Interpretation of sonotubometric data based on phase-shift detection.
BACKGROUND
Sonotubometry is a non-invasive means of assessing Eustachian tube (ET) function. Its interpretation remains a complex task with questionable results due to wide variation between trials. A study was conducted to ascertain whether the measurement of phase shift in sonotubometric signals would be a more reliable indicator of ET patency than fluctuating Sound Pressure Level (SPL).


METHODS
The ears of six healthy participants and two participants with patulous ET (PET) were probed with a 100 Hz signal. Five recordings of SPL were performed at the external auditory canal. Cross-correlation was performed among filtered SPL signals and among extracted phase shift waveforms. Peak coefficients were averaged to provide a measure of waveform similarity between trials.


RESULTS
Mean peak cross correlation coefficient for SPL signal measured 0.603 ± 0.057 Standard Error of Mean (SEM) whilst that for Phase-Shift signal measured 0.884 ± 0.027 (SEM). All normal participants demonstrated an observable phase change between the ear and nasal signal during swallowing indicating an acoustic impedance change during the event. For the PET patients tested, the phase measurements in ear and nasal signals follow one another reasonably closely, indicating little or no impedance change during swallowing. It is thought that this impedance change is indicative of opening of the ET in normal patients, and the lack impedance change indicates ET either remaining open or remaining closed throughout the swallow.


CONCLUSIONS
Experimental data suggest that phase-shift detection is a more consistent means of interpreting sonotubometric data than SPL analysis.
Faculty of Medicine, Dalhousie University, 1459 Oxford Street, Halifax, Nova Scotia, B3H 4R2, Canada. yaw.tuffour@dal.ca.
Yaw
Y
Amoako-Tuffour
Department of Mechanical Engineering, University of New Brunswick, 15 Dineen Drive, P.O. Box 4400, Fredericton, New Brunswick, E3B 5A3, Canada.
Philip
P
Garland
Division of Otolaryngology - Head and Neck Surgery, Dalhousie University, 3rd Floor Dickson Building, VG Site, QE II Health Sciences Centre, 5820 University Ave, Halifax, Nova Scotia, B3H 2Y9, Canada.
Manohar
M
Bance
D000158:Acoustic Impedance Tests; D005064:Eustachian Tube / Q000502:physiology* / Q000503:physiopathology; D064368:Healthy Volunteers; D006801:Humans; D012016:Reference Values
Eustachian tube; Phase-shifting; Sonotubometry