Heart Physiology: Afterload and Ventricular Wall Stress
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Questions and Answers

What is the primary determinant of myocardial O2 demand?

  • Transmural pressure
  • Ventricular wall thickness
  • Ventricular wall stress (correct)
  • Ventricular radius

What is the formula for wall stress (S) in a thin-walled sphere or tube?

  • T = P x r / 2
  • P x r / 2w (correct)
  • P = 2T / r
  • S = T / w

What would increase ventricular wall stress?

  • Increased ventricular radius and transmural pressure (correct)
  • Decreased ventricular radius
  • Increased ventricular wall thickness
  • Decreased transmural pressure

What is the relationship between ventricular wall stress and myocardial O2 demand?

<p>Increased ventricular wall stress increases myocardial O2 demand (A)</p> Signup and view all the answers

What is the term for the impedance that the heart must overcome to eject blood into the arterial circulation?

<p>Afterload (B)</p> Signup and view all the answers

Study Notes

Afterload

  • Afterload is the impedance that the heart must overcome to eject blood into the arterial circulation, related to ventricular wall stress.
  • It is the major determinant of myocardial O2 demand.

Indices/Surrogates of Afterload

  • The Law of Laplace is used to determine ventricular wall stress.
  • For thin-walled spheres or tubes, the Law of Laplace is expressed as: P = 2T/r, or T = P x r/2.
  • For thick-walled spheres or tubes, the Law of Laplace is expressed as: Tension = wall stress (S) / wall thickness (w).
  • Ventricular wall stress is calculated as: S = P x r / 2w.

Factors Affecting Wall Stress

  • Wall stress increases with increased transmural pressure (P) in the ventricle (e.g., increased MAP).
  • Wall stress increases with increased radius (r) of the ventricle (e.g., dilated heart).
  • Wall stress decreases with increased wall thickness (w) of the ventricle (e.g., LVH).
  • Increased wall stress leads to increased myocardial O2 demand.

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Description

Learn about afterload, the impedance that the heart must overcome to eject blood into the arterial circulation, and its significance in myocardial O2 demand.

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