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

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 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 fluidpressure 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 2k Hz) Note that at frequencies from 6k~8k Hz, the umbo displacement in Group 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 in (thin solid lines with symbols) decreased over all frequencies from the control curve Compared with Group 1, the umbo displacement reduction in Group was less at low frequencies (f 2k Hz) Similar to Group 1, higher middle ear pressure caused more umbo movement reduction at low 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 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 and Fig 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 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 temporal bones in this study was first compared with the results reported by Gan et al (2006) from bones when the middle ear pressure was varied or 0.3 ml of saline was infused into the middle ear cavity (Figure and Figure 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 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 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 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 Pure tone air and bone conduction audiometric thresholds at standard frequencies (0.25, 0.5, 1, 2, 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 subacute hearing loss (3 weeks to 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 Air-bone data obtained from 30 OME patients and umbo displacement reduction measured from temporal bones in Group experiments Mean air-bone gap data from 30 OME ears at frequencies of 250, 500, 1k, 2k, 3k and 4k Hz B Data extracted from Group results Figure 8A shows the hearing loss in the OME patients is higher at 250 Hz and 4k Hz than that at 500, 1k, 2k or 3k Hz This change was similar to the displacement reduction shown in Figure 8B and Figure 8C (0.3 ml fluid and ±20 cm H2O combination) except that the air-bone gap was highest at 250 Hz and the highest reduction in our temporal bones occurred at 3k Hz The averaged conductive hearing losses collected from 30 OME patient ears were larger than the umbo displacement reduction measured from temporal bones These clinical findings differ from the results of temporal bones (Figure 8B and Figure 8C) and those of Gan et al (2006) and Ravicz et al (2004) in the amount of low frequency conductive hearing loss that is recorded in the clinical setting These differences may reflect the small amount of fluid volume that was used in this experimental setup, the chronicity of the fluid noted in our clinical patients, the possible effects of viscosity, inflammation and pressure differences which are not measurable within the scope of the clinical setting Other effects which may result in more low frequency loss in the clinical setting include chronic effects on the tympanic membrane, such as stretching, entrained fluid or thickening of the inner membranous layer and the possibility of effects on the ossicular chain However, Figure 8A shows the OME patients have about 27 dB loss at high frequencies (4k Hz) and that is similar to the results of Gan et al (2006) when the temporal bone model was filled with fluid The similar results between a filled middle ear cavity and clinical OME patients indicate that the fluid was the primary cause of hearing loss in OME patients and this was verified by recovery of hearing loss when the fluid was drained in these patients The volume of the tympanic cavity in humans ranges between 0.5 and ml The maximum volumes were found to be 0.6~0.7 ml in the post-experiment check of the four bones used in this study In this experimental setup, the fluid amount of 0.3 ml was selected since it was the critical amount that caused significant umbo movement change in the previous study reported by Gan et al (2006) In this preliminary study for understanding the effect of fluid and pressure combination on umbo movement, the selected 0.3 ml fluid volume in the middle ear might also show some critical effect on middle ear function In fact, the results obtained from Group show that 0.3 ml is most sensitive to the umbo movement reduction However, we realized that partially filling the temporal bones does not predict the hearing loss from patients who have hearing levels consistent with completely filled ears It is similar to the work of Ravicz et al (2004) in which they provided a good model for hearing loss in patients with fluid filled middle ears, but not good for assessing hearing loss in patients with partially filled middle ear So it is not surprising that in the present study, which partially filled the middle ear cavity, the model did not demonstrate the same amount of hearing loss as is seen in patients who had completely filled middle ears (Figure 8) In future temporal bone studies, larger amounts of fluid will be used in the middle ear along with pressure to simulate OME in the clinical setting 2 Possible Mechanism of Combined Effect on Middle Ear Function At low frequencies, the umbo displacement reduction by the combination of middle ear fluid and pressure was less than that by pressure alone (Figure 2–Figure 5) One possible explanation is the combined changes of TM stiffness with the fluid and air pressure in the middle ear Stiffness of the TM increased when the middle ear pressure increased and the mobility of the umbo was decreased at low frequencies, where the stiffness of the TM dominated its motion According to the report by von Unge et al (1995), OME seems to decrease the stiffness of TM promptly and it may relate to the edema When fluid was present in the middle ear and attached to the TM, the water entrained in TM may result in the stiffness decrease of the TM Thus, the stiffness of the TM in fluid-pressure combination was lower than that in pressure alone case, and the displacement reduction of the umbo was accordingly lower in fluid-pressure combination case (Group 3) Ravicz et al’s (2004) study indicated that a fluid-related reduction in middle ear compliance due to a reduction in middle ear air volume was another possible explanation for the reduction at low frequencies At low frequencies, changes of movement of the umbo is compliancedominated in the normal state and continues to be compliance-dominated as the middle ear air volume is changed by fluid (Ravicz et al 2004) At high frequencies, the displacement reduction of the TM was mainly caused by fluid in the middle ear as reported by Gan et al (2006) The main mechanism behind this reduction seemed to be the increased TM mass by entrained fluid Compared with middle ear fluid alone, the reduction of umbo displacement by fluid-pressure combination was smaller This observation reflects the influence of middle ear pressure on umbo displacement reported by Gan et al (2006) and shown in Fig and Fig of present study The peak frequency of the displacement curve was shifted toward the high frequencies when middle ear pressure was changed, which helped to release the displacement reduction at high frequency Thus, the mobility of the umbo in fluidpressure combined state was lightly better than the fluid only case at high frequencies The laser measurements displayed in Figure 4, Figure and Figure show some differences between positive and negative pressure effects on TM or umbo movement For example, 0.3 ml middle ear fluid combined with −20 cm H2O pressure caused 12 dB loss at 300 Hz and 15 dB at 3k Hz while 0.3 ml fluid with +20 cm H2O pressure caused and 11 dB at the 300 Hz and 3k Hz respectively The reason for more reduction by negative pressure in the fluid-pressure combination may be due to the air volume change in the middle ear cavity in response to pressure variation Positive middle ear pressure increases the tympanic space air volume by pushing the TM laterally and negative pressure decreases this volume by retracting the TM medially This phenomenon was similar to the observation by Murakami et al (1997) Calculated from the data in Fig and Fig 3, the increased cavity volume by 20 cm H2O pressure was about 0.005 ml, about 0.9% of the whole normal middle ear cavity, and −20 cm H2O pressure only caused 0.6% middle ear cavity decrease Thus, the small difference of the TM motion between positive and negative pressures may not completely, but slightly relate to the small cavity volume change by middle ear pressure At low frequencies of 250 and 500 Hz, the umbo displacement reduction (Figures 7B and 7C) increased when the pressure in the middle ear varied from ±10 to ±15 and ±20 cm H2O At frequencies of 4k and 6k Hz, the umbo displacement reduction increased as the pressure varied from −10 to −15 and −20 cm H2O (Figure 7B) while the umbo displacement reduction decreased as pressure changed from 10 to 15 and 20 cm H2O A possible explanation for the different effect of negative and positive pressure is the geometric changes of the TM induced by different pressure variations CONCLUSSION Both laser interferometry and tympanometry were used to detect the combined effects of fluid and pressure changes on middle ear function The combination of fluid and pressure reduced the TM (umbo) movement at all audible frequencies tested The fluid and pressure effects on the umbo movement are not additive in the fluid-pressure combination The combined effect of fluid and pressure on TM movement is different from that of fluid or pressure only in the middle ear The negative pressure in the fluidpressure combination has more effect on umbo movement than that of positive pressure Tympanometry can detect the middle ear pressure of the fluid-pressure combination This study provides useful, quantitative information for analysis of the combined effect of fluid and pressure on TM movement The mechanism behind TM movement reduction by a combination of middle ear fluid and pressure variations needs further studies ACKNOWLEDGMENTS This work was supported by NIH/NIDCD Grant R01DC006632 The authors thank Don Nakmali at Hough Ear Institute for his expert technical help Footnotes Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication As a service to our customers we are providing this early version of the manuscript The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain Article information Hear Res Author manuscript; available in PMC 2009 February 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 PMCID: PMC2346543 NIHMSID: NIHMS40738 Chenkai Dai, MD, MS,1 Mark W Wood, MD,2 and Rong Z Gan, PhD1 University of Oklahoma, Norman, OK 73019 Hough Ear Institute, Oklahoma City, OK 73112 Corresponding author: Rong Z Gan, Ph D., Professor of Biomedical Engineering, School of Aerospace and Mechanical Engineering and Bioengineering Center, University of Oklahoma, 865 Asp Avenue, Room 200, Norman, OK 73019, Phone: (405) 325-1099, Fax: (405) 325-1088, E-mail: rgan/at/ou.edu Copyright notice and Disclaimer Publisher's Disclaimer The publisher's final edited version of this article is available at Hear Res See other articles in PMC that cite the published article REFERENCES Dai C, Wood MW, Gan RZ Tympanometry and laser Doppler interferometry measurements on otitis media with effusion model in human temporal Bones Otol Neurotol 2007;28(4):551–558 [PubMed] Dirckx JJJ, Decraemer WF Area change and volume displacement of the human tympanic membrane under static pressure Hear Res 1992;62:99–104 [PubMed] Gan RZ, Dai C, Wood MW Laser interferometry measurements of middle ear fluid and pressure effects on sound transmission J Acoust Soc Am 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pressure in the fluidpressure... Mechanism of Combined Effect on Middle Ear Function At low frequencies, the umbo displacement reduction by the combination of middle ear fluid and pressure was less than that by pressure alone (Figure... information for analysis of the combined effect of fluid and pressure on TM movement The mechanism behind TM movement reduction by a combination of middle ear fluid and pressure variations needs