Define afterload and describe the physiological factors that may affect afterload
Definitions for afterload vary slightly amongst common physiology textbooks, and
candidates were expected to mention any one commonly accepted definition. Essentially
afterload is the resistance to ventricular ejection - the "load" that the heart must eject blood
against and is related to ventricular wall stress (Law of Laplace, T=Pt.r/u). Candidates were
expected to mention aortic valve and systemic vascular resistance, aortic impedance, blood
viscosity, intathoracic pressure and relationship of ventricular radius and volume.
Candidates generally did well, but few substantially good answers, with a lack of detail being
the biggest limiting factor.