5 Questions
What is the primary determinant of myocardial O2 demand?
Ventricular wall stress
What is the formula for wall stress (S) in a thin-walled sphere or tube?
P x r / 2w
What would increase ventricular wall stress?
Increased ventricular radius and transmural pressure
What is the relationship between ventricular wall stress and myocardial O2 demand?
Increased ventricular wall stress increases myocardial O2 demand
What is the term for the impedance that the heart must overcome to eject blood into the arterial circulation?
Afterload
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.
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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