Detection of respiratory sounds within the ear canal

Twenty healthy male and female subjects were studied. Each breathed through a pneumotachograph at targeted shallow (3.0 mL/s/kg) and tidal (7.5 mL/s/kg) airflows normalized to body mass. The resulting breathing sound was recorded from a microphone in an earplug that acoustically isolated the ear canal from the room environment. Measured sound levels during breath hold provided a measure of the noise floor. Shallow and tidal expiratory flows produced SNRs of 6.9 ± 4.2 dB and 14.3 ± 5.5 dB across all subjects. Time series of the sounds were band-pass filtered, full-wave rectified, and then processed by a "leaky" integrator to produce an amplitude-enveloped signal. These processed signals were observed to graphically correspond to the simultaneously measured respiratory flow. Thus, the ear canal shows promise as an anatomic site to detect and monitor breathing in a relatively noninvasive manner.