Effect of air flow and flow transducer on tracheal breath sounds

Tracheal breath sounds (TBSs) were analysed in 12 normal adult subjects at the air flow levels of 1.6, 2.1 and 2.6 litres-1, using a low-resistance flow transducer, and at an estimated flow of 2.1 litres-1 without the flow transducer. The major findings were that the TBSs were significantly distorted by the flow transducer, but were independent of air flow. We therefore conclude that true TBSs can only really be recorded when an oral flow transducer is not used. The within-subject reproducibility of TBS was relatively good, while the cross-subject comparison of TBS showed that each subject produced their own unique spectral pattern, although the TBSs of normal subjects fall in a common frequency range. Also, inspiratory sounds were significantly lower in peak frequency than expiratory TBSs.