Isovolumetric contraction: Difference between revisions

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Isovolumetric contraction is a term used in cardiac physiology to refer to an event occurring in early systole during the cardiac cycle. In a healthy young adult, blood from the venous return 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 of this situation is that, while contraction causes ventricular pressure to rise sharply, there is no overall change in volume because of the closed valves. The isovolumetric contraction lasts for about 0.03 s, but this short period of time is enough to build up a sufficiently high pressure that will eventually overcome that of the aorta and the pulmonary trunk upon opening of the semilunar valves, therefore allowing the correct unidirectional flow of blood.