Жүрек бұлшық етінің диастола кезіндегі созылуы

Heart muscle stretch at rest

In cardiac physiology, preload is the amount of sarcomere stretch experienced by cardiac muscle cells, called cardiomyocytes, at the end of ventricular filling during diastole. Preload is directly related to ventricular filling. As the relaxed ventricle fills during diastole, the walls are stretched and the length of sarcomeres increases. Sarcomere length can be approximated by the volume of the ventricle because each shape has a conserved surface area to volume ratio. This is useful clinically because measuring the sarcomere length is destructive to heart tissue. It requires cutting out a piece of cardiac muscle to look at the sarcomeres under a microscope. It is currently not possible to directly measure preload in the beating heart of a living animal. Preload is estimated from end diastolic ventricular pressure and is measured in millimeters of mercury (mmHg).

Though not exactly equivalent to the strict definition of preload, end diastolic volume is better suited to the clinic. It is relatively straightforward to estimate the volume of a healthy, filled left ventricle by visualizing the 2D cross section with cardiac ultrasound. This technique is less helpful for estimating right ventricular preload because it is difficult to calculate the volume in an asymmetrical chamber. Pulmonary wedge pressure will overestimate left ventricle pressure in people with mitral valve stenosis, pulmonary hypertension and other heart and lung conditions. Estimation of preload may also be inaccurate in a chronically dilated ventricles because additional new sarcomeres cause the relaxed ventricle to appear enlarged.