Advances in Middle Ear Analysis Techniques

Transcription

1 T H E U N I V E R S I T Y O F B R I T I S H COLUMBIA Advances in Middle Ear Analysis Techniques Navid Shahnaz, Ph.D. School of Audiology & Speech Sciences 6/7/2009 Overview Immittance Principles Standard Tympanometry Multifrequency Tympanometry Wide Band Reflectance Laser Doppler Vibrometry 1

2 Terminology Immittance: Immittance is a generic term that encompasses impedance, admittance, and their components Impedance (Z - in acoustic ohms) in the middle ear system is defined as the total opposition of this system to the flow of the acoustic energy. Admittance (Y - in acoustic mmhos) is the reciprocal of impedance and is the amount of acoustic energy that t flows into the middle ear system. Currently available immittance instruments typically measure admittance. Simple Harmonic Motion M 2

3 Variables That Determine Admittance Compliance (the inverse of the stiffness) C/S : the admittance offered by stiffness elements in the middle ear system which is called compliant susceptance and is denoted by B S (also stiffness reactance, negative reactance, or -X s in impedance terms) Mass M: the admittance offered by mass elements in the middle ear system which is called mass susceptance and is denoted by B m (also mass reactance, positive reactance, or X m in impedance terms) Friction or Resistance R:determines the absorption or dissipation of acoustic energy. In admittance terms, this element is called conductance and is denoted by G (also resistance, or R in impedance system). Complex Acoustic Admittance 90 Y a Polar Notation Y = 2.1 mmho ϕ = 45 jb stif ness jb a ϕ - jb mas s G a Rectangular Notation Ya = Ga + jba = Ga + j(bma + Bsa)

4 Standard Low Frequency Tympanometry Traditional parameters obtained from low frequency tympanometry: t Static admittance (SA) Tympanometric Shapes Tympanometric peak pressure (TPP) Ear Canal Volume (ECV) Tympanometric width (TW) Sensitivity & Specificity of Tympanometry & Otoscopy Varia bles Criter ion Sens (%) Spec (%) PPV (%) NPV (%) OT AR Absent Y tm tm TW > Nozza et al., 1994; N = 249; diagnosis of MEE; Gold Standard = Myringotomy 4

5 Race Multi-frequency Multi frequency Tympanometry 5

6 Recording Methods Sweep Frequency (SF): pressure is held constant t while frequency is swept across multiple frequencies Sweep Pressure (SP): frequency is held constant while the pressure is swept across a given range Sweep Frequency (SF) 6.00 nce (mmho) Admitta Hz 500 Hz 1000 Hz Air Pressure (dapa) 6

7 How much time A sweep frequency recording from Hz takes approximately 120 seconds Divided into two 60 second recordings: one from Hz and one from Hz Multifrequency Tympanometry Parameters Tympanometric configuration - Vanhuyse Pattern Resonant frequency (RF) Frequency corresponding to admittance phase angle of 45 degree (F45 ) SA at multiple frequencies 7

8 Vanhuyse Pattern & Frequency Source: Fowler & Shanks, 2002 Vanhuyse Pattern Interpretation Except in neonates (< 6 months of age), notched tympanograms should always be considered abnormal. With high probe frequency, a notched tympanogram should be considered normal if the following conditions are met: The number of peaks (both maxima and minima) must not exceed five for B and 3 for G tympanograms. The distance (in dapa) between the outermost G maxima must not exceed the distance between the B maxima The distance between the outermost maxima must not exceed 75 dpa for tympanograms with three pekas (3B3G0 and must not exceed 100 dapa for tympanograms with five peaks (e.g., 5B3G) 8

9 Calculating SA from Notched Tympanogram GSI & Virtual 6.00 Right 900 Hz Tympanogram Air Pressure (dapa) Ga: Ba: RF Estimation-GSI & Virtual 6.00 Right 900 Hz Tympanogram Positive Tail Air Pressure (dapa) Ga: Ba: 9

10 F45 Estimation 6.00 Right 710 Hz Tympanogram ittance - mmho Adm G B Air Pressure (dapa) RF Norms Children & Adults Source: Fowler & Shanks,

11 Resonant Frequency (RF) SF The Choice of Probe Tone Frequency For Measuring SA Shahnaz & Polka (2002) Immittance Magnitude - mmho SI/Y+ - Healthy Ears SI/Y+ - Otosclerotic Ears SI/B+ - Healthy Ears SI/B+ - Otosclerotic Ears Probe Tone Frequency - Hz 11

12 Low vs. High Probe Tone Frequency Hz 226 Hz 80 Se ensitivity False Positive 12

13 Shahnaz & Davies, 2006 Shahnaz et al Comparison of resonant frequency (RF) and frequency corresponding to admittance phase angle of 45 degree to static admittance (SA) and tympanometric width (TW) obtained at 226 Hz 13

14 Shahnaz et al Comparison of individual test performance between resonant frequency (RF) and frequency corresponding to admittance phase angle of 45 degree to static admittance (SA) and tympanometric width (TW) obtained at 226 Hz Otosclerotic Group Pattern#1 Pattern#2 Pattern#3 Pattern#4 Pattern#5 Pattern#6 Pattern#8 Pattern#9 Pattern#11 Pattern#13 HR% SA? 0.57 mmho TW? dapa F45 > 600 Hz RF > 1020 Hz Total Protocol Loose-TW-F Strict-TW-F Normal Group Pattern# 1 Pattern# 2 Pattern# 3 Pattern# 5 Pattern# 6 Pattern# 7 Pattern# 8 Pattern# 9 Pattern#1 0 Specificity % FA% SA 0.57 mmho TW dapa F45 > 600 Hz RF > 1020 Hz Total Protocol Loose-TW-F Strict-TW-F MFT Issues Cannot go above 2000 Hz due to standing waves A pressure change in newborn could change the area of the ear canal by 70% due to a very compliant nature of the canal wall Lack of normative data Specific recording parameters Race based norms Significant racial differences found between Caucasian and Chinese young adults (Davies, M.Sc. Thesis, 2003) 14

15 MFT Issues, cont. Low clinical use Too time consuming? Lack of understanding of underlying principles and diagnostic value? Difficult to interpret findings? Case Studies- Adult -Case 1: OM (Fowler & Shanks, 2002) 15

16 Case 2: OM (Fowler & Shanks, 2002) Case 3: TM Pathology vs. Disarticulation (Fowler & Shanks, 2002) 16

17 Case 4: Otosclerosis (Fowler & Shanks, 2002) Case 5: Middle Ear Problems (Fowler & Shanks, 2002) 17

18 Newborn Procedure 12:47 Comparison between Newborns and Adults Modified from Ballachanda,

19 Newborn s Middle-ear ear Some of the important structural changes that occur postnatally that can affect the mechano-acoustical properties of conductive mechanism include: The external auditory canal will increase in size and diameter and becomes less compliant (due the formation of the bone) post-natally until about one year of age (Anson & Donaldson, 1981). This can potentially reduce the resonance gain and shift the resonant frequency of the canal to the higher value in younger infants. Growth of middle-ear cavity from the tympanic membrane to the stapes footplate in the first 6 months after birth (Eby & Nadol, 1986) and an increase in pneumatization of mastoid air cells (Anson & Donaldson, 1981) which will contribute to the enlargement of volume in the middle-ear cavity. The volume of air is important in determining the tympanic membrane compliance and controlling the conduction of low frequencies a decrease in the overall mass of the middle-ear due to presence amniotic fluid and mesenchyme in the middle-ear cavity which may last for up to 5 months after birth (Paparella et al.1980). a decreases in the density of stapes due to internal bone erosion which could lead to a reduction in mass for this structure (Anson & Donaldson, 1981) tightening of the osssicle joints and stapes footplate attachment to the oval window which may decrease the resistive component (Saunders et al.,1983). What Would be the Effect of These Changes on the Tympanogram? The overall maturation of the external and middle-ear may result in an increase in mass at birth which will gradually decrease as infants become older. This prediction has been confirmed by multi-frequency tympanometry (Holte et al., 1993; Shahnaz, 2002) 19

20 Distribution of the Vanhuyse patterns at different probe tone frequencies in adults & 3-weeks old infants-shahnaz et al The proportion (in %) of single peak Yauncompensated Tympanograms in 3-weeks old Infants and Adults- Shahnaz et al

21 Ytm and Btm and Gtm at+250 dapa as a function of probe tone frequency in 3-weeks old and adults- Shahnaz et al Distribution of the Vanhuyse patterns at different probe tone frequencies in adults & NICU babies-shahnaz et al

22 The proportion (in %) of single peak Yauncompensated Tympanograms in NICU babies and Adults- Shahnaz et al a: NICU Hz 2 Admittance - mmho dapa B G Y b: NICU Hz 4 Admittance - mmho dapa B G Y Shahnaz et al

23 Proportion (in %) of different type of tympanograms (A & B) at 1000-Hz probe tone frequency for high priority hearing registry (HPHR) babies that passed/failed the TEOAE results. Shahnaz et al Frequency Analysis of OAE Results r of sed Average Num ber Freq uencies Pas Ears 7 Ears 9 Ears 20 Ears TYPE A TYPE B Tympanogram Type PASS FAIL 23

24 Shahnaz et al Newborns Tympanogram Classification Adapted from Marchant s methodology (1986), Buldwin (2006) using Y measurements rather than B classified Newborns Y tymps A baseline was drawn between +200 and -400 dapa. A vertical line was drawn from he baseline to the peak of the trace either above (positive peak), or below (negative peak) the baseline (The traces were classified as: Positive peak: i.e. normal Negative: i.e. abnormal Indeterminate: traces which the tester could not classify as, Positive or Negative 24

25 Review of the Normal Tympanogram Shape Shahnaz, 2006 Maturation of The Equivalent Ear Canal volume-shahnaz, Li, & Cai,

26 Maturation of The Equivalent Ear Canal volume-shahnaz, Li, & Cai, 2008 Maturation of The Equivalent Ear Canal volume- Li, Shahnaz,Cai, Bingham, & Funnell 2008 Y+ tail at 226 Hz Y+ tail at 1 khz 26

27 Li, Shahnaz,Cai, Bingham, & Funnell 2008 Proportion of Single-peak and Multiple-peak Tympanogram 100% tiple on of Single Peak and Mult Peak in % Prporti 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 226 V1 1k V1 226 V2 1k V2 226 V3 1k V3 226 V4 1k V4 226 V5 1k V5 226 V6 1k V6 Single Peak Multiple Peak 27

28 Proportion of Vanhuyse Pattern Mean ΔB in 12 Infants from Birth to 6 Months of Age Shahnaz, Cai, & Li, :47 28

29 Maturation of Conductance (G) Shahnaz, Cai, & Li, 2008 Compensated Susceptance (Btm) from Birth to 6 Months of Age Visit Compensated Susceptance (Btm) at positive tail (mmho) Compensated Susceptance (Btm) at negative tail (mmho) 226 Hz 1000 Hz 226 Hz 1000 Hz Median 5 th -to-95 th Median 5 th -to-95 th Median 5 th -to-95 th Median 5 th -to-95 th

30 Visit Computed From C ompensated Admittance (Ytm ) at positive tail (mmho) Compensated Admittance (Ytm) at negative tail (m mho) 226 Hz 1000 Hz 226 Hz 1000 Hz Median 5 th -to-95 th Median 5 th -to-95 th Median 5 th -to-95 th Median 5 th -to-95 th 1 B/G Ya B/G Ya B/G Ya B/G Ya B/G Ya B/G Ya Aural Acoustic Reflex (AAR) in Newborns The ability to obtain reflex in newborns depends d on the probe tone frequency It is highly unlikely to obtain aural reflexes in newborns at standard 226 Hz probe tone frequency (Weatherby & Bennett, 1980; margolis, 1993; McMillan et al., 1985; Sprague et al., 1985) 30

31 AAR in Newborns Weatherby & Bennet, 1980 found that newborn reflexes are clearly present when higher probe frequencies are used The detection threshold varies with probe tone frequency By 800 Hz the reflexes of newborns are present in the same proportion as adults AAR in Newborns The optimum probe tone frequency for adult is 800 Hz and for neonates is around Hz (Benette & Weatherby, 1982) The frequency at which the reflex pattern shifts is considerable higher h in newborns (1200 Hz) compared with adults (665 Hz) 31

32 Sprague, 1985 (44 neonates) Percentage of Present Reflexes Mean Reflex Threshold Activator 220 Hz 660 Hz 220 Hz 660 Hz Ipsi-1000 Hz Ipsi-BBN Contra-1000 Hz Contra- BBN Probe tone frequency: 1200 Hz; all dbs are in SPL; Total N: 28 newborns Type BBN 0.5K 1K 2K 4K N Median th Percentile th Percentile Benette & Weatherby, 1982 Mazlan et al.,

33 Mazlan et al., neonates (88 boys and 109 girls)-chronological age ranged from 24 to 192 hr (mean 54.4 hr, SD 28.4) Technical Issues to be Considered in Newborn AAR If using pure tone as an activator: Probe tone should not be the same as or harmonic of the activator tone; in this scenario the choice of 1200 Hz probe tone frequency is desirable In order to avoid artifact due to crossover (in contralateral mode) and separating the probe tone from BBN in ipsi or contra mode a notch filter with the same center freq. as the probe tone with very steep roll off rate should be used 33