Discussion

The pathophysiology of Eustachian tube dysfunction is complex and not completely understood. Dysfunction can be divided into the better known (and more common) dilatory dysfunction and an inability to adequately close the tube's lumen in its resting position, the ‘patulous Eustachian tube’. Dilatory dysfunction is thought to result in an inadequate supply of air to the middle-ear cleft, thereby contributing to the creation of negative pressure in this chamber.^{Reference Buckingham and Ferrer19} Factors contributing to the pathogenesis of dilatory dysfunction include inadequate peri-tubal muscular activity, congenital malformation such as cleft palate, obstructing masses, chronic and acute inflammation, and surface factors, such as the lack of adequately functioning surfactant.

Eustachian tube dysfunction can result in significant morbidity (and exceedingly rarely in mortality, as a complication of otitis media). Traditionally, treatment was based on circumnavigating the Eustachian tube malfunction by placing a ventilation tube through the tympanic membrane. The advent of balloon Eustachian tuboplasty^{Reference Ockermann, Reineke, Upile, Ebmeyer and Sudhoff20} has allowed for the direct treatment of Eustachian tube dysfunction. Despite these advancements, possible prevention by modifying risk factors could be better utilised.

A number of methods have been developed to measure Eustachian tube dysfunction. Each method has its own merit, but none has been found to be an accurate and clinically relevant tool. McCoul et al. developed the Eustachian Tube Dysfunction Questionnaire;^{Reference McCoul, Anand and Christos21} its Hebrew version has been validated.^{Reference Ungar, Cavel, Golan, Oron, Wasserzug and Handzel18} The questionnaire is emerging as an important tool for assessing Eustachian tube function.^{Reference Van Roeyen, Van de Heyning and Van Rompaey22}

Inspiratory and expiratory upper airway resistance values are higher in OSAS patients than in normal subjects, both during wakefulness and sleep.^{Reference Hudgel23,Reference Anch, Remmers and Bunce24} In individuals with OSAS, airway abnormalities occur both during expiratory and inspiratory phases of ventilation. In order to maintain upper airway patency during inspiration, it appears reasonable that the forces generated by the respiratory pump muscles, which decrease intraluminal upper airway pressure and tend to collapse the airway, should be balanced by dilating forces. The upper airway dilator muscles deliver these dilating forces in normal subjects but fail to do so among OSAS patients.

In candidates for palate surgery due to OSAS, Eustachian tube dysfunction, as measured by the validated Hebrew version of the Eustachian Tube Dysfunction Questionnaire-7, differed significantly from healthy controls. This is a selected group of patients with OSAS severe enough to warrant surgery, with pharyngeal and palatal underlying pathologies. However, others have found an association between obstructive sleep apnoea (OSA) and an increased risk for Eustachian tube dysfunction. Magliulo et al. found that 20 per cent of adults with OSAS had Eustachian tube dysfunction as measured by the Eustachian Tube Dysfunction Questionnaire-7, a metrics combining manometric measurements with additional subjective and objective tools.^{Reference Magliulo, de Vincentiis, Iannella, Ciofalo, Manno and Pasquariello25} In a population-based study, patients with sleep-disordered breathing had a 1.54-times higher risk for Eustachian tube dysfunction.^{Reference Pinto, Ribeiro, da Silva Cavallini, Duarte and Freitas26} The Eustachian tube dysfunction prevalence of 32 per cent in infants with OSA is increased compared to the general paediatric prevalence of 4–7 per cent.^{Reference Robison, Wilson, Otteson, Chakravorty and Mehta6} Sivri et al. found that OSAS treatment with six months of CPAP increased middle-ear pressure,^{Reference Sivri, Sezen, Akbulut and Coskuner27} although Aksoy et al. found no such change.^{Reference Aksoy, Serin, Polat, Ünal and Tanyeri28}

Several studies have investigated possible mechanisms associating OSAS and Eustachian tube dysfunction. In the paediatric population, it is possible that the relationship between OSA and Eustachian tube dysfunction reflects two different clinical manifestations of a common anatomical abnormality such as adenoid hypertrophy.^{Reference Robison, Wilson, Otteson, Chakravorty and Mehta6} Adenoid hypertrophy and adenoiditis may then lead to functional obstruction of the nasopharynx, which subsequently leads to OSA and Eustachian tube dysfunction through blockage and inflammation of the nasal airway and Eustachian tube, respectively.

The increased prevalence of Eustachian tube dysfunction in OSA patients promotes the suggestion that any patient being evaluated for OSAS should also be screened for Eustachian tube dysfunction, to help provide more comprehensive care. In the adult population, where adenoid hypertrophy is less common, smoking, rhinosinusitis, allergic rhinitis, gastroesophageal reflux disease and obesity are risk factors for both OSAS and Eustachian tube dysfunction, and may serve as confounders in this setup.^{Reference White, Heavner, Hardy and Prazma2–Reference Brunworth, Mahboubi, Garg, Johnson, Brandon and Djalilian4,Reference McNicholas, Tarlo, Cole, Zamel, Rutherford and Griffin29–Reference Yasan, Doǧru, Tüz, Çandir, Uygur and Yariktaş31} The effect of these possible confounders on the development of Eustachian tube dysfunction has been analysed previously; it was found that the risk of developing Eustachian tube dysfunction was significantly higher in the OSAS patients, even those without any confounders.^{Reference Chou, Chang, Lin, Li and Tsou8} Eustachian tube dysfunction has been shown to be more prevalent among OSAS patients than in the general population using several Eustachian tube assessment methods.^{Reference Magliulo, de Vincentiis, Iannella, Ciofalo, Manno and Pasquariello25} This is possibly because patients with OSA often show severe nasal obstruction, chronic sinusitis, and/or a deficit of nasal mucociliary clearance with nasopharyngeal stagnation of secretions.^{Reference Robison, Wilson, Otteson, Chakravorty and Mehta6,Reference Pinto, Ribeiro, da Silva Cavallini, Duarte and Freitas26,Reference McNicholas, Tarlo, Cole, Zamel, Rutherford and Griffin29,Reference Olsen, Kern and Westbrook30}

The immediate and prolonged impact of conservative interventions (such as CPAP) and surgical procedures (such as expansion sphincter pharyngoplasty) for OSAS, is a subject of controversy in the literature. Because the risk of Eustachian tube dysfunction was found to be increased in patients with OSAS,^{Reference Robison, Wilson, Otteson, Chakravorty and Mehta6–Reference Chou, Chang, Lin, Li and Tsou8} treatment of OSAS could potentially improve Eustachian tube dysfunction. The possible benefits of OSAS surgery include a reduction in the obstructive pressure of the Eustachian tube, as well as an increase in the normal physiological function of this structure. For example, adenoid enlargement has been reported to not only occlude the nasopharyngeal opening of the Eustachian tube but also to impair mucociliary clearance through fibrotic changes in the neighbouring adenoid tissue.^{Reference Yasan, Doǧru, Tüz, Çandir, Uygur and Yariktaş31} Additionally, septoplasty and turbinoplasty are associated with improved nasal mucociliary clearance.^{Reference Polat and Dostbil32,Reference Cassano, Granieri, Del Giudice, Mora, Fiocca-Matthews and Cassano33}

In our study, there was immediate impairment in Eustachian tube function post-operatively, probably due to local oedema, a change in peri-tubal muscular activity, the presence of an NG tube and oral breathing. In addition to their direct effect of Eustachian tube dysfunction, these factors may negatively impact mucociliary clearance. Mucociliary function has been found to differ in patients with OSAS compared to controls.^{Reference Magliulo, de Vincentiis, Iannella, Ciofalo, Manno and Pasquariello25} From post-operative day 7 to 70, during a 9-week period, there was a gradual but persistent improvement in Eustachian tube function. At post-operative day 70, 10 weeks after the operation, the surgical wound had healed completely, and the Eustachian Tube Dysfunction Questionnaire scores were similar to those pre-operatively. This suggests that, in the long term, expansion sphincter pharyngoplasty had no effect on Eustachian tube dysfunction. A temporary negative effect of OSAS surgery on middle-ear function was observed after palatopharyngoplasty^{Reference Lin, Friedman, Chang, Shao, Pulver and Chen34} and the placement of Pillar^® implants.^{Reference Lin, Friedman, Chang, Lai, Chin and Lin35}

Conservative management of OSA included CPAP, among other treatment options (e.g. weight reduction and use of a dental appliance), which is always offered prior to surgical intervention. In our cohort (n = 31), 25 patients (81 per cent) tried using CPAP prior to expansion sphincter pharyngoplasty. Six patients did not try CPAP: three refused a trial, two were unable to appropriately seal the face mask and one suffered claustrophobia. Hence, the majority of pre-operative (basic) Eustachian Tube Dysfunction Questionnaire-7 scores were calculated among active CPAP-using patients. A parallel cohort (n = 43) with moderate to severe OSA patients who efficiently use CPAP with good results (making surgery unnecessary) could not be compared to the surgical cohort, because significant demographic and metabolic (age, gender distribution and BMI) differences were found, and these are likely to be confounders (age and BMI).

This study has two major limitations. One is the relatively small cohort size (31 OSAS patients vs 99 controls). The second limitation, which is common to other studies, is the possible presence of confounders that might be independent risk factors for Eustachian tube dysfunction, such as morbid obesity, gastroesophageal reflux disease and sinusitis, which are more common among OSAS patients than in healthy controls. In addition, tympanometry was not routinely performed in the cohort. Manometry may pose significant discomfort for patients undergoing pharyngopalatal surgery.