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Definition of Afterload

Babylon English

(In Cardiac Physiology) tension caused by the heart muscle after contraction
Afterload Definition from Medicine Dictionaries & Glossaries
Aging Hearts and Arteries Glossary
The mechanical load encountered by the heart following the onset of contraction; the forces that resist the flow of blood from the heart. The afterload may increase with age due to increasingly stiff arteries and an increased tone of the smaller arteries.
Source: National Institute on Aging
Afterload Definition from Encyclopedia Dictionaries & Glossaries
English Wikipedia - The Free Encyclopedia
Afterload is the pressure in the wall of the left ventricle during ejection. In other words, it is the end load against which the heart contracts to eject blood. Afterload is readily broken into components: one factor is the aortic pressure the left ventricular muscle must overcome to eject blood. The greater the aortic/pulmonary pressure, the greater the after load on the left/right ventricle, respectively. Following Laplace's law, the tension upon the muscle fibers in the heart wall is the pressure within the ventricle multiplied by the volume within the ventricle divided by the wall thickness (this ratio is the other factor in setting the afterload). Therefore, when comparing a normal heart to a heart with a dilated left ventricle, if the aortic pressure is the same in both hearts, the dilated heart must create a greater tension to overcome the same aortic pressure to eject blood because it has a larger internal radius and volume. Thus, the dilated heart has a greater total load (tension) on the myocytes, i.e., has a higher afterload. This is also true in the eccentric hypertrophy consequent to high intensity aerobic training. Conversely, a concentrically hypertrophied left ventricle may have a lower afterload for a given aortic pressure. When contractility becomes impaired and the ventricle dilates, the afterload rises and limits output. This may start a vicious circle, in which cardiac output is reduced as oxygen requirements are increased.

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