1. The arrangement of a muscle so that, in shortening, it lifts a weight from an adjustable support or otherwise does work against a constant opposing force to which it is not exposed at rest. 2. The load or force thus encountered in shortening.
- ventricular a. formerly and erroneously, the arterial pressure or some other measure of the force that a ventricle must overcome while it contracts during ejection, contributed to by aortic or pulmonic artery impedance, peripheral vascular resistance, and mass and viscosity of blood; now, more rigorously expressed in terms of the wall stress, i.e., the tension per unit cross-sectional area in the ventricular muscle fibers (calculated by an expansion of Laplace law using pressure, internal radius, and wall thickness) that is required to produce the intracavitary pressure required during ejection.

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af·ter·load 'af-tər-.lōd n the force against which a ventricle contracts that is contributed to by the vascular resistance esp. of the arteries and by the physical characteristics (as mass and viscosity) of the blood

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af·ter·load (afґtər-lōd″) in cardiac physiology, the force against which cardiac muscle shortens. In isolated muscle it is the force resisting shortening after the muscle is stimulated to contract; in the intact heart it is the pressure against which the ventricle ejects blood, as measured by the stress acting on the ventricular wall following the onset of contraction, determined largely by the peripheral vascular resistance and by the physical characteristics of and blood volume in the arterial system. It is often estimated by determining systolic arterial pressure, from which can be determined the systolic wall stress; see also Laplace's law, under law.

Medical dictionary. 2011.

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