart Ventricular Function Curve The inflow equals the output

  21. Increased afterload LV Systolic ejection pressure shorter ejection time reduced stroke volume Afterload depends on systolic ejection pressure mmHg kPa 16 120 12 80 Pressure 8 40 4 0 0 Left Ventricle Volume (ml) 150 100 50 0

  22. mmHg kPa 16 120 12 80 LV Systolic ejection pressure Pressure 8 40 4 0 0 Afterload depends on systolic ejection pressure

  23. Contractility • Anything that influences stroke volume without acting through preload or afterload • Sympathetic Nervous System • Health of Heart Muscle • Coronary Perfusion • Drugs

  24. Contractility “Squeezability”: How tightly can the ventricle squeeze by the end of ejection.

  25. phosphorylates L-type Ca++ channel phosphorylates SR Ca++ ATPase to increase Ca++ reuptake ß-adrenoceptor influence on contractility phosphorylates troponin to desensitize actin Enhanced Relaxation Enhanced Contraction

  26. EKG Pressure Aortic Left ventricular Left ventricular volume Sympathetic Effect on the Heart

  27. Stroke Volume Ejection Fraction = End-Diastolic Volume Measuring ContractilityA. Ejection Fraction Volume Left Ventricle 150 (ml) 100 Stroke Volume End-Diastolic LV Volume 50 0 End-Systolic LV Volume

  28. Stroke Volume Ejection Fraction = End-Diastolic Volume Measuring ContractilityA. Ejection Fraction

  29. mmHg kPa 16 120 12 Slope = LV dP/dt 80 Pressure 8 40 4 0 0 Left Ventricle Volume (ml) 150 100 50 0 Measuring ContractilityB. LV dP/dt Max

  30. A B C D E LV dP/dT 1225 1700 900 1233 1209 Measuring ContractilityB. LV dP/dt Max

  31. Increased contractility Decreased contractility Measuring ContractilityC. Ventricular Function Curve 16 12 Cardiac 8 Output (liters/min) 4 0 0 4 8 12 (mm Hg) (kPa) 0 1 2 Right Atrial Pressure

  32. 100 50 0 Measuring ContractilityC. Ventricular Function Curve B A D Stroke E C Volume (ml) (mm Hg) 0 8 16 3 0 1 2 Left Atrial Pressure (kPa)

  33. Measuring Contractility • Ejection Fraction • LV dP/dt max • Ventricular Function Curve • Maximal Systolic Elastance

  34. Diastolic Pressure-Volume Curve Left Ventricular Pressure Left Ventricular Volume (ml)

  35. Eccentric (dilated) Normal Stiff Ventricle Diastolic dysfunction Pressure Overload Px r stress = 2h stress = P xr 2h Hypertrophy of Left Ventricle Left Ventricular Pressure Left Ventricular Volume (ml)

  36. End-systolic Pressure Volume Curve Left Ventricular Pressure End-systolic (contracted myocardium) mm Hg kPa 40 300 30 200 20 Diastolic (relaxed myocardium) 100 10 0 0 0 50 100 150 200 Left Ventricular Volume (ml)

  37. elastance The “time-varying elastance” model Left Ventricular Pressure mm Hg kPa 40 300 Emax 30 200 20 100 10 minimum elastance 0 0 0 50 100 150 200 Left Ventricular Volume (ml)

  38. Emax “Afterload” Preload Measuring ContractilityD. Emax Left Ventricular Pressure mm Hg kPa Contractility (slope of end-systolic PV line) 40 300 30 200 20 100 10 0 0 0 50 100 150 200 Left Ventricular Volume (ml)

  39. same contractility same afterload Increased preload stroke volume Left Ventricular Pressure Increased Preload Left Ventricular Volume (ml)

  40. same contractility increase afterload stroke volume same preload Left Ventricular Pressure Increased Afterload Left Ventricular Volume (ml)

  41. Preload increased Left Ventricular Pressure Afterload compensation same contractility increase afterload Stroke volume restored Left Ventricular Volume (ml)

  42. Hypertension and Cardiac Work Left Ventricular Pressure External Work increase afterload Contraction I Contraction 3 Left Ventricular Volume (ml)

  43. Hypertension and Cardiac Work Left Ventricular Pressure Internal work increase afterload Left Ventricular Volume (ml)

  44. stroke volume Left Ventricular Pressure Increased Contractility increased contractility same afterload same preload Left Ventricular Volume (ml)

  45. Left Ventricular Pressure Decreased Contractility decreased contractility same afterload same preload Left Ventricular Volume (ml)

  46. Preload compensation Left Ventricular Pressure decreased contractility same afterload Left Ventricular Volume (ml)

  47. Which Hearts Are Healthy?

  48. Left Ventricular Pressure (mmHg)

  49. Which Hearts Are Healthy? A. Pregnant 3rd trimester

  50. Which Hearts Are Healthy? B.Exercising