EFFECTS OF BREATHING PATHWAYS ON TRACHEAL SOUND SPECTRAL FEATURES

The spectra of sounds recorded over the trachea of adults typically re veal peaks near 700 and 1500 Hz. We assessed the anatomical determinan ts of these peaks and the conditions contributing to their presence. W e studied five adult subjects with normal lung function, measuring sou nds at the suprasternal notch and on the right cheek. The subjects bre athed at target airflows of 15 and at 30 ml sec(-1) kg(-1) both throug h the mouth with nose clips and then through the mouth and nose using a cushioned face mask. The mouth breathing maneuvers were performed wi th three lengths (3.6, 21.1 and 38.6 cm) of 2.6 cm diameter tubing bet ween the mouth and the pneumotachograph. The nose breathing maneuver w as performed with the longest tube (between the mask and pneumotachogr aph). The signals occurring at the target flows +/-20% were used to cr eate averaged, spectral estimates. We found that all subjects had two predominant spectral peaks: a approximate to 700 Hz peak loudest over the cheek and a approximate to 1500 Hz peak loudest over the trachea. The frequency of both peaks negatively correlated with body height lan d presumably, airway length). There was no systematic effect of breath ing phase, flow rate or length of the tube connecting the mouth to the pneumotachograph on the spectral peaks. Breathing into the mask and b reathing through the nose did markedly alter the spectra. We conclude that the higher tracheal sound peak reflects resonance within the majo r airways and is relatively independent of extrathoracic influences du ring mouth breathing through a tube. Published by Elsevier Science B.V .