Cardiology Lecture Notes: Section Six

Introduction

• Focus on Starling curve and cardiac & vascular function curves.

Starling Curve

• Y-Axis: Cardiac output
• X-Axis: Preload
• Normal Curve:
  • Increased Preload: Cardiac output increases up to a point, beyond which it tapers off.
  • Sarcomere Basics:
    • Fundamental unit of striated muscle, including cardiac.
    • Components: Z line, Actin, Myosin heads.
    • Increased Blood Volume: Stretches sarcomere, increases tension between myosin heads and actin, allowing greater force of contraction.
  • Optimal Length-Tension Relationship: Basis for the Starling curve.

Inotropy and the Starling Curve

• Inotropy: Changes in contractility.
  • Positive Inotropes (e.g., epinephrine, norepinephrine):
    • Increase intracellular calcium.
    • More troponin C moves tropomyosin, increases actin-myosin binding, contractility.
    • Curve shift: Heart pumps more with same preload.
  • Negative Inotropes (e.g., beta-blockers):
    • Decrease intracellular calcium.
    • Reduce cardiac output with the same preload.
• Afterload Effects:
  • Decrease Afterload: Heart pumps against less resistance, increasing cardiac output, shifting curve left.
  • Increase Afterload: Opposite effect, shifting curve right.

Cardiac and Vascular Function Curves

• Figure 2.9: Overlapping graphs, multiple variables on axes.
• X-Axis Variables:
  • Right Atrial Pressure: Pressure exerted by blood volume.
  • End Diastolic Volume (EDV): Volume of blood in the ventricle.
  • Both essentially represent the same concept, expressed differently.
• Y-Axis Variables:
  • Cardiac Output (Green Curve): Blood leaving the heart.
  • Venous Return (Blue Curve): Blood returning to the heart.

Summary

• Starling curve measures cardiac output as a function of preload.
• Shifts in the Starling curve are caused by changes in inotropy and afterload.
• Cardiac and vascular function curves illustrate the relationship between right atrial pressure/EDV and cardiac output/venous return.