Introduction: Infrasound (<20 Hz) is generated by many natural and biological phenomena. A stethoscope has been developed to record infrasound, however, such auscultation would be subject to ambient and body surface noise along with interposed tissue dampening.

Aim: To record respiratory infrasound from oronasal breath sounds inside a mask before and during bilevel positive airway pressure (BiPAP) ventilation.

Methods: A wireless 16 bit accelerometer was mounted securely inside an oronasal mask. 30 s audio epochs were sampled from DC at 1600 Hz and transmitted via Bluetooth (BLE) to a host computer running Ubuntu 22.04 Linux using a custom Python3 script in healthy adult subjects. Ambient unattached and applied mask with and without BiPAP (20/16 cmH2O) .wav files were plotted as spectrograms using Audacity 2.4.2. audio software.

Results: Nonambient inspiratory 4 to 5, 9 to 10, and 20 Hz infrasound peaks as fundamental, first overtone, and second overtone frequencies were evident. These peaks were not substantially affected by differences in respiratory rate or by BiPAP.

Conclusion: Digital accelerometry can effectively identify oronasal inspiratory infrasound.