Acoustic analysis as a surrogate for gas exchange

Abstract

Measurement of ventilatory (VT) and respiratory compensation (RCT) threshold is a standard practice during exercise testing with measurement of respiratory gas exchange (RGE). Previous work suggested the feasibility that a conceptually simple breath sound analysis (BSA) technique might be an alternative to direct RGE. This study extends observations of the relationship between VT and RCT detection using RGE and BSA. Healthy subjects (n=20) performed two incremental, maximal cycle ergometer exercise tests (25W + 25W per 2 min). Heart rate (HR) and Rate of Perceived Exertion (RPE) were recorded during the last thirty seconds of each stage using radiotelemetry and the Category Ratio RPE scale. RGE was performed using open circuit spirometery with VT and RCT determined from v-slope and ventilatory equivalents. BSA was performed using proprietary software from a microphone in the breathing valve, and included measurements of respiratory rate and sound intensity (the product of tidal volume/inspiratory and expiratory time). There was a significant relationship between the HR at VT and RCT combined (R2=0.72) and power output (PO) at VT and RCT combined (R2=0.78) between the RGE and BSA, with the best fit line basically equivalent to the line of identity. The conceptually simple BSA appears to be a viable surrogate for direct measurement of VT and RCT using RGE.