A robust respiratory phase identification scheme based on a new mixing index

This paper introduces a novel method to identify inspiratory and expiratory phases from single channel tracheal breath sound (TBS) of different types, by proposing a new annotating index name as “mixing index” (MI). An alignment scheme based on phase shift difference information has been firstly introduced to align the consecutive respiratory phase segments. MI is then proposed based on similarity measurements to annotate the respective inspiration/expiration in each aligned respiratory phase segment pair. By incorporating the novel alignment scheme, the presented index overcomes the problem of phase cancellation which affects the cross-coherence of the input segment pairs. As MI is invariant to spectral content and amplitude dynamics, the proposed method maintains a good performance even in the presence of adventitious sounds. A high averaged accuracy of 97.4% for adventitious sounds and 100% for normal TBS have been thereby achieved. The proposed method has been a successful attempt to solve the clinical application challenge faced by the existing phase identification methods in terms of respiratory dysfunctions.