New insight in the auscultation of respiratory sounds.

Sir,

I have read with interest the paper from Sarkar et al. on auscultation of the respiratory system.[1] It is an excellent and exhaustive review on neglected fields of the research in medicine. We want to add some data which may be of interest for the readers of the journal. The spectrum of tracheal sounds lies between 60 and 600 Hz for inspiration and between 60 and 700 Hz for expiration. At the thoracic level, the normal breath sound, namely the vesicular murmur, is characterized by a low-pitch but very audible noise during inspiration. It is generally accepted that the frequency of lung sounds ranges between 50 and 2500 Hz, whereas tracheal sounds can reach up to 4000 Hz.[2] From a respiratory viewpoint, it should be emphasized at this juncture that only a few sounds are currently well identified and qualified on a physical level, including wheezing and crackles.[2] The availability of novel representations of these sounds, as pneumo-phonogram (a tool providing simultaneous representation in time of the respiratory phases), or pneumo-spectrogram (a tool where time is indicated in abscissa, frequency in ordinate, and intensity of the signal is represented by a color palette for the respiratory) [Figure 1], or heart signal, therefore, opens interesting perspectives in the context of diagnostic aids (automatic detection in the third generation electronic stethoscope), but also in education and pedagogy.[3] A preliminary study conducted by our group with a population of medical graduate students at the University Hospital of Strasbourg allowed us to quantify better diagnostic “performance” (more than 80% of good diagnosis) with these new auscultatory signal visualization tools in a setting of heart and lung disease assessment.[4]

Figure 1

Representation of a recording of a lung auscultation in an normal subject in the form of a pneumo-phonogram and a spectrogram (data collected in the ASAP and PRI projects; Grants from ANR Technology 2006 and HUS 2009)

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Conflicts of interest

There are no conflicts of interest.