Annals of Indian Academy of Otorhinolaryngology Head and Neck Surgery

ORIGINAL ARTICLE
Year
: 2021  |  Volume : 5  |  Issue : 1  |  Page : 8--11

Effects of probe tip placement on static acoustic admittance at the plane of measurement


Preeti Sahu1, Debadatta Mahallik2,  
1 Audiology Unit, EYE and ENT Hospital, Raipur, Chhattisgarh, India
2 Department of ENT, Audiology and Speech Language Pathology Unit, Dr. BRAM Hospital, Pt.J.N.M. Medical College, Raipur, Chhattisgarh, India

Correspondence Address:
Mr. Debadatta Mahallik
Department of ENT, Audiology and Speech Language Pathology Unit, Room No-237, Pt. JNM Medical College, Raipur - 492 001, Chhattisgarh
India

Abstract

Introduction: Tympanograms are recorded at the plane of the probe tip in the ear canal, consequently, this recording is called a tympanogarm in the plane of measurement and it includes both the acoustic admittance of the trapped volume of air between the probe tip and the tympanic membrane and the admittance of the middle ear system at the tympanic membrane. Materials and Methods: Eighty three participations (166 ears- 85 right ears, 81 left ears) were selected for the study. participants who had negative middle ear pressure greater than -50dapa and + 50 dapa and air and bone conduction thresholds gap of equal or more than 15 dB were excluded from the study. Data Analysis: Pearson correlation coefficient was carried out to see the relationship between residual ear canal volume (RECV) and acoustic admittance (Ya) and as well as for the tympanometric peak pressure (TPP). Results: Results shows there is strong positive correlation (r =0.854, P <0.001) between the residual volume in the ear canal and admittance. Acoustic admittance were well correlated with the residual ear canal volume with coefficient of determination of r^2 = 0.793. In case of the middle ear pressure, it has been shown that there is positive moderate correlation (r = 0.679, P < 0.001) between the middle ear pressure and acoustic admittance with coefficient of determination of r^2 = 0.473. Conclusion: The shift of probe tip placement in the ear canal and middle ear pressure variation changes the acoustic admittance value during immitance audiometry.



How to cite this article:
Sahu P, Mahallik D. Effects of probe tip placement on static acoustic admittance at the plane of measurement.Ann Indian Acad Otorhinolaryngol Head Neck Surg 2021;5:8-11


How to cite this URL:
Sahu P, Mahallik D. Effects of probe tip placement on static acoustic admittance at the plane of measurement. Ann Indian Acad Otorhinolaryngol Head Neck Surg [serial online] 2021 [cited 2021 Nov 29 ];5:8-11
Available from: https://www.aiaohns.in/text.asp?2021/5/1/8/320571


Full Text



 Introduction



Tympanometry is one of the most frequently performed and important components of the basic audiologic evaluation. Tympanometry is an objective, physiological measure of acoustic admittance of the middle ear as a function of air pressure in a sealed ear canal. Acoustic immittance is a general term that refers to acoustic admittance (Ya), acoustic impedance (Za) or both terms (ANSI S3.39. 1987). The subscript “a”, appended to each abbreviation, indicates that each term refer to an acoustic quantity or measure. Acoustic admittance (Ya) refers to the ease of sound flow through an acoustic system and acoustic impedance (Za) refers to the opposition to sound flow through an acoustic system. Both Acoustic admittance and impedance are direct reciprocal (Za = 1/Ya). If an acoustic system like the human middle ear has high admittance, it has a low impedance and if the middle ear has low admittance, it has high impedance. The acoustic admittance (Ya) of an acoustic system, such as the human middle ear, is defined by the complex ration of volume velocity (U) to sound pressure (P). The ratio is termed complex because it involves a phase relation between volume velocity (V) and sound pressure (P).[1]

The immittance measured by a probe inserted into the ear canal is determined by the complex combination of all the acoustical elements that comprise the ear. One of these elements is the volume of air that occupies the ear canal between the probe tip and the tympanic membrane. Tympanograms are recorded at the plane of the probe tip in the ear canal, consequently, this recording is called a tympanogram in the plane of measurement and it includes both the acoustic admittance of the trapped volume of air between the probe tip and the tympanic membrane and the admittance of the middle ear system at the tympanic membrane.[2] The residual air medial to the probe tip influences on total acoustic immittance value, which can affect the clinically significant middle ear immittance value.[3]

The aim of this study is to see the correlation between the residual volume in the ear canal and static acoustic admittance.

 Materials and Methods



The study sample included adults with normal-hearing or sensorineural hearing loss. They were recruited consecutively from the Department of ENT, tested in the Audiology unit at Pt. JNM Medical College associated with Dr. BRAM Hospital, Chhattisgarh during their audiological consultation. Eight-three participants (166 ears-85 right ears, 81 left ears) were selected for the study. Participants with mean age and standard deviation of 31.00 ± 4.43 years (range of 22–43 years).

Inclusion criteria

Young adults with normal hearing sensitivity or sensorineural hearing loss were included in the study. Those who had external auditory canal clean and dry with clear visualized of all anatomical landmarks of the tympanic membrane and air-bone gap of less than or equal to 10 dBin conventional audiometry in at least one ear were recruited for the study.

Exclusion criteria

Participants who had negative middle ear pressure >−50dapa and +50 dapa and air and bone conduction thresholds gap of equal or more than 15 dB were excluded from the study.

Procedure

Initially, the otoscopic examination was performed for all cases. Tuning fork tests were conducted at 256 Hz and 512 Hz and Conventional pure-tone air and bone conduction audiometry (Interacoustic, AC40, Denmark, with TDH 39 earphone mounted with supra-aural cushions (MX51/AR) was conducted at each octave frequencies from 250 Hz to 8000 Hz for air conduction and from 250 Hz to 4000 Hz for bone conduction (Radioear B71 bone vibrator) using the modified HughsonWestlake procedure.[4] For tympanometry, GSI TympStar version 2 Immittance Audiometry (GrasonStadler, A/S, Kongebakken 9, 2765 Smⱷrum, Denmark) was used for middle ear analyzer. Before the collection of data, a calibration was performed through on a. 5cc, 2.0 cc, 5.0cccavities (provided by the manufacturer) to check if the system worked within the limits of specifications.[5] Tympanometry was performed using 226 Hz pure tone with the pump speed of 200 dapa/second. The direction of pressure was swept from positive (+200 daPa) to negative (–400 daPa) and the recordings were taken in each ear for all subjects without paying attention toward shallow and deep insertion of probe tip into the ear canal. To get hermetic seal, first pulled up and back the pinna to straighten the ear canal and probe tip-sized was choose based on the opening of the ear canal. Instructions were given before test, that not to shake your head and shallow during the test session. Measures of residual ear canal volume (RECV), static acoustic admittance (Ya), and Tymanometric peak pressure (TPP) were obtained and reordered in datasheets. All the tests were executed in the sound treated room with ambient noise level within permissible limits.[6]

Data analysis

Statistical package for the social sciences (SPSS) software (version 17, Chicago, USA) was used for data analysis. Descriptive statistics were explored. For Symmetry (Skewness) of the data for normal distribution was carried out. An absolute value of “Z” score > 1.96 or <−1.96 is significant at P < 0.05. Pearson correlation coefficient was carried out to see the relationship between RECVand static acoustic admittance (Ya) and as well as for TPP. P of 0.01 was used for interpretation of significance.

 Results



The mean and standard deviation of all three parameters are shown in [Table 1]. In the present study, results show there is a strong positive correlation (r = 0.854, P < 0.001) between the residual volume in the ear canal and admittance [Table 2]. As the RECV increases the admittance value also increases and as the RECV decreases the admittance value decreases. Estimation of acoustic admittances was well correlated with the RECV with the coefficient of determination is (r^2 = 0.793) [Figure 1].{Figure 1}{Table 1}{Table 2}

In the case of middle ear pressure, it has been shown that there is a moderate correlation (r = 0.679, P < 0.001) between the middle ear pressure and static acoustic admittance [Table 3]. As the middle ear pressure gets negative the admittance gets decrease with coefficient of determination is (r2 = 0.473) [Figure 2].{Figure 2}{Table 3}

 Discussion



As the trapped volume of air between the probe tip and tympanic membrane increases the pressure on the tympanic membrane will decrease. Hence, the impedance at the tympanic membrane decreases and we know, both acoustic admittance and impedance are direct reciprocal (Za = 1/Ya) to each other. As the impedance decreases the admittance increases and vice versa. According to Boyle's law, states that at a constant temperature the volume of an ideal gas is inversely proportional to its absolute pressure. In other words, the product of pressure and volume is constant for a fixed mass of ideal gas at constant temperature. P1 X V1 = P2 X V2. The other way to express Boyle's Law is V α 1/P.[7] As the trapped volume of air between the probe tip and tympanic membrane increases the pressure on the tympanic membrane will decrease. Hence, the impedance at the tympanic membrane decreases and as we know, both acoustic admittance and impedance are direct reciprocal (Za = 1/Ya) to each other. As the impedance decreases the admittance increases and vice versa. As the volume of the ear canal changes, the admittance tympanogram simply shifts higher or lower on the Y-axis without affecting the shape of the tympanogram. In the present study, it has been shown that the RECV has a linear effect on admittance tympanograms which is supported to the previous study.[8] There is no exact 1:1 relation between specific middle-ear pathology and a specific tympanogram pattern. The same pathology can produce several different types of tympanogram patterns and conversely, the same type of tympanogram pattern can arise from different types of middle-ear pathologies. Similarly, a tympanogram can be obtained as low admittance when the eardrum is immobilized by fluid, fixed malleus, thickening of the tympanic membrane or by Otosclerosis, apart from these still we can get low admittance tympanogram from ears with smaller RECV (if the probe tip is inserted deeply into the ear canal). Similarly, a tympanogram can be obtained as high admittance when the eardrum is thinning, hypermobile tympanic membrane or by ossicular discontinuity, apart from these still we can get high admittance tympanogram from ears with higher RECV (if the probe tip is inserted shallowly into the ear canal). As the volume gets smaller the sound pressure will get higher on the tympanic membrane, as a result of the impedance at tympanic membrane increases and hence the admittance decreases and vice versa. In case of middle ear pressure, in this study showed, as the tympanometric peak pressure gets negative the admittance value slightly decreased because the negative pressure put the tympanic membrane under tension. Once it gets tensed, the impedance at tympanic membrane will get higher, hence the admittance gets lower, and this is supported to previous findings.[9]

 Conclusions



Patients with low admittance value due to some conductive pathologies may have normal admittance value due to larger RECV because of shallow placement of probe tip in the ear canal. Similarly, the patient whose middle ear is functioning normally may have low admittance tympanogram because of smaller RECV due to deeply placement of probe tip in the ear canal. The shift of probe tip placement in the ear canal and the pressure variation changes the acoustic admittance value during immittance audiometry.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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