Eustachian Tube Function in Adults Without Middle Ear Disease

Abstract

Objectives

We sought to develop normative values for 5 eustachian tube function (ETF) test protocols in adults without otitis media (OM).

Methods

Twenty adults (19 to 48 years of age) without a recent history of OM (5 had OM in childhood) underwent unilateral myringotomy and were evaluated for ETF by use of the forced response, inflation, deflation, forcible “sniff,” and Valsalva test protocols. When possible, these tests were repeated on a second day.

Results

Normative values for the parameters of these protocols in adult subjects without a recent history of OM were developed. Between-day data for the forced response test were highly correlated. A percentage of these tests showed eustachian tube “constriction” during swallowing — an abnormal condition. The percent reduction in applied pressures for the inflation and deflation tests was high, indicative of good ETF. Few subjects had a positive “sniff” test, whereas most had a positive Valsalva test, and the results for both tests were effort-dependent.

Conclusions

Results of ETF tests in adults with and without recent OM have not been published. Normative data are now available for comparison with ETF test results in adults with OM. These protocols will be used to evaluate the efficacy of surgical procedures designed to improve ETF.

INTRODUCTION

Although primarily a disease of infants and children, otitis media (OM) also occurs with significant frequency in adolescents and adults.^{1, 2} It is defined as an inflammation of the middle ear (ME) mucosa with or without the presence of an effusion in the normally air-filled ME cavity. The most common complication of OM is a fluctuating conductive hearing loss³ that can accentuate the sensorineural hearing loss that often accompanies aging.⁴ A variety of causes have been advanced to explain OM in adults, including upper respiratory tract virus infection, ⁵ nasopharyngeal carcinoma, ⁶ sniffing-induced ME underpressures, ⁷ exposure to hyperbaric oxygen, ⁸ allergy, ⁹ gastroesophageal reflux disease, ¹⁰ sinusitis and chronic rhinitis, ¹ and abnormal eustachian tube function (ETF), ¹¹ among others. Of these, abnormal ETF plays an integrating role, because the other causes either adversely affect ETF or reflect functional insufficiencies. Moreover, experimental eustachian tube (ET) dysfunction is a sole and sufficient cause for the development of persistent OM in animals.¹²

The usual treatment for poor ETF and/or persistent OM (lasting from months to years) in adults is to aerate the ME either by performing a myringotomy or by inserting a ventilation tube through the tympanic membrane (TM). However, although these procedures provide temporary relief of the condition and improve hearing, the disease often recurs after the myringotomy has healed or the tympanostomy tube has been either blocked or extruded, and otorrhea through the tube is a common problem.²

More recently, a variety of surgical procedures focusing on the nasopharynx and the nasopharyngeal orifice of the ET were developed and were reported to provide a long-term cure for physician-diagnosed ET dysfunction or persistent OM in adults.^13–17 However, those studies did not include a control group, and few documented the effects on the ostensible goal of the procedures, ie, improved ETF.^{16, 17} When evaluated, the methods used to test ETF and the information obtained from those tests were found to be limited.

There are a variety of tests to measure ETF in ears with an intact TM, including modifications of tympanometry, ¹⁸ sonotubometry, ¹⁹ forcible sniffing, ⁷ the Valsalva maneuver, ²⁰ nasal endoscopy, ²¹ the Toynbee maneuver, ²² and the inflation and deflation tests, ²³ among others. However, many of these tests provide limited or selective information regarding ETF, and the best results for some are obtained in a pressure chamber, ²³ an expensive and complicated instrument that is not readily available. In contrast, a variety of protocols to evaluate ETF in ears with a non-intact TM have been described, and these provide more complete information on both the active and passive properties of the ET.²⁴ However, although these tests have been used extensively in children with tympanostomy tubes inserted to prevent and/or treat OM, and have been used in animals to characterize “normal” and “abnormal” ETF, ¹² there is little information on the results of those tests in individuals without a recent history of OM, because they require a non-intact TM. Indeed, the only data available for these tests on “normal” adults (or children) are the results for three test protocols (the forced-response test [FRT], the inflation test, and the deflation test) performed on only 6 adults (average age, 29 years) with traumatic perforations of the TM — a condition that may or may not be representative of a normal ME.²⁴

The purposes of the present study were to evaluate ETF by use of a variety of test protocols in adult subjects without ME disease after an experimental myringotomy and to establish normative test values for those protocols.

METHODS

The study was approved by the University of Pittsburgh Institutional Review Board. Healthy male and female subjects of more than 18 years of age of any race were recruited by advertisement. The respondents signed an Institutional Review Board–approved informed consent and were screened for generally good health by history and physical examination, normal ME status by pneumatic otoscopy and tympanometry, normal hearing by audiometry using standard clinical tests, and, if female, pregnancy by a urine pregnancy test. They were also asked whether they had had OM as a child. Subjects were excluded if they were unable to comprehend the risks of the study and/or to provide written informed consent; or if they had any chronic health problem, a baseline hearing threshold of more than 15 dB or a more than 10-dB air-bone gap at any of the speech frequencies, abnormal mobility of the TM or ear disease at the time of presentation, a history of sensitivity or allergic reaction to lidocaine or related compounds, or a positive pregnancy test.

For qualifying subjects, the protocol included a general otolaryngological examination; a unilateral myringotomy performed by an otolaryngologist; ETF testing on that day (session 1); and repeat testing on the next day (session 2). At approximately weekly intervals until the TM had healed, the status of the TM was evaluated by pneumatic otoscopy and tympanometry. Audiological testing was repeated after the perforation healed.

Before performing the myringotomy, the physician examined both external auditory canals and TMs to determine which would be most suitable for use in the experiment. The subjects lay supine on an examination table with the head rotated to expose the experimental ear, the TM was visualized through a speculum with the aid of an operating microscope, and 4% lidocaine hydrochloride (with epinephrine) was applied topically for 20 minutes. An approximately 3- to 4-mm radial incision was made unilaterally in the anterior-inferior quadrant of the TM with a myringotomy knife. A non-patent TM was confirmed by pneumatic otoscopy and tympanometry.

The ETF tests consisted of 5 protocols: the FRT, the inflation test, the deflation test, the “sniff” test, and the Valsalva test. Before each set of tests, the patency of the TM was checked by pneumatic otoscopy and tympanometry.

For the FRT, a hermetically sealed plastic probe was introduced into the ear canal of the incised TM. The probe was coupled to a flow sensor, a pressure transducer, and, via a 3-way valve, a variable-speed, constant-flow pump as described by Cantekin et al.²⁴ For the test, the pump delivered a constant airflow (QO) through the TM incision to the ME, increasing the ME pressure until it caused the ET to passively open (opening pressure; PO). Continued flow usually resulted in an equilibrium system pressure (PS). Once the equilibrium pressure was established, the subject was instructed to swallow — an action that is associated with ET opening — and the pre-swallow system pressure (PA) and the maximum airflow (QA) during the swallow were recorded. The pump was then turned off to allow the ET to passively close (PC). The FRT variables analyzed for this report are the PO, the PC, passive ET resistance (RS = PS/QO), active ET resistance (RA = PA/QA), and ET dilatory efficiency (DE = RS/RA). Because the RA and DE were not normally distributed, they were log-transformed before the analyses. At each session, this test procedure was performed at two constant airflow rates: approximately 11 mL/ min and approximately 23 mL/min.

For the inflation test, the probe was sealed in the ear canal and attached to the measuring system. By use of the constant-flow pump (flow rate, 10 mL/min), the ME pressure was increased to a positive pressure of approximately 150 daPa (reference ambient), and the subject was asked to swallow repeatedly until the ME pressure no longer changed. The analytic variable was this final pressure divided by the applied pressure. The deflation test was performed and analyzed in a similar manner with an applied pressure of approximately −150 daPa.

For the “sniff” and Valsalva tests, the probe, attached to the measuring system, was sealed in the ear canal and then purged to ambient pressure (0 daPa). During the test, the nasal pressure was measured by a second pressure sensor connected to a nasal olive held against one naris. The subject was asked to perform a forcible “sniff,” and concurrent pressures in the nose (ie, nasopharynx) and ME during the maneuver and any residual ME pressure were recorded. The ME system pressure was reduced to 0 daPa, and the subject was asked to perform the Valsalva maneuver, and those variables were again recorded.

Comparison of values between conditions was made with a 2-tailed Student t-test evaluated at α = 0.05. Relationships between variables were quantified with the Pearson product-moment correlation coefficient (r) with a significance of r > 0 evaluated at α = 0.05. Standard summary statistics were expressed as the average ± SD and the range of values.

RESULTS

A total of 47 subjects were screened; 14 did not qualify, and 13 were lost to follow-up before the myringotomy. Of the 20 subjects enrolled, there were 8 women and 12 men with a self-reported racial distribution of 12 white, 7 black, and 1 Asian. Their average age was 30 ± 10 years (range, 19 to 48 years), and 5 reported a history of OM during childhood. Seven right ears and 13 left ears were studied.

No adverse events were recorded during the study period, and the pre-myringotomy and post-myrin- gotomy audiometric testing results were within 5 dB of the baseline values at the different frequencies. The TM perforation of 5 subjects healed within 1 day of the myringotomy; therefore, they could not complete session 2. The average duration of the TM perforation was 12 ± 8 (range, 1 to 25) days.

For the session 1 FRTs, none of the variables were recorded for 1 subject at the 23 mL/min flow rate because of an inability to maintain an adequate probe–ear canal seal. Also, for 1 subject at that flow rate and 2 subjects at the 11 mL/min flow rate, the RS, RA, and DE could not be recorded, because the flow rate never achieved an equilibrium condition; instead, it oscillated, possibly reflecting passive ET opening and closing. Table 1 reports the sample size, average value, SD, and range of the 5 variables recorded during session 1 at the 2 flow rates. Similar results were observed for the FRTs at session 2 (data not shown), and there was no significant between-session difference for any variable (p > 0.162 for all comparisons).

TABLE 1.

VALUES FOR FIVE FORCED-RESPONSE VARIABLES RECORDED AT FLOW RATES OF 11 AND 23 ML/MIN DURING SESSION 1

Variable	11 mL/min	23 mL/min	Student’s t	p
PO
N	20	19
Average	328	318	0.34	0.740
SD	90	93
Minimum	164	161
Maximum	486	434
PC
N	20	19
Average	80	66	1.05	0.301
SD	46	33
Minimum	10	12
Maximum	194	120
RS
N	18	18
Average	15.8	8.3	4.48	<0.001
SD	6.0	3.8
Minimum	7.7	3.0
Maximum	31.1	18.7
RA*
N	18	18
Average	0.51	0.69	−0.75	0.456
SD	0.56	0.79
Minimum	−0.33	−0.15
Maximum	2.33	2.47
DE*
N	18	18
Average	0.66	0.19	2.15	0.039
SD	0.54	0.74
Minimum	−1.07	−1.46
Maximum	1.42	0.93

PO — opening pressure (daPa); PC — closing pressure (daPa); RS — steady-state resistance (daPa/mL per minute); RA — active resistance (daPa/mL per minute); DE — dilatory efficiency (log ratio).

^*Log-transformed.

For session 2, no results were obtained on 5 subjects, because their perforation had healed. No results were recorded at either flow rate in 1 subject, or in 1 additional subject at the 11 mL/min flow rate, because the pressure-flow patterns were interrupted by repeated swallowing. Also, the RS, RA, and DE could not be recorded in 1 subject at the 11 mL/min flow rate or in 1 subject at the 23 mL/min flow rate, because the ET opened and closed passively.

Table 2 reports the available sample size, Pearson correlation coefficient (r), 2-tailed Student t-value, and associated probability for the comparisons of the 5 variables between the first and second FRTs at the 11 and 23 mL/min flow rates. All correlations were statistically significant, with the percent explained variance ranging between 36% and 89%.

TABLE 2.

CORRELATION BETWEEN FIVE FORCED-RESPONSE VARIABLES RECORDED AT TWO TEST SESSIONS FOR FLOW RATES OF 11 AND 23 ML/MIN

Variable		Session 1 vs Session 2 at 11 mL/min	Session 1 vs Session 2 at 23 mL/min
PO
	N	13	13
	r	0.830	0.688
	Student’s t	5.148	3.142
	p	<0.001	0.009
PC
	N	13	13
	r	0.665	0.624
	Student’s t	3.084	2.651
	p	0.010	0.023
RS
	N	10	11
	r	0.598	0.886
	Student’s t	2.239	5.717
	p	0.050	<0.001
RA*
	N	10	11
	r	0.911	0.793
	Student’s t	6.606	3.907
	p	<0.001	0.004
DE*
	N	10	11
	r	0.831	0.703
	Student’s t	4.481	2.964
	p	0.002	0.016

r — Pearson product-moment correlation coefficient.

^*Log-transformed.

During the FRT, a variety of pressure-flow patterns were observed with swallowing. Of interest are those tests in which the RA was greater than the RS (ie, DE < 1) — an abnormal condition that has been associated with poor ETF.¹² For session 1, this occurred in 1 of 18 subjects (6%) at the 11 mL/min flow rate and in 4 of 18 subjects (22%) at the 23 mL/min flow rate. For session 2, this occurred in 1 of 12 subjects (8%) at the 11 mL/min flow rate and in 3 of 13 subjects (23%) at the 23 mL/min flow rate.

For the inflation test at session 1 (N = 17; 3 subjects could not maintain applied positive pressures) and session 2 (N = 12), the average values of the percent pressure equilibrated by swallowing were 83% ± 22% (range, 28% to 100%) and 82% ± 30% (range, 0% to 100%), respectively. For the deflation test at sessions 1 and 2, the average values of the percent pressure equilibrated by swallowing were 67% ± 26% (range, 17% to 100%) and 71% ± 37% (range, 0% to 100%), respectively.

The Figure shows the nasal, ME, and residual pressures during forced sniffing and during the Valsalva maneuver for session 1. Two subjects did not complete these tests. For the “sniff” test at session 1, ME underpressures during sniffing occurred in only 2 subjects (−485, −376 daPa), and only 1 of these had a residual pressure (−233 daPa). The average nasopharyngeal pressure was −598 ± 188 (range, −1, 023 to −334) daPa. Similar results were observed at session 2 (N = 13), in which 3 subjects developed an ME underpressure (−132, −265, −83 daPa) and 2 had a residual pressure (−132, −82 daPa). The average nasopharyngeal pressure was −555 ± 163 (range, −1, 039 to −300) daPa. In general, greater induced nasopharyngeal underpressures were related to a positive “sniff” response, and for the combined data set (sessions 1 and 2), this correlation was statistically significant (p < 0.001).

For the Valsalva test at session 1 (N = 18), 5 subjects failed to develop a positive ME pressure and 7 failed to maintain a residual ME pressure after completion of the maneuver. The average nasopharyngeal pressure was 707 ± 318 (range, 200 to 1, 153) daPa, the peak ME pressure was 449 ± 414 (range, 0 to 1, 109) daPa, and the residual ME pressure was 54 ± 68 (range, 0 to 243) daPa. Similar results were observed at session 2 (N = 14), in which 2 subjects failed to develop a positive ME pressure and 4 failed to maintain a residual ME pressure after completion of the maneuver. The average nasopharyngeal pressure was 702 ± 275 (range, 285 to 1, 156) daPa, the peak ME pressure was 485 ± 387 (range, 0 to 1, 156) daPa, and the residual ME pressure was 68 ± 77 (range, 0 to 267) daPa. In general, greater nasopharyngeal pressures were related to a positive Valsalva test, and for the combined data set (sessions 1 and 2), this correlation was statistically significant (p < 0.011).

DISCUSSION

Persistent OM and clinically diagnosed ET dysfunction are relatively common in adults, and these conditions are usually treated with myringotomy and/or ventilation tubes.² This treatment provides an ideal opportunity to use sophisticated tests of ETF that require a non-intact TM to confirm the clinical diagnosis in the latter case and to test the efficacy of various procedures designed to improve ETF for both conditions. The purpose of this report is to establish normative values for the FRT, inflation and deflation tests, “sniff” test, and Valsalva maneuver in otherwise healthy adults with no current or recent history of ear disease. To accomplish this goal, we performed a unilateral myringotomy on 20 adult subjects.

The FRT was first described by Cantekin et al²⁴ and has been used to evaluate ETF in children with ventilation tubes inserted for OM, in populations “at risk” for the disease, and in animals with and without surgical manipulations designed to debilitate the ET.¹² However, few data on FRT results are available for “normal” adults.²⁴ Our data for the parameters of this test show moderate reproducibility across days. Moreover, our data for the PO and RS at the two flow rates are similar to those reported by Cantekin et al²⁴ for their “control group” of 6 adult subjects with traumatic perforations and for 5 adults with chronic perforations, but the values we recorded for the RA are larger and those for the DE are smaller. This is a consequence of the observed values of the DE that were less than 1 for the FRTs in our study — a phenomenon that was not reported in the earlier study for either group of adults irrespective of ME status. However, in later studies, this type of response was observed frequently in adults and children with concurrent OM, in those “at risk” for that disease, and in animals in which the ETF was debilitated by various means.^{11, 12} When compared to the results of one study of older children and adults with ventilation tubes inserted for OM, ¹¹ our values for the PC and RS are similar, those for the PO and RA are less, and those for the DE are greater — findings indicative of better function in the “normal” adult population.

Our results for the inflation and deflation tests are difficult to compare with those for previous studies of “normal” adults, in which testing was typically done in a pressure chamber.²³ Those results followed the classification scheme developed by Elner (cited by Bylander et al²³) and were qualitative in nature. We chose to quantify these test results as the percent of applied pressure that was equilibrated by swallowing. For the inflation test, an average of approximately 83% of the applied pressure was equilibrated, and for the deflation test, that percentage was approximately 69%. These results reflect good ETF.

The “sniff” test was developed by Magnuson and Falk, ⁷ who reported that approximately 70% of children evidencing OM with effusion developed ME underpressures by forcible sniffing and suggested that this response indicated ET closing failure.²⁵ In a population with “normal ears,” Falk²⁵ used tympanometry to evaluate the percentage of subjects who had a residual pressure after forcible sniffing and reported a value of 14%. In this study, we were able to quantify both the percentage of subjects who induced ME underpressures with forcible sniffing and the percentage who maintained a residual ME pressure after the maneuver. In our series of 32 tests, only 5 subjects (16%) showed a change in ME pressure during the maneuver and only 3 (10%) maintained a residual underpressure — a value not different from that reported by Falk²⁵ for “normal” subjects. Those who developed greater nasopharyngeal underpressures were more likely to induce ME underpressures during the maneuver; this finding suggests that the test results are effort-dependent.

The Valsalva maneuver is often used to equilibrate ME pressure to ambient during descent in an airplane and during diving to reduce ear pain and prevent barotitis, but it is limited as a test of ETF.^{20, 26} Across sessions, our data indicated that the majority of adult subjects (81%) could induce ME overpressures and that 66% maintained post-maneuver ME overpressures. Similar to the results for forcible sniffing, the frequency of positive test results was directly dependent on the induced nasopharyngeal pressure, and the success of the procedure is effort-dependent.

In summary, the results of this study provide normative data for adults without concurrent or a recent history of ME disease. These data provide the context for the results of similar tests done in patients with clinically diagnosed ET dysfunction in order to thereby confirm or refute that diagnosis. Additionally, the set of tests documenting ETF effects before and after the newer surgical procedures designed to improve ETF in adults with ME disease were relatively primitive, ^{16, 17} and their results suggesting improved function following the procedures can be questioned. Ideally, the efficacy of these interventions should be evaluated in a controlled clinical study implementing these more objective tests of ETF.