Lecture Notes on Pressure-Volume Loops

Introduction

• Pressure-volume loops can seem overwhelming and complex.
• Commonly not well-taught in medical schools.
• Goal: Simplify the topic to make it easily understandable.
• Importance: Understanding it well can help score easy points in tests.

Basics of Pressure-Volume Loops

• Graph Structure:
  • Y-axis: Pressure
  • X-axis: Volume
• Focus on the left ventricle (left ventricular pressure and volume).
• Shape resembles a piece of bread.

Key Points on the Loop

• Four crucial points:
  • Orange: Aortic valve closes
  • Red: Mitral valve opens
  • Blue: Mitral valve closes
  • Green: Aortic valve opens
• Recommendation: Memorize the orange and blue points.

Analyzing the Loop

• Systole:
  • Starts at the blue point (mitral valve closes).
  • Includes green to orange (aortic valve opens to closes) as ejection phase.
  • Volume decreases as blood is ejected.
• Diastole:
  • Starts at the orange point (aortic valve closes).
  • Ends at the blue point (mitral valve closes).
  • Volume increases due to filling.

Iso-Volumetric Phases

• Definition: Phases where volume doesn't change.
• Isovolumetric Contraction: Blue to Green
• Isovolumetric Relaxation: Orange to Red
• All heart valves are closed during isovolumetric phases.

Inferring Cardiac Physiology

• Stroke Volume:
  • Calculated as End Diastolic Volume (EDV) - End Systolic Volume (ESV).
  • Can be determined from the graph.
• Phases Influence:
  • Systole starts when diastole ends (blue point).
  • Diastole starts when systole ends (orange point).

Changes in the Graph

• Contractility Increase:
  • Graph shifts left.
  • Increase in stroke volume and ejection fraction.
  • Decrease in end systolic volume.
• Afterload Increase:
  • Graph shifts due to increased aortic pressure.
  • Decrease in stroke volume.
  • Increase in end systolic volume.
• Preload Increase:
  • Graph shifts right.
  • Increase in stroke volume.

Conclusion

• The lecture covered:
  1. Setting up and labeling the graph.
  2. Understanding various phases.
  3. How the graph changes with physiological variations.
• Aim: Simplify the complex concepts of pressure-volume loops.