Heart as a pump

Cardiac cycle

Phase1. Atrial systole:AV valves open; aorticand 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 openAV valves closed

Heart as a pump

Cardiac cycle

Phase4. Reduced ejection:Pulmonic valves open AV valves closed

Heart as a pump

Cardiac cycle

Phase5. Isvolumetric relaxationAll valves closed

Heart as a pump

Cardiac cycle

Phase 6:Rapid filling:AV valves openSemilunar valves closed

Heart as a pump

Cardiac cycle

Phase7. Reduced filling:AV valves open; aorticAnd pulmonic valvesclosed

Heart as a pump

Heart as a pumpSummary of intracardiac pressures

Heart as a pump

At heart rates up to about 180, filling is adequate as long as there is ample venous return

Heart as a pump

Preload is the initial stretching of the cardiac myocytes prior to contraction.

Preload

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Heart as a pump

Tricuspid valve stenosis

• Pulmonic valve stenosis• Pulmonary

Hypertension

Factors Determining Ventricular Preload

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Heart as a pump

Plays an important role in balancing the output of the

two ventricles.ventricular function curve

Frank-Starling Mechanism

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Heart as a pumpFrank-Starling Mechanism

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Heart as a pump

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:

1. Increased sensitization of troponin C to calcium

2. Change in calcium homeostasis within the cell

3. Closer of myosin molecules to each other

What mechanisms are responsible for the increase in force generation with increased preload in the heart?

Heart as a pump Afterloa

d

Heart as a pump Inotropy

Heart as a pump Inotropy

↑ Heart Rate ↑ Inotropy ↑ Afterload ↑ Preload*

Changes in preload affect oxygen consumption much less than do changes in the other factors

Factors Increasing Myocardial Oxygen Consumption

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%.