Chapter 16: Mechanical Aspects of Cardiac Performance•The parts of the heart normally beat in an orderly sequence:1) contraction of the atria (atrial systole)2) contraction of the ventricle (ventricular systole)3) during diastole, the ventriclesare relaxedBE501 T. K. Hsiai, MD, PhD, FACCObjectives
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Cardiac Performance: preload and afterloadFrom molecular to cellular and macrostructuresStretch the muscle to desired length by hanging appropriate weight (preload°at the end of ventricular filling) from the relaxed muscle. The desired preload is determined for the passive length:force relationship.a) Place a support beneath the muscle to allow additional weights (afterload°in the intact heart just before opening of the aortic valve) to be added without stretching the muscle. b) Stimulate the muscle electrically. c) Record change in muscle length once muscle generates sufficient force to lift total load (preload+ afterload). d) Repeat series for different afterloads.