Combined effect of fluid and pressure on middle ear function có nói VAI TRÒ NLĐ

Keywords: laser vibrometer, middle ear mechanics, otitis media, temporal bone, tympanometry INTRODUCTION Otitis media with effusion OME is defined as the presence of fluid in the middle

Hearing research http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2346543/

Author Manuscript

NIH Public Access

Chenkai Dai, Mark W Wood, Rong Z Gan

Hear Res Author manuscript; available in PMC 2009 February 1

Published in final edited form as: Hear Res 2008 February; 236(1-2): 22–32 Published online 2007 November 24 doi: 10.1016/j.heares.2007.11.005

Combined Effect of Fluid and Pressure on Middle Ear Function

Chenkai Dai, MD, MS, Mark W Wood, MD, and Rong Z Gan, PhD

Additional article information

Abstract

In our previous studies, the effects of effusion and pressure on sound transmission were investigated separately The aim of this study is to investigate the combined effect of fluid and pressure on middle ear function An otitis media with effusion model was created by injecting saline solution and air pressure simultaneously into the middle ear of human temporal bones Tympanic membrane displacement in response to 90 dB SPL sound input was measured by a laser vibrometer and the compliance of the middle ear was measured by a tympanometer The movement of the tympanic membrane at the umbo was reduced up to 17 dB by the combination of fluid and pressure in the middle ear over the auditory frequency range The fluid and pressure effects on the umbo movement

in the fluid-pressure combination are not additive The combined effect of fluid and pressure on the umbo movement is different compared with that of only fluid or pressure change in the middle ear Negative pressure in fluid-pressure combination had more effect on middle ear function than positive pressure Tympanometry can detect the middle ear pressure of the fluid-pressure combination This study provides quantitative information for analysis of the combined effect of fluid and pressure on tympanic

membrane movement

Keywords: laser vibrometer, middle ear mechanics, otitis media, temporal bone,

tympanometry

INTRODUCTION

Otitis media with effusion (OME) is defined as the presence of fluid in the middle ear and is usually associated with the middle ear pressure change because of poor Eustachian tube function or an inflammatory response following acute otitis media The amount of effusion in OME patients varied from partially filling the middle ear to

fully filling the cavity The properties of the effusion are highly variable and related to the pathology process of OME The middle ear effusion is classified as serous, mucoid and glue-like with different viscosities tính sền sệt, tính lầy nhầy, tính nhớt -tính dẻo, tính dính in various pathology processes of OME The high prevalence of OME and

difficulties in diagnosis make the mechanisms behind middle ear function change seen with OME an important issue in hearing research

Several studies (Goodhill and Holcomb, 1958; Majinma et al., 1988; Ravicz et al., 2004; Gan et al., 2006; Dai et al., 2007) have investigated possible mechanisms of hearing loss associated with the presence of middle ear effusions Ravicz et al (2004)

suggested that the primary mechanism responsible for hearing loss at low frequencies was the reduction of middle ear compliance by a reduction in the middle ear air volume The increased mass of the tympanic membrane (TM) by entrained fluid caused the hearing loss at high frequencies In Gan et al.’s study (2006), the amount of fluid in middle ear was manipulated and the vibration of the TM and stapes were measured with intact and opened cochlea in human temporal bones The displacement transmission ratio

of the TM to footplate was derived and the results show that the effect of fluid on middle ear function is different between three frequency ranges

The effect of middle ear pressure on TM mobility has been investigated in human

temporal bones and animals (Teoh et al., 1997; Lee and Rosowski, 2001; Rosowski and Lee, 2002; Murakami et al., 1997; Dirckx and Decraemer, 1992; Huttenbrink 1998; Gan

et al., 2006; Dai et al., 2007) The results of Murakami et al and Gan et al show that the middle ear pressure mainly decreased the TM movement at low frequencies (f <1k Hz)

In these published studies, the effects of middle ear fluid and pressure were investigated separately The literature is lacking evidence that identifies how combined fluid and air pressure in the middle ear affect the middle ear function In fact, the effusion in patients with OME is commonly associated with negative pressure We feel that it is important to further investigate the combined effect of pressure and fluid on middle ear function in order to explain the complex mechanisms behind these combined effects

In this study, we completed three groups of experiments in which the middle ear pressure, fluid, and fluid-pressure combination were manipulated respectively in human temporal bones Saline solution was selected for simulation of a serous effusion and 0.3 ml was found to be the critical amount of fluid which produced significant changes in umbo displacement in our previous studies of the OME model in human temporal bones (Gan et al., 2006; Dai et al., 2007) In those temporal bones, 0.3 ml fluid filled about half of the middle ear cavity and the fluid level was about to the umbo, which was observed under microscope The TM (umbo) displacement in response to 90 dB SPL sound input in the ear canal was measured by a laser Doppler vibrometer and the middle ear compliance change under these three conditions was measured by tympanometry

METHODS

1 Human temporal bone preparation

Four fresh-frozen cadaver temporal bones, obtained through the Willed Body Program, University of Oklahoma Health Sciences Center, were used in this study The ages of individual donors ranged from 50 to 93 with a mean of 69 years (3 females and 1 male)

To retard putrefaction and maintain soft tissue compliance, the bones were immersed in 1:10,000 Merthiolate in 0.9% saline solution at 5° C until use All bones were used within one week of acquisition

Before acceptance into the study, each temporal bone was visually inspected under an operating microscope (OPMI-1, Zeiss, Thornwood, NY) to confirm a normal ear canal and an intact TM, and the absence of overt pathology The 4 bones reported in this paper were all from normal ears without evidence of pathology in the middle ear after the post-experimental check

The Eustachian tube (ET) meatus was identified at the nasopharyngeal end The

cartilaginous portion of the ET was then bisected and removed up to the boney meatus A soft silicone tube, outer diameter of 1 mm, with a white tip was then advanced through the remnant of the ET into the middle ear while visualizing the TM with an operating microscope Once the tip was visualized though the TM, the tube was glued in place at the skull base using cyanoacrylate gel glue (Henkel Consumer Adhesives, Avon, OH) The silicone tube was then connected to a syringe for injecting fluid into the middle ear cavity or adjusting the middle ear air pressure to simulate a middle ear effusion or

pressure variation The second silicone tube (2 mm outer diameter, named the outflow tube) was placed through a hole that was drilled through the epitympanic tegmen, being careful not to touch the ossicles The tube was glued in place and connected to a syringe and a U-tube manometer through a three-way stopcock as shown in Fig 1 The

manometer was used to measure middle ear pressure and an attached syringe was used to release the middle ear pressure

Figure 1

Schematic of the experimental setup with laser vibrometer and tympnometry in human temporal bones

All surgically opened areas were sealed airtight using cyanoacrylate glue and silicone polymer (Reposil, DDI Inc., Milford, DL) A leaking test was then conducted in every bone using the procedure described by Gan et al (2006)

After the leaking test, a piece of laser reflective tape of 0.5 mm2 and 0.04 mg (3M Co.,

St Paul, MN) was placed as a laser target on the lateral surface of the umbo The bone was wrapped in wet gauze (normal saline) to prevent desiccation of the specimen during the experiment Before conducting any laser measurement on temporal bones, we used a tympanometer (Zodiac 901, Madsen, GN Otometrics, Denmark) to verify normal

compliance of the tympanic membrane

After all experiment measurements, a mastoidectomy was performed by a facial recess approach to check the middle ear cavity and mastoid Among the four mastoids in the temporal bones used in this study, two of them were air-filled, one is diploetic, and the other one was mixed type of the above two Some fibrous tissues were found near the aditus in two bones with air filled mastoid No substantial amount of water was found in the mastoid processes of the four bones

2 Experimental setup with laser vibrometer

Figure 1 shows the temporal bone experimental setup with a laser vibrometer and a tympanometer, which was similar to studies reported by Gan et al (2006) and Dai et al (2007) Briefly, the temporal bone was placed in a temporal bone holder and the bone assembly was set on a vibration isolation table Pure tones at 90 dB SPL from a function generator (Model 193, Wavetek, San Diego, CA) were delivered to the ear canal near the

TM by an inserted earphone (Model ER-2, Etymotic Research, ELK, Grove Village, IL)

A probe microphone (Model ER-7, Etymotic Research) used for monitoring the input sound pressure level (SPL) was secured parallel to the sound delivery tube and was positioned approximately 2 mm from the umbo (Gan et al., 2001, 2004)

A laser Doppler vibrometer (Model CLV-700, Polytec PI, Tustin, CA) was used to measure the vibration of the TM at the umbo The helium–neon laser with an associated positioner-aiming prism was coupled to an operating microscope (Model OPMI-1FC, Zeiss) Velocity measurements with the HLV were acquired in the frequency domain by back-weighted averaging of a live, fast-Fourier transform A fast acquisition,

multichannel, digitizing signal analyzer (Model DSA 601, Tektronix, Beaverton, OR) was used for analysis of the spectral magnitude and phase data from the laser vibrometer and all the data were recorded on a personal computer Only data with a total harmonic distortion of less than 10% of pure tone signals according to the distortion index shown

on the signal analyzer were accepted The peak-to-peak displacement (dp-p) of the umbo was directly calculated from the voltage output of the laser vibrometer velocity decoder

by a formula: dp-p = k (Avolt / πf), where Af), where Avolt is voltage amplitude in mv, f is frequency in kHz, k is a constant related to selected scale and calibration factor in unit of µm/mv/s (.Gan et al., 2001,2004)

A tympanometer (Zodiac 901, Madsen, GN Otometrics Denmark) with a constant

frequency of 226 Hz was used in this study The detailed tympanometric measurements

in human temporal bones were reported by Dai et al (2007) The tympanogram, a

graphic display of acoustic admittance with respect to ear canal pressure variation, provides information about the mobility and integrity of the middle ear using three parameters shown in the tympanogram: static compliance (SC), middle ear pressure

energy absorbed by the middle ear system presented in the vertical peak of the

tympanogram The MEP refers to the pressure in the ear canal corresponding to the peak

of the tympanogram, which is approximately equal to the middle ear pressure TW refers

to the ear canal pressure range corresponding to a 50% reduction in static compliance and presented in daPa (Onusko et al., 2004)

3 Experimental protocols

The temporal bone was oriented approximately as a patient would be seated at a hearing test The control study in which the middle ear pressure remained at zero with no fluid in the cavity was performed first Three types of experiments were performed in temporal bones after the control data were acquired Although the effects of middle ear pressure and fluid alone have been studied by Gan et al (2006), Groups 1 and 2 experiments of either variable pressures only or constant (0.3 ml) fluid level in the cavity were conducted for comparison with the combined effect of fluid and pressure in Group 3 OME patients commonly have negative pressure in the middle ear; however, we studied both positive and negative pressure changes to try to gain a comprehensive understanding of the effects

of pressure changes on middle ear function Therefore, in our Group 3 experiment, both positive and negative pressures were ombined with fluid to complete the study Both laser and tympanometry measurements shared the same protocols as follows In Group 3 experiments, the fluid amount of 0.3 ml was selected because it was reported to be a critical volume of fluid in the middle ear, which caused significant umbo movement change (Gan et al 2004) In their experiments on temporal bones, the maximum amount

of fluid to fill up the middle ear cavity was between 0.6 and 0.7 ml With 0.3 ml about half of the middle ear cavity was filled, and the fluid level was about to the umbo which was observed microscopically during the experiment Although such partially filling resulted in smaller decreases in umbo displacement or velocity compared to the decreases observed when the middle ear was completely filled as reported by Gan et al (2006) and Ravicz et al (2004), we prefer to use 0.3 ml fluid level as a standard amount of fluid to see the fluid and air combined effect on middle ear function

Group 1 – Effect of middle ear pressure

The outflow tube was connected to the U-tube manometer The middle ear air pressure was increased stepwise from 0 to +10, +15, +20, then down to 0, −10, −15, −20 cm H2O (1 cm H2O = 98 Pa), and finally, back to zero using the syringe attached to the ET

catheter Displacement of the umbo was measured at each middle ear pressure level by laser vibrometer and the compliance was measured by tympanometry

Group 2 – Effect of middle ear fluid

0.3 ml normal saline solution was injected into the middle ear cavity through the ET catheter with the outflow tube open to the atmosphere The fluid level was maintained in the cavity and visualized through the ear canal using a light microscope Displacement of the umbo and the compliance of middle ear were measured by laser vibrometer and tympanometry, respectively

Group 3 – Effect of combination of middle ear fluid and pressure

After the Group 2 experiment, 0.3 ml fluid was kept in the middle ear The middle ear pressure was increased or decreased from 0 to ± 10, ± 15, and ± 20 cmH2O, respectively

The displacement of the umbo was measured by laser vibrometer and the middle ear compliance change was measured by tympanometer at each pressure level

RESULTS

Figure 2 shows the mean spectral peak-to-peak displacement of the TM at the umbo measured from 4 temporal bones in three groups with 0.3 ml middle ear fluid or/and positive pressures The bold solid line is the TM displacement of control or zero fluid and pressure in response to 90 dB sound input in the external ear canal at frequencies of 200~8k Hz The thin lines without symbols represent the mean curves of TM

displacement obtained in Group 1, in which positive air pressure was introduced in the middle ear The broken bold line shows the mean TM displacement curve of Group 2 (0.3ml middle ear fluid) The lines with symbols show the mean TM displacements curves of Group 3 Results from Group 1 show TM movement decreased mainly at low frequencies (f < 2k Hz) and there was no significant reduction at high frequencies (f > 2k Hz) Note that at frequencies from 6k~8k Hz, the umbo displacement in Group 1 was higher than the control and interestingly, umbo displacement in response to 20 cm H2O middle ear pressure was higher than that in response to 10 cmH2O In Group 2, the TM displacement was almost the same as the control at low frequencies of 250~450 Hz and decreased significantly at high frequencies (f >1 k Hz) The TM displacements of Group

3 in (thin solid lines with symbols) decreased over all frequencies from the control curve Compared with Group 1, the umbo displacement reduction in Group 3 was less at low frequencies (f <1k Hz), but significantly more at high frequencies (f >2k Hz) Similar to Group 1, higher middle ear pressure caused more umbo movement reduction at low frequencies (f <1k Hz), but less reduction was observed at high frequencies (f <2k Hz)

Figure 2

Averaged peak-to-peak umbo displacement measured in four bones using a laser

vibrometer in response to 90 dB SPL sound in the ear canal The curves with standard

deviations represent control (bold solid line) and three experimental groups of positive

Figure 3 shows the mean spectral displacement of the TM at the umbo under conditions

of fluid or/and negative pressure in the middle ear in Group 1, Group 2 and Group 3 The curves obtained in control and Group 2 are the same as those in Fig 2 In Group 1, negative middle ear pressures resulted in decreases of umbo movement at low

frequencies (f <3k Hz) The negative pressure shifted the umbo displacement peak from 1k Hz at Control to 1.8k Hz In Group 3, umbo displacement was reduced at all

frequencies by the combination of fluid (0.3 ml) and negative pressures At low

frequencies (f <1k Hz), the umbo displacement reduction in Group 3 was less than that in Group 1 However, umbo displacement decreased significantly at high frequencies while

no obvious change was observed in Group 1 (f >2k Hz) There are some differences for Group 3 results at high frequencies (f > 2k Hz) between Fig 1 and Fig 2 The TM

displacements in Fig 2 decreased a little more than those in Fig.1 Negative pressure had more effect on TM movement than positive pressure

Figure 3

Averaged peak-to-peak umbo displacement measured in four bones using a laser

vibrometer in response to 90 dB SPL sound in the ear canal The curves with standard

deviations represent control (bold solid line) and three experimental groups of negative

Figure 4 shows the TM movement changes relative to the control (in dB) derived from the three groups in Fig 2 Solid lines with hollow symbols represent the umbo

displacement magnitude change in response to positive pressure in Group 1 The umbo displacement magnitude change mainly occurred at low frequencies (f <1k Hz) and 20 cmH2O middle ear pressure caused up to 10 dB loss at frequencies below 1k Hz No significant change was observed at frequencies of 2~6k Hz and the displacement

magnitude increased at frequencies > 6k Hz In Group 2 (bold solid line), umbo

displacement magnitude increased slightly to about 2 dB at 300 Hz and decreased

significantly up to 12~19 dB loss at high frequencies (f >1k Hz) In Group 3 (solid lines with solid symbols), umbo displacement magnitude decreased across all frequencies of 200~8k Hz At low frequencies (f <1k Hz), 0.3 ml fluid combined with 10 cmH2O middle ear pressure caused 3 to 5 dB loss while 0.3 ml fluid and 20 cmH2O pressure caused 5 to

10 dB loss At frequencies of 4~5k Hz, 0.3 ml fluid combined with 10–20 cmH2O middle ear pressure caused 7~12 dB reduction of the umbo displacement At low frequencies (f <

1000 Hz), TM movement decreased more in Group 1 than that in Group 3 At high frequencies (f > 2k Hz), TM displacement decreases in Group 3 are more than that in Group 1 and less than that in Group 2

Figure 4

Averaged changes of umbo displacement magnitude in dB measured from three

experiments in the three groups of positive pressure (Group 1, solid lines with hallow symbols), 0.3ml fluid (Group 2, bold solid line) and combined fluid-positive pressure (Group

The results in Figure 5 were derived from Figure 3 and display the change of TM (umbo) displacement magnitude related to the control data in the three experimental groups Similar to Figure 4, significant umbo displacement reduction occurred at low frequencies (f < 1k Hz) in Group 1, when negative pressures were induced in the middle ear A 14 dB reduction was observed at low frequencies when the middle ear pressure reached −20 cm

H2O At the high frequencies (1~3k Hz), the umbo displacement reduction was smaller than that at low frequencies A slight increase in umbo displacement magnitude occurred

at frequencies of 7k~8k Hz In Group 3, the combination of fluid and negative pressures reduced umbo displacement at all frequencies tested Fluid combined with −20 cmH2O middle ear pressure caused 6~11 dB loss at low frequencies (200~500 Hz) and a

maximum of 14 dB loss at 2.7k Hz Umbo displacement changes in Group 1 and 3 in Figure 5 at high frequencies were larger than those in Figure 4

Figure 5

Averaged changes of umbo displacement magnitude in dB measured from three

experiments in the three groups of negative pressure (Group 1, solid lines with hallow symbols), 0.3ml fluid (Group 2, bold solid line) and combined fluid-negative pressure (Group

Figure 6 shows the tympanometric results of middle ear pressure (MEP), static

compliance (SC) and tympanometric width (TW) under control and three experimental groups Figure 6A illustrates that the tympanometric MEP values are almost equal to the middle ear air pressure directly read from the manometer (1 cm H2O ≈ 10 daPa) in all tested ears Figure 6B shows the mean SC (in ml) values for Control and experimental Groups The Control SC value was about 0.58 ml and the SC value decreased slightly to 0.41 (still in normal range) when the middle ear pressure increased to 20 cmH2O in Group 1 The mean SC value in Group 2 was 0.52 ml, almost equal to the Control value

In Group 3, the SC values (hollow squares) decreased slightly when 0.3 ml fluid

combined with +10, +15 and +20 cmH2O air pressures was induced into the middle ear Figure 6C shows the TW changes in Control and experimental groups The TW value (in daPa) was about 80 in control No significant change was observed in Group 1 (hollow triangle) or Group 2 (circle) The TW value increased when fluid combined with negative pressures was introduced in the middle ear

Figure 6

Averaged tympanometric data in response to variation of pressure and fluid in control and three experimental groups A Middle ear pressure (MEP) data in daPa, B Static compliance (SC) data in ml, C Tympanometric width (TW) data in daPa

1 Summary of Results and Comparison with Published Data

Results of this study show that the umbo movement was reduced by a combination of fluid and pressure at all frequencies At low frequencies (f < 1k Hz), the TM movement reduction caused by the combination of middle ear fluid and pressure (Group 3) was higher than that by middle ear fluid alone (Group 2), but less than that by middle ear pressure alone (Group 1) At high frequencies (f> 2k Hz), the umbo displacement

reduction by the combination of fluid and pressure was more significant than that by middle ear pressure alone, but less significant than that by middle ear fluid alone The results also show that the combination of fluid with negative pressure had more effect on umbo movement than positive pressure This indicates that the influence of negative and positive pressure in combination with fluid in the cavity on TM movement is not the same

The tympanometric results show that the MEP can predict the middle ear pressure

changes with the combination of fluid and pressure No significant change of middle ear static compliance (SC) as middle ear pressure changes (Fig 6 B) does not mean the middle ear compliance is independent of pressure However, this indicates that the primary reason for the change in compliance is a change in middle ear static pressure as measured by laser Doppler vibrometer in temporal bones with zero ear canal pressure The fluid has little effect on the tympanometric static compliance (Fig 6), which is consistent with the umbo displacement measurement at low frequency (i.e., 200 Hz) shown in Fig 4 and Fig 5 The introduction of positive or negative middle ear pressure shifts the tympanogram peak to the right or left and reduces compliance at zero ear canal pressure This is consistent with the umbo displacement measured in temporal bone in Fig 4 and Fig 5, and reported by Dai et al (2007) in previous study In the clinical setting, the tympanograms of OME patients are flat without a tympanometric peak The tympanometric peak shown in the measurements in the experimental partially filled ears indicates the artificial conditions which is different from the measurements in OME patients However, tympanograms from patients with air/fluid levels often show a slight peak

The experimental data measured from 4 temporal bones in this study was first compared with the results reported by Gan et al (2006) from 7 bones when the middle ear pressure was varied or 0.3 ml of saline was infused into the middle ear cavity (Figure 3 and Figure

9 in Gan et al.’s paper, 2006) As can be seen in Figure 7, the displacement curves

obtained in this study at control (without fluid and zero middle ear pressure), 0.3 ml fluid

in the cavity (Group 2), and ±20 cm H2O of middle ear pressure (Group 1) are in good agreement with Gan et al’s (2006) results This indicates our experimental setup was reliable for the fluid-air pressure combination study

Figure 7

Comparison of the data obtained from this study with the published results by Gan et al (2006) A Umbo displacements measured in control and filled with 0.3 ml saline in the middle ear cavity (Group 2) B Umbo displacements measured in bones with middle Furthermore, we compared the results from our Group 2 in this present study with the results from comparable studies by Ravicz et al (2004) The frequency range covered by Ravicz et al was up to 3k Hz while the current study measured up to 8k Hz There were some variations between our data and Ravicz et al.’s (2004) results, but the

measurements reported here generally agree with the data obtained by Ravicz et al

The effect of graded variations in middle ear pressure on umbo movement in human temporal bones was also reported by Murakami et al (1997) They used a video

measuring system to detect umbo displacement when a constant sound pressure of 134

dB was delivered at the TM across the frequency range of 200 to 3.5k Hz In our Group 1 experiment of middle ear pressure, the umbo displacement had a significant reduction at frequencies below 1.5k Hz which is similar to Murakami et al.’s results

The experimental measurements (Group 3) were compared with clinical data and are illustrated in Figure 8 Pure tone air and bone conduction audiometric thresholds at standard frequencies (0.25, 0.5, 1, 2, 4 kHz) were obtained from 30 OME patients in the private clinical practice of Dr Mark Wood (co-author) The 30 patients were diagnosed with OME by otoscopy and tympanometric acoustic reflex testing in a sound booth The averaged age of the 30 patients was 56 years old ranging from 23 to 72 (14 male and 16 female) Figure 8A shows the averaged air-bone gap data from the 30 patients who had middle ear effusions examined by the pneumatic otoscopy None of the patients had other middle ear pathology or a history of ear surgery, and none of the middle ear effusions were associated with clinical signs of infection All patients complained of acute or sub-acute hearing loss (3 weeks to 3 months) and most of the tympanic membranes appeared

to be retracted None of the middle ears had bubbles or observable air-fluid levels, thus it was concluded that the middle ear was filled with fluid

Figure 8