these non-breathing events can modify the phase alternation in an unpredictable fashion. One of the few studies on respiratory phase detection from only tracheal sounds is an early work reported in [7] using time and spectral features, such as maximum amplitude of the tracheal sound, its root-mean-square value, duration of the phase and peak, median and maximum frequencies. The method was developed based on the recorded data of 10 healthy subjects under controlled condition and was validated on data of 2 subjects being recorded in a normal and noisy clinical setting. All recordings were during normal alternating breathing. No accuracy was given, but it was implied that the method was successful in determining all the phases correctly.