Pressure Volume Loops Lecture Notes

Introduction to Pressure Volume Loops

• Pressure volume loops are often perceived as complex.
• Poorly taught in medical schools; aim to simplify for clear understanding.
• Aim to understand as if explaining to a fifth grader for better retention on test day.

Basics of Pressure Volume Loops

• Axes:
  • Y-axis: Pressure
  • X-axis: Volume
• Focus on the left ventricular pressure and volume.
• Commonly referred to as left ventricular pressure volume loop.

Key Points on the Curve

• Important Points:
  • Orange: Aortic valve closes
  • Red: Mitral valve opens
  • Blue: Mitral valve closes
  • Green: Aortic valve opens
• Memorize orange and blue points to deduce others.

Understanding Systole and Diastole

• Systole:
  • Begins at blue point (mitral valve closes).
  • Aortic valve opens at green point, ejection phase until orange point (aortic valve closes).
  • Volume drops on x-axis during ejection phase.
• Diastole:
  • Begins at orange point (aortic valve closes).
  • Mitral valve opens at red point, ends at blue point.
  • Volume increases as left ventricle fills.

Isovolumetric Phases

• Isovolumetric Contraction:
  • Blue to green point; volume unchanged, pressure increases.
• Isovolumetric Relaxation:
  • Orange to red point; volume unchanged, pressure decreases.
• During both phases, all heart valves are closed.

Stroke Volume and Its Importance

• Stroke Volume = End Diastolic Volume (EDV) - End Systolic Volume (ESV).
• Calculated using points on the x-axis:
  • EDV at diastole end (blue point).
  • ESV at systole end (orange point).

Effects of Contractility, Afterload, and Preload

Contractility

• Increased contractility:
  • Increases stroke volume and ejection fraction.
  • Decreases end systolic volume.
  • Graph shifts to the left.

Afterload

• Increased afterload:
  • Increases aortic pressure, decreases stroke volume.
  • Increases end systolic volume.
  • Graph shifts to the right.

Preload

• Increased preload:
  • Increases stroke volume.
  • Graph stretches to the right.

Conclusion

• Three parts of understanding:

  1. Setting up and labeling the graph.
  2. Phases represented on the graph.
  3. Graph changes with contractility, preload, and afterload adjustments.

• Simplification helps understand a complex topic.