The mechanism of balloon Eustachian tuboplasty: a biomechanical study

Abstract

Obstructive Eustachian tube dysfunction (OETD) is a common condition resulting from inadequate opening of the Eustachian tube (ET). A new surgical treatment involves high-pressure inflation of a balloon within the ET, with the aim of dilating the soft tissue structure. However, the mechanical effects of this intervention have not been established, nor the impact of changing device size or other technical parameters. A novel experimental technique allowed quantification of plastic and elastic tissue deformation in model materials and then human cadaver ETs during balloon dilation, based on the measured balloon inflation pressure-volume relationship. Plastic tissue deformation was found to be greater using larger balloons and deeper device insertion, but increasing the inflation pressure had a more limited effect, with most deformation occurring well below the clinically used pressures. Histological assessment of ET tissue suggested that mucosal tearing and cartilage cracking were in part responsible for the mechanical changes. Balloon dilation of the ET has huge potential if found to be clinically effective, but currently there is a need to understand and develop the technique further. The novel methods employed in this study will be valuable in future laboratory and in vivo studies of ET balloon dilation. Pressures are reported in Bar as this unit is used for medical balloon dilation procedures in clinical practice. 1 Bar = 100,000 Pa. Graphical abstract caption Dilation of the Eustachian tube for obstructive dysfunction is performed clinically with 3- and 6-mm-diameter balloons of approximately the same overall length. Our data suggest that dilation with a 6-mm balloon causes greater deformation of the soft tissue structure than dilation with a 3-mm balloon. This difference has yet to be demonstrated clinically. Plastic deformation was measured in terms of energy (J) dissipated during balloon inflation.

Keywords: Balloon; Deformation; Dilation; Eustachian tube; Histology; Mechanics; Pressure.

Graphical abstract caption

Dilation of the Eustachian tube for obstructive dysfunction is performed clinically with 3- and 6-mm-diameter balloons of approximately the same overall length. Our data suggest that dilation with a 6-mm balloon causes greater deformation of the soft tissue structure than dilation with a 3-mm balloon. This difference has yet to be demonstrated clinically. Plastic deformation was measured in terms of energy (J) dissipated during balloon inflation.

Fig. 1

Precision high-pressure syringe driver

Fig. 2

Example pressure-volume loops obtained from BET at 10 bar in silicone (top) and plasticine (bottom) model materials

Fig. 3

Pressure-volume loops for an example 3 mm balloon in a cadaver ET. Three distinct types of pressure-volume loop can be seen; the first cycle, subsequent cycles (2&3) and a balloon-only unconstrained inflation

Fig. 4

Plastic energy dissipation (work done in plastic deformation) during BET with 6 × 15 mm and 3 × 20 mm diameter balloons. n = 5 paired data are included (from opposite ears in the same cadaver head). On each box, the central mark indicates the median, and the bottom and top edges of the box indicate the 25th and 75th percentiles, respectively. The whiskers extend to the most extreme data points

Fig. 5

Pressure-volume loops (with deflation stage removed for clarity) for an example 6.5 × 15 mm balloon in a cadaver ET. Pressure was increased in 4 stages (protocol 2). A different colour has been used for each inflation pressure. The solid line represented the first inflation at each pressure, and the dashed line of the same colour is the second inflation to that pressure. The third inflation had a similar pressure-volume relationship to the second

Fig. 6

Plastic energy dissipation (work done in plastic deformation) for 3.0 × 20 mm and 6.5 × 15 mm balloons (performed in contralateral ears) in 5 heads. Box plots as per Fig. 4

Fig. 7

Histological section showing the apex of the curved ET cartilage in a BET-treated ear. Triangles indicate areas of mucosal tearing and shearing from the submucosa. Arrowheads indicate two cracks in the cartilage radiating from the apex of the ET lumen. Haematoxylin and eosin stain with Alcian blue stain introduced into the ET lumen before BET. ×4 magnification

Fig. 8

Scale diagram of the 3 × 20 mm TubaVent (TV) balloon overlying the 6 × 15 mm EverCross (EC) balloon (6.5 × 15 mm Sterling Monorail balloon not shown on this figure for clarity). Full insertion of both TubaVent and AERA devices is intended during clinical use. The red dashed line indicates the mean point of the narrowest part of the ET based on histological studies