This paper reviews methods for airflow measurement and describes a new acoustical respiratory phase detection method without the aid of airflow measurement. The method uses breath sound signals recorded from both the chest and trachea to detect respiratory phases and the timing of breath. The method finds the respiratory phases from the sound envelope of the lung sound signal and the onset of breath from the sound envelope of the tracheal signal.

The detection of respiratory phases by acoustical means simplifies the experimental apparatus and provides more accurate timing of breaths than many other airflow measurement methods.