Fig. (1) Phases of the respiratory cycle illustrated via breath sound patterns. The vertical axis is breath sound intensity, while the horizontal axis is time in seconds. Note how the intensity of the early expiratory breath sounds in this case are stronger than the intensity of the inspiratory breath sounds and tend to diminish throughout expiration. From Abushakra A, Faezipour M. Acoustic signal classification of breathing movements to virtually aid breath regulation. IEEE J Biomed Health Inform. 2013; 17(2): 493-500. doi: 10.1109/JBHI.2013.2244901. PubMed PMID: 24235120.
iiFor a sampling of normal and pathological breath sounds, the interested reader is directed to https://soundcloud.com/sam-alsmadi, http://www.cvmbs.colostate.edu/clinsci/callan/breath_sounds.htm and https://www.thinklabs.com/lung-sounds