In this work we study in time-frequency domain what has been termed "tea-kettle" sounds found in audio recordings of arteriovenous fistulas with severe stenosis. These sounds appears as frequency modulated signals (chirps) in the time-frequency plots. We first developed a simple model for generating synthetic bruits containing chirps. Then we performed tracking of the time-varying frequency signals using an Extended Kaiman filter (EKF). Finally we analyzed a data base of recordings from 5 patients suffering from venous stenosis EKF frequency tracker, the results shows the chirps mean frequencies (fundamental) can vary in a rather wide range of frequencies from about 200 Hz to 600 Hz and that up to two harmonics can also be found in the considered cases.
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