Ann Otol 88 :1979
AIRFLOW THROUGH THE EUSTACHIAN TUBE ERDE~I
1.
C~~,
CARLOS A. SAEZ, PhD
PhD
SAMUEL A. BERN
CHARLES D. BLUESTONE, MD PITTSBURGH, PENNSYLVANIA
In an attempt to distinguish normal from abnormal eustachian tube function, two groups of adults with nonintact tympanic membranes were tested. Six subjects had traumatic perforations of the tympanic membrane and a negative otologic history while five subjects had perforations as a sequela of otitis media. The subjects were tested with two methods: the middle ear inflation-deflation technique and a newly introduced forced-response technique. The comparison of the two groups revealed marked differences between normal subjects and patients with middle ear disease in active tubal dilation mechanisms and biomechanics of the eustachian tube. The forced-response test appeared to be a better method to determine the degree of actual tubal function.
= = = =
Middle ear pressure P Q Airflow rate Inflation-Deflation Test PM Level of applied middle ear pressure TA Duration of eustachian tube opening during swallowing Q.IAX Maximum airflow rate during swallowing V Total volume of air passing through eustachian tube during one swallow l>P Change in middle ear pressure during one swallow
Forced-Response Test j> Application rate of middle ear pressure Forced-opening pressure P.. Steady-state middle ear pressure durPo ing forced-response study Steady-state airflow rate during Qo forced-response study QA Maximum airflow rate by active dilation during forced-response study Passive tubal resistance (Po/Qo) Ro RA Active tubal resistance (P/Q.. )
The eustachian tube (ET) is a compliant conduit which connects the closed gas cavity of the middle ear (ME) and mastoid air cells to the open gas cavity of the nasopharynx. In the normal resting state, this conduit is collapsed and the airway between the ME and nasopharynx is closed. The ET is opened intermittently during swallowing, ventilating the ME to the nasopharynx. The tubal opening is accomplished by contractions of the tensor veli palatini muscle which displaces the lateral wall from the cartilage-supported medial wall of the ET, thus breaking the mucus seal of the collapsed lumen. This is defined as active opening since it involves an exertion of muscle pull. During this process the ME cavity is ventilated by a bolus of air passing through the ET. A second mechanism for tubal opening involves the pressure gradient between the ME and the nasopharynx. When the pressure difference between the two
ends of the ET exceeds the collapsing forces of the tubal lumen, the ET will open spontaneously. This type of opening is called passive opening since it does not involve the active mechanism of the tensor veli palatini muscle.
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It has been recognized that the status of the ME cavity is to a large degree dependent upon the ventilatory function of the ET. Certain diseases of the ME are consequences of ET ventilatory dysfunction. In order to understand the underlying causes of tubal dysfunction, several investigators have studied the ET ventilatory function using various techniques.tv They evaluated the tubal function of subjects with and without ME disease to establish a comparative data base for normal and abnormal ET ventilatory function. The focus of these studies was directed towards an assessment of active tubal opening during different pressure conditions for the ME and nasopharynx. The most Widely used
From the Department of Otolaryngology, University of Pittsburgh School of Medicine Children's Hospital of Pittsburgh, Pittsburgh, Pennsylvania. ' Presented at the meeting of the Association for Research in Otolaryngology, St. Petersburg Beach, Florida, January 31, 1978.
603
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604
CANTEKIN ET AL
I
OSCILLOGRAPH
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Fig. 1. Schematics of the instrumentation used for evaluation of the ventilatory function of the ET. See text for detailed explanation.
technique for the ventilatory function evaluation of the ET is the inflationdeflation test.':" During this procedure, the subjects are asked to equilibrate applied over- and under-pressures in the ME cavity by swallowing. In subjects with nonintact tympanic membranes the ME is directly accessible to air pressureflow monitoring devices, facilitating evaluation. But the causal interpretation of failure to equilibrate induced ME pressures is not obvious. Lack of active tubal function during this test, especially when negative pressure is applied to the ME, is not necessarily evidence of absence of physiological tubal function. Therefore, some attempts were made recently to study the passive opening of the ET by over-pressure applied to either the ME or nasopharynx.v" The as-
a
o
sessment of passive tubal function in conjunction with active function revealed more information about airflow through the ET. But even today, the underlying mechanisms of tubal dysfunction remain unresolved and speculative. The present investigation was conducted in an attempt to understand the ventilatory function of the ET by studying airflow through it in subjects with normal and abnormal tubal function. The airflow dynamics of the ET were evaluated by using the inflation-deflation test and a new method, the forcedresponse test. The latter technique is described in detail in the Methods and Materials section. A comprehensive evaluation of active and passive ET function was conducted in two groups of
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Fig. 2. An example of forced-response study of airflow through the ET. Using a constant-flow source, the ME is inflated with a fixed pressure rate (P) and the ET is forced open (PF). Lower trace shows the abrupt change in flow rate (Q) during forced opening. The flow source maintains a constant O. The ME pressure reaches a steady level (Po) and the flow rate through the ET stabilizes (Qo I. The pressure-to-flow ratio at this steady-state is taken as the passive tubal resistance (Ro). The spike in the flow trace and the corresponding drop in the ME pressure reveal an active tubal opening. This is when the subject swallows voluntarily. The ratio of ME pressure before the drop to the maximum flow rate during swallowing (QA) is defined as the active tubal resistance (~). The ET stays closed for approximately 11 seconds (arrows), followed br a second forced opening and steady-state pressure-flow condition similar to the initia situation. The second spike on the flow trace denotes another swallow and the cycle of events is repeated.
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AIRFLOW THROUGH EUSTACHIAN TUBE
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Fig. 3. Equilibration of applied ME pressure by voluntary dry and wet swallowing. The dry swallowing equilibration attempt shows consistent resl?onses for applied positive ME pressure (inflation). The same pressure drops (L'l.P), maximum flow rates ( QMAX), volume of flow passing through the ET (V) and duration of tubal opening (TA) are recorded in two different attempts. Flow direction is positive when air evacuates the ME cavity. TA is defined as the elapsed time between two consecutive steadypressure levels. Dry swallowing with negative ME pressure (deflation) shows reproducibility as good as the inflation study. Equilibration attempt during wet swallowing (left frame) shows reduced L'l.P and V in comparison to dry swallowing. Subsequent wet swallows at five-second intervals depict diminished responses. A 35-second interval restores the response to the initial level.
patients, one with and one without a history of ME disease. This was designed to establish a comparative data base for normal and abnormal tubal function and to identify the possible mechanisms of tubal dysfunction. METHODS AND MATERIALS The study population was comprised of two groups of subjects. The first group had no history of ME disease and traumatic perforations of the tympanic membrane; they were defined as the normal group. The abnormal group had recent histories of otitis media with effusion and resultant chronic perforations of the tympanic membrane. There were six subjects with a mean age of 29 years in the normal group and five subjects with a mean age of 24 years in the abnormal group. Only volunteers were included in the study, since each experimental session lasted about two hours. In addition, the subjects had to be tested on three different occasions within a one-month period to establish reproducibility for the test results.
After otoscopic examination of the ME, the ear canal of the subject was connected to the manometric system, shown in Figure 1, by a modified soft rubber Foley catheter. Only subjects with dry ME were chosen. They were tested in a comfortable sitting position. The manometric monitoring system was comprised of a variable-speed constant-flow pump, two pressure transducers, a flow meter with a differential pressure transducer, two valves to isolate different parts of the system, transducer signal conditioners, and an oscillograph. The technical details of this system have been previously described.' After obtaining a hermetic connection between the manometric system and the ear canal, two types of tests were conducted. During the first test, the inflation-deflation test, various magnitudes of over- and under-pressure were applied to the ME and the subject was asked to equilibrate the pressure by swallowing. The second procedure was the forcedresponse test. The ME was inflated at a constant flow rate (fixed pressure rate), forcing the ET open. Following the passive opening
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606
CANTEKIN ET AL
ABNORMAL
NORMAL No. 3D
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Fig. 4. Typical pressure-flow recordings of normal subjects and patients with ME disease during inflation-deflation studies. The first and second horizontal rows are pressure-flow traces of equilibration of aPl?lied positive ME pressure (inflation), whereas the responses to ME negative pressure (deflation) are shown in rows three and four. The arrows on the traces mark the duration of ET opening (TA ) • of the ET, the pump continued to deliver a constant flow rate. This held the ET open. After a steady-state condition for ME pressure and flow rate through the ET was reached, the subject was instructed to swallow. Thus, the increased dilation due to active muscle function was assessed. An example of the forced-response test is shown in Figure 2. Active openings of the ET during voluntary dry swallowing and during swallowing of small amounts of water, called wet swallowing, were compared. This was to determine which type of swallowing induces effective and reproducible tubal opening. Figure 3 shows the comparison of these two kinds of swallowing for the equilibration of applied ME pressure. The tubal openings were more consistent and dilations were larger during dry swallowing. Therefore only dry swallows were used during the study. In every testing session, the same procedural sequence was used. The testing began with an initial detennination of the forcedopening pressure. The ME cavity was pressurized at a rate of 13 mm H20/sec until the ET spontaneously opened. Then the pump was stopped and valve 1 (Fig. 1) was closed, disconnecting the pump volume from the testing volume (28.6 cc). The patient was instructed to dry swallow at will. After this equilibration attempt, the ME was inflated at a rate of 28 mm H20/sec. The pressure was increased to 250 mm H 20 or 60%
of the forced-opening pressure, whichever was less. This was a precaution taken to prevent passive tubal openings from sustained ME over-pressure. After attempting to equilibrate applied positive pressure, the ME pressure was decreased to negative 250 mm H20 at the previous pressure rate. Again the subject was instructed to swallow at will to equilibrate. This inflation-deflation test was repeated until three data points for each pressure interval of 50 mm H20 were obtained. Valve 1 was alwars closed after the desired ME pressure leve had been reached. Then the forced-response test was conducted using five discrete pump speeds delivering flow rates of 3, 5.5, 12, 22.5, and 44 cc/min, respectively. These flow rates approximately corresponded to ME inflation rates of 6, 13, 28, 47 and 102 mm H.O/sec. The pump speeds were chosen in a random order. Upon completion of a test with a given flow rate, a five-minute rest period was allowed before starting with a different pump speed. This presumably permitted the ET to return to normal, RESULTS
The results are presented in two sections: 1) inflation-deflation test and 2) forced-response test. The data for the normal group are presented as the means and standard deviations for the measured parameter. However, the data
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AIRFLOW THROUGH EUSTACHIAN TUBE
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Fig. 5. Duration of ET opening (TA) during active equilibration attempts as a function of applied ME pressure (PM). Mean values for six normal subjects are shown by open circles over an ME pressure range of - 250 mm H20 to 150 rom H20 (upper left frame). Confidence intervals represent one standard deviation of the mean. The other frames depict data points from five patients with ME disease. Note that the duration of tubal opening is independent of the ME pressure level for normal subjects.
points for each individual in the abnormal group are shown in order to elucidate the variations from the normal group. Inflation-Deflation Test. Examples of pressure-flow recordings during this test are shown in Figure 4. The first two columns are recordings from normal subjects and the following three columns are from three subjects with ME disease. Patients in the abnormal group had active tubal openings that showed reduced ET dilations. This was indicated by the magnitude of the pressure drop (L::-.P), the maximum flow rate (QMAX), and the total volume of flow (V) passing through the ET during swallowing. The area of the flow-time trace is the measure of the total volume of flow. Duration of ET opening (TA) is shorter for patient 21. The tubal opening duration as a function of applied ME pressure (PM) is shown in Figure 5 for the normal group and for the five individual subjects of the abnormal group. The top left frame shows that the duration of tubal opening was not affected by the ME
pressure in normal subjects. Between applied ME pressures of -250 and 150 mm H 20, the duration was independent of the pressure level. This, however, was not the case for the abnormal subjects. Subject 22 showed active openings of the ET for all tested values of ME pressure with variable duration. In this case, ET opening duration ranged between 0.15 and 0.34 seconds as a function of ME pressure. Subjects 4, 21, and 10 exhibited active openings for a limited range of ME pressures, and the duration of tubal opening was affected by the pressure level. No active openings were recorded with patient 13. In the abnormal group, the duration of ET opening did not show a discernible dependence on, or independence of, the magnitude of the applied ME pressure. Airflow characteristics through the ET during inflation-defla tion tests are shown in Figure 6. The relationships between maximum airflow rate (QMAX), total volume of air passing through the ET (V), and change in ME pressure (L::-.P) as a function of applied ME pressure (PM)
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CANTEKIN ET AL
608
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Fig. 6. Maximum airflow ( Qmx) through the ET (top), total volume of air (V) passing through the ET (middle), and change in ME pressure (,0.P) (bottom) during one swallow; all are plotted against applied ME pressure (PM). Mean values for six normal subjects are denoted by open circles and the confidence intervals are for one standard deviation of the mean. Symbols represent data points for patients 4 (T), 10 CA.), 13 (+),21 (.), and 22 (e). For the normal group Q'IAX, V, and P are linear functions of PM between ME pressure levels of -200 to 100. The data points for QMAX adapted from Flisberg's" study of normals (0) are in close agreement with the present study. Also, the data points for V adapted from the study by Rundcrantz° of normals is shown by a symbol (0). ,0.P is not compared with previous studies, since the magnitude of ~P depends on the volume of the manometric monitoring system.
were plotted. In normal subjects, these three parameters of airflow exhibited a linear dependence on the applied ME pressure (between -200 and 100 mm H 20 ) . The individual data points document the responses of subjects with a history of ME disease, reflecting reduced dilations of ET during active openings. The differences between normal and abnormal subjects were easily identifiable. Two previous studies of inflationdeflation tests on normal subjects are shown in the top and middle frames. Data points for the maximum airflow rate at two levels of applied negative ME pressure are in close agreement with the present investigation (top frame )," Also, the previous data for total volume of air passing through the ET are within the limits of the normal group's response in this study (middle frame)." This volume corresponds to an average applied positive ME pressure of 30 mm H 2 0 . Forced-Response Test. During this test, the ET function was assessed by evaluating three parameters: the forcedopening pressure (PF ) , the passive tubal resistance (R o), and the active tubal resistance (R A ) . Examples of tubal resistance studies are shown in Figure 7. The recordings presented here are pressure-flow traces following the forced opening of the ET due to ME over-pressure. The top two frames show tubal resistance studies in two normal subjects. The ET was held open by continuous airflow. This steady-state pressureflow condition through the ET was temporarily perturbed when the subject swallowed. During active function (swallowing), the tubal lumen was further dilated. This was displayed as a transient spike in flow rate and an abrupt drop in ME pressure. Following this active opening, the ME pressure gradually resumed its steady-state level since the pump maintained a constant airflow. The passive tubal resistance (R o) is defined as the pressure-flow ratio at this steady state. The active tubal resistance (R A ) is defined as the ratio of ME pressure (prior to active opening) to maximum flow rate during swallowing.
The bottom two frames in Figure 7 show tubal resistance studies of two abnormal subjects. The most striking difference between normal and abnormal
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AIRFLOW THROUGH EUSTACHIAN TUBE
609
NORMAL
ABNORMAL
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O±~:::::==========:::::::r::::::::±:±±:::::±t Fig. 7. Examples of forced-response studies for normal subjects and patients with ME disease. All frames are for constant flow source delivering a nominal 12 cc/min flow rate. The top two frames illustrate recordings from two normal subjects. A tenfold increase in flow, denoted by spikes in the flow trace, corresponds to voluntary swallowing. During this muscular dilation of the ET, ME pressure drops temporarily. The constant flow builds up the pressure to a steady-state level at which the passive tubal resistance is calculated. The left bottom frame shows a recording from a patient with ME disease. Note that the active dilation of the ET during swallowing is quite small in comparison to normal subjects. The tube stays open about 1.5 seconds and there is a drop in the pressure level. The right bottom frame depicts a recording of another patient with ME disease. The swallowing activity is quite ineffective in further dilating; the ET while a constant flow of air is passing through it. Note that following the swallow, the tube closes and, instead of a drop in ME pressure, there is a slight increase.
subjects is the magnitude of the flow spike during swallowing. In the normal subjects, the swallowing activity induced a ten-fold increase in the flow rate, whereas in the abnormal subjects the change was very small, indicating ineffective tubal dilation during active opening. In subject 10, the active opening mechanism dilated the ET two-fold above the predilated state. But in subject 21, the swallowing induced constrictions of the ET lumen (increase in ME pressure and decrease in flow rate). Forced-opening pressure (P F ) as a function of the application rate of ME pressure (j» is graphed in Figure 8. Forced-opening pressure increases with higher rates of ME inflation. In the normal group, passive opening of the ET by ME over-pressure varied from 320 to 400 mm H 20 depending upon the application rate. Forced-opening pressure of the ET in normal subjects was re-
ported by Elner et al.' who used a single ME inflation rate of 40 mm H 2 0 / s e c to open the ET. The results of the one flow rate used by Elner et al were similar to the findings in the present study. In the abnormal group, subjects 4, 10, and 21 had considerably higher forcedopening pressures than the normal subjects. Also, the forced-opening dependence on the application rate of ME pressure was more pronounced. Subject 22 exhibited lower opening pressures, but subject 13 was within the limits of the normal group. Four subjects of the abnormal group could be separated from the normals by evaluating this parameter of tubal function. Passive (R o) and active (R A ) tubal resistances were computed for the steady-state airflow rates (Qo) between 5.5 and 44 cc/min. Flow rates below 5.5 cc/min could not be used for resistance studies because most ET exhibited an
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CANTEKIN ET AL
610
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Fig. 8. Relationship between the forced-opening pressure (PF) and the application rate of ME pres~ur~ (P). Open circles connected by a solid line and confidence limits denote mean values and one standard deviation of the mean for six normal subjects. Mean values for five patients with ME disease are shown by the same symbol convention as Figure 6. displays data adapted from Symbol the Elner et al' study of normals. Note that increasing the ME inflation rate raises the forced-opening pressure and this rate dependence is more pronounced for patients with ME disease.
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unstable behavior manifested by flutterlike flow patterns. The patients were uncomfortable when flow rates in excess of 44 cc/min were employed. These two conditions determined the upper and lower limits of the resistance studies. The relationship between tubal resistance and airflow rate is shown in Figure 9. The top frame depicts the passive tubal resistance (R o) monotonically decreasing with increasing predilating flow rate (Qo). With the exception of subject 22, all of the patients in the abnormal group had higher passive resistances than did the subjects of the normal group. The one data point adapted from the study by Elner et al" of normals is in close agreement with the results obtained from our normal subjects. The bottom frame shows that the active tubal resistance (R A ) of the normal group is independent of the predilating flow rate (Qo). Subjects in the abnormal group (except subject 22) had considera1;lly higher active resistances. The active tubal resistances of subjects 10 and 13 showed definite dependence on the predilating flow rate. These two measures of ET resistance, especially active resistance, discriminated four abnormal subjects from the normals. In an effort to combine the passive
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Fig. 9. Passive tubal resistance (Ro ) ( top) and active tubal resistance ( RA ) (bottom) as a function .of steady-state airflow rate (Qo). For SIX normal subjects, the mean ,:alues ~or passive tubal resistance and active resistance are shown by open circles connected by solid lines. Confidence intervals represent one standard deviation of the mean. Patients with ME disease are symbolized by the same convention as Figure 6. Passive tubal resistance data adapted from Elner et al' are shown by (0). Increased constant flow rate reduces the passive tubal resistance (top). Note that the active tubal resistance for normal subjects is less than 2 mm H,O/cc/min and is independent of Qo (bottom) .
and active resistance in one measure which could discriminate the normal from the abnormal subjects, the ratio of these two resistances was computed. The ratio of passive to active tubal resistance (Ro/R A ) as a function of the steady-state airflow rate (Qo) is shown in Figure 10. For the normal group, the resistance ratio decreased steeply for the flow range of 5.5 to 22.5 cc/min, and then it remained unchanged, at about a value of five with increasing flow rates. This measure clearly discriminated all
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AIRFLOW THROUGH EUSTACHIAN TUBE
the intraluminal mucus, leading to a descriptive recording of tubal dilations by the tensor veli palatini muscle contractions. The combination of passive and active tubal resistance in a ratio fonn could normalize the geometric differences between individuals, revealing a quantitative measure for tubal dilation efficiency (Fig. 10) .
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AIRFLOW THROUGH THE EUSTACHIAN TUBE ERDE~I
1.
C~~,
CARLOS A. SAEZ, PhD
PhD
SAMUEL A. BERN
CHARLES D. BLUESTONE, MD PITTSBURGH, PENNSYLVANIA
In an attempt to distinguish normal from abnormal eustachian tube function, two groups of adults with nonintact tympanic membranes were tested. Six subjects had traumatic perforations of the tympanic membrane and a negative otologic history while five subjects had perforations as a sequela of otitis media. The subjects were tested with two methods: the middle ear inflation-deflation technique and a newly introduced forced-response technique. The comparison of the two groups revealed marked differences between normal subjects and patients with middle ear disease in active tubal dilation mechanisms and biomechanics of the eustachian tube. The forced-response test appeared to be a better method to determine the degree of actual tubal function.
= = = =
Middle ear pressure P Q Airflow rate Inflation-Deflation Test PM Level of applied middle ear pressure TA Duration of eustachian tube opening during swallowing Q.IAX Maximum airflow rate during swallowing V Total volume of air passing through eustachian tube during one swallow l>P Change in middle ear pressure during one swallow
Forced-Response Test j> Application rate of middle ear pressure Forced-opening pressure P.. Steady-state middle ear pressure durPo ing forced-response study Steady-state airflow rate during Qo forced-response study QA Maximum airflow rate by active dilation during forced-response study Passive tubal resistance (Po/Qo) Ro RA Active tubal resistance (P/Q.. )
The eustachian tube (ET) is a compliant conduit which connects the closed gas cavity of the middle ear (ME) and mastoid air cells to the open gas cavity of the nasopharynx. In the normal resting state, this conduit is collapsed and the airway between the ME and nasopharynx is closed. The ET is opened intermittently during swallowing, ventilating the ME to the nasopharynx. The tubal opening is accomplished by contractions of the tensor veli palatini muscle which displaces the lateral wall from the cartilage-supported medial wall of the ET, thus breaking the mucus seal of the collapsed lumen. This is defined as active opening since it involves an exertion of muscle pull. During this process the ME cavity is ventilated by a bolus of air passing through the ET. A second mechanism for tubal opening involves the pressure gradient between the ME and the nasopharynx. When the pressure difference between the two
ends of the ET exceeds the collapsing forces of the tubal lumen, the ET will open spontaneously. This type of opening is called passive opening since it does not involve the active mechanism of the tensor veli palatini muscle.
= = =
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It has been recognized that the status of the ME cavity is to a large degree dependent upon the ventilatory function of the ET. Certain diseases of the ME are consequences of ET ventilatory dysfunction. In order to understand the underlying causes of tubal dysfunction, several investigators have studied the ET ventilatory function using various techniques.tv They evaluated the tubal function of subjects with and without ME disease to establish a comparative data base for normal and abnormal ET ventilatory function. The focus of these studies was directed towards an assessment of active tubal opening during different pressure conditions for the ME and nasopharynx. The most Widely used
From the Department of Otolaryngology, University of Pittsburgh School of Medicine Children's Hospital of Pittsburgh, Pittsburgh, Pennsylvania. ' Presented at the meeting of the Association for Research in Otolaryngology, St. Petersburg Beach, Florida, January 31, 1978.
603
Downloaded from aor.sagepub.com at East Carolina University on June 29, 2015
604
CANTEKIN ET AL
I
OSCILLOGRAPH
I
Fig. 1. Schematics of the instrumentation used for evaluation of the ventilatory function of the ET. See text for detailed explanation.
technique for the ventilatory function evaluation of the ET is the inflationdeflation test.':" During this procedure, the subjects are asked to equilibrate applied over- and under-pressures in the ME cavity by swallowing. In subjects with nonintact tympanic membranes the ME is directly accessible to air pressureflow monitoring devices, facilitating evaluation. But the causal interpretation of failure to equilibrate induced ME pressures is not obvious. Lack of active tubal function during this test, especially when negative pressure is applied to the ME, is not necessarily evidence of absence of physiological tubal function. Therefore, some attempts were made recently to study the passive opening of the ET by over-pressure applied to either the ME or nasopharynx.v" The as-
a
o
sessment of passive tubal function in conjunction with active function revealed more information about airflow through the ET. But even today, the underlying mechanisms of tubal dysfunction remain unresolved and speculative. The present investigation was conducted in an attempt to understand the ventilatory function of the ET by studying airflow through it in subjects with normal and abnormal tubal function. The airflow dynamics of the ET were evaluated by using the inflation-deflation test and a new method, the forcedresponse test. The latter technique is described in detail in the Methods and Materials section. A comprehensive evaluation of active and passive ET function was conducted in two groups of
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Fig. 2. An example of forced-response study of airflow through the ET. Using a constant-flow source, the ME is inflated with a fixed pressure rate (P) and the ET is forced open (PF). Lower trace shows the abrupt change in flow rate (Q) during forced opening. The flow source maintains a constant O. The ME pressure reaches a steady level (Po) and the flow rate through the ET stabilizes (Qo I. The pressure-to-flow ratio at this steady-state is taken as the passive tubal resistance (Ro). The spike in the flow trace and the corresponding drop in the ME pressure reveal an active tubal opening. This is when the subject swallows voluntarily. The ratio of ME pressure before the drop to the maximum flow rate during swallowing (QA) is defined as the active tubal resistance (~). The ET stays closed for approximately 11 seconds (arrows), followed br a second forced opening and steady-state pressure-flow condition similar to the initia situation. The second spike on the flow trace denotes another swallow and the cycle of events is repeated.
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AIRFLOW THROUGH EUSTACHIAN TUBE
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Fig. 3. Equilibration of applied ME pressure by voluntary dry and wet swallowing. The dry swallowing equilibration attempt shows consistent resl?onses for applied positive ME pressure (inflation). The same pressure drops (L'l.P), maximum flow rates ( QMAX), volume of flow passing through the ET (V) and duration of tubal opening (TA) are recorded in two different attempts. Flow direction is positive when air evacuates the ME cavity. TA is defined as the elapsed time between two consecutive steadypressure levels. Dry swallowing with negative ME pressure (deflation) shows reproducibility as good as the inflation study. Equilibration attempt during wet swallowing (left frame) shows reduced L'l.P and V in comparison to dry swallowing. Subsequent wet swallows at five-second intervals depict diminished responses. A 35-second interval restores the response to the initial level.
patients, one with and one without a history of ME disease. This was designed to establish a comparative data base for normal and abnormal tubal function and to identify the possible mechanisms of tubal dysfunction. METHODS AND MATERIALS The study population was comprised of two groups of subjects. The first group had no history of ME disease and traumatic perforations of the tympanic membrane; they were defined as the normal group. The abnormal group had recent histories of otitis media with effusion and resultant chronic perforations of the tympanic membrane. There were six subjects with a mean age of 29 years in the normal group and five subjects with a mean age of 24 years in the abnormal group. Only volunteers were included in the study, since each experimental session lasted about two hours. In addition, the subjects had to be tested on three different occasions within a one-month period to establish reproducibility for the test results.
After otoscopic examination of the ME, the ear canal of the subject was connected to the manometric system, shown in Figure 1, by a modified soft rubber Foley catheter. Only subjects with dry ME were chosen. They were tested in a comfortable sitting position. The manometric monitoring system was comprised of a variable-speed constant-flow pump, two pressure transducers, a flow meter with a differential pressure transducer, two valves to isolate different parts of the system, transducer signal conditioners, and an oscillograph. The technical details of this system have been previously described.' After obtaining a hermetic connection between the manometric system and the ear canal, two types of tests were conducted. During the first test, the inflation-deflation test, various magnitudes of over- and under-pressure were applied to the ME and the subject was asked to equilibrate the pressure by swallowing. The second procedure was the forcedresponse test. The ME was inflated at a constant flow rate (fixed pressure rate), forcing the ET open. Following the passive opening
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606
CANTEKIN ET AL
ABNORMAL
NORMAL No. 3D
No. 31
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Fig. 4. Typical pressure-flow recordings of normal subjects and patients with ME disease during inflation-deflation studies. The first and second horizontal rows are pressure-flow traces of equilibration of aPl?lied positive ME pressure (inflation), whereas the responses to ME negative pressure (deflation) are shown in rows three and four. The arrows on the traces mark the duration of ET opening (TA ) • of the ET, the pump continued to deliver a constant flow rate. This held the ET open. After a steady-state condition for ME pressure and flow rate through the ET was reached, the subject was instructed to swallow. Thus, the increased dilation due to active muscle function was assessed. An example of the forced-response test is shown in Figure 2. Active openings of the ET during voluntary dry swallowing and during swallowing of small amounts of water, called wet swallowing, were compared. This was to determine which type of swallowing induces effective and reproducible tubal opening. Figure 3 shows the comparison of these two kinds of swallowing for the equilibration of applied ME pressure. The tubal openings were more consistent and dilations were larger during dry swallowing. Therefore only dry swallows were used during the study. In every testing session, the same procedural sequence was used. The testing began with an initial detennination of the forcedopening pressure. The ME cavity was pressurized at a rate of 13 mm H20/sec until the ET spontaneously opened. Then the pump was stopped and valve 1 (Fig. 1) was closed, disconnecting the pump volume from the testing volume (28.6 cc). The patient was instructed to dry swallow at will. After this equilibration attempt, the ME was inflated at a rate of 28 mm H20/sec. The pressure was increased to 250 mm H 20 or 60%
of the forced-opening pressure, whichever was less. This was a precaution taken to prevent passive tubal openings from sustained ME over-pressure. After attempting to equilibrate applied positive pressure, the ME pressure was decreased to negative 250 mm H20 at the previous pressure rate. Again the subject was instructed to swallow at will to equilibrate. This inflation-deflation test was repeated until three data points for each pressure interval of 50 mm H20 were obtained. Valve 1 was alwars closed after the desired ME pressure leve had been reached. Then the forced-response test was conducted using five discrete pump speeds delivering flow rates of 3, 5.5, 12, 22.5, and 44 cc/min, respectively. These flow rates approximately corresponded to ME inflation rates of 6, 13, 28, 47 and 102 mm H.O/sec. The pump speeds were chosen in a random order. Upon completion of a test with a given flow rate, a five-minute rest period was allowed before starting with a different pump speed. This presumably permitted the ET to return to normal, RESULTS
The results are presented in two sections: 1) inflation-deflation test and 2) forced-response test. The data for the normal group are presented as the means and standard deviations for the measured parameter. However, the data
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AIRFLOW THROUGH EUSTACHIAN TUBE
607
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Fig. 5. Duration of ET opening (TA) during active equilibration attempts as a function of applied ME pressure (PM). Mean values for six normal subjects are shown by open circles over an ME pressure range of - 250 mm H20 to 150 rom H20 (upper left frame). Confidence intervals represent one standard deviation of the mean. The other frames depict data points from five patients with ME disease. Note that the duration of tubal opening is independent of the ME pressure level for normal subjects.
points for each individual in the abnormal group are shown in order to elucidate the variations from the normal group. Inflation-Deflation Test. Examples of pressure-flow recordings during this test are shown in Figure 4. The first two columns are recordings from normal subjects and the following three columns are from three subjects with ME disease. Patients in the abnormal group had active tubal openings that showed reduced ET dilations. This was indicated by the magnitude of the pressure drop (L::-.P), the maximum flow rate (QMAX), and the total volume of flow (V) passing through the ET during swallowing. The area of the flow-time trace is the measure of the total volume of flow. Duration of ET opening (TA) is shorter for patient 21. The tubal opening duration as a function of applied ME pressure (PM) is shown in Figure 5 for the normal group and for the five individual subjects of the abnormal group. The top left frame shows that the duration of tubal opening was not affected by the ME
pressure in normal subjects. Between applied ME pressures of -250 and 150 mm H 20, the duration was independent of the pressure level. This, however, was not the case for the abnormal subjects. Subject 22 showed active openings of the ET for all tested values of ME pressure with variable duration. In this case, ET opening duration ranged between 0.15 and 0.34 seconds as a function of ME pressure. Subjects 4, 21, and 10 exhibited active openings for a limited range of ME pressures, and the duration of tubal opening was affected by the pressure level. No active openings were recorded with patient 13. In the abnormal group, the duration of ET opening did not show a discernible dependence on, or independence of, the magnitude of the applied ME pressure. Airflow characteristics through the ET during inflation-defla tion tests are shown in Figure 6. The relationships between maximum airflow rate (QMAX), total volume of air passing through the ET (V), and change in ME pressure (L::-.P) as a function of applied ME pressure (PM)
Downloaded from aor.sagepub.com at East Carolina University on June 29, 2015
CANTEKIN ET AL
608
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Fig. 6. Maximum airflow ( Qmx) through the ET (top), total volume of air (V) passing through the ET (middle), and change in ME pressure (,0.P) (bottom) during one swallow; all are plotted against applied ME pressure (PM). Mean values for six normal subjects are denoted by open circles and the confidence intervals are for one standard deviation of the mean. Symbols represent data points for patients 4 (T), 10 CA.), 13 (+),21 (.), and 22 (e). For the normal group Q'IAX, V, and P are linear functions of PM between ME pressure levels of -200 to 100. The data points for QMAX adapted from Flisberg's" study of normals (0) are in close agreement with the present study. Also, the data points for V adapted from the study by Rundcrantz° of normals is shown by a symbol (0). ,0.P is not compared with previous studies, since the magnitude of ~P depends on the volume of the manometric monitoring system.
were plotted. In normal subjects, these three parameters of airflow exhibited a linear dependence on the applied ME pressure (between -200 and 100 mm H 20 ) . The individual data points document the responses of subjects with a history of ME disease, reflecting reduced dilations of ET during active openings. The differences between normal and abnormal subjects were easily identifiable. Two previous studies of inflationdeflation tests on normal subjects are shown in the top and middle frames. Data points for the maximum airflow rate at two levels of applied negative ME pressure are in close agreement with the present investigation (top frame )," Also, the previous data for total volume of air passing through the ET are within the limits of the normal group's response in this study (middle frame)." This volume corresponds to an average applied positive ME pressure of 30 mm H 2 0 . Forced-Response Test. During this test, the ET function was assessed by evaluating three parameters: the forcedopening pressure (PF ) , the passive tubal resistance (R o), and the active tubal resistance (R A ) . Examples of tubal resistance studies are shown in Figure 7. The recordings presented here are pressure-flow traces following the forced opening of the ET due to ME over-pressure. The top two frames show tubal resistance studies in two normal subjects. The ET was held open by continuous airflow. This steady-state pressureflow condition through the ET was temporarily perturbed when the subject swallowed. During active function (swallowing), the tubal lumen was further dilated. This was displayed as a transient spike in flow rate and an abrupt drop in ME pressure. Following this active opening, the ME pressure gradually resumed its steady-state level since the pump maintained a constant airflow. The passive tubal resistance (R o) is defined as the pressure-flow ratio at this steady state. The active tubal resistance (R A ) is defined as the ratio of ME pressure (prior to active opening) to maximum flow rate during swallowing.
The bottom two frames in Figure 7 show tubal resistance studies of two abnormal subjects. The most striking difference between normal and abnormal
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AIRFLOW THROUGH EUSTACHIAN TUBE
609
NORMAL
ABNORMAL
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O±~:::::==========:::::::r::::::::±:±±:::::±t Fig. 7. Examples of forced-response studies for normal subjects and patients with ME disease. All frames are for constant flow source delivering a nominal 12 cc/min flow rate. The top two frames illustrate recordings from two normal subjects. A tenfold increase in flow, denoted by spikes in the flow trace, corresponds to voluntary swallowing. During this muscular dilation of the ET, ME pressure drops temporarily. The constant flow builds up the pressure to a steady-state level at which the passive tubal resistance is calculated. The left bottom frame shows a recording from a patient with ME disease. Note that the active dilation of the ET during swallowing is quite small in comparison to normal subjects. The tube stays open about 1.5 seconds and there is a drop in the pressure level. The right bottom frame depicts a recording of another patient with ME disease. The swallowing activity is quite ineffective in further dilating; the ET while a constant flow of air is passing through it. Note that following the swallow, the tube closes and, instead of a drop in ME pressure, there is a slight increase.
subjects is the magnitude of the flow spike during swallowing. In the normal subjects, the swallowing activity induced a ten-fold increase in the flow rate, whereas in the abnormal subjects the change was very small, indicating ineffective tubal dilation during active opening. In subject 10, the active opening mechanism dilated the ET two-fold above the predilated state. But in subject 21, the swallowing induced constrictions of the ET lumen (increase in ME pressure and decrease in flow rate). Forced-opening pressure (P F ) as a function of the application rate of ME pressure (j» is graphed in Figure 8. Forced-opening pressure increases with higher rates of ME inflation. In the normal group, passive opening of the ET by ME over-pressure varied from 320 to 400 mm H 20 depending upon the application rate. Forced-opening pressure of the ET in normal subjects was re-
ported by Elner et al.' who used a single ME inflation rate of 40 mm H 2 0 / s e c to open the ET. The results of the one flow rate used by Elner et al were similar to the findings in the present study. In the abnormal group, subjects 4, 10, and 21 had considerably higher forcedopening pressures than the normal subjects. Also, the forced-opening dependence on the application rate of ME pressure was more pronounced. Subject 22 exhibited lower opening pressures, but subject 13 was within the limits of the normal group. Four subjects of the abnormal group could be separated from the normals by evaluating this parameter of tubal function. Passive (R o) and active (R A ) tubal resistances were computed for the steady-state airflow rates (Qo) between 5.5 and 44 cc/min. Flow rates below 5.5 cc/min could not be used for resistance studies because most ET exhibited an
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CANTEKIN ET AL
610
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Fig. 8. Relationship between the forced-opening pressure (PF) and the application rate of ME pres~ur~ (P). Open circles connected by a solid line and confidence limits denote mean values and one standard deviation of the mean for six normal subjects. Mean values for five patients with ME disease are shown by the same symbol convention as Figure 6. displays data adapted from Symbol the Elner et al' study of normals. Note that increasing the ME inflation rate raises the forced-opening pressure and this rate dependence is more pronounced for patients with ME disease.
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unstable behavior manifested by flutterlike flow patterns. The patients were uncomfortable when flow rates in excess of 44 cc/min were employed. These two conditions determined the upper and lower limits of the resistance studies. The relationship between tubal resistance and airflow rate is shown in Figure 9. The top frame depicts the passive tubal resistance (R o) monotonically decreasing with increasing predilating flow rate (Qo). With the exception of subject 22, all of the patients in the abnormal group had higher passive resistances than did the subjects of the normal group. The one data point adapted from the study by Elner et al" of normals is in close agreement with the results obtained from our normal subjects. The bottom frame shows that the active tubal resistance (R A ) of the normal group is independent of the predilating flow rate (Qo). Subjects in the abnormal group (except subject 22) had considera1;lly higher active resistances. The active tubal resistances of subjects 10 and 13 showed definite dependence on the predilating flow rate. These two measures of ET resistance, especially active resistance, discriminated four abnormal subjects from the normals. In an effort to combine the passive
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Fig. 9. Passive tubal resistance (Ro ) ( top) and active tubal resistance ( RA ) (bottom) as a function .of steady-state airflow rate (Qo). For SIX normal subjects, the mean ,:alues ~or passive tubal resistance and active resistance are shown by open circles connected by solid lines. Confidence intervals represent one standard deviation of the mean. Patients with ME disease are symbolized by the same convention as Figure 6. Passive tubal resistance data adapted from Elner et al' are shown by (0). Increased constant flow rate reduces the passive tubal resistance (top). Note that the active tubal resistance for normal subjects is less than 2 mm H,O/cc/min and is independent of Qo (bottom) .
and active resistance in one measure which could discriminate the normal from the abnormal subjects, the ratio of these two resistances was computed. The ratio of passive to active tubal resistance (Ro/R A ) as a function of the steady-state airflow rate (Qo) is shown in Figure 10. For the normal group, the resistance ratio decreased steeply for the flow range of 5.5 to 22.5 cc/min, and then it remained unchanged, at about a value of five with increasing flow rates. This measure clearly discriminated all
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AIRFLOW THROUGH EUSTACHIAN TUBE
the intraluminal mucus, leading to a descriptive recording of tubal dilations by the tensor veli palatini muscle contractions. The combination of passive and active tubal resistance in a ratio fonn could normalize the geometric differences between individuals, revealing a quantitative measure for tubal dilation efficiency (Fig. 10) .
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