Time dependent autoregressive spectrum estimation of heart wall vibrations

We present a new method for estimation of spectrum transition of a nonstationary signals in low signal-to-noise ratio cases. Instead of basic functions which are employed by the previously proposed time-varying AR modeling, we introduce the spectrum transition constraint in the cost function described by the partial correlation coefficients so that the method is applicable to noisy nonstationary signals of which spectrum transition patterns are complex. By applying this method to the analysis of vibration signals on the interventricular septum of the heart, noninvasively measured by the method developed in our laboratory using ultrasonics, spectrum transition pattern is clearly obtained during one beat period for a normal individual and a patient