Acoustic reflection technique non-invasively measures airway cross- sectional area vs. distance function and uses a wave tube with a constant cross-sectional area to separate incidental and reflected waves introduced into the mouth or nostril. The accuracy of estimated cross-sectional areas gets worse in the deeper distances due to the nature of marching algorithm, i.e., errors of the estimated areas in the closer distances accumulate to those in the further distances. Here, we present a new technique of acoustic reflection from measuring transmitted acoustic waves in the airway with three microphones and without employing a wave tube. Using miniaturized microphones mounted on a catheter, we estimated reflection coefficients among the microphones and separated incidental and reflected waves. A model study showed that the estimated cross-sectional area vs. distance function was coincident with the conventional two-microphone method and it did not change with altered cross-sectional area at microphone position, although the estimated cross-sectional areas are relative values to that at microphone position. The pharyngeal cross-sectional areas including retro-palatal and retro-glossal regions and the closing site during sleep was visualized in patients with obstructive sleep apnea. The method can be applicable to larger or smaller bronchus to evaluate the airspace and function in these localized airways.
- reflection coefficient
- intra-airway microphone
- pharyngeal cross-sectional area
- sleep apnea
- Copyright © 2013, Journal of Applied Physiology