The Caloric Test: Using the newest technology to better understand our oldest vestibular test ERIN G. PIKER, AUD, PHD

Transcription

1 The Caloric Test: Using the newest technology to better understand our oldest vestibular test ERIN G. PIKER, AUD, PHD RUTH SYMPOSIUM 2016

2 Disclosure I have relevant financial relationship(s) with the products or services described, reviewed, evaluated, or compared in this presentation. James Madison University Salaried employee Research reported in this presentation was supported, in part, by the National Institute on Deafness and Other Communication Disorders (NIDCD) of the National Institutes of Health (NIH) under Award Number 5T32DC

3 Acknowledgements Dennis Frank-Ito, PhD Co-PI David Kaylie, MD Alok Patki, MD Ofri Ronen, MD David Carpenter, BS Elizabeth Burnett Associate Professor ENT Resident ENT Resident Medical Student Undergraduate student

4 Learning Outcomes 1. Describe factors, other than vestibular function, that contribute to the variability in the caloric response 2. Define the minimal detectable change in a caloric response that reflects a true change in vestibular function

5 Vestibular function in CI patients? Significant changes to the horizontal SCC (as measured using calorics): 0 58% (Buchman, Joy, Hodges, Telischi, & Balkany, 2004; Enticott, Tari, Koh, Dowell, & O'Leary, 2006; Fina et al., 2003; Krause, Louza, et al., 2009; Krause, Louza, Wechtenbruch, & Gurkov, 2010; Melvin, Della Santina, Carey, & Migliaccio, 2009; Todt, Basta, & Ernst, 2008; Wagner et al., 2010) Significant changes to the saccule (as measured using cervical VEMPs): 9 86% (Basta, Todt, Goepel, & Ernst, 2008; Krause et al., 2010; Krause, Wechtenbruch, Rader, & Gurkov, 2009; Licameli, Zhou, & Kenna, 2009; Melvin et al., 2009; Todt et al., 2008; Wagner et al., 2010) Despite changes in objective measures, there were no correlations with patientreported symptoms

6 Why do caloric findings differ between studies? 1. Inherent variability in the caloric test 2. Validity of the caloric test relies on the assumption that the temporal bone anatomy is either symmetrical in both ears, or if assessing function postoperatively, unchanged 3. Different definitions of what constitutes a significant change in the caloric response

7 Background on the Caloric Test 1907 Barany publishes Physiologie und pathologie des bogengangappaates beim menschen 1914 Barany wins the Nobel prize for his work on the physiology and pathology of the vestibular apparatus 1942 Fitzgerald and Hallpike first described the bithermal caloric test used clinically in humans.and little has changed since Caloric test is considered to be the gold-standard Caloric test is most widely used diagnostic test

8 From Barin, 2009

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10 Mechanism of caloric stimulation How does temperature result in excitation/inhibition of vestibular system? Barany: gravity-dependent theory --- temperature changes the volume of the endolymph Spacelab experiments 1980s: gravity-independent theory --- direct effect of temperature on the vestibular nerve Hood (1987) conclude that caloric stimulation probably consists of 2 components, one gravity dependent and the other gravity-independent ---suggest that the gravity-independent component was very small (~10%) and change in endolymph density was dominant mechanism (90%)

11 Mechanism of caloric stimulation How is the temperature transferred? Schmaltz (1932) ---proposed that heat transfer takes place via the bony connection between the external meatus and lateral canal (heat radiation) Young (1972) --- compared temperature measurements in skulls using a one-dimensional mathematical model of heat transfer in a solid --- supported Schmaltz s bony connection/heat radiation hypothesis Harrington (1969) --- compared temperature measurements in human cadavers and anesthetized cats ---- findings did not support bony connection hypothesis, concluded main route for heat transfer is via the air in the middle ear (heat convention) O Neill (1987) --- measured temperature in human temporal bones --- concluded that heat transfer was mainly a process of heat convection through the air within the middle ear

12 Variables affecting heat transfer Theoretically 1. Conductivity of bone 2. Volume and shape of middle ear cleft 3. Surface area of the tympanic membrane 4. Degree of pneumatization of the mastoid 5. Diameter of the horizontal SCC and its orientation

13 Back to answering those questions Dr. Frank-Ito is an expert in computational fluid dynamics (CFD) sinus passages --- he predicts airflow dynamics in the nasal passage and uses CSD to simulate are and temperature flow Can we simulate heat transfer through bone and skin and air-filled spaces? New collaboration began!

14 Why caloric findings differ between studies? 1. Inherent variability in the caloric test Studies 1 and 2 2. Validity of the caloric test relies on the assumption that the temporal bone anatomy is either symmetrical in both ears ear, or if assessing function postoperatively, unchanged Study 1 (effects of temporal bone anatomy on the response) 3. Different definitions of what constitutes a significant change in the caloric response Study 2 (calculation of minimal detectable changes in the response over time)

15 Study 1 Anatomic Variations in Temporal Bones Affect the Intensity of Nystagmus During Warm Caloric Irrigation

16 Study 1: Anatomic Variations in Temporal Bones Affect the Intensity of Nystagmus During Warm Caloric Irrigation Mechanism of heat transfer during caloric irrigation not clearly established BUT, first we needed to understand the relationship between anatomy of the temporal bone and caloric response Zangmeister & Bock (1979) --- subjects with poorly pneumatized mastoid cavities showed nearly twice the response magnitude O Neill (1987) ---- used CT scans to correlate temperature in the horizontal SCC with anatomical measurements --- only 1 significant correlation was found between temperature and the diameter of the internal auditory meatus Proctor (1982) --- used caloric nystagmus intensity as an indirect measure of heat transfer and compared it to radiological data --- could not demonstrate any significant correlations Studies done on cadavers or limited by available imaging techniques

17 Study 1: Anatomic Variations in Temporal Bones Affect the Intensity of Nystagmus During Warm Caloric Irrigation The purpose of this study is to determine whether anatomic characteristics of temporal bones affect the magnitude of the maximum velocity of slow phase nystagmus during caloric testing with warm irrigation. Provide a preliminary description of inter-aural differences in temporal bone anatomy and subsequent effects of temporal bone asymmetry on the caloric response

18 Methods Retrospective chart review Patients who had a normal caloric test Patients who had a normal high resolution temporal bone CT scan 22 temporal bones 3D anatomic reconstruction of the temporal bone Performed statistical analyses to determine if correlations existed between caloric test results and temporal bone anatomy

19 3-D Anatomic Reconstruction 3D reconstructions of temporal bones were created from CT scans using Avizo 8.1 standard Reported to be accurate to the hundredth of a millimeter (Calloway et al. 2013) Following parameters were computed Mastoid airspace volume (V) Mastoid airspace surface area (SA) Mastoid bone V Mastoid bone SA Lateral semicircular canal (LSCC) V LSCC SA LSCC to tympanic membrane distance Internal auditory canal (IAC) diameter SA/V ratios were chosen for analysis because the ratio gives more information about temporal bone anatomy than either SA or V alone

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22 Results

23 Results: Inter-aural asymmetries

24 Discussion Warm caloric is correlated with anatomic features of the temporal bone Mastoid cavity with large air cells -> smaller caloric response Mastoid cavity with greater volume of bone -> larger caloric response Combined differences in inter-aural temporal bone anatomy predicted caloric asymmetry Average inter-aural asymmetry for temporal bone parameters was 13% Complexity of caloric response, so outcome cannot be adequately predicted by a single anatomic parameter

25 Discussion Still have not determined how temperature is transmitted through the temporal bone, but findings support the conclusion that bone acts as a major transmitter of temperature during a caloric irrigation During mastoidectomy, bone volume is removed and a larger airspace is created Our model would predict a reduction in warm caloric response post CI surgery Hypothesize that caloric results may be significantly affected by surgical alteration of the temporal bone following otologic surgery

26 Study 2 Serial caloric testing: minimal detectable change

27 Caloric test-retest Davidson (1988) Total caloric response: ICC =.98 (young group);.92 (older group) Henry (1999) UW: r =.82 Right/Left Warm/Cool individual irrigations: range of r = But a reliability coefficient doesn t tell us what a true change in response looks like

28 Minimal Detectable Change 1. Relative reliability --- do repeated measurements revealed consistent ranking of individual scores within a group (i.e. if my score was on the lower end relative to others, is it still on the lower end during re-test) Test-retest reliability Measured with correlation coefficients (e.g. intraclass correlation coefficients [ICC]) 2. Absolute reliability --- do repeated measurements show little variability (i.e. delineate the expected change from the true change in performance) Statistically: standard error of measurement (SEM) Clinically: minimal detectable change (MDC) score --- derived from the SEM

29 Purpose of study Determine the TRT reliability of the caloric test in normal subjects Determine the MDC scores of the following caloric parameters: Unilateral weakness Right warm Right cool Left warm Left cool Right total score (right warm + right cool) Left total score (left warm + left cool) Total response (right warm + right cool + left warm + left cool)

30 Methods 15 subjects (10 female, 5 male) Mean age 24.3 (range 18 38) No history of vestibular disorders, concussion, or neurological disease Screened with otoscopy and tympanometry Bithermal caloric testing completed 3 times at 3 different test sessions (1 week between each test session) Tests were conducted with the patient supine and head elevated 30 degrees Both warm (44 deg/sec) and cool (30 deg/sec) water was infused into EAC at a calibrated rate and duration of 250 ml over a 30 second interval Order of irrigations was randomized Analysis: 1) ICC (2,1) 2) SEM = sd * (1-ICC) 3) MDC 90 = SEM * 1.65 * 2

31 Unilateral Weakness (%) Results Session 1 Session 2 Session 3

32 Results Caloric Outcome Mean SD ICC SEM MDC 90 Right Warm Right Cool Left Warm Left Cool Right Total Left Total Total Response Unilateral Weakness

33 Discussion Variability within subjects for the caloric response may be due to: Subject alertness, subject state, body temperature, head/body placement, habituation effects, technical error Clinicians can interpret MDC scores as the minimal change that is not due to error Scores above or below the MDC level are due to changes in patient s end organ function, rather than measurement error

34 Conclusions from all studies Using new methods, we were able to enhance our understanding of the precise mechanisms of caloric stimulation 1. Describe factors, other than vestibular function, that contribute to the variability in the caloric response Mastoid bone and airspace, distance from the lateral SCC to the TM 2. Define the minimal detectable change in a caloric response that reflects a true change in vestibular function Table shows MDC for caloric parameters Why does this matter? Helps explain findings in CI patients Caloric test not an accurate measure of vestibular function in this patient population Widely used clinical test Could someday lead to improvement in test procedures

35 Thank you Questions/comments?

36 Right Total Left Total

37 Shapiro-Wilk: p =.513