Relaxation
Isovolumetric relaxation: The second heart sound is produced when the aortic and pulmonary valves close when the ventricular pressures fall below the diastolic aortic and pulmonary pressures (80 mmHg and 10 mmHg, respectively). he average duration of this period during the cardiac cycle is 44%.
Following isovolumetric relaxation (phase IV), ventricular filling starts when left ventricular pressure drops below left atrial pressure.
seven stages of the cardiac cycle:-
Isovolumic relaxation time (IVRT) is the period of time between the commencement of filling caused by the opening of the mitral valve and the aortic component of the second heart sound. It can be applied as a diastolic dysfunction indication.
It can be determined by simultaneous Doppler echocardiography and M-mode sonography, or even better, by transmitral Doppler and phonocardiogram.
IVRT that is prolonged shows inadequate myocardial relaxation. A typical IVRT lasts about 70+-12 ms and 10 ms longer in adults over the age of 40. In cases of aberrant relaxation, IVRT typically exceeds 110 ms. It is often less than 60 milliseconds with tight ventricular filling.
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