Preload

Preload may refer to:

See also

Preload (cardiology)

In cardiac physiology, preload is the end diastolic volume that stretches the right or left ventricle of the heart to its greatest dimensions under variable physiologic demand. In other words, it is the initial stretching of the cardiomyocytes prior to contraction; therefore, it is related to the sarcomere length at the end of diastole. Parameters such as ventricular end diastolic volume or pressure are used to measure preload since the ideal length of the cardiac sarcomere cannot be measured. Passive filling of the (heart) ventricle and subsequent atrial contraction thus allows an echocardiographically volumetric measurement. Preload is theoretically most accurately described as the initial stretching of a single cardiomyocyte prior to contraction. This cannot be measured in vivo and therefore other measurements are used as estimates. Estimation may be inaccurate, for example in a chronically dilated ventricle new sarcomeres may have formed in the heart muscle allowing the relaxed ventricle to appear enlarged. The term end-diastolic volume is better suited to the clinic, although not exactly equivalent to the strict definition of preload. Atrial pressure is a surrogate for preload.

Preload (engineering)

Preload is a mechanical engineering term with several meanings. In the general sense, it refers to the internal application of stress to certain mechanical systems.

Fastener preload

The most common usage is to describe the load applied to a fastener as a result of it being installed, before any external loads are applied (e.g. tightening the nut on a bolt). Preload in such cases is important for several reasons.

Second, a nut which is correctly tightened will resist coming loose under the influence of vibration, temperature cycling, etc.

Bearing preload

Internal stress to a bearing through application of negative clearance is known as bearing preloading. Advantages of preloading include the following: maintain axial and radial position for accurate displacements of angular movements; increase bearing rigidity; prevent sliding or gyroscope-like movements, especially with high acceleration or rotation rates; maintain relative position of bearing elements. Preloading methods include position preload and constant pressure preload.