Define preload and describe the determinants of preload.
A definition based on stretch of the isolated myocyte prior to contraction, and
extrapolation to the human heart, was expected. Surrogate measures of preload
used in clinical practice needed to be explained and related to the definition (for
example, end-diastolic volume and central venous pressure). The Frank-Starling
Law was relevant to discussion of the significance of preload to cardiac performance.
A diagram illustrating the interaction of important factors would have been helpful in
answering this question. At a minimum, detail should have included atrial
contractility, diastolic filling time, ventricular compliance, and the determinants of
Better answers included discussion of the effects of afterload, arrhythmias, and
valvular pathology. A distinction between the factors determining left and right
ventricular preload would have demonstrated a more sophisticated understanding of
Syllabus: C1c, 2b,c.
Reference: Cardiovascular Physiology, Berne and Levy, p64-65
It is not remarkable that only 10% of the candidates passed this question, because preload is something that has always defied definition.
Norton, James M. "Toward consistent definitions for preload and afterload."Advances in physiology education 25.1 (2001): 53-61.
ROTHE, CARL. "Toward consistent definitions for preload and afterload—revisited." Advances in physiology education 27.1 (2003): 44-45.