Parametric estimation of phase delay for sound transmitted through human lung

Sonic noise between 300 and 1600 Hz was introduced into the mouths of 11 healthy adult male subjects and detected over the anterior extrathoracic trachea and at three sites on the right posterior chest wall. The phase delay r ( f ) of propagation between the trachea and the chest wall was estimated using a linear parametric ARX-type statistical model. The results show a clear trend of decreasing ~ ( f ) with increasing frequency, that is, sound at higher frequencies reaches the chest wall faster than sound at lower frequencies. This suggests that airway wavespeeds and/or propagation pathways change significantly with increasing frequency.