Acoustic analysis of breath sounds as a surrogate for gas exchange thresholds.

Author:Peterson, Amanda J.
Position::Letter to the editor

Dear Editor-in-Chief

Respiratory gas exchange threshold measurements are a reference standard for measuring sustainable exercise capacity (McLellan and Skinner, 1981). A recent consensus report suggested that 'threshold based' exercise prescription may be superior (Mezzani et al., 2012) to the relative percent of V[O.sub.2] reserve or heart rate (HR) reserve that has been the standard for exercise prescription for a generation (ACSM, 2014). Further, respiratory gas exchange has technical requirements that place it out of the range of the health-fitness community. An alternative approach, which takes advantage of the fact that air moving into and out of the respiratory system creates sound (detectable as breathing frequency and sound volume) might provide an viable approach to threshold determination (Foster et al., 2012). This approach suggests that ventilatory threshold (VT) can be identified by an increase in breathing frequency and that respiratory compensation threshold (RCT) can be identified by a large increase in the perceived sound intensity. Breath sounds from digital recording are at least potentially capable of being analyzed in a way that allows investigators to distinguish changes in the acoustic character of breathing. The purpose of this study was to determine whether acoustic analysis of breath sounds, based on a proprietary algorithm and similar to that used previously (Foster et al., 2012), was systematically related to VT and RCT.

The subjects were healthy young adults aged 1855 (males n = 9, females n = 11). The university human subjects committee approved protocol and the subjects provided written informed consent prior to participation. The subjects performed two incremental cycle ergometer exercise tests until maximal exertion, with at least 24 hr between tests. Power Output began at 25W and was incremented 25 W every two minutes. HR and the Rating of Perceived Exertion (RPE) were recorded during the last thirty seconds of each stage using radiotelemetry and RPE was measured using the Category Ratio scale. Breath sound recordings were captured using a small microphone inserted into a Hans Rudolph breathing valve through the saliva port. Acoustic analysis from the last 30s of each exercise stage was analyzed from digital recordings for breathing frequency and a variable referred to as 'intensity' (obtained from the expiratory phase of the acoustic signature); which is conceptually similar to tidal volume divided by the expiratory...

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