Biomechanics of Eustachian Tube Dysfunction: From Mechanics to Assessment

Abstract

The Eustachian tube (ET) is a narrow canal connecting the throat with the middle ear. In the UK 0.9 % of the population suffers from obstructive ET dysfunction (ETD), a condition where the ET does not open. Recent breakthroughs in the treatment of ETD highlighted the need for more accurate assessment methods for the ET. Sonotubometry is the only method to measure the ET function under physiological conditions. However, sonotubometry research has been stagnant due to inconsistent results and a lack of understanding of the acoustical processes. In addition, the opening mechanics of the ET is also poorly understood, which limited progress in ET research. This work investigates the acoustics of sonotubometry with the aim of optimising the methodology. In addition, the mechanics of the ET is studied in both human and sheep cadaver specimens to gain a better understanding of the ET opening process. First, this research investigated the acoustics of the ET in a controlled environment using three models of the ET transmission line. Based on these results, a healthy volunteer study was designed where the impact of the sound amplitude and sound type (8.3 kHz sinus tone, white noise and sweep) was evaluated and optimised. Subsequently, a patient study was performed to assess the sensitivity and specificity, as well as the clinical usability of sonotubometry. Based on the volunteer study, the best results were achieved at high sound amplitudes (i.e., above 115 dB) using the sinus tone. Most studies in the past used a significantly lower sound level, which is expected to have caused the inconsistency in the reported results. Nevertheless, certain gaps persist in understanding the ET opening process. In a second project, the mechanics of the ET was studied using an in situ approach. Five sheep cadaver heads were mechanically loaded and imaged using CT scanning. The data was also compared to a CT scan of a human cadaver specimen. The in situ study allowed for the first time to gain a detailed insight into the ET mechanics. However, when comparing the human and sheep anatomy significant differences were observed, which questions the validity of the commonly used sheep model to understand the human ET. The results provided novel insight into the challenges of studying the ET. However, they also demonstrated the potential of the developed in situ approach, which could also be applied to a human cadaver study to gain more insight into the mechanics of ET.