[Circulatory system's elasticity and viscoelasticity. III. Isovolumetric relaxation of the left ventricle]

Both in health and in diseases characterized by abnormal diastolic performance in which there is no evidence of strong asynchrony or abnormal myocardium, the ventricular isovolumetric relaxation index more often applied has been the relaxation constant T that assumes a monoexponential pressure decay. Its choice is based on its independence from systolic pressure, mean aortic pressure, telesystolic pressure and volume, auricular pressure and other factors. Nevertheless in patients with gross asynchrony or abnormal myocardium the pressure decay is not exponential and the results obtained with relaxation constant T do not describe adequately the relaxation and are sometimes controversial. Other indexes have been used that do not require a mono-exponential pressure decay. In this paper some models of pressure decay during isovolumetric ventricular relaxation are examined. Some procedures for determination of the relaxation constant T and asymptomatic pressure as well as for other indexes that do not demand pressure decay monoexponentiality (such as the time constants t1/2 and T40 and the dP/dt (20/60) are reviewed. The effects of age and physical exercise on the index T are analyzed. In particular, the suitability of the monoexponential model to ischemic and ventricular hypertrophic states is studied, some results of application of the reported indexes do not requiring pressure isovolumetric decay monoexponentiality are considered and advantages and inconveniences of its use are analysed.