Cardiac Preload vs. Afterload

Introduction

• Presenter: Sarah Thread Sterner
• Topic: Cardiac preload and afterload
• Objective: Understand the difference between preload and afterload and their impact on cardiac output
• Resource: Free quiz available after the video

Cardiac Output

• Definition: Amount of blood the heart pumps per minute
• Significance: Maintains tissue perfusion by delivering oxygenated blood to cells
• Calculation: Cardiac Output = Heart Rate x Stroke Volume

Stroke Volume

• Definition: Amount of blood pumped by a ventricle with each beat
• **Factors Affecting Stroke Volume: **
  • Contractility (strength of cardiac cells to contract)
  • Preload
  • Afterload

Preload

• Definition: The amount the ventricles stretch at the end of diastole
  • Diastole: Relaxation/filling phase of the cardiac cycle
• End-Diastolic Volume: Volume of blood in the ventricle at the end of diastole

Increasing Preload

• IV Fluids: Increase blood volume returning to the heart
• Sympathetic Nervous System: Vasoconstriction increases venous return
  • Drugs like vasopressors can stimulate this

Decreasing Preload

• Diuretics (e.g., Furosemide): Remove extra fluid via urination
• Vasodilation (e.g., Nitroglycerin): Causes blood pooling and reduces venous return

Afterload

• Definition: Pressure ventricles must work against to open semilunar valves
  • Right Ventricle: Pulmonary vascular resistance
  • Left Ventricle: Systemic vascular resistance

Increasing Afterload

• Vasoconstriction: Narrows arteries, increases vascular resistance
• Pulmonary Hypertension: Increases pulmonary vascular resistance
• Valve Problems (e.g., Aortic Stenosis): Narrows valve, increases pressure needed to pump blood

Decreasing Afterload

• Vasodilators: Dilate vessels, decrease vascular resistance, reduce ventricular workload

Conclusion

• Summary: Understanding preload and afterload helps in managing conditions that affect cardiac output
• Next Steps: Take the free quiz and subscribe for more videos