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Isovolumetric contraction
Isovolumetric contraction is a term used in cardiac physiology to refer to an event occurring in early systole, during which the ventricles contract with no corresponding volume change. This short-lasting event takes place when both the AV valve and SL valve are closed.
==Description==
In a healthy young adult, blood enters the atria and flows to the ventricles via the opened tricuspid and mitral valves. Atrial contraction rapidly follows, actively pumping about 20% of the returning blood. As diastole ends, the ventricles start depolarizing and, while ventricular pressure starts to rise due to contraction, the atrioventricular valves close, so as to prevent back flow to the atria. At this stage, which corresponds to the R peak or the QRS complex seen on an ECG, the aortic and pulmonary valves are also closed. The net result is that, while contraction causes ventricular pressures to rise sharply, there is no overall change in volume because of the closed valves. The isovolumetric contraction lasts about 0.03 s, but this short period of time is enough to build up a sufficiently high pressure that eventually overcomes that of the aorta and the pulmonary trunk upon opening of the semilunar valves, therefore allowing the correct unidirectional flow of blood.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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