DIAGNOSIS AND TESTS OF FUNCTION
ET function tests can distinguish between normal and abnormal function, but the most physiologic test is the status of the patient’s ears over time when the tympanic membranes are intact.
The chapter includes
• Currently available clinical and laboratory diagnostic tests of the function of the ET system.
• Pressure chamber for ET function test for intact tympanic membrane.
New in this second edition is the description of our relatively unique pressure chamber that can test ET function in our laboratory when the tympanic membrane is intact, which is more physiologic than tests that are used when the eardrum in not intact, such as perforation, tympanotomy tube, or when a mastoidectomy is present.1,2 Many of these procedures are briefly referred to in other chapters, but here they are described in detail. The reader should use this chapter as a reference for a more comprehensive description of the available diagnostic tests and procedures.
Several of these tests are fairly accurate in distinguishing between normal and abnormal structure and function of the ET system, but none is truly physiologic because most only measure a short period in an individual’s life and some are invasive. The most physiologic assessment of the function of the tubal system is to observe the status of the individual patient and his or her ears, when the tympanic membranes are intact, over a relatively prolonged period of time. The best test is how is the patient doing? But because some middle-ear diseases and disorders are relatively asymptomatic (silent), periodic evaluation of the patient is prudent.
The methods described are presented related to the access to the middle ear (intact vs nonintact tympanic membrane) because the testing will not be the same. Assessment of the nasopharyngeal end of the tube is dependent on the age and cooperation of the patient.
Methods to assess the pressure-regulation function of the system are readily available to the clinician and should be performed when indicated (described later). Also, function tests available for clinical and laboratory studies are presented. The pressure-regulation function is the most important of the three functions since adequate hearing depends on relatively equal air and gas pressure on both sides of the tympanic membrane being maintained. In addition, impairment of the pressure-regulation function can result not only in middle-ear under-pressures and symptoms of ET dysfunction but also otitis media and certain related diseases (such as perforation of the tympanic membrane) and disorders (atelectasis or retraction pocket). Tests to assess the protective and clearance functions are also addressed.
History and Physical Examination
When assessing patients who have diseases and disorders related to the ET system, a medical history related to the whole body is important because there are conditions that affect ET function. For example, a history of recent weight loss could indicate a patulous ET. Specific information on recurrent or chronic symptoms referable to the ears, nose, and throat is also important, such as pharyngeal, nasal, and sinus disease (allergy) that can affect the tubal system. In obtaining the history, it is important to determine the frequency, severity, and duration of otitis media and related diseases and disorders (signs and symptoms of ET dysfunction, such as fluctuating hearing loss, otalgia, vertigo, and tinnitus, including popping and snapping sounds in the ear or autophony). Otologic symptoms during pregnancy, puberty, flying in airplanes, swimming, and diving (especially scuba diving) can be helpful.
The physical examination should include the ears, nose, and throat, even if the patient only has symptoms referable to the ears. In addition to the otoscopic examination, an examination of the nasopharynx may reveal the underlying pathology of the proximal end of the ET system. Examination of the nasal cavities and nasopharynx may reveal obstruction that can affect the ET and middle ear. An example of how nasal and nasopharyngeal obstruction, in conjunction with ET dysfunction, is in our recent publication of a case of alternobaric vertigo.3 Following examination of the external ear and canal, the clinician may proceed to the most important part of the physical assessment, the otoscopic examination.
Otoscopy, using a pneumatic attachment, to visually inspect the tympanic membrane is one of the simplest and oldest ways to assess the middle-ear end of the ET system. The appearance of a middle-ear effusion, the presence of high negative middle-ear pressure, or both, determined by a pneumatic otoscope,4 is presumptive evidence of ET dysfunction; however, the type of impairment, such as functional or mechanical obstruction, and the degree of abnormality cannot be determined by this method. A reasonable assessment of middle-ear pressure is possible by proper use of the pneumatic otoscope (see later). Moreover, a normal-appearing tympanic membrane is not evidence of a normally functioning ET; for example, a patulous or semi-patulous ET may be present when the tympanic membrane appears to be normal, with normal mobility to pneumatic otoscopy. In addition, the presence of one or more of the complications or sequelae of otitis media (e.g., a perforation or atelectasis that can be seen through an otoscope) may not correlate with dysfunction of the ET at the time of the examination because tubal function may have improved with growth and development.
For proper assessment of the tympanic membrane and its mobility, a pneumatic otoscope in which the diagnostic head has an adequate seal should be used. The quality of the otoscopic examination is limited by deficiencies in the designs of commercially available otoscopes. The speculum employed should have the largest lumen that can comfortably fit in the patient’s cartilaginous external auditory meatus. If the speculum is too small, adequate visualization may be impaired and the speculum may touch the bony canal, which can be painful. In most models, an airtight seal is usually not possible because of a leak of air within the otoscope head or between the stiff ear speculum and the external auditory canal; leaks at the latter location can be stopped by cutting a small section of rubber tubing and slipping it over the tip of the ear speculum (Figure 8–1).
Many otolaryngologists prefer to use a Bruening or a Siegle otoscope with the magnifying lens. Both of these instruments allow for excellent assessment of drum mobility because they have an almost airtight seal. A head mirror and lamp or a headlight is necessary to provide light for the examination. The examination is most accurate with the use of an otomicroscope and a nonmagnifying lens on the otoscope (Figure 8–2). It is important to examine a patient who is suspected of having a patulous ET while in the sitting position.
Inspection of the tympanic membrane should include evaluation of its position, color, degree of translucency, and mobility.
Tympanic Membrane Position
The normal eardrum should be in the neutral position, with the short process of the malleus visible but not prominent through the membrane. Mild retraction of the tympanic membrane usually indicates negative middle-ear pressure, an effusion, or both. The short process of the malleus and the posterior mallear fold are prominent, and the manubrium of the malleus appears to be foreshortened. Severe retraction of the tympanic membrane is characterized by a prominent posterior mallear fold and short process of the malleus and a severely foreshortened manubrium. The tympanic membrane may be severely retracted, presumably owing to high negative pressure in association with a middle-ear effusion. Fullness of the tympanic membrane is initially apparent in the posterosuperior portion of the pars tensa and pars flaccida because these two areas are the most highly compliant parts of the tympanic membrane.5 The short process of the malleus is commonly obscured. The fullness is caused by increased air pressure, effusion, or both within the middle ear. When bulging of the entire tympanic membrane occurs, the malleus is usually obscured, which occurs when the middle ear–mastoid system is filled with an effusion. A bulging tympanic membrane can be visualized in infants (who have no middle-ear effusion) during crying, which is indicative of positive pressure in the middle ear. Presumably, the positive pressure is related to insufflation of nasopharyngeal air into the middle ear; infants have short, floppy ETs (see Chapter 4, “Physiology”). Smith and colleagues identified positive pressure tympanograms in infants who were otoscopically without middle-ear effusion.6
Tympanic Membrane Appearance
Normally, the tympanic membrane has a ground-glass appearance; a blue or yellow color usually indicates a middle-ear effusion seen through a translucent tympanic membrane (Figure 8–3). A red tympanic membrane alone may not be indicative of a pathologic condition because the blood vessels of the drum head may be engorged as a result of the patient’s crying, sneezing, or nose blowing. It is critical to distinguish between translucency and opacification of the eardrum to identify a middle-ear effusion. The normal tympanic membrane should be translucent, and the observer should be able to look through the drum and visualize the middle-ear landmarks (the incudostapedial joint promontory, the round window niche, and, frequently, the chorda tympani nerve) (Figure 8–4). When middle-ear effusion is present medial to a translucent drum, an air-fluid level or bubbles of air admixed with the liquid may be visible. An air-fluid level or bubbles can be differentiated from scarring of the tympanic membrane by altering the position of the head while observing the drum with the otoscope (if fluid is present, the air-fluid level will shift in relation to gravity) or by seeing movement of the fluid during pneumatic otoscopy. The line frequently seen when a severely retracted membrane touches the cochlear promontory will disappear (the drum will pull away from the promontory) if sufficient negative pressure can be applied with the pneumatic otoscope. Inability to visualize the middle-ear structures indicates opacification of the drum, which is usually the result of thickening of the tympanic membrane, an effusion, or both.
Tympanic Membrane Mobility and Middle-Ear Pressure
To visualize a retracted tympanic membrane (atelectasis and retraction pocket notwithstanding) or to assess the mobility of the tympanic membrane, using the pneumatic otoscope is one of the simplest ways to diagnose abnormal pressures within the middle ear, which can provide some insight into ET function; however, pneumatic otoscopy is not an ET function test.
Abnormalities of the tympanic membrane and the middle ear are reflected in the pattern of tympanic membrane mobility when first positive and then negative pressure is applied to the external auditory canal with the pneumatic otoscope. As shown in Figure 8–5, this is achieved by first applying slight pressure on the rubber bulb (positive pressure) and then, after momentarily breaking the seal, releasing the bulb (negative pressure) (Figure 8–6). When the tympanic membrane and middle ear are normal, forceful application of positive and negative pressure (deeply depressing and releasing the thumb on the rubber bulb) can be painful, especially in children because the tympanic membrane is overdistended. If the tympanic membrane does not move when slight pressure is applied, more pressure is applied. The presence of effusion, high negative pressure, or both within the middle ear can markedly dampen the movements of the eardrum. Figure 8–7 shows the relationship between applied positive and negative pressures. When the middle-ear pressure is ambient, the normal tympanic membrane moves inward with slight positive pressure in the ear canal and outward with slight negative pressure. The motion observed is proportionate to the applied pressure and is best visualized in the posterosuperior quadrant of the tympanic membrane. If a two-layered membrane or an atrophic scar (owing to a healed perforation) is present, mobility of the tympanic membrane can also be assessed more readily by observing the movement of the flaccid area.
HYPERCOMPLIANT TYMPANIC MEMBRANE Movement of the tympanic membrane to the applied pressure from the rubber bulb attached to the otoscope can determine, in general, whether there is relatively normal or abnormal pressure within the middle ear, a possible effusion, or both. A hypermobile eardrum is seen most frequently when the tympanic membrane is either atrophic or flaccid. If the mobility of the tympanic membrane is greater than normal, the eardrum will move when even slight positive and negative external canal pressure is applied. The drum is highly compliant, which is usually due to ET dysfunction because the tympanic membrane has gone through excessive movement during pressure regulation. The pattern of a tympanogram also shows a hypercompliant tympanic membrane pattern; however, this pattern on a tympanogram can also indicate a dimeric membrane and not a totally flaccid eardrum; otoscopy is important in distinguishing if just a segment of the eardrum or the entire tympanic membrane is floppy. Even in the face of a hypercompliant eardrum, the drum could move equally well to both applied positive and negative pressures, which indicates that the middle-ear pressure is probably normal; however, if the tympanic membrane is hypermobile to applied negative pressure but immobile when positive pressure is applied, the tympanic membrane is flaccid and negative pressure is present within the middle ear. A middle-ear effusion is rarely present when the tympanic membrane is hypermobile, even though high negative middle-ear pressure is present, because the effusion will dampen the movement of the eardrum.
NEGATIVE MIDDLE-EAR PRESSURE Normal middle-ear pressure is reflected by the neutral position of the tympanic membrane as well as by its response to both positive and negative pressures (described earlier). In other cases, the eardrum may be retracted, usually because negative middle-ear pressure is present. The compliant membrane is maximally retracted by even moderate negative middle-ear pressure and hence cannot visibly be deflected inward further with applied positive pressure in the ear canal; however, negative pressure produced by releasing the rubber bulb of the otoscope will cause a return of the eardrum toward the neutral position if a negative pressure equivalent to that in the middle ear can be created by releasing the rubber bulb. This is a condition that can occur when gas, with or without an effusion, is present in the middle ear. When middle-ear pressure is even lower, there may be only slight outward mobility of the tympanic membrane because of the limited negative pressure that can be exerted through the otoscopes currently in use. If the eardrum is severely retracted, owing to extremely high negative middle-ear pressure, application of maximum negative pressure with the rubber bulb will not produce significant outward movement.
It is possible, with some experience, to make a reasonable estimate of the degree of negative pressure in the middle ear. Comparing the otoscopist’s estimate with the tympanometric measurement of middle-ear pressure, which is a relatively accurate “gold standard,” can improve the otoscopist’s expertise (see Tympanometry).
POSITIVE MIDDLE-EAR PRESSURE A tympanic membrane that exhibits fullness will move to applied positive pressure but not to applied negative pressure if the pressure within the middle ear is positive and if gas, with or without an effusion, is present. In such an instance, the tympanic membrane is stretched laterally to the point of maximal compliance and will not visibly move outward any farther to the applied negative pressure; it will move inward to applied positive pressure as long as some air is present within the middle ear–mastoid air cell system. Positive middle-ear pressure has been identified in infants who had no middle-ear effusion,6 which is most likely secondary to insufflation of nasopharyngeal air into the middle ear during crying. When this system is filled with an effusion and little or no gas is present, the mobility of the bulging tympanic membrane is severely decreased or absent to both applied positive and negative pressure.
PATULOUS ET Despite mobility of the tympanic membrane being normal to applied positive and negative pressures with an otoscope, there can still be dysfunction of the tubal system, such as when the patient has a patulous ET (too open). When this occurs, the observer should be able to detect slight movement of the tympanic membrane synchronous with respirations. When attempting to diagnose this dysfunction of the tube, it is important to have the patient in a sitting position because a patulous tube is usually asymptomatic while in the recumbent position (sleeping).7 This phenomenon is due to congestion of the ET secondary to venous engorgement of the tube; veins of the head and neck have no valves, in contrast to the extremities.
Nasopharyngoscopy and Endoscopy of the ET
Indirect mirror examination of the nasopharyngeal end of the ET system is also an old but still important part of the clinical assessment of a patient with middle-ear disease. This is especially true in adults, in whom a neoplasm in the fossa of Rosenmüller may be diagnosed. The development of endoscopic instruments has greatly improved the accuracy of this type of examination (Figure 8–8). The flexible fiberoptic telescope has been used to examine the ET from the nasopharyngeal and middle-ear end of the tube (Figure 8–9).5 Figure 8–10 shows a nasopharyngeal carcinoma as viewed with the endoscope.
Not only can certain aspects of the structure of the ET be determined with the aid of currently available instruments, but some investigators have assessed ET function.9–12 Yagi and colleagues used a fiberscope—a photoelectric device (phototubometry) to evaluate the patency of the ET.13 Takahashi and colleagues used transtympanic endoscopy to examine the protympanic (osseous) portion of the ET to determine the presence (and degree) or absence of inflammation.14 Poe and colleagues, using slow-motion videoendoscopy of the ET, assessed tubal function in 44 adults and observed inflammation of the tube and patulous tube dysfunction.15 Alper and colleagues (2015) (Image analysis—ET opening) reported a direct relationship between ET opening during swallowing using videoendoscopy and sonotubometry.16 Also reported in 2015 from the same team using transnasal videoendoscopy, visualized the ET movements during swallowing.17
Imaging the ET
In the past, many investigators used radiographs (with and without contrast media) to evaluate the middle ear and ET (see Radiographic Studies of Protective and Clearance Functions), but only recently has imaging technology been used to better define the anatomy and pathology of the tubal system. Magnetic resonance imaging (MRI) has been used to visualize the ET and to assess tubal anatomy and pathology of patients with nasopharyngeal carcinoma.18,19 Also, MRI has been used to evaluate inflammation of the middle-ear cleft in animals.20 It has more accurately identified the effect on the middle-ear cleft of experimentally induced (botulinum toxin A) functional obstruction of the ET.21
Computed tomographic (CT) scans have been used to assess the clearance function of the ET.22 Others have used CT scans to assess the tube in normal subjects, in those who had otitis media,23 and in patients with a patulous ET.24 But these imaging studies were static assessments of anatomy and clearance function of the tube, whereas standard fluoroscopy with contrast provided more dynamic studies, such as those by Bluestone and Honjo and colleagues.25,26 In 2015, digital video imaging was used to validate ET mucosal inflammation scale.27 Hashimoto and colleagues (2015) using high-resolution cone-beam CT assessed the osseous ET and peritubal cells and compared the healthy side with other with unilateral cholesteatoma and found no significant difference.28
A recent study showed that when performing 3-D CT scans to image patients with patulous ETs, a sitting positon is used and correlates with sontubometry.29
In the near future, dynamic imaging should become available, which should provide greater insight into not only the anatomy and pathology of the tubal system but also its pressure regulation, protective, and clearance functions (see Chapter 11, “Future Directions”).
Tests of Pressure Regulation Function of the ET
In addition to the otoscopic examination, which includes assessment of middle-ear pressure using the pneumatic attachment, there are tests that can assess the pressure regulation (ventilation) function of the ET system. Some of the tests are employed when the tympanic membrane is intact (tympanometry), whereas others are used when there is a nonintact eardrum (forced-response test). Still others can be used irrespective of the integrity of the tympanic membrane (sonotubometry) Schroder and co-workers used tubomanometry to diagnose ET dysfunction.30
When the tympanic membrane is intact, the microflow technique31 or an impedance method32 (both of which require a pressure chamber), sonotubometry,33–37 sequential scintigraphy,38 microendoscopy,10 or directly inserting a balloon catheter into the cartilaginous ET39,40 may be used. When the tympanic membrane is not intact, the forced-response test may be used.41 Sonotubometry is currently in use in routine research studies but is not yet available for clinical use.42–44 A new measurement of ET mechanical properties using a modified forced-response test is currently being tested in animals and humans.45 Kumazawa and colleagues devised the tubotympanoaerodynamic graphy (with Valsalva’s maneuver), which can be employed when the tympanic membrane is or is not intact.46 These tests are described in detail subsequently.
Prior to the 1960s, most tests of the pressure-regulation function of the ET were, in reality, only assessments of the tubal patency. The classic methods of Valsalva, Politzer, and Toynbee for assessing the ET are still in use today, as is catheterization of the ET. But of these tests, the Toynbee, albeit crude, provides some insight into the patient’s ET regulatory function. These tests are traditionally used when the tympanic membrane is intact, but some are used when the eardrum is not intact, such as Valsalva’s test.
The effect of high positive nasopharyngeal pressures at the proximal end of the ET system can be evaluated qualitatively by Valsalva’s test. The test results are considered to be positive (normal) when the tube and middle ear can be inflated by a forced expiration (with the mouth closed and the nose held by the thumb and forefinger) (Figure 8–11). The amount of overpressure thus created is variable and may be as much as 2000 mm H2O.
When the tympanic membrane is intact, the overpressure in the middle ear can be observed as a bulging tympanic membrane by visual inspection of the tympanic membrane with a pneumatic otoscope or, more precisely, with the aid of the otomicroscope and a nonmagnifying Bruening or Siegle otoscope. The tympanic membrane moves inward when positive canal pressure is applied, but outward mobility in response to applied negative canal pressure is decreased or absent if positive pressure is present within the middle ear.
A more accurate method of assessing changes in middle ear pressure is tympanometry, but because the positive pressure created in the middle ear for such a test may only be momentary—inflation followed by immediate equilibration before tubal closing—the alteration in middle-ear pressure may not be visualized or recorded by tympanometry. When the tympanic membrane is not intact, the sound of the air entering the middle ear can be heard with a stethoscope or with the Toynbee tube (a rubber tube with an olive tip at either end, one for the patient’s test ear and one for the ear of the examiner). However, these methods are outmoded, and measurements are now made with a manometric system or tympanometry, preferably one equipped with a strip-chart recorder.
Unfortunately, regardless of the testing technique or method of assessment, the Valsalva’s test results are not reliable indicators of ET pressure-regulation function. When positive, they indicate only an anatomically patent and probably a distensible tube. Indeed, without inflation of the middle ear during this test, no useful information concerning tubal function is obtained. Elner and colleagues found that 85% of 101 adults with normal ears had positive results on Valsalva’s test.47 More recently, Valsalva has been used to visualize the tube using computed tomography.48
Politzer’s test is performed by compressing one naris into which the end of a rubber tube attached to an air bag has been inserted while compressing the opposite naris with finger pressure. The subject is asked to repeat the letter K or is asked to swallow to close the velopharyngeal port (Figure 8–12). When the test result is positive, the overpressure that develops in the nasopharynx is transmitted to the middle ear, thus creating positive middle-ear pressure. Assessment of the middle-ear pressure and the significance of the test results are the same as with Valsalva’s test in that a normal result indicates only tubal patency; however, both Valsalva’s and Politzer’s methods can be of benefit as a treatment when effusion or high negative pressure is present within the middle ear if the patient can successfully inflate the middle ear. Valsalva’s and Politzer’s maneuvers may be more beneficial as management options in selected patients than they are as methods to assess tubal function, although there is controversy about the efficacy of these procedures for treatment of middle-ear effusion (see Chapter 9, “Role in Management of Middle-Ear Disease”).49,50
Transnasal catheterization of the ET with the classic metal cannula has been used to assess tubal function for more than a century (Figure 8–13). Cannulation can be performed by blindly rooting for the orifice of the tube, by indirect visualization with a nasopharyngoscope, or by the use of the transoral right-angle telescope. Successful transferring of applied positive pressure from the proximal end of the cannula into the middle ear signifies only tubal patency. Catheterization of the tube has been used for over 100 years to insufflate medications into the middle ear (see Chapter 9); however, the use of this method as a test or treatment is limited in children because it can be frightening and difficult to perform in the awake child.
In performing the Toynbee test, the subject is asked to swallow when the nose is manually compressed (Figure 8–14). This maneuver usually creates a positive pressure within the nasopharynx, followed by a negative pressure phase.51 If the ET opens during the test, the middle-ear pressure changes; the way in which it changes is determined by the timing of the tubal opening and the nasopharyngeal pressure gradient.
Change in middle-ear pressure is assessed using the Toynbee test in the same way that it is assessed on Valsalva’s test. If negative pressure is present within the middle ear, the tympanic membrane will be retracted and will not move inward to applied positive pressure with the pneumatic otoscope. It will move outward to applied negative pressure if the pressure applied exceeds the negative pressure within the middle ear.
The test results are usually considered positive when there is an alteration in the middle-ear pressure. Negative middle-ear pressure after the Toynbee test or only momentary negative middle-ear pressure followed by normal middle-ear gas pressure usually indicates good tubal function because it shows that the tube can open actively (the tensor veli palatini muscle contracts) and that the tubal structure is sufficiently stiff to withstand nasopharyngeal negative pressure.
When the tympanic membrane is intact, tympanometry can be used to assess the outcome of the test (Figure 8–15); however, some abnormal tubes that are either patulous or have low tubal resistance may transfer gas from the middle ear into the nasopharynx during the Toynbee test (as they may with sniffing). The finding of only positive middle-ear pressure signifies tubal patency but does not have the same significance as transitory negative pressure. When the tympanic membrane is not intact, the manometer of the immittance instrument can be observed to determine middle-ear pressure.
Unfortunately, the absence of any alteration in middle-ear pressure during the Toynbee test does not indicate poor ET function. Zollner and Thomsen reported that 30% of the adults with negative examination findings had normal results on the Toynbee test.52,53
In the study by Elner and colleagues, the results of the Toynbee test were positive in 79% of normal adults.47 Cantekin and colleagues reported that only 7 of 106 ears (6.6%) of subjects (mostly children) who had had tympanostomy tubes inserted for otitis media could show positive results when given a modification of the Toynbee test (closed-nose equilibration attempt with applied negative middle-ear pressure of 100 or 200 mm H2O).54 Likewise, in a series of patients, most of whom were older children and adults with chronic perforations of the tympanic membrane, only 3 of 21 (14.3%) passed the test.54 However, in children with a traumatic perforation of the tympanic membrane but who otherwise had a negative otologic history, 3 of 10 (30%) could pass the test.54 In the study by Bluestone and colleagues of “normal” children with traumatic perforations, six of seven children could change the middle-ear pressure, but none of the 21 ears of children who had a retraction pocket or a cholesteatoma showed pressure change.55 The test is of greater value in determining normal or abnormal tubal function in adults than it is in children. The test is still of considerable value because, regardless of age, if negative pressure develops in the middle ear during or following the test, the ET function is most likely normal because the tube actively opens and is sufficiently stiff to withstand nasopharyngeal negative pressure (i.e., it does not “lock”). If positive pressure is noted or no change in pressure occurs, the function of the ET may still be normal, and other tests of tubal function should be performed.
Tests of Pressure Regulation Function When the Tympanic Membrane Is Intact
ET function in individuals with intact tympanic membranes may be determined by manometry, tympanometry, sonotubometry or a pressure chamber can be employed.
Middle-ear pressure is measured indirectly by the response to pressure changes in a pressure chamber. Decompression of the chamber creates relative positive pressure in the middle ear, whereas chamber compression results in relative negative pressure in the middle ear.
Investigation of ET function by means of pressure chambers dates back more than a century to 1864, when Magnus first reported his findings on tubal function in a diving bell.56 Using rising external pressures, Magnus was able to make several observations:
• He confirmed Toynbee’s assumption that the ET is closed under normal conditions.
• He realized the importance of deglutition for the opening of the tube.
• He noted that if the pressure difference between the middle ear and the bell became too pronounced (relative negative pressure in the middle ear), it could not be equilibrated by swallowing.
These findings were confirmed by Mach and Kessel when they conducted experiments in a primitive pressure chamber.58 The chamber consisted of a wooden box in which the pressure could be varied between 200 and 140 mm H2O with the aid of an organ pump. Since that time, pressure chambers have been used to test the function of the ET. In 1958, Thomsen reported using a pressure chamber using tympanometry, which is described later.53
Bluestone’s Experience With a Pressure Chamber for ET Function Tests
Following a visit to Sven Ingelstadt (1918–1979) in 1979 to view his ET laboratory in Malmo, Sweden, I was given a grant to establish a similar laboratory in Pittsburgh. In 1975, when I returned from my Boston posts, we attempted to build our own chamber, and I contracted a friend of mine who had a metal manufacturing factory in Pittsburgh to build it. I wanted to create a chamber to mimic a space rocket that would be attractive to children. It was built but when tested at pressures in retrospect that were higher than needed, it imploded and the project was abandoned. The purpose of this project was to enable our new laboratory to test ET function in patients and research subjects who had intact tympanic membranes. Before that, we were testing tubal function in patients with intact eardrums with the nine-step test which I designed using standard tympanometry.59 When the tympanic membrane was not intact, such as when a perforation or tympanostomy tube was present, we used the inflation–deflation test.60 Then in 2013, my colleague William J. Doyle was successful in acquiring NIH funding to install a pressure chamber that is now in use today in our ET Tube Physiology Laboratory at the University of Pittsburgh (Figure 8–16). Despite the uncertainty expressed by some (Smith and Tysome, 2015) about the usefulness of ET function tests, the pressure chamber promises to be quite useful in the future.57
MICROFLOW TECHNIQUE Early volume-displacement measurements of the tympanic membrane were done by means of closed manometry in the external ear, with simultaneous direct measurements of middle-ear pressure. This was abandoned as a clinical procedure because of the difficulties encountered in direct measurements, which were usually made by inserting a mandarin needle into the middle-ear cavity. Later, however, tympanic membrane displacements were recorded by use of microflow techniques. When the drum is moving, airflow is produced in the external ear canal. This flow is recorded by a flowmeter and then integrated to give quantitative measurements of volume displacement. Displacements as small as 1 µL have been recorded with up to 95% accuracy.
The microflow method was the only method used to assess normal ET tube function quantitatively in adults who had intact tympanic membranes (see Chapter 4).47,61–63 This technique permits continuous recording of the volume deviation of the tympanic membrane resulting from changes in ambient pressure and changes in pressure within the middle ear. During the test, the tympanic membrane is in permanent and free contact with ambient air (Figure 8–17).
Under an otomicroscope, the subject is fitted with a catheter through a rubber disk inserted into the bony part of the ear canal. The rubber disk maintains an airtight seal with the canal walls. The air cushion between the tympanic membrane and the disk is connected to a sensitive flowmeter through the catheter; the other end of the flowmeter is open to ambient air. An identical flowmeter is connected to a reference volume simulating the air-cushion volume between the tympanic membrane and the rubber-disk seal. The signal from the reference flowmeter is subtracted from that of the ear-canal flowmeter, compensating for the flow changes owing to compression or expansion of air in the pressure chamber. This corrected airflow rate is integrated to obtain the volume displacement of the tympanic membrane. Then, by changing the ambient pressure in the chamber, the tympanic membrane displacement as a function of middle-ear pressure is obtained.
In this way, this procedure calibrates the tympanic membrane as a pressure transducer so that after this measurement has been made, the subjects can be tested for their abilities to equilibrate various middle-ear pressures created by the changes in chamber pressure. Within the elastic limits of the tympanic membrane (150 mm H2O pressure differential between the middle ear and ear canal), an accurate inflation–deflation test can be conducted; however, because this technique requires a pressure chamber and sophisticated equipment, it is practical only for use in research centers.
Recently, the pressure chamber was reported to be helpful in diagnosing aviators who were fit and unfit for flying.64
Determination of middle-ear pressure and acoustic immittance using electroacoustic impedance equipment was introduced by Metz about 50 years ago.65 These same techniques have been used to perform tympanometry, which is the measurement of the acoustic driving-point immittance as a function of the static pressure in the canal. If low-frequency tones are used for the measurement, the static pressure that produces the maximal acoustic immittance is approximately equal to the gas pressure in the middle ear.
TYMPANOMETRY IN A PRESSURE CHAMBER Thomsen adapted the acoustic impedance method for use in a pressure chamber.53 He varied the chamber pressure and measured the percentage of absorption of a tone presented into the ear canal. He found that there was a fall in absorption as the pressure difference between the middle ear and the chamber was increased. The absorption reached a peak when the two pressures were identical. Unfortunately, Thomsen’s technique failed to account for the change in middle-ear pressure caused by the measurement procedure. As the pressure in the chamber is varied (in search of maximal loudness or absorption), the tympanic membrane moves from its original position to a new position, thus changing the volume of the middle-ear cavity; however, according to Boyle’s law, as the volume of the cavity changes, the pressure must also change. Thus, by knowing the volume displacement and “measuring” the final pressure, the original pressure can be deduced.
Bylander used tympanometry with a pressure chamber to evaluate ET function in normal children.32 With this method, the resting middle-ear pressure is obtained from the initial tympanogram. Then the chamber pressure is lowered to 100 mm H2O relative to ambient pressure, and a second tympanogram is obtained, verifying the relative overpressure in the middle ear. After this deglutition of the subject, a tympanogram is recorded to determine middle-ear pressure. The same procedure is repeated with 100 mm H2O relative overpressure in the chamber to assess the subject’s ability to actively equilibrate relative underpressure in the middle ear. With use of this method, the inflation–deflation test was conducted on 50 children, and the results were compared with the results of tests that measured tubal function in adults. In this way, the first database for tubal function in otologically normal children was established.
In Israel, Shupak and colleagues also used tympanometry inside a pressure chamber to assess the ability of naval scuba divers to equilibrate negative middle-ear pressure.66
TYMPANOMETRY WITHOUT A PRESSURE CHAMBER Tympanometry has been widely used in clinical and basic research investigations. A variety of commercially available instruments allow this method to be used routinely in most clinical settings without a pressure chamber. Figure 8–18 shows a block diagram of an immittance instrument, which can be used when the tympanic membrane is intact, but as described later, the pump-manometer portion of the system can be used as a relatively simple instrument to assess middle-ear pressure when the eardrum is not intact. In a study in the monkey at our center, Alper and colleagues assessed the middle-ear pressure by tympanometry and directly in the middle-ear cleft and showed that tympanometry does indeed accurately measure middle-ear pressure.67
Using an immittance instrument to obtain a tympanogram is an excellent way of determining the status of the tympanic membrane–middle-ear system, and it can be helpful in assessing ET function.68 In 1973, my colleagues and I reported that tympanometry was an excellent method to detect middle-ear effusions in children after we compared it with otoscopy and the findings at myringotomy as the “gold standard” and found audiometry to be a poor test of the presence or absence of middle-ear effusion.69 (This report was selected as 1 of the 12 “classic” articles of the past 100 years for the centenary celebration of Laryngoscope and republished in that journal in 1996.)
There are several methods for the clinical evaluation of ET function by tympanometry without the need of a pressure chamber. Each of these methods is based on an indirect determination of middle-ear pressure under various conditions. The pressure is obtained by finding the peak in the tympanogram; however, only relative qualitative information can be obtained by use of these methods. If the subject fails to induce pressure changes in the middle ear, tubal function cannot be evaluated; therefore, no truly satisfactory clinical test is indicative of tubal function in subjects with intact tympanic membranes using standard tympanometry. But, as described by Richert and colleagues, who described the use of tympanometry in specialty clinic for assessment and management of children and adults with dysfunction of the ET, but it was in conjunction with a panel of tests, which included sonotubometry, tubomanometry, manometric testing and a pressure chamber.70
Resting pressure. When the tympanic membrane is intact, tympanometry is a reliable method to determine the middle-ear pressure in the absence of a severely distorted tympanic membrane. Figure 8–19 is a tympanogram of a patient with normal middle-ear resting pressure. But one test represents the middle-ear pressure only at one moment. A single measurement of normal resting middle-ear pressure does not necessarily indicate normal tubal function, but a measurement of negative middle-ear pressure is presumptive evidence of ET dysfunction. Serial determinations are more indicative of the dynamics of tubal function in a single patient; therefore, the chief drawback of this procedure is that it gives no indication of the pressure-regulation function of the tube under various conditions of induced middle-ear pressure. For this reason, the remaining tests using tympanometry were developed (see later in this section).
A resting pressure that is highly negative is associated with some degree of ET obstruction, but the presence of normal middle-ear pressure does not necessarily indicate normal tubal function; a normal tympanogram is obtained when the ET is patulous (see Patulous Test).
The presence of a middle-ear effusion or high negative middle-ear pressure determined by this method usually indicates impaired ET function. Figure 8–20 is a tympanogram of a patient with high negative middle-ear resting pressure, which is indicative of obstruction of the tube. (Such obstruction may be functional, mechanical, or both.) However, unlike the otoscopic evaluation, tympanometry is an objective way of determining the degree of middle-ear negative pressure. Unfortunately, assessing the abnormality of values of negative pressure is not so simple: high negative pressure may be present in some patients, especially children who are asymptomatic and who have relatively good hearing. In others, symptoms such as hearing loss, otalgia, vertigo, and tinnitus may be associated with modest degrees of negative pressure or even with normal middle-ear pressures. The middle-ear air pressure may depend on the time of day, season of the year, or condition of the other parts of the system, such as the presence of an upper respiratory tract infection.71 For instance, a young child with a common cold may have transitory high negative middle-ear pressure while he or she has the cold but may otherwise be otologically normal.72 The decision as to whether high negative pressure is abnormal or is only a physiologic variation should be made taking into consideration the presence or absence of signs and symptoms of middle-ear disease. If severe atelectasis or adhesive otitis media of the tympanic membrane–middle-ear system is present, the tympanogram may not be a reliable indicator of the actual pressure within the middle ear. Doyle and colleagues performed daily tympanometry as functional measure of middle-ear status and ET function.73